Need some help with an Addison model 21

[David Sharpe]

I have an Addison model 21 that has no power going through it.It has power to the 35z5 tube but beyond that I can’t get the tubes to power up at all.Its had two other people work on it before I got it so not sure what the problem is.I know the tubes are good.I checked the wiring,all the caps have been changed,and any resistors that were off.I have some pictures of the underside.Any help would be greatly appreciated.

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[Cameron Burns]

Hi Dave,

I’m no expert, but here are my thoughts just the same. I always thought the filaments of all the tubes were in series, so if one is out they are all out. Have you tried doing a voltage check on the 35Z5 and see if it reads correctly? I’m thinking if the 35Z5 is shorted(?) this may happen? What about a dim bulb test?

If you’re fairly new to this as i am just be VERY careful around the AC/DC’s.

Sorry, that’s all ive got. 🙁

[John Greenland]

Hi David;
I agree with Cameron, if one of the tubes has an open heater, then it needs to be replaced because they are all connected in series. The easiest way to check this ( from my point of view ) is to check each tube’s heater voltage on pins 2 and 7, when they are plugged in and powered. You can easily find an open heater because the voltage will be 120 volts AC across that tube. Assuming that the tubes check Ok then the most like culprit would be the 22 ohm series resistor from the plate of the 35Z5 rectifier to the AC supply.
BTW be careful, this radio has no transformer to isolate you from the commercial power. If you have an isolation transformer, then you should use it.
I would also suggest that you connect the side of the AC cable with the small connector to the 35Z5 and when you get it working move the power switch to that side as well. This will at least make sure when it is plugged in, the neutral will be connected to the chassis.

Good luck and be careful !!

[David Sharpe]

I have tested all of the tubes and in fact I have tried them in my test radio which happens to be an ac/dc radio with the same tubes.I tested the voltage this morning and I have 110 volts ac on all the pins on all of the tubes. That’s from the live side of the switch to any pin on any of the tubes. Not sure if that is what it should be or not. I’m missing something here,just not sure what yet.Maybe something hooked where it shouldn’t be. I tested the transformer with a 9 volt battery and I get static in the speaker so I am assuming it is ok. I do have a dim bulb tester but there is nothing there. I am using the isolated transformer because I have been zapped more than once.I appreciate all of the comments and suggestions and the help.

[Gerry O’Hara]

Hi David,

If you have tested all the tubes and you are measuring 110v on all the filaments, it sounds like you have an open circuit on the opposite end of the heater string (12SQ7 to chassis?). I suggest that you check for a dry joint or mistake in the wiring if someone has been there before you.

Gerry

[David Sharpe]

Hi Gerry.I finally found the problems.First was the on/off switch.It was dead.The other was an electrolytic cap was soldered on the wrong pin.Once I fixed those two problems,it came back to life.Thanks for the reply though.Every bit helps when your a novice.Trying to understand the schematics can be a challenge sometimes.I was just happy to hear some sound come out of it again.It belongs to an 86 year old man who bought it new back in the day.It should out last him now because everything in it is new or replaced.He’s one happy camper now.Thanks again and have a good day!

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