Late 1920s Eveready Model 1 TRF Set need info

[vortalexfan]

Originally Posted by Electronic M

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

[vortalexfan]

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.

[vortalexfan]

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).

[Kevin Kuehn]

Originally Posted by vortalexfan

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?

[vortalexfan]

Originally Posted by Kevin Kuehn

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.

[vortalexfan]

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.

[Kevin Kuehn]

Originally Posted by vortalexfan

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.

[vortalexfan]

Originally Posted by Kevin Kuehn

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.

[vortalexfan]

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.

[vortalexfan]

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!

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.

[Kevin Kuehn]

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.

[vortalexfan]

Originally Posted by Kevin Kuehn

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.

I'm sure it was!

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.

[Kevin Kuehn]

Originally Posted by vortalexfan

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.

Originally Posted by vortalexfan

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.

[Kevin Kuehn]

Originally Posted by vortalexfan

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.

[Titan1a]

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!