[NostalgiaRadioTime]

Once I removed the chassis, I found a decades old "patchwork pete" repair:

   

It appears I'm missing a choke?

   

In its place are two .05 mfd capacitors and two 50K resistors tied to two terminal strips. Not sure how this worked but it must've at one time, judging by how old the caps look.

Can anyone suggest a more proper replacement that would look correct?

[morzh]

I think it is the can. As for values, look in the sch.

[Radioroslyn]

No your missing the driver transformer(#83). Unless there is phase inversion circuit the output stage isn't going to work properly. It may have been rework to have a resistor in the plate circuit of the 42 driver tube (to act like the transformer pri) and capacity coupled to the control grid of one the 42 output tubes. The other 42 control grid might be connected to the the screen grid of the first 42 though a cap. Much like the late 30's and early 40's philcos. The problem it that the original set up the 42's have the screen and plate connected together in a triode configuration in what Philco their super class A 10w audio output stage.

Any way what you have is a mess but it can be fixed by replacing the driver transformer with    https://www.tubesandmore.com/products/tr...i-158k-sec
Simple enough to wire it like the original and dig up a cover to cover this replacement.
From the top I looks just like my 660 AAAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Terry

[NostalgiaRadioTime]

Once again, I am SO grateful for your help, Terry. I literally just took the chassis out of the cabinet this afternoon, and as soon as I noticed that botched up mess on top of the chassis, I knew something wasn't right. I'm waiting on the schematic material from Chuck which should make it a lot more clear where that fits in. The one on Nostalgia Air is rather blurry. Since this set supposedly worked...according to the seller's description...I did bring it up slowly on the variac just long enough to check for signs of life after testing the tubes. When I touched the center tap of the volume control with a screwdriver, I did get a loud hum that could be increased and decreased by the volume control. So I know at least some of the audio output is working as is. I will order the driver transformer from AES as you suggested and will get back to you. THANKS!!

[NostalgiaRadioTime]

OK, this set has 7 electrolytic caps in it, which I replaced. None of the original cans on top of the chassis (there are 3 cans) are the originals, and the one which contained a bank of 4 caps was replaced with one that only contains 2 caps, while the other two were mounted underneath the chassis. None of the values were even close to what the schematic calls for (the 2 mfd was replaced with a 20 mfd!) So I carefully replaced them and was going to slowly bring the set up on my variac to see if I could coax some sound from it. I felt confident enough that the crude bank of caps and resistors used to replace the missing driver transformer must've worked at one point and would at least help me determine if there are any signs of life in the set.

Well...at 60 volts on the variac I was already drawing 5 amps, followed quickly by a steady trickle of smoke rising from under the chassis. Not good. I quickly unplugged it. I checked the transformer and it's still where it should be, so I don't believe that was the culprit. So, having made no other changes other than the electrolytics, can anyone verify for me where the main electrolytics (#91 and #98 on the sch) are connected? I just want another pair for more skilled eyes to check out the schematic for me, as I keep thinking perhaps I inadvertently put one in with the polarity reversed. Thanks.

http://www.nostalgiaair.org/pagesbymodel...013141.pdf

[Radioroslyn]

Hi Greg,
It's ur other pair of eyes. #73, Capacitance isn't very critical I used 4.7mf @450v. You can mount the replacements (4) under the chassis or cut the can and install them inside. The important thing is to be sure the old ones disconnected. + goes to the terminals - to the chassis.

#90 (8mf @450v) a 10mf is fine too + goes to the 80 filament - to the power transformer HV center tap.

#91 has two caps inside an 8mf (or or 10mf @450v) + goes to the filter choke - to the tap. The 10mf (@50v or so) the + side goes to the chassis and - to the tap. It filters the negative bias voltage for the audio stages.

Don't power it up without the spkr plugged in. Monitor the HV at the 80 filament to the chassis. If the power supply is working well and have no shorts should see about 350vdc. If you are at 250v or less you've still got a problem. You may notice plates of the 80 glowing a dull red, not good indicates a short in the HV.

GL
Terry

[NostalgiaRadioTime]

Thanks so much, Terry. The 10 mfd section of #91 is what confused me and where I may have made a mistake. I'm pretty sure I have the negative side to chassis ground instead of the positive. I'll double check and if so try reversing it tomorrow.

[NostalgiaRadioTime]

Well I did indeed have the 10 mfd #91 cap in backwards. I re-soldered it in the correct way and....still no change. I'm still creeping up around 5 amps of draw at 50 volts. When you (Terry) said I have a mess, you weren't kidding. I'm having a heck of a time trying to isolate what is causing such a current draw. I took all of the tubes out to try to eliminate the filament circuit and slowly brought it up on the variac with the same results (5 amps at 50 volts). Momentarily I even tried it without the speaker connected, just to eliminate that. Again, same result. I only did this to try to isolate where the problem may be. The only work I have done to the set was to replace the 7 electrolytics. None of the bakelite blocks show any signs of leaking tar or any indication that they are shorted or getting hot. As soon as I climb up to around 30 volts it starts to draw, and by 50 it's up to the 5, so I quickly shut it down. I don't want to risk further damaging anything. Knowing that I have that kind of draw with no tubes in the circuit (and briefly no speaker) where would you look first?

[Steve Davis]

Greg, you should probably toss the capacitor and put in a new one.

Steve

[Radioroslyn]

+1
When you charge an electrolytic cap backwards it shorts. Only good for a trashcan filler!

Terry

[NostalgiaRadioTime]

Thanks for reminding me of that. I'm embarrassed for making such a dumb mistake. I will try a new cap tonight after work.

[Arran]

  With regard to the audio interstage transformer that is missing, it would be nice to know what the original DC resistances were of the windings. I've been looking at the service information for other sets that used a class B or class A-B power output and not only was the interstage between the driver tube or tubes and the power outputs a step down transformer but the DC resistances were quite a bit lower, such as under 1000 ohms for the primary and the secondary. The RCA schematics list the values, the Philco ones don't for some reason, they just give part numbers.
Regards
Arran

[NostalgiaRadioTime]

Well I replaced the 10 mfd cap with a new one and, as I figured, no change. Same current draw. So I tried to further isolate the problem by concentrating on just the power supply section around the rectifier tube. Long story short, I had everything BUT the transformer disconnected from the circuit, even the line cord and the transformer itself was still drawing 5 amps at 50 volts. I compared it with a known good transformer connected the same way, and there was no current draw to speak of up to 120 VAC. So, after double checking everything, again with the transformer itself isolated from the rest of the radio (it was disconnected from the circuit at the first 8 mfd cap #98) I am confident the culprit is a bad transformer. Not the news I wanted to find.

So now I'm faced with trying to find a rather large, flat transformer (it measures 2 5/8" tall, by 3 7/8" wide, and  4 3/4" long) with a 120 VAC primary, and secondary windings of 5.0, 6.3, and an (approx.) 600 volt winding with center tap.

Anyone know where I could find something like that, that would look like it belongs on the chassis? Since the transformer sits out in front, it's plainly visible, and I'd hate to put a new-looking modern replacement there.

[Arran]

Well I replaced the 10 mfd cap with a new one and, as I figured, no change. Same current draw. So I tried to further isolate the problem by concentrating on just the power supply section around the rectifier tube. Long story short, I had everything BUT the transformer disconnected from the circuit, even the line cord and the transformer itself was still drawing 5 amps at 50 volts. I compared it with a known good transformer connected the same way, and there was no current draw to speak of up to 120 VAC. So, after double checking everything, again with the transformer itself isolated from the rest of the radio (it was disconnected from the circuit at the first 8 mfd cap #98) I am confident the culprit is a bad transformer. Not the news I wanted to find.

So now I'm faced with trying to find a rather large, flat transformer (it measures 2 5/8" tall, by 3 7/8" wide, and  4 3/4" long) with a 120 VAC primary, and secondary windings of 5.0, 6.3, and an (approx.) 600 volt winding with center tap.

Anyone know where I could find something like that, that would look like it belongs on the chassis? Since the transformer sits out in front, it's plainly visible, and I'd hate to put a new-looking modern replacement there.

 Maybe there is an issue with the filament wiring, that is unless there is a something connected to the transformer center tap that could cause the problem? By isolating the transformer you mean that absolutely everything is disconnected from it? The only other possibilities other then a shorted winding is that the windings are shorted or  are suffering leakage to the iron core, or that one of the leads is shorting to the cover through a break in the insulation.
Regards
Arran

[NostalgiaRadioTime]

Yes the transformer was totally disconnected from the filaments. Center tap was also disconnected.