I am just starting work on an Atwater Kent Model 55C.

The schematics on here do not indicate the number of the pilot bulb (screw base) for this receiver. Anyone know?

Also, I have zero audio output from this unit ( no hum, nothing!!!! - B+ is there).I have measured the primary and secondary resistance of the audio output xfrmr, and it looks ok.

Anyone have any thoughts on the pitfalls of working on this unit? I noticed that most of the electronics is potted ( oh , joy!!).

Also, the unit uses TWO type 45 tubes in its output.

I may not work on it very long ( depending on my patience!!).

Thanks
Lou

If you are getting B+ at each of the 45 plates, and you have checked the transformer over thoroughly, then it would be wise to check the voice coil of the speaker. Sometimes flex wires stress and break, voice coil wires break, etc. Also, if the tone condenser shorts in that radio, there could be good enough phase matching that the two phases would completely cancel eachother out, and you'd get no audio. Not definitely, but possibly.

That's a nice radio. I'd keep at it if I was you. I think that you'll like it. Hopefully there is programming in your area that's actually worth listening to.

T.

:If you are getting B+ at each of the 45 plates, and you have checked the transformer over thoroughly, then it would be wise to check the voice coil of the speaker. Sometimes flex wires stress and break, voice coil wires break, etc. Also, if the tone condenser shorts in that radio, there could be good enough phase matching that the two phases would completely cancel eachother out, and you'd get no audio. Not definitely, but possibly.
:
:That's a nice radio. I'd keep at it if I was you. I think that you'll like it. Hopefully there is programming in your area that's actually worth listening to.
:
:T.

Lou: I just restored an early 55C mostly through the help of people on this forum and the AK website. I ended up replacing the input and output transformers, the bypass and phono condensors and a couple of open resistors. The potted condensors are usually ok and mine were all good. It was well worth the effort. Thomas is correct it is a great sounding TRF and worth the time. Al

:Thanks for the thoughts, both of you.

I just needed a little encouragement before I jumped into this one.

I will give status updates as they occur.

PS : Happy Holidays to the entire NostalgiaAir Forum. You guys have provided a lot of interesting stuff this year and I hope to listen to and provide more stuff about restoration this year . I have a house full of stuff to carry on with!!

Ciao
Lou

:If you are getting B+ at each of the 45 plates, and you have checked the transformer over thoroughly, then it would be wise to check the voice coil of the speaker. Sometimes flex wires stress and break, voice coil wires break, etc. Also, if the tone condenser shorts in that radio, there could be good enough phase matching that the two phases would completely cancel eachother out, and you'd get no audio. Not definitely, but possibly.
::
::That's a nice radio. I'd keep at it if I was you. I think that you'll like it. Hopefully there is programming in your area that's actually worth listening to.
::
::T.
:
:Lou: I just restored an early 55C mostly through the help of people on this forum and the AK website. I ended up replacing the input and output transformers, the bypass and phono condensors and a couple of open resistors. The potted condensors are usually ok and mine were all good. It was well worth the effort. Thomas is correct it is a great sounding TRF and worth the time. Al
:

Check the voltages on all the tube pins: http://www.atwaterkent.info/TechData/Drawings/Images/AK14902sch.pdf

Check the audio interstage xfmr, primary and secondary, between the detector and the 45 grids for continuity.

What type speaker are you using? This receiver is set up for an AK F-4 dynamic speaker, but others can be adapted.
Doug

Hi

Yes, I started looking at the tube bias, especially the two output tubes. The grids are heavily biased negative. That would account for no output. It looks like the caps in the power supply may be shorting, causing excess current draw. The excess current will raise the negative bias. The fact that the two AF output bias resistors in the PS are hot makes this make sense.

Lou

:Check the voltages on all the tube pins: http://www.atwaterkent.info/TechData/Drawings/Images/AK14902sch.pdf
:
:Check the audio interstage xfmr, primary and secondary, between the detector and the 45 grids for continuity.
:
:What type speaker are you using? This receiver is set up for an AK F-4 dynamic speaker, but others can be adapted.
:Doug

Latest Update on the 55C

Doing some resistance checks has shown that some of the tube bias resistors have risen in value and/or opened up.

Does anyone have a different resource that would show what the resistor wattage values are?

The audio transformers look like they are OK.

Thanks All and Merry Xmas!!

:Hi
:
:Yes, I started looking at the tube bias, especially the two output tubes. The grids are heavily biased negative. That would account for no output. It looks like the caps in the power supply may be shorting, causing excess current draw. The excess current will raise the negative bias. The fact that the two AF output bias resistors in the PS are hot makes this make sense.
:
:Lou
:
::Check the voltages on all the tube pins: http://www.atwaterkent.info/TechData/Drawings/Images/AK14902sch.pdf
::
::Check the audio interstage xfmr, primary and secondary, between the detector and the 45 grids for continuity.
::
::What type speaker are you using? This receiver is set up for an AK F-4 dynamic speaker, but others can be adapted.
::Doug

Just guestimate the maximum voltage across the reistors, using the voltages shown on the modern schematic. Calculate wattage, P = V^2/R. Double for safety.
Doug

:
:Doing some resistance checks has shown that some of the tube bias resistors have risen in value and/or opened up.
:
:Does anyone have a different resource that would show what the resistor wattage values are?
:

Lou: also check continuity on the rf chokes. Mine was playing beautifully for a day after restoration when it quit altogether. It turns out that one of the rf chokes opened up. It was one of those really fine wire chokes that probably got the dreaded green wire crud. Replacement values are not too critical. As Thomas mentioned earlier also be sure the tone cap across the output transformer primary is not shorted.
Steve

Thanks for all the hints, guys.

Lots of work to do!!

Lou

:Lou: also check continuity on the rf chokes. Mine was playing beautifully for a day after restoration when it quit altogether. It turns out that one of the rf chokes opened up. It was one of those really fine wire chokes that probably got the dreaded green wire crud. Replacement values are not too critical. As Thomas mentioned earlier also be sure the tone cap across the output transformer primary is not shorted.
:Steve

Well, so far so good on the 55C

I now have some weak audio filtering through. I had an open cathode bias resistor on the '27 driver tube.

It does appear that the plate voltage on both '45s is varying considerably with audio modulation, but my audio output is weak. I suppose the capacitor that is internal to the audio output xfrmr (the unit across both '45 plates) could be shorted. If so, do I have to "cook" the transformer in an oven to remove the tar, first, or can it be chipped out?

Thanks Again, Guys
LOu

:Thanks for all the hints, guys.
:
:Lots of work to do!!
:
:Lou
:
::Lou: also check continuity on the rf chokes. Mine was playing beautifully for a day after restoration when it quit altogether. It turns out that one of the rf chokes opened up. It was one of those really fine wire chokes that probably got the dreaded green wire crud. Replacement values are not too critical. As Thomas mentioned earlier also be sure the tone cap across the output transformer primary is not shorted.
::Steve

If the primary and secondary of each audio tranformer is good, you probably don't need to replace them. If the tone cap across the primary was shorted, I don't think you'd hear anything. One of my audio tranformers was bad, so I replaced both in the same can. Antique Radio Supply has suitable replacements that fit inside the can. It's not too hard to do. I inverted one and glued it on top the other with epoxy and turned it 90 degrees to minimize any interaction. I don't remember the model numbers I used, but if you remind me in a week, I can dig it out of my files.
Steve

Thanks Steve

Right now, I am seeing a 50V drop in the plate voltage of each '45, when modulation is present. That seems like a lot, and tells me that I am drawing heavy plate current.

For now, I am going to keep looking thru the circuitry. I am also going to "burn in" the chassis for awhile before I start again.

I think what I might do, if you remember those numbers, is do an external substitution prior to cleaning out the transformer can.Looks like all the necessary terminals can be accessed.

Thanks - this is an interesting one.

Lou

:If the primary and secondary of each audio tranformer is good, you probably don't need to replace them. If the tone cap across the primary was shorted, I don't think you'd hear anything. One of my audio tranformers was bad, so I replaced both in the same can. Antique Radio Supply has suitable replacements that fit inside the can. It's not too hard to do. I inverted one and glued it on top the other with epoxy and turned it 90 degrees to minimize any interaction. I don't remember the model numbers I used, but if you remind me in a week, I can dig it out of my files.
:Steve