Working on this radio for a friend who's Dad passed. The goal is to "just make it play again" so making the chassis look new and making all the parts look 100% original is not exactly necessary.

Cleaning it up enough so I could even work on it was a real job in itself...
http://i.imgur.com/G2toL15.jpg

And after..
http://i.imgur.com/DkLitYV.jpg

I did the obvious and recapped the power supply section with modern components.
Re-stuffed the caps that I could. One was impossible to get the tar out of no matter how much heat was applied so I just skipped it for now and put the replacement capacitors under it for the time being. Yeah I know the ugly black thing aka capacitor bank lol..
http://i.imgur.com/GWxqQI5.jpg

Finally got the front back on and the glass cleaned..
http://i.imgur.com/02RYN7r.jpg

Now the questions :scratch2:

First of all it plays... IT PLAYS!
I was absolutely amazed that this thing is picking up stations and works as good as it does considering this is my first antique restoration.

One problem though... the speaker makes an occasional popping scratchy sound even when volume is all the way down and/or the RF tubes are removed.
This seems to be occurring only in the 6F6 amp stages or the power supply. Could it be a noisy resistor?
To make matters stranger depending on the pair of 6F6 tubes I use makes a difference in how noisy it gets. My tubes are good BTW.

When I crank the volume 2/3 of the way on a loud station the radio suddenly distorts badly. Almost sounds like it is breaking out in oscillation or something. I know it is not the speaker.
What could cause that?

Finally.. the radio requires a good antenna to pick up stations. My outdoor 120' wire makes it pick up all the AM stations my other radios can and it picks up some basic shortwave but it seems lacking in the reception department.
I calibrated and peaked everything so either it is just not a sensitive radio or it is a weak RF tube? I do not think I have replacement tubes to check this, will have to check later.

Thanks for the help.

Like I said the goal here is to just make the radio play. They do not care how authentic it looks under the chassis obviously. Heck they will probably never even look at the back of the radio after I set it up for them.

One last question: How much do you think I should ask for payment for this kind of work? I was thinking $5 for each replacement tube. It came with 3 bad tubes. Maybe 20 bucks plus cost of parts?

A little more info:

The tuning gear above the variable capacitor was completely locked up. Took a lot of effort to pry that loose.
What kind of oil did they use back then that got hard and froze up over time?
After some lubrication it spins freely now and the tuning is smooth.

The power cord it came with was literally falling apart lol. The plastic was flaking off and near the radio the cord was down to bare wire.

Someone in the history of this radio pulled apart the power transformer. Both screws were missing and the top was hanging off with the 5Y4 dangling about.
This worried me thinking that the transformer may be dead. Oddly after putting it back together it was fine but the 5Y4 had a blown filament so someone must have thought the transformer was bad not realizing it was the tube sitting right on top?

The fine tune control is missing the rubber thingy behind it. I read elsewhere that putting a plastic round washer behind it with some glue will fix that.
the whole cone-centric tuning thing is rather odd but for 1937/38 it must have been neat :D

When all is done I will post a video of it working in its cabinet for your viewing pleasure :)

If all you did was replace the electrolytic capacitors then you are a long way from done with a proper electronic restoration. All of the brown tubular paper capacitors and the block cap need to be changed. The paper caps are likely what is causing the ticks and distortion in your audio, and are also likely contributing to it's weak reception.

The block caps in those are usually there to filter the AC line by bypassing noise on it it to the chassis. You really need to replace them with AC line rated safety capacitors...Some sets have them installed before the power switch, and if they fail when no one is around to deal with it, the results could be a fire and a lawsuit.

I concur. The bakelite block with the AC line caps is the one where you have your black line cord attached.

This is what will happen eventually if not replaced...
https://farm4.staticflickr.com/3173/3066786159_ddf4e3d74e.jpg (https://flic.kr/p/5F15Fr)

I concur. The bakelite block with the AC line caps is the one where you have your black line cord attached.

This is what will happen eventually if not replaced...
https://farm4.staticflickr.com/3173/3066786159_ddf4e3d74e.jpg (https://flic.kr/p/5F15Fr)
Well that is frightening :yikes:
Guess that will be the next job I will get on lol. Yeah I know that I am no where near done with this yet.
I replaced the capacitors in the audio section and the noise is still there yet so I can rule out bad capacitors, or at least I think?
One step at a time...

Bad caps in the RF/IF/det system can also cause that popping...

Like others have said--replace ALL of those paper caps--and BTW_-there is a "bakelite block" off of that control on the left--it contains one or more paper caps. ALL of those caps are dead by now !! If you want it to work welland SAFE-do it.

Like others have said--replace ALL of those paper caps--and BTW_-there is a "bakelite block" off of that control on the left--it contains one or more paper caps. ALL of those caps are dead by now !! If you want it to work welland SAFE-do it.
Wow I feel like an idiot. I had no idea the other bakelite blocks had capacitors in them but looking at the schematic made me have an uh duh moment.
Going to try and replace the capacitors in those blocks as shown on this page..
http://www.philcorepairbench.com/capbuild.htm
I hope the tar releases without too much trouble.

That would probably explain the popping clicking noises I hear on the audio even with the other (RF) sections not in use.
It was really making me scratch my head hearing that noise even with the volume all the way down. Now I see there is caps in those blocks that I overlooked.

Thanks for the help so far guys.
I am used to working on much more modern electronics even though I have built and repaired stuff with tubes before but this is quite a bit older than I am used to :D

edit: Just removed the tar and caps from the first bakelite block for the power line filter and it actually ended up being really easy. I used a lighter to heat up the outside of the block and just pushed a solid piece of wire into the terminal hole like shown in the link and it just popped right out after loosening the sides of the tar some with a knife :)

Like others have said--replace ALL of those paper caps--and BTW_-there is a "bakelite block" off of that control on the left--it contains one or more paper caps. ALL of those caps are dead by now !! If you want it to work welland SAFE-do it.

If you look up the information about bakelite block capacitors, some also have resistors inside, as well. :scratch2:

[quote]One last question: How much do you think I should ask for payment for this kind of work? I was thinking $5 for each replacement tube. It came with 3 bad tubes. Maybe 20 bucks plus cost of parts?[quote]

List all the tubes, caps and misc. parts five bucks for each tube is good, maybe a buck each for the caps.
Parts should add up to $30, and for the level of work you're doing, a $75 bill would be reasonable considering what $$$ a working console brings.

BTW-For the full safety treatment: Two 'Y2' capacitors for the line-to-ground caps, put on a grounded cord and pigtail fuse it at 1.5 or 2 amps.
That way, you ground the chassis by plugging it in and a shorter wire antenna would work better.

Its nice to see that Philco did not use that lousy rubber wiring on this one.

Can also chip the tar out with a screwdriver on most of them...it's faster than melting it.

Good info on that Philco repair bench. And as they state, there is no need at all to refill the block with tar or anything else. The modern parts are well sealed and better to start with than the paper caps used back then.

Can also chip the tar out with a screwdriver on most of them...it's faster than melting it.

That was some good potting compound they used. They claim that the caps were vacuum impregnated. The best system ever devised.
I find using a little heat, makes the potting pop right out. I use a H-F heat gun, set on low, hot enough for the job.
The caps are remarkably good, considering their age, proving that Philco was ahead of their time.
They still can't be trusted. :sigh:

I have a 1932 cathedral that as found (all original except for the 40's lytics tacked in parallel with the originals) 2-3 years ago ran on it's original caps...Albeit with weak reception and audio distortion. It used all block caps for it's paper types. Re-stuffing the blocks brought it back to being a strong performer.

I don't own a heat gun, and have not encountered a block with one of the harder potting materials that, I seem to recall reading, were made so the chipping method is the easiest means at my disposal....The tar is so soft a little bit of pressure will sink the blade of a flathead screwdriver a surprising distance into it...

All the wax capacitors are now replaced along with the ones inside the bakelite blocks.
Found a 3.5k resistor that was going bad and overheating in the audio section which was causing the popping sound. Replaced with a higher wattage value and fixed that right up!

Radio sounds great now except that I am still having two problems:

When I turn the volume up past a point there is a crackling sound from the speaker. Sounds like real bad distortion and is sudden.
I wonder if this could be the speaker itself? I noticed before that when moving the voice coil by hand that it sounded like it would rub sometimes but wasn't sure if that was just from me manually moving it or if it does have a problem. If so is there an easy fix if that is the cause?

Other problem may have to do with the 6F6 tubes. With a few different tubes the radio can go from sounding good to sounding like there is motorboating or some kind of feedback with the volume all the way down, or up.

Reception has improved greatly after recapping and a tuneup but I still think it should pick up more stations on SW and not need such a long antenna on MW. Maybe I am expecting too much out of such a simple design :scratch2:
The wall voltage also worries me. How do these old sets fare on modern AC wall voltage? I think our voltage runs close to 125v here.

Just checked the speaker, now I know that is not the issue!
There is definitely feedback getting into the amplifier section from the RF section.
With volume all the way down, and even the dial disengaged (audio muted) I notice when turning the dial that I can hear RF feedback getting into the audio that sounds like hissing/squeeling. Changing the tone control effects this also. The problem seems to come and go at will.
Not sure how RF is getting back into the 6K5 tube but it must be. Tube shields are on by the way.
All capacitors check out fine so maybe it is just odd wire placement or something similar?
Stranger yet this only happens when the set is fed full line voltage. When I lower the voltage through a variac down to 100-110v the problem seems to goes away.

Edit: I tried a different 6A8G osc/det. tube that I had laying around and it seems to have cleared up the problem mentioned above. Not sure exactly why that is though.
Going to give it a few days of play and if no new problems pop up I am going to call it a done job since all seems to be working well and is playing nicely.
Thanks again everyone.

If you have 125VAC line voltage, wouldn't be a bad idea to install a bucking transformer. Radio Shack used to sell, may still sell, a filament transformer for 12.6 and 6.3 volts via a center tap. I'd hook it up for the full 12 volts drop on that set.

If you look up the information about bakelite block capacitors, some also have resistors inside, as well. :scratch2:
Yeah this Philco has none in the bakelite blocks.

I have been running the radio hard for a few hours now with good volume and notice there is still distortion when cranked up on a local station yet it sounds fine on distant stations at same volume.
I swear there is some feedback happening somewhere under the chassis. I would hate to give it back like this but the damn thing works perfect except at the most random time. All caps check out, resistors and so on.
Only thing I can figure is the higher AC line voltage used today makes the osc/mixer tube feedback more than originally expected.

I don't know at this point. The radio is playing so great but on strong stations I swear there is distortion on high volume that is not there on distant stations at same volume level with volume control compensated for weak stations.

Also switching the two 6F6 tubes around provides different volume/distortion levels even though both tubes are good. I tried a few different tubes but I am getting fustrated because the circuits itself does not seem consistant more so than the tubes themselves.

Sorry I am rambling.
The radio sounds perfect at regular volume but on strong stations and loud volume I hear distortion. I am thinking it should provide the volume or am I pushing the radio itself beyond the limits of audio amplification?

I got to keep in mind that the speaker will probably sound louder in the cabinet also. So maybe I am hearing distortion on loud volume because I am hearing it at higher volume than meant for w/o the cabinet to reinforce the amplification.

Could be an AVC issue. AVC or automatic volume control is meant to retard the amplification factor of the RF and IF stages on strong stations so that the volume of stronger stations better matches that of weak ones. It could be insufficiently retarding amplification on stronger stations resulting in signal overloading. If it bugs you then check the values of the resistors in the AVC feedback system (usually gets it's input from an extra detector diode that is not part of the audio signal chain), and those in the RF and IF system if any are outside of tolerance then it could affect AVC opperation....However it is good to know when to quit.

It will definitely sound better with the speaker in the cabinet as that will allow bass tones to come out. +1 on the possible AVC problem: local stations overloading somewhat.

Yeah thanks a ton guys. I am connecting the radio to a damn good outdoor 120' wire antenna plus a good set of radials so that alone may be overloading the AVC.
I guess at this point I will just send the radio back to its home and mount it back in its cabinet. Like you guys suggested and I thought, it will bring out the bass and loudness.
Being on this good of an antenna is probably overkill and more than the original AVC was designed to handle at the time.
With a 30' wire in the house it plays fine, it is just on the real long wire it distorts. All parts check out so that is not the problem.
This is the first antique radio of this age I have worked on so thanks for baring with me.
I am 29 and only have this much " " experience on tube electronics. I have built a few HF RF and AF tube amps but that is the extent of my knowledge.
This has been really fun to work on but I think it is time to give it back and let the owners enjoy it. Had her playing all night with Coast to Coast AM on multiple channels (thanks to syndication lol).
I have my limits, and this pushed it. I have a good part collection but this hit the replacement part limit, especially parts rated 400v DC+. I am damn lucky I had some old spare tubes from an old Philco I got as a kid that was junked.
Going to try and poke around the chassis with some bypass caps and see if that cleans up any residual RF bleed. After a few hours of play there is still RF getting back into the AF, though at almost unaudable levels, it is enough to cause distortion at fuller than loud audio.

One last thing.. I can not believe the fidelity had by this old radio. This seriously outperforms all the other SW/MW radios I have owned including modern units like my ratshack DX398 (ATS909) for sound reproduction and it somehow maintains good selectivity though the modern radio outperforms the antique for sensitivity.
I guess those big old coils w/o slugs really perform better for Q?

There are some bypass (one end to chassis ground) capacitors on the AVC bus. I beleive these may need to be checked to see if a different capacitance helps reduce feedback.

i've also seen where a capacitor across the audio output transformer needs its value changed to fully eliminate high-frequency feedback.

Well just found the final problem and now I am screwed.
The bad audio was coming from the transformer on the speaker. One of the 3 coil wires used for the push-pull tubes was bad so only one tube was driving the speaker. Oddly it did sound good for just running on one tube until turned up as described above.
So now I am stuck with a speaker that has no PP transformer :(
Does anyone have an idea where I could find a replacement transformer?
I feel so let down right now after having the radio partially working after all that work only to find the speaker transformer was partially bad.

Try Play Things of the Past. http://www.oldradioparts.com/index.html

Try Play Things of the Past. http://www.oldradioparts.com/index.html
Thanks, looking at the site now.

I also had the idea to rewind the transformer but not sure how insane that would actually be. If only I could get the primary wire out w/o breaking it all up to see the full length.
Got the EI plates out and unwound the secondary but the primary is so small and fragile.
That may be a lost cause though.

Measurements show 3.2 ohm on the voice coil with the bucking coil. From a few minutes of research shows 10,000 ohms or so for the secondary P to P.
So That would be a 50:1 transformer that can handle 5 watts audio.
New is out unless it is cheap.

This is a pretty common spec, lacking more creative options bolt this to the side of the chassis and abandone the one on the speaker in place
http://www.tubesandmore.com/products/P-T125C

You said it has P-P 6F6 amps. I would think ANY 6F6 P-P OPT would work, say a 15 watt power rating or so. With a 4 ohm or 3.2 ohm VC winding.

Thanks, looking at the site now.

I also had the idea to rewind the transformer but not sure how insane that would actually be. If only I could get the primary wire out w/o breaking it all up to see the full length.
Got the EI plates out and unwound the secondary but the primary is so small and fragile.
That may be a lost cause though.

Measurements show 3.2 ohm on the voice coil with the bucking coil. From a few minutes of research shows 10,000 ohms or so for the secondary P to P.
So That would be a 50:1 transformer that can handle 5 watts audio.
New is out unless it is cheap.


With P-P 6F6, running at maybe 300 volts on the plates----it will be MUCH higher power than 5 watts !! More like 12-15 watts. Like I said--a 15 watt tranny will work fine.

This likely will work. 42 tubes are the same electrically as the 6F6 tube ::

http://www.ebay.com/itm/PHILCO-PUSH-PULL-42-OUT-PUT-TRANSFORMER-/281341412659?pt=LH_DefaultDomain_0&hash=item4181414533

Yeah, any pp transformer designed for 6V6 tubes will work... I would say cabnibalize a console stereo but I don't endorse such behaviour :)

235 volts on the plates and the Philco service info specifies 5 watts undistorted output.

That is sorta defeating the purpose of P-P isn't it?

A SINGLE 6F6 can do 5 watts or so, if driven the right way !!

Might have been a marketing thing so they could charge more for a higher tube count ?

Two Philco consoles, with PP 41 tubes, I restored had defective output transformers. I took one of them apart and the wire is so fine, you can't move the leads without breaking them off.

I bought a spare PP output trans from Tubesandmore, so Im ready for the next one. At least its not your power trans, more of an issue in Zenith radios, which I see few of in comparison.

You guys may not believe this but I just found a power supply transformer that has exactly the same ohms on its secondary winding and the 6.3v taps come out to be around 3 ohms so it matches the blown audio transformer.
I wired it in place of the broken transformer and IT WORKS!
Not only does it work but it sounds good too!
It is a slightly larger transformer but it mounted to the original holes on the speaker where I removed the old audio transformer and rivets.
I know it is not meant for audio usage but heck it sounds better than the original and all the voltages check out.
Sometimes luck does exist.

Congratulations, you have discovered a solution we can use.

What was the secondary voltage on the power transformer you found and did you use the primary winding for anything?

What did you do to get that grime off the chassis?

You guys may not believe this but I just found a power supply transformer that has exactly the same ohms on its secondary winding and the 6.3v taps come out to be around 3 ohms so it matches the blown audio transformer.
I wired it in place of the broken transformer and IT WORKS!
Not only does it work but it sounds good too!
It is a slightly larger transformer but it mounted to the original holes on the speaker where I removed the old audio transformer and rivets.
I know it is not meant for audio usage but heck it sounds better than the original and all the voltages check out.
Sometimes luck does exist.
Yessir, a power tranny will work. Response rolls off dramatically above about 5khz, but that's still plenty adequate broadcast quality.

When i was a dumb kid and didn't know any better:nerd:, i used two TV power xfmrs hooked back-to-back to plate-modulate a CW transmitter for voice. The primaries, 6.3V, and 5V windings were all in series and in-phase as shown.
It worked great.
(I didn't understand about core saturation then. The xfmrs were 25 cycle type with lots of iron, and that's probably what prevented any core saturation issues.)

Congratulations, you have discovered a solution we can use.

What was the secondary voltage on the power transformer you found and did you use the primary winding for anything?

I'm curious how it was wired up too. The schematic shows about 340 ohms on either side of the primary center tap of the output transformer.

Was the primary center tapped on the power transformer you used ? I would expect the primary of a power transformer to have a much lower resistance than 340 x 2 ohms :scratch2:

I believe he used the secondary (B+) winding of the xfrmr as his audio primary.

Congratulations, you have discovered a solution we can use.

What was the secondary voltage on the power transformer you found and did you use the primary winding for anything?
The transformer came out of a gutted Heathkit AG-9a audio generator. I think the HV output was probably around 300v, and the fil. voltage at 6.3.
I used the HV B+ winding of the transformer for the audio primary (red, yellow-red, red) and the fil. voltage for the speaker output (greed, green).
117v wires (black, black) are unused but they do come out to around 15 ohms I believe, so theoretically they could have been used for another speaker supporting a higher impedance.

Measuring with a multimeter I got around 320ohms from Common to each red wire. and 3ohms on the filament wires.

Yessir, a power tranny will work. Response rolls off dramatically above about 5khz, but that's still plenty adequate broadcast quality.
I haven't swept the transformer yet on a scope but it sounds like the highs are there just fine. It may roll off some but with the design of the radio I doubt the speaker itself would reproduce much above 5kHz.

What did you do to get that grime off the chassis?
Just a good dusting, then scrubbed with a cloth and some warm water. Owners do not care how shiny the metal looks when finished so just went for a basic clean.

Oddly the transformer sounds really good and distortion free.
Trying this transformer was a shot in the dark but it works wonderfully!