Hello everyone, today I found on Facebook Marketplace locally a late 1920s Eveready Model 1 TRF Neutrodyne Radio with its original matching speaker attachment for $75 and according to the owner he says it needs to be rewired and the speaker's cone is torn (to what extent it is torn I am unsure, but more than likely it should be easily repaired by just using brown coffee filter paper and diluted Elmer's Glue).

My question is, how fair is the asking price (I haven't gotten it yet as I just messaged the seller about 45 minutes ago and I more than likely won't hear from him until tomorrow) and if its not a fair asking price what should I offer him price wise?

Also how hard are these early TRF Neutrodyne Sets to repair? I'm asking as this would be my first TRF Set I've ever repaired.

Any help or advice in this matter would be appreciated.

Thanks.

P. S. I do have the pictures of the unit in question from the Facebook Marketplace posting.

That isn't a bad price given cabinet condition assuming all the tubes are correct types and most aren't bad.

TRF sets vary from a walk in the park to an endless hunt for unobtainium. If all that's bad is a tube or two, some caps and maybe a fixed resistor or 5 TRFs are simple and easy....but if a transformer is bad on a 20s set it can be very difficult to impossible to find one and if you don't have the engineering skills (or are stuck on exact replacement for originality) to figure out a non-correct but functional replacement your going to be stuck with a paper weight. Some sets have goofy problems like potmetal chassis that crack and shatter and are irrepairable (I had a radiola 44/46 like that).

On the rare occasion I accept a set like that for repair I tell the owner "I'm going to try to verify the continuity of the coils and make sure it's repairable before I work on it. If its missing something I can't get I'm returning it as is and not fixing it. If I don't find anything wrong but can't fix it I'm going to waive my labor charge collect the cost of the installed parts, and return it to you as is". If they know there is no guarantee it is repairable going in that generally prevents troublesome levels of dissapointment on occasional unfixable patients.

That isn't a bad price given cabinet condition assuming all the tubes are correct types and most aren't bad.

TRF sets vary from a walk in the park to an endless hunt for unobtainium. If all that's bad is a tube or two, some caps and maybe a fixed resistor or 5 TRFs are simple and easy....but if a transformer is bad on a 20s set it can be very difficult to impossible to find one and if you don't have the engineering skills (or are stuck on exact replacement for originality) to figure out a non-correct but functional replacement your going to be stuck with a paper weight. Some sets have goofy problems like potmetal chassis that crack and shatter and are irrepairable (I had a radiola 44/46 like that).

On the rare occasion I accept a set like that for repair I tell the owner "I'm going to try to verify the continuity of the coils and make sure it's repairable before I work on it. If its missing something I can't get I'm returning it as is and not fixing it. If I don't find anything wrong but can't fix it I'm going to waive my labor charge collect the cost of the installed parts, and return it to you as is". If they know there is no guarantee it is repairable going in that generally prevents troublesome levels of dissapointment on occasional unfixable patients.

Ok, thanks for the info, from what I can see in the pictures, the tubes look like they're all there and accounted for, the cabinet looks pristine and so does the speaker cabinet. I'll let you know what I find out if I end up getting it. I do have some of the tubes that this radio uses in my tube stash already, including several known good 80 rectifier tubes and a NOS RCA 26 tube.

I've seen several YouTube videos posted by someone with the username Glasslinger who does nothing but restore old TRF sets from the 1920s and it seems like all he ever has to do to them is just clean them and maybe replace the fixed resistor (the one that fits into a socket similar to a fuse socket) and maybe change out a tube or two, other than that they seem to come to life with very little work done to them (grant it the ones he works on are battery units rather than AC units like this one is).

Anyways thanks for the feedback.

Ok, I got the radio, and the cabinet in in really nice shape, but the wiring is atrocious inside, it has dry rotted rubber wiring inside and the original power cord was cut at some point in time. It has it has its grid leak resistors intact, the 2 megohm and a smaller one of unknown value as the part of the original label that said the value of the resistor was missing.

It has its original speaker intact which had its original grille cloth replaced at some point in time and the speaker cone is torn in several spots including a spot where there's a small section of the cone missing (see pictures below).

It also has all of the correct tubes in the unit, which are all RCA or RCA Cunningham branded tubes.

I hope this unit will be fairly easy to bring back to life.

I found the Rider's manual for this radio but its kind of hard to decipher what's what in it because it doesn't give values for the capacitors or resistors just part numbers which doesn't even have a crossreference chart on the manual to tell you which part is which.

It looks like its mainly a bunch of bad rubber wire, and there's a couple of transformers that are just hainging loose inside the chassis, one of them is the output transformer and the other one I'm not sure what it is and a third transformer on the tuner section of the chassis which is also kind of just hanging loose on the tuner chassis.

See picture below.

Rubber wiring sucks. If I know a set has it I tend to think twice about getting it as rewiring an entire radio is a pain...it's uncommon for a large amount of rubber wiring to be used in a 20s set.

If riders isn't helpful look for a Beitmans covering 20s sets. They were a competitor to riders and one of the only second sources of literature for sets that old.

Some 20s sets the wax paper caps used as coupling, bypass and as B+ filters (lytics weren't used much back then) go bad and others they are fine...I don't know that brand well enough to say which it's likely to be. If you have a good leakage current tester you should check the original caps.

Rubber wiring sucks. If I know a set has it I tend to think twice about getting it as rewiring an entire radio is a pain...it's uncommon for a large amount of rubber wiring to be used in a 20s set.

If riders isn't helpful look for a Beitmans covering 20s sets. They were a competitor to riders and one of the only second sources of literature for sets that old.

Some 20s sets the wax paper caps used as coupling, bypass and as B+ filters (lytics weren't used much back then) go bad and others they are fine...I don't know that brand well enough to say which it's likely to be. If you have a good leakage current tester you should check the original caps.

Well the problem is I didn't think this thing was going to be full of rubber wiring, I just thought maybe it was going to be old crumbly cloth wiring which would of been a little bit easier to replace than old rubber wire.

The strange thing about the rubber wire in this set is that it looks almost like the rubber wiring in this set just melted at some point in time from being stored in a hot location like an attic and then the rubber hardened afterwards which caused the wires rubber insulation to "weld" together.

Also the rubber grommets did the same thing, they melted and then hardened up and the rubber insulation from the wires that were going through those grommets became part of the grommets.

As for the capacitors the only capacitors I see in this unit are 3 block capacitors that are mounted to the underside of the tuner chassis 2 of them of which are 2 section caps that have one section soldered to the metal housing of the can and the third one is utilizing both sections.

as for the grid leak resistors, there are 2 of them total, one is a 2 Meg unit that measures around 2.8 Meg, and the other one is an unknown value as the paper label that told the value of the resistor is partially missing, and when I tried to get a reading from that resistor I couldn't get a solid reading from it, it measured anywhere from 500k to 22 Meg but it wouldn't settle on a specific value.

When I looked up this radio online it said this was a Neutrodyne TRF Set, but when I looked at the chassis closer it appears to have IF transformers with trimmer condensers on the top of the chassis which I didn't think that TRF Sets used IF cans or Adjustment trimmers, the way this set is set up it reminds me more of an early Superheterodyne set.

Also what's the purpose of the rotating coil that's attached to the left knob?

Most TRF sets have a an antenna transformer and a coupling/tuning transformer between each TRF RF amp stage. Some sets leave the transformers out in the open turning each one 90 degrees to prevent coupling, some sets put the transformer tube and tuning cap of each stage in its own dedicated stage shield, others individually shield the can so it looks like an IF can.
Your set looks to be a single knob TRF those require a trimmer on each coupling transformer to adjust the set so each stage is peaked at the same freq and track properly with each other.

A transformer with one winding connected to a knob and one winding fixed is a variable coupling transformer...it's probably in the antenna circuit and probably acts as a RF attenuator (which was usually effectively the volume control in a TRF).

Rubber wiring sucks. If I know a set has it I tend to think twice about getting it as rewiring an entire radio is a pain...it's uncommon for a large amount of rubber wiring to be used in a 20s set.

If riders isn't helpful look for a Beitmans covering 20s sets. They were a competitor to riders and one of the only second sources of literature for sets that old.

Some 20s sets the wax paper caps used as coupling, bypass and as B+ filters (lytics weren't used much back then) go bad and others they are fine...I don't know that brand well enough to say which it's likely to be. If you have a good leakage current tester you should check the original caps.

Look under Riders National Carbon model 20. It's on the same page showing models 1,2,3.
Dave

Look under Riders National Carbon model 20. It's on the same page showing models 1,2,3.
Dave

I looked there. Didn't have much luck with it. It seems to be incomplete.

I looked there. Didn't have much luck with it. It seems to be incomplete.

Take a look at American Bosch model 28. I'm pretty sure Bosch made those for Eveready. http://www.nostalgiaair.org/Resources/767/M0040767.htm

Take a look at American Bosch model 28. I'm pretty sure Bosch made those for Eveready. http://www.nostalgiaair.org/Resources/767/M0040767.htm

Yep, took a look at that and it sure was the same unit, the Eveready version of the service information was missing quite a bit of helpful information including the parts listing and the information about the transformer and the "filter can" assembly and how to service them, and the rest of the resistors and capacitors and their values.

So as far as the Filter Can assembly goes, since it was meant to be removed and replaced as a whole assembly I'm assuming that in order to replace the old filter capacitors I would need to just cut out the old filter caps and just solder new capacitors onto where the old capacitors that were in the filter can soldered to?

Also I'm going to assume the original Filter Choke is more than likely fine yet so it should be fine to leave that in circuit am I correct?

As for the old filter capacitors go, I'm assuming I should just go with 450V Caps to be on the safe side since they didn't specify a voltage in the service information?

Also I see the 3 Meg Grid Leak Resistor in the parts list, but I don't see the second fuse looking resistor that was on top of the chassis listed in the parts list, unless I'm missing something...:scratch2:

Thanks for your help.

Edit: I figured out what that second fuse style resistor is on the top of the radio chassis, its the 50,000 Ohm (50k Ohm) Plate Resistor which measures open and I searched eBay and couldn't find anything.
I know of someone who might have the part (its an older gentleman who goes by Glasslinger on YouTube, who works on these old 1920s vintage TRF sets all the time) but I'm not sure how to go about contacting him and or if he would even be willing to send me one of his resistors if he had one.

How about leave the defective 50k above chassis for originality, snip the wiring below and add a modern replacement under chassis? It's no more sacrilegious than changing caps. The filter choke, who knows, you'll find out if it's good once you trace the wiring or fire the set up under load. These things are so old that the copper wire used had impurities along with not so good insulating varnish which allows the wire to oxidize and corrode open over time. Same issues with the stage coupling transformers. The finer wire winding's are most subject to corroding open.

How about leave the defective 50k above chassis for originality, snip the wiring below and add a modern replacement under chassis? It's no more sacrilegious than changing caps. The filter choke, who knows, you'll find out if it's good once you trace the wiring or fire the set up under load. These things are so old that the copper wire used had impurities along with not so good insulating varnish which allows the wire to oxidize and corrode open over time. Same issues with the stage coupling transformers. The finer wire winding's are most subject to corroding open.

Ok, thanks! I might just do that. What wattage should I use for that plate resistor? They didn't specify a wattage in the service manual.

Also if the filter choke is bad, could I just replace that with a resistor?

Thanks.

Ok, thanks! I might just do that. What wattage should I use for that plate resistor? They didn't specify a wattage in the service manual.

Also if the filter choke is bad, could I just replace that with a resistor?

Thanks.

Half watt should be more than enough. You could use a resistor but you won't get as much filtering with the stock value capacitors.

Here's an interesting post from over on ARF.

https://antiqueradios.com/forums/viewtopic.php?f=6&t=72312

Towards the end is an explanation of how to neutralize the set(as in Neutradyne). Good to know since the manufacture didn't include it in the Riders service literature. Actually they probably did include that process in a more complete service manual available to their dealers.

How about leave the defective 50k above chassis for originality, snip the wiring below and add a modern replacement under chassis? It's no more sacrilegious than changing caps. The filter choke, who knows, you'll find out if it's good once you trace the wiring or fire the set up under load. These things are so old that the copper wire used had impurities along with not so good insulating varnish which allows the wire to oxidize and corrode open over time. Same issues with the stage coupling transformers. The finer wire winding's are most subject to corroding open.

Some of those plug in fuse like grid bias resistors I've seen gutted and the ends attached to a hollow tube with a modern resistor inside. Either approach is valid and which to choose depends on how much of a stickler for originality you are and/or how much time and effort you want to spend.

Some of those plug in fuse like grid bias resistors I've seen gutted and the ends attached to a hollow tube with a modern resistor inside. Either approach is valid and which to choose depends on how much of a stickler for originality you are and/or how much time and effort you want to spend.

I have no idea how I would go about gutting this fuse style resistor without breaking it.

Also I did take a look over at Playthings of the Past's Website and they seem to have what I'm looking for resistor wise (the glass fuse style resistors) but I didn't see any in the 50,000 Ohm rating so I shot the owner a message to see if he could look through his glass resistor stash to see if he had any that were rated for 50,000 Ohms. I'm waiting to hear back from him yet (I sent him a message at 10 o'clock this morning and it is the weekend so I may not hear back until next week sometime).

I have no idea how I would go about gutting this fuse style resistor without breaking it.

Also I did take a look over at Playthings of the Past's Website and they seem to have what I'm looking for resistor wise (the glass fuse style resistors) but I didn't see any in the 50,000 Ohm rating so I shot the owner a message to see if he could look through his glass resistor stash to see if he had any that were rated for 50,000 Ohms. I'm waiting to hear back from him yet (I sent him a message at 10 o'clock this morning and it is the weekend so I may not hear back until next week sometime).

Just a heads up. The owner of PTOP passed away a while back and apparently someone bought the entire inventory, but he's not saying who he is at this point or when he'll be able to reopen the business. I'd be very surprised if you hear anything back via the old email.

https://antiqueradios.com/forums/viewtopic.php?f=2&t=373920&hilit=gary+play+things+of+past

https://antiqueradios.com/forums/viewtopic.php?f=2&t=376075&hilit=gary+play+things+of+past

Just a heads up. The owner of PTOP passed away a while back and apparently someone bought the entire inventory, but he's not saying who he is at this point or when he'll be able to reopen the business. I'd be very surprised if you hear anything back via the old email.

https://antiqueradios.com/forums/viewtopic.php?f=2&t=373920&hilit=gary+play+things+of+past

https://antiqueradios.com/forums/viewtopic.php?f=2&t=376075&hilit=gary+play+things+of+past

Ok, I didn't know, I just saw a reference to the website in a few posts over at the Philco Phorum, but I didn't pay much attention to how old the threads were that the posts were in.

I'll just have to keep a look out on ebay I guess.

Just a heads up. The owner of PTOP passed away a while back and apparently someone bought the entire inventory, but he's not saying who he is at this point or when he'll be able to reopen the business. I'd be very surprised if you hear anything back via the old email.

https://antiqueradios.com/forums/viewtopic.php?f=2&t=373920&hilit=gary+play+things+of+past

https://antiqueradios.com/forums/viewtopic.php?f=2&t=376075&hilit=gary+play+things+of+past

OK, so I found some regular resistors in my stash that I think might work in my radio as a replacement for the bad fuse style resistor.

I found a box of 47k Ohm 1W 2% tolerance Flameproof resistors that are branded RCA, a package with a 56K Ohm 1W 2% Flameproof Resistor that is Branded Sylvania and I have a package of 56k Ohm 1/2W Carbon Film Resistors that I had left over from when I was restoring my Meck TV last year that either one of those I think should work in this unit.

I think I could just solder it under the chassis between the two points where the resistor holder above ties into the circuit and then just leave the old fuse style resistor in the holder above the chassis for appearances sake (I cleaned up the glass housing of the old resistor and I looked inside and it looked like there wasn't anything in there anymore which might explain why it measured open).

Does any of these resistors I mentioned stick out as far as one that might work better than the other in this position?

Also I found a couple of capacitors in my capacitor stash that might work in place of the old filter caps in the filter supply circuit, one is a 4.7 MFD 250 WVDC Electrolytic and the other is a 2.2 MFD 100 WVDC Electrolytic.

Would those work fine in the filter cap positions on this radio seeing as they didn't specify a Working Voltage for the original filter caps?

Also the 5,000 Ohm "B" Resistor in this radio's Power Supply/Audio Circuit measures open as well, and I was wondering what kind of wattage of resistor it is, its rather large and looks like it might be a 5 or 10 Watt WW Power Resistor but I'm not sure as it doesn't have any information written on it.

Thanks for your help.

I found a box of 47k Ohm 1W 2% tolerance Flameproof resistors that are branded RCA, a package with a 56K Ohm 1W 2% Flameproof Resistor that is Branded Sylvania and I have a package of 56k Ohm 1/2W Carbon Film Resistors that I had left over from when I was restoring my Meck TV last year that either one of those I think should work in this unit.

I think I could just solder it under the chassis between the two points where the resistor holder above ties into the circuit and then just leave the old fuse style resistor in the holder above the chassis for appearances sake (I cleaned up the glass housing of the old resistor and I looked inside and it looked like there wasn't anything in there anymore which might explain why it measured open).

Does any of these resistors I mentioned stick out as far as one that might work better than the other in this position?

Really any of them should be fine. According to the voltage/current chart that resistor will be dropping around 45v, so 45v x 2ma is a whopping 90mw of dissipation.


Also I found a couple of capacitors in my capacitor stash that might work in place of the old filter caps in the filter supply circuit, one is a 4.7 MFD 250 WVDC Electrolytic and the other is a 2.2 MFD 100 WVDC Electrolytic.

Would those work fine in the filter cap positions on this radio seeing as they didn't specify a Working Voltage for the original filter caps?

Assuming B+ at the second filter around 175v, I would use 4.7 mfd @ 250wvdc for 102 and 103. That'll give you some good headroom and a little extra filtering. For that matter you could use a couple 10mfd.


Also the 5,000 Ohm "B" Resistor in this radio's Power Supply/Audio Circuit measures open as well, and I was wondering what kind of wattage of resistor it is, its rather large and looks like it might be a 5 or 10 Watt WW Power Resistor but I'm not sure as it doesn't have any information written on it.

175v - 90v = 85v across the 5k.
85v/5000 = 17ma.
85v x 17ma = 1.45watts. So a 5 watt should be very conservative.

Everything is ballpark based on the values listed in the Bosch model 28 voltage/current chart and schematic.

Many early AC powered TRF sets used paper caps for filtering since lytic technology wasn't there yet. Higher uF paper caps get bigger and more expensive as capacitance increases so many TRFs had less than ideal filter capacitance as a result. Increasing filter capacitance is advisable if mild to moderate hum exists post recap or as a preventative measure now.

Many early AC powered TRF sets used paper caps for filtering since lytic technology wasn't there yet. Higher uF paper caps get bigger and more expensive as capacitance increases so many TRFs had less than ideal filter capacitance as a result. Increasing filter capacitance is advisable if mild to moderate hum exists post recap or as a preventative measure now.

True enough, although when using a choke filter it's possible to get the input capacitor too large and the B+ will go higher than intended. If hum is a problem I'd first try increasing only the cap on the output of the choke.

I'm now having reservations on my recommendation of 250wvdc for the caps. If the 80 rectifier turns on before the other tubes fully conduct, B+ could temporarily become much higher than normal. 350-450wvdc may be the safer bet given how small modern electrolytic are. What are you guy's thoughts?

Ultimately once you get the set operational you can monitor the B+ and see how high it surges at turn on.

True enough, although when using a choke filter it's possible to get the input capacitor too large and the B+ will go higher than intended. If hum is a problem I'd first try increasing only the cap on the output of the choke.

I'm now having reservations on my recommendation of 250wvdc for the caps. If the 80 rectifier turns on before the other tubes fully conduct, B+ could temporarily become much higher than normal. 350-450wvdc may be the safer bet given how small modern electrolytic are. What are you guy's thoughts?

Ultimately once you get the set operational you can monitor the B+ and see how high it surges at turn on.

OK, good point.

When I get paid on Friday (just had to drop $100 between my desktop and laptop computer because my laptop's cooling fan decided it was going to start failing on me and my desktop wouldn't let me get on the internet) I will order 2 4.7 MFD 450 VDC capacitors from AES (they don't sell 2.2 MFD caps but they sell 4.7 MFD caps).

Then order the replacement speaker from ebay for my radio as I think the original speaker is too far gone to try and fix using the diluted glue and coffee filter paper method, because the wiring is also messed up on it and I don't want to have to mess around having to try and special order from Radio Daze or Merry Tunes the wiring and special pin connectors that these speakers need to work because they're kind of pricey.

As for the bypass caps that are in those rectangular aluminum cans, could I just get away with restuffing those? They look easy enough to take apart and gut. Or should I not bother?

Re-stuffing those cans would be ideal if you can get inside them. Take pictures and try to keep the external wiring as close to original as possible.

Re-stuffing those cans would be ideal if you can get inside them. Take pictures and try to keep the external wiring as close to original as possible.

That's what I was planning on doing, I'm assuming that film caps would be used there as well? I'm asking because if you take a look at the picture of the caps there is a definite "ground" and positive lead to these capacitor cans and I was wondering why if they just used non-polar paper caps why would it matter if there was a ground and a positive lead to these capacitors (in this case the can's housing is the "ground" and the capacitor hookup terminals are the "positive" leads.)

Or is the "ground" more of an "RF Ground" to keep the noise down in the radio, since these capacitors are associated with the Tuner/RF stages of the radio?

That's what I was planning on doing, I'm assuming that film caps would be used there as well? I'm asking because if you take a look at the picture of the caps there is a definite "ground" and positive lead to these capacitor cans and I was wondering why if they just used non-polar paper caps why would it matter if there was a ground and a positive lead to these capacitors (in this case the can's housing is the "ground" and the capacitor hookup terminals are the "positive" leads.)

Or is the "ground" more of an "RF Ground" to keep the noise down in the radio, since these capacitors are associated with the Tuner/RF stages of the radio?

Yes Film. Definitely for RF grounding. Relocating them or their wiring can be a big no no.

Yes Film. Definitely for RF grounding. Relocating them or their wiring can be a big no no.

Ok I have a question, concerning the bypass caps in this radio.
Two of the bypass caps are marked on the base of the caps and on the schematic .5 (they are two singles marked at that value) and one cap is a double cap marked 1. on the bottom of the cap and on the schematic, what's the purpose of the decimal point (.) after the 1 on the double cap? I'm assuming it's a 1 MFD capacitor which if that's the case why bother with a decimal point after the 1 on the capacitor markings?

Also how would I restuff the 1 MFD bypass caps? I ask because I think a 1 MFD 630 VDC film cap is going to be too big of diameter to fit inside the can, let alone two of them.

Also as far as the .5 MFD caps go, I'm assuming a .47 MFD 630 VDC cap will work fine in its place?

Also I was wondering how I would go about handling the wiring going to the RF bypass caps because while the rubber insulation of the wiring is still intact and isn't falling apart, it is very brittle to the point that just moving the wires just slightly causes the rubber insulation on those wires to crack and chip off the wire which if I'm going to restuff those bypass caps I would have to move those wires and I don't want to have to replace any more wiring than I have to in this radio to get it up and running.

Ok I have a question, concerning the bypass caps in this radio.
Two of the bypass caps are marked on the base of the caps and on the schematic .5 (they are two singles marked at that value) and one cap is a double cap marked 1. on the bottom of the cap and on the schematic, what's the purpose of the decimal point (.) after the 1 on the double cap? I'm assuming it's a 1 MFD capacitor which if that's the case why bother with a decimal point after the 1 on the capacitor markings?

Also how would I restuff the 1 MFD bypass caps? I ask because I think a 1 MFD 630 VDC film cap is going to be too big of diameter to fit inside the can, let alone two of them.

Also as far as the .5 MFD caps go, I'm assuming a .47 MFD 630 VDC cap will work fine in its place?

Also I was wondering how I would go about handling the wiring going to the RF bypass caps because while the rubber insulation of the wiring is still intact and isn't falling apart, it is very brittle to the point that just moving the wires just slightly causes the rubber insulation on those wires to crack and chip off the wire which if I'm going to restuff those bypass caps I would have to move those wires and I don't want to have to replace any more wiring than I have to in this radio to get it up and running.

I'm not sure on the cap values. It's possible the double cap marked 1. is the total for the two .5 mfd combined, but that's just a hunch. You need to remember that back when these things were built the technology was still very experimental in nature. Personally I would try to baseline the radio using a dim bulb tester, then divide and conquer one component at a time. A complete strip down will only introduce more unknowns. I'd begin with the 80 rectifier removed, testing the transformer with only the filaments of the other tubes installed. Then with the 80 still removed measure between each of the two high voltage wingdings to ground. Next the 80 goes back in to see if the B+ comes up without drawing too much current. Start with a low wattage bulb and work your way up. As long as you limit the current you can't get yourself into too much trouble. At some point you'll have a better idea of where the problem areas are. I agree with leaving the wiring alone until you get all the other bugs worked out, and then only replacing a section at a time with testing in between.

Forgot to mention..I honestly can't think of any good reason you'll need film caps rated for 630v for bypass in this radio. Folks use them simply because they have them on hand and the rational better safe than sorry. I'll be surprised if the B+ swings above 250v for more than a couple seconds on power up. It should settle out around 170v at the second filter cap. The 71 output tubes had a 180v max design value, which I doubt they exceeded.

Forgot to mention..I honestly can't think of any good reason you'll need film caps rated for 630v for bypass in this radio. Folks use them simply because they have them on hand and the rational better safe than sorry. I'll be surprised if the B+ swings above 250v for more than a couple seconds on power up. It should settle out around 170v at the second filter cap. The 71 output tubes had a 180v max design value, which I doubt they exceeded.

OK, so maybe a 250vdc film caps for the bypass caps would be acceptable then? Those would be much smaller and would probably fit into the cans better than the 630vdc ones.

OK, so maybe a 250vdc film caps for the bypass caps would be acceptable then? Those would be much smaller and would probably fit into the cans better than the 630vdc ones.

Probably. But once you get that power supply operational and measure we'll know more precisely. :)

Probably. But once you get that power supply operational and measure we'll know more precisely. :)

Ok. I was able to get my hands on an old desktop PC power supply to get the wires off of for the radio, and it didn't cost me a dime.

Well I got the power supply umbilical rewired with new wire that I nabbed out of an old desktop computer power supply, and I was able to use the same color wires as the original wires too.

Now all I have left to do is replace the dry-rotted wiring in the power supply itself and that is only a couple sets of wire going to the plugin for the power supply umbilical cable for the tuner section of the radio and then put some color coded shrink wrap on the dry rotted wiring that's not replaceable (the wires coming out of the power transformer for the 80 Rectifier Tube Filiments) and then stick a power cord onto the radio and also replace the wiring for the dial lamp socket, and I'll be ready to do a test run of the radio once I get the replacement loudspeaker in once I get it ordered Friday.

Just a little update, I have nearly finished rewiring the radio and I will be getting paid tomorrow so I will be getting the speaker and some resistors
and the two filter caps tomorrow to finish rewiring this radio, and get a cord wired up to this thing.

OK so a little update:

I finished rewiring the power supply on this radio and got a temporary cord wired up to this radio and powered it up without the rectifier tube in circuit and the unit was drawing a little over an amp once it settled down.

Which that sounds about right (even though I don't have the original cover from this radio that had the power consumption label on it) and nothing smoked and nothing sparked or arced and the pilot lamp worked as it should.

I think we're off to a good start with this thing (of course I didn't have a speaker hooked up to this thing or the output tubes in either so that might affect the current draw as well.

I wasn't able to monitor the B+ voltage because I'm not sure where to hook up my DMM to monitor that.

So it seems we might have a winner here!

With the rectifier out there's no B+ to measure. There is the high voltage winding on the power transformer that supplies AC to the rectifier that you could measure by sticking your DMM leads in the skinny pin holes on the 80 rectifier socket and fishing around for the contacts.

With the rectifier out there's no B+ to measure. There is the high voltage winding on the power transformer that supplies AC to the rectifier that you could measure by sticking your DMM leads in the skinny pin holes on the 80 rectifier socket and fishing around for the contacts.

High Voltage is working as it should it seems. I measured the plate voltage for the 80 Rectifier Tube socket (the small pins) as you suggested and there was a little over 400V AC on the plates of the Rectifier Tube socket which sounds about right.

OK so I checked the B+ voltage with the rectifier tube in (just the rectifier tube in) and I got around 320V DC and with the 2 71A output tubes in it dropped to 160V DC so I think the B+ voltage is working as it should, which I think the voltage will drop down to around the 90V DC ballpark range specified on the schematic once the tuner section is hooked back into the circuit (that will add the rest of the 5 tubes in the radio into the circuit).

So it seems like besides having to install the modern plate resistor into the circuit in place of the old fuse style one (by soldering it onto the connector leads under the chassis for the plate resistor socket above) I think this radio will be ready to go once I get the replacement speaker in.

OK so an update:

I installed the 47K Ohm resistor for the plate resistor, and hooked the tuner portion of the radio up to the power supply and installed the tubes and powered it on and monitored the B+ voltage and it was nearly spot on at around 89.7 VDC, so it looks like everything is working as it should! :thmbsp:

Now all I need to do is wait for the replacement speaker to come so I can repair the speaker for this thing and so I can test the radio out and see if it can pick any stations up! :music:

Bravo!

Bravo!

Thanks! I figured this thing wasn't going to be too hard to get going seeing as there isn't much to these old TRF sets, mainly all I had to do was replace a bunch of old crumbling wiring which was pretty easy because all I had to do was steal the wiring out of an old junk desktop computer power supply and use that to replace the old crumbling wiring in the radio and I was pretty much set to go! :yes: :thmbsp:

I hope all your work bears fruit. I've always loved old radios. I look forward to hearing that your radio works. I still have one radio project left.

I hope all your work bears fruit. I've always loved old radios. I look forward to hearing that your radio works. I still have one radio project left.

Yes, me too. I also have a GE L-640 and a Philco 116B up next to finish up and then I have someone on another forum I'm a part of that's sending me a couple more radios to monkey with, and then someone else from that same forum has an eye out for me for some radio parts that came from someone that was part of the Schenactedy Radio Club that recently passed away. So I'll be quite busy for a while. :thmbsp:

When you say new speaker it makes me wonder; have you made sure the speaker impedance is correct in your replacement. 20's speakers were usually some where in the 1k-10k impedance range and new ones are usually 3-8 ohms (which won't sub for a high impedance speaker without a matching transformer).

When you say new speaker it makes me wonder; have you made sure the speaker impedance is correct in your replacement. 20's speakers were usually some where in the 1k-10k impedance range and new ones are usually 3-8 ohms (which won't sub for a high impedance speaker without a matching transformer).

Don't worry, I found on eBay a speaker that was the same exact speaker as what was in the original speaker box for this radio, which was an American Bosch Model 612 Dynamic Speaker.

Now if the person I bought it from on ebay will actually just ship the speaker (as I have yet to get a notification about it being shipped yet from eBay) I will be good.

See link below to see the speaker I bought for my radio.

https://www.ebay.com/itm/333554478891

OK so I took and hooked up my radio's original speaker up to the radio (I had to use an aligator clip lead with a mini banana plug on the end to hook one of the leads from the speaker up to the radio as the original pin plug was missing on one of the speaker leads and I powered on the radio and it actually worked (albeit with a loud hum) which I assumed was because the set needed neutralizing so I got my signal generator out and set it to 1400 KC and I was able to get the hum to partially clear up, but it still had some hum to it.

So I went to turn the radio off and check something out underneath the power supply to see if maybe a ground wire was loose or something, and there wasn't and so I went to turn the set back on again and now the output tubes aren't glowing anymore and there is absolutely no audio coming out of the speaker except for a little crackling noise when I wiggle the output tubes in their sockets.

I checked the heaters on the output tubes for continuity and they still have continuity but they for some reason just refuse to light and I checked the filiment winding for those tubes on the power transformer and its still has continuity (its not open or shorted).

I'm not sure what's wrong with this radio right now and I'm so close to getting this radio going I'm just not sure what's going on with this thing right now and why the audio section suddenly decided to take a dump on me.

Any ideas?

Also can a tube die and still have continuity on the heater pins? Just wondering because it seems weird that both of my output tubes would of died at the same time but I guess its not completely unheard of just really uncommon.

OK, so I was testing my voltages and my power resistors under the power supply of the radio and apparently my 1.5k Ohm 10W WW Resistor just died on me somehow instead of measuring 1.5k Ohms on the multimeter it measured 14 Ohms which is weird because the 5k Ohm "B" Resistor and the 300 Ohm Bias Resistors test fine the 1.5k Ohm Bias resistor is measuring only 14 Ohms, any ideas as to why that would be?

Which I think that might be why I'm not getting any filiment glow or anything out of the Output tubes because the 1.5k Ohm Bias Resistor is part of the output tube filiment wiring.

Thanks for your help.

EDIT: I removed the 1500 Ohm Bias Resistor from the circuit and retested it and it tested fine, apparently I was just reading the resistance wire windings between the two terminal strips where the filiment wires attached to across the bias resistor to ground rather than the bias resistor's actual value.

I think what actually is wrong is that the output tubes are just bad and I think they failed because the output tubes weren't replaced as a matched pair when one of the tubes failed at one point in time (which apparently according to my Rider's Tube Substitution Guidebook with the 71A tube when you go to replace the tubes when they are in a push-pull configuration they need to be replaced as a matched set or they could fail prematurely due to biasing issues between the two tubes, which I think is precisely what happened in my case).

OK so I took and hooked up my radio's original speaker up to the radio (I had to use an aligator clip lead with a mini banana plug on the end to hook one of the leads from the speaker up to the radio as the original pin plug was missing on one of the speaker leads and I powered on the radio and it actually worked (albeit with a loud hum) which I assumed was because the set needed neutralizing so I got my signal generator out and set it to 1400 KC and I was able to get the hum to partially clear up, but it still had some hum to it.

So I went to turn the radio off and check something out underneath the power supply to see if maybe a ground wire was loose or something, and there wasn't and so I went to turn the set back on again and now the output tubes aren't glowing anymore and there is absolutely no audio coming out of the speaker except for a little crackling noise when I wiggle the output tubes in their sockets.

I checked the heaters on the output tubes for continuity and they still have continuity but they for some reason just refuse to light and I checked the filiment winding for those tubes on the power transformer and its still has continuity (its not open or shorted).

I'm not sure what's wrong with this radio right now and I'm so close to getting this radio going I'm just not sure what's going on with this thing right now and why the audio section suddenly decided to take a dump on me.

Any ideas?

Also can a tube die and still have continuity on the heater pins? Just wondering because it seems weird that both of my output tubes would of died at the same time but I guess its not completely unheard of just really uncommon.

If the 71 filaments aren't open they should still light. Did you measure the 71's filament voltage, both at the 71 sockets and wherever it exits the power supply?

Edit - Also, neutralizing a Neutrodyne has nothing to do with eliminating hum in the audio. It's purpose is to neutralize capacitance in the RF tubes. Hum is an entirely different problem. Did you replace the power supply filter caps like you planned?

If the 71 filaments aren't open they should still light. Did you measure the 71's filament voltage, both at the 71 sockets and wherever it exits the power supply?


The filiment pins on the tubes had continuity on them, which is the strange part.

Also I measured the filiment voltage on both 71A tube sockets and they both had 5 VAC on them, the filiment winding for the output tubes on the power transformer has continuity, between the transformer and the tube sockets, so its not an open winding either.

Edit - Also, neutralizing a Neutrodyne has nothing to do with eliminating hum in the audio. It's purpose is to neutralize capacitance in the RF tubes.
Hum is an entirely different problem.


I had just read in a Rider's tube substitution buidebook that I have that the 71A tubes need to be replaced as a matched set or else they will hum which these 71A tubes were NOT a matched pair, one was the original RCA Radiotron branded 71A tube and the other was a Tung-Sol branded tube, which I think might of been where the hum was coming from the fact that the tubes weren't matched.

Did you replace the power supply filter caps like you planned?

Yes I replaced the filter caps like I said I would, I replaced them both with 4 MFD 450 VDC Electrolytics wired in the exact same spots as the originals were.

I just rechecked the filiment voltage for the 71A tubes and they were only measuring about 300 mV and I rechecked the continuity between the wire going from the terminal strip for the output tube winding to the tube sockets and I'm getting intermittent continuity and I looked at the wire and there was spots where the wire was bare and was shorting against the output transformer and the chassis of the radio so I think if I replace the wire going from the terminal strip to the tube sockets I think it might fix the problem.

I just rechecked the filiment voltage for the 71A tubes and they were only measuring about 300 mV and I rechecked the continuity between the wire going from the terminal strip for the output tube winding to the tube sockets and I'm getting intermittent continuity and I looked at the wire and there was spots where the wire was bare and was shorting against the output transformer and the chassis of the radio so I think if I replace the wire going from the terminal strip to the tube sockets I think it might fix the problem.

Sounds like you found your problem, hopefully before you damaged the winding. Partial grounding of one side of the filament could have something to do with the hum too. For such reasons it's a good idea to keep the set plugged into a dim bulb tester until you're very confident everything is working reliably.

Sounds like you found your problem, hopefully before you damaged the winding. Partial grounding of one side of the filament could have something to do with the hum too. For such reasons it's a good idea to keep the set plugged into a dim bulb tester until you're very confident everything is working reliably.

The problem with this thing is that the wiring is so hard to get to in this portion of the chassis and trying to clean the solder off the holes where the wires go into on the tube sockets is a pain in the butt because the ouptut and the interstage transformer are in the way and I can't move them very easily.

OK, so I got the wiring replaced for the 71A tubes and that fixed the issue, now I just need to figure out how to properly neutralize this set and get the tuning dial to track correctly because several of the known local (and distant) stations are not showing up at the correct positions on the dial and one of the local high powered Mexican stations on the AM Dial is showing up on two spots on the dial.

OK well she's good to go now, all I need is a period correct cloth cord (a reprodution one of course), and this radio will be ready to go back together! :music::thmbsp:

This thing is super sensitive for a TRF set because most of the time these TRF sets get a bad rap for being very lousy at getting anything in (radiotvphononut for example says these things are horrible as DX'ing) but I was receiving stations from Cincinatti, Chicago, Waterloo, Iowa, Fort Wayne, Indiana, etc on this radio earlier this morning with no problems and all I had hooked up to it was a 6' length of wire.

Sounds like a fun radio. With 4 tuning stages and push-pull audio I'm sure it was a pretty impressive performer back in it's day. :yes:

Sounds like a fun radio. With 4 tuning stages and push-pull audio I'm sure it was a pretty impressive performer back in it's day. :yes:

I'm sure it was! :yes:

I got a glimpse of the radio that mine is based on (the American Bosch Model 28) and it was made of Mohogany with a Maple Inlay around where the tuning dial went and the speaker for that radio looked like a Gothic Cathedral, it was quite an impressive looking set.

I noticed that my radio has 2 volume controls, one that is a potentiomenter that is controlled by a knob that is linked to the potentiometer with 2 pulleys and a belt (dial string), and another one that is a knob linked to a of some sort, any ideas as to what those two volume controls are for?

Also the inside of the speaker cabinet has some chunks of wood missing from where the speaker itself attached to the cabinet and the cabinet took a tumble at some point in time in its life and the weight of the speaker was enough to blow out the wood around where the screws were that fastened the speaker to the front of the cabinet, do you have any suggestions about how to repair that damage?

I was thinking of using a wood epoxy of some sort if such a thing exists and filling in the missing wood chunks and then putting the speaker back in the way it was originally.

I noticed that my radio has 2 volume controls, one that is a potentiomenter that is controlled by a knob that is linked to the potentiometer with 2 pulleys and a belt (dial string), and another one that is a knob linked to a of some sort, any ideas as to what those two volume controls are for?

Hard to say without seeing where second is wired into the circuit. A guess is that someone added a second volume at the input to the 1st audio amp so they could run the gain of the RF stages higher.

Also the inside of the speaker cabinet has some chunks of wood missing from where the speaker itself attached to the cabinet and the cabinet took a tumble at some point in time in its life and the weight of the speaker was enough to blow out the wood around where the screws were that fastened the speaker to the front of the cabinet, do you have any suggestions about how to repair that damage?

I was thinking of using a wood epoxy of some sort if such a thing exists and filling in the missing wood chunks and then putting the speaker back in the way it was originally.

Wood glue or epoxy mixed with sawdust pressed into the voids. When it hardens sand flush and re-drill the holes.

I noticed that my radio has 2 volume controls, one that is a potentiomenter that is controlled by a knob that is linked to the potentiometer with 2 pulleys and a belt (dial string), and another one that is a knob linked to a of some sort, any ideas as to what those two volume controls are for?


I just realized that the second volume control you speak of must be the variable antenna coupling transformer? I guess you could say it's a second volume control, although technically an antenna tuning control. It has something to do with the very good selectivity. :thmbsp:

TRF radios are known to be sensitive but not selective. Superhets were the "cure" for the problem. You found out that some TRF designs were as good, or better than superhets. Grebes were known to be excellent DX radios!

Kevin:
I think you might be right on the money for the one "volume control" because it is a coil that moves with the knob and depending on how the coil is positioned it makes the selectivity of the radio better or worse (better or worse separation between stations on the dial and also makes the overall reception better or worse depending on the position of the coil) and the second "volume control" which is the one that is actually a rheostat type control is the actual volume control because the overall volume of the set is made louder or quieter when that knob is turned.

Titan1a: This radio I think is on par with Grebe as far as being a great DX'ng TRF set because as I said previously this radio was picking up stations loud and clear from as far away 300+ miles away or more, and this radio is still using the original bypass caps for the RF cans!

Also I got my replacement speaker in for this radio's speaker cabinet which was an American Bosch Model 612 8" Dynamic Speaker just like what was in there originally so right now I'm working on repairing the blown out wood around the original screw holes that were used to hold the original speaker in place when the speaker was made back in 1927, and I'm making the repairs with Elmer's Stainable/Paintable and Sandable Wood Filler that also resists shrinking and cracking.

Once I'm done repairing the damage I'll re-drill the holes back where they were originally and install the speaker and put it back together and wire up the speaker and test out the radio with the newly repaired speaker and see how it sounds and works. :thmbsp: :music:

It is finished! I have uploaded a video showing the after results of the restoration including what it sounds like with the speaker repaired (I actually had to repair the replacement speaker because apparently the speaker I got off ebay even had some damage to it (fairly minor damage compared to the original).

Enjoy!

Pictures below showing what the radio looks like.

YouTube Video Link Below:

https://www.youtube.com/watch?v=P-1rXkXH_IY

You did real good, it sounds very nice for a radio from that period. Now if you only had an outdoor antenna away from buildings with a shielded lead-in connected to a good ground, you could lose a lot of that buzz riding on the rf. With an indoor antenna you're actually picking up a lot of your signal that's being re-radiated from your AC wiring. In other words your houses AC wiring acts like a long wire antenna, but it's also got all the noise on it.

You did real good, it sounds very nice for a radio from that period. Now if you only had an outdoor antenna away from buildings with a shielded lead-in connected to a good ground, you could lose a lot of that buzz riding on the rf. With an indoor antenna you're actually picking up a lot of your signal that's being radiated from your AC wiring.

Well Unfortunately I don't own my own place so a long wire antenna is just going to have to suffice for the time being since I can't drill holes in the wall at my place.

Well Unfortunately I don't own my own place so a long wire antenna is just going to have to suffice for the time being since I can't drill holes in the wall at my place.

Understandable. Sometimes just getting the radio connected to a good earth ground can help, or even a separate long wire connected to the antenna ground can act as a counterpoise and cancel out some of that noise. Often it takes a lot of experimenting to find the best solution.

You did the best you could. To cut through the "crud" I use a very expensive amplified loop antenna. Listening to WSM as I type.

You did the best you could. To cut through the "crud" I use a very expensive amplified loop antenna. Listening to WSM as I type.

I was able to pick up WSM just fine on my radio with just a long wire antenna at 10 o'clock at night, I was also able to pick up the Oldies station out of Toronto, Ontario, Canada just fine on my radio as well on my radio at 10 o'clock at night one night with just a longwire antenna.

Excellent! Maybe I need to get one of these.

Excellent! Maybe I need to get one of these.

Yes, this radio actually has really good sound for its age and also it has great DX'ing abilities for a TRF set.

I know I'm late to the party here, but I own two of these. Mine are Model 2's, which are the same radio but in a green metal case. $75 is a good price; I paid about $100 each for mine.

On a whim I powered up the nicer of the two and was surprised to find it still worked! It's encouraging to hear it'll be a decent performer after restoration. I'm not a big fan of 1920s sets, but the Art Deco styling of these won me over.

I know I'm late to the party here, but I own two of these. Mine are Model 2's, which are the same radio but in a green metal case. $75 is a good price; I paid about $100 each for mine.

On a whim I powered up the nicer of the two and was surprised to find it still worked! It's encouraging to hear it'll be a decent performer after restoration. I'm not a big fan of 1920s sets, but the Art Deco styling of these won me over.

Yes, I've always wanted a 1920s radio so that my radio collection could be rounded out to include all of the various style of radios ever made over past 100 years.

One question Tim, did your radio when you powered it up make a high pitched whistling noise out of the speaker while it was warming up?
The reason I ask is because my radio when its first powered on and while its warming up makes a high pitched whistling noise out of the speaker before finally putting out an audio signal.

Yes, I've always wanted a 1920s radio so that my radio collection could be rounded out to include all of the various style of radios ever made over past 100 years.

One question Tim, did your radio when you powered it up make a high pitched whistling noise out of the speaker while it was warming up?
The reason I ask is because my radio when its first powered on and while its warming up makes a high pitched whistling noise out of the speaker before finally putting out an audio signal.

The reason is that your detector tube , which should be a #27 if I looked at the right schematic , is an indirectly heated cathode type of tube , whereas your #80 B+ rectifier and #71A audio output tubes are directly heated cathodes . When you turn the power on the directly heated cathode tubes are conducting pretty much instantly VS the one indirectly heated cathode taking it's sweet time to begin passing signal . For all that time you have the audio amp section operating wide open but with no signal to process . In the absence of signal to force a bit of bias onto the circuit the tubes become very sensitive to "Microphonics" , having loose elements in the tube actually rattle and give off squeals . This is of course assuming that you did a full recap on the radio (haven't kept up with the entire thread here) because an electrical cause could be if the capacitor listed on the schematic as "43 - By pass condenser .002 mfd." were bad that could cause the amp to squeal till the detector warmed up and began supplying it with audio as well .

The reason is that your detector tube , which should be a #27 if I looked at the right schematic , is an indirectly heated cathode type of tube , whereas your #80 B+ rectifier and #71A audio output tubes are directly heated cathodes . When you turn the power on the directly heated cathode tubes are conducting pretty much instantly VS the one indirectly heated cathode taking it's sweet time to begin passing signal . For all that time you have the audio amp section operating wide open but with no signal to process . In the absence of signal to force a bit of bias onto the circuit the tubes become very sensitive to "Microphonics" , having loose elements in the tube actually rattle and give off squeals . This is of course assuming that you did a full recap on the radio (haven't kept up with the entire thread here) because an electrical cause could be if the capacitor listed on the schematic as "43 - By pass condenser .002 mfd." were bad that could cause the amp to squeal till the detector warmed up and began supplying it with audio as well .

I did not replace any of the bypass caps just the filter caps, and that's how it operates.

No. 43 the .002 MFD Cap is a mica cap so I didn't even bother with that cap.

I did not replace any of the bypass caps just the filter caps, and that's how it operates.

No. 43 the .002 MFD Cap is a mica cap so I didn't even bother with that cap.

If you want the squeal to go away I'd try replacing that cap , yes I realize it's mica but in very very rare instances those can fail and go open just like any other cap .

Always remember , NOTHING in life in infallible , from the "unsinkable" Titanic to our "Always good" mica caps :thmbsp:

If you want the squeal to go away I'd try replacing that cap , yes I realize it's mica but in very very rare instances those can fail and go open just like any other cap .

Always remember , NOTHING in life in infallible , from the "unsinkable" Titanic to our "Always good" mica caps :thmbsp:

Ok, I'll give it a shot. But taking this thing apart again is going to be a pain because of the way they have this thing assembled into the case.

The whistling noise it makes when it first powers on isn't that annoying , because it does go away once the radio is warmed up, it doesn't really bother me that much it was more of a curiosity than anything.

If it's a difficult set to take apart and the brief warm up whistle doesn't bother you then I wouldn't blame you in the least for not going after it . If it does ever have a future failure that requires opening it maybe then would be a good time to try replacing that cap .

If it's a difficult set to take apart and the brief warm up whistle doesn't bother you then I wouldn't blame you in the least for not going after it . If it does ever have a future failure that requires opening it maybe then would be a good time to try replacing that cap .

That's what I was thinking, because the radio works great with just the power supply reworking, and the rewiring job that I did.

The bypass caps probably should of been replaced because when I listen to more distant stations (late night DX'ing), the stations will cut in and out sometimes (the station's volume will go really quiet for about 2 or 3 minutes and then get blaring loud for about 20 minutes or so and then back down to barely listenable levels again for a couple of minutes, so on and so forth).