Philco 38-4 questions

[darklife]

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...


And after..


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..


Finally got the front back on and the glass cleaned..


Now the questions

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?

[darklife]

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

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

[Electronic M]

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.

[bandersen]

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...

[darklife]

Originally Posted by bandersen

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...

Well that is frightening
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...

[Electronic M]

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

[rca2000]

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.

[darklife]

Originally Posted by rca2000

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

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

[dieseljeep]

Originally Posted by rca2000

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.

[DavGoodlin]

[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.

[Electronic M]

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

[dieseljeep]

Originally Posted by Electronic M

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.

[Reece]

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.

[Electronic M]

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...

[darklife]

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
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.