[garyh1]

What would cause the rectifier tube to fill with sparks and burn out, I did a complete recap and resistor replacement several months ago and the radio has been performing well untill now. I replaced the rectifier with a new one and got the same result. Where should I begin looking?

[codefox1]

First have a look for any burned resistors or evidence of arcing. Then check out the wiring to the speaker field coil and output transformer to rule out any short circuit to ground.

It is also possible that one of the filter capacitors has failed even after only a few months of service.

[garyh1]

A failed electrolytic was the problem. Radio up and running now. My only issue is lots of noise which sounds like interference when moving across the am band. It makes it difficult to hear weaker stations. Also loud popping when switching between bands. I have tried moving wires around under chassis with no improvement. Any suggestions, as always thanks so much for the help. Gary

[TA Forbes]

Check the tuning assembly for items that are rubbing when the tuning knob is turned. The mechanism could also need lubrication. There is a great article in this site about rebuilding the 116 dual drive tuner.

[garyh1]

Disassembled the tuning mechanism and found the veneer assembly rubbing on the support bracket. Everything working great now. Thanks for the advice. Gary

[garyh1]

Whoops. Spoke to soon. After about 20 minutes the same problem with rectifier reappears. Looks like it took out the filter cap again. Done for today, will get back after it tomorrow...

[Marsupial]

did you make measurments around the rectifier tube?

[garyh1]

not yet I will in the morning

[garyh1]

795 across plates with rectifier removed. 398 Plate to ground.

[garyh1]

These voltages measured at 117v through variac. House voltage is 127.

[Ron Ramirez]

What are the working voltages of your electrolytic caps? What type are they? Where did you get them?

[garyh1]

The caps are MIEC brand purchased from Dave at just radios. The values are 10uf 450 volts. I have used these same caps in probably 10 radios with no issues. The caps I put in the radio last night were 20uf because I used up all the 10uf I had on hand. Needed to get caps in the radio to check voltages.

[TA Forbes]

I'm having a similar problem with an AK 92, sparklers in the rectifier and blew one of the 8mFd fiilters. Like as in POP--sssssssssssss.

That's how my day started.....

[Ron Ramirez]

OK, just wondering. Of the last bag of twenty-five 10 uF 450V electrolytics I bought from Bob at radioantiques.com , one failed prematurely in a Philco 60. (Fortunately, it failed open, not shorted, so it only caused a loud hum, not failure of the rectifier.) The others have been OK so far. First time this has ever happened with any caps I have bought from Bob.

In your 116, with a higher input B+ voltage (especailly if you were to run it at full line voltage), you may have to switch to a 500 volt electrolytic. There is someone who sells these much cheaper than anyone else I have found so far on the Web - Studio Electronics.

http://www.studioelectronics.biz/sunshop...ail&p=1729

I think I might try some of these in some future projects of my own. I have some high tube count sets yet to restore, such as a 116B, two 16Bs, and a 17B - and I think I will invest in some of these for use as input filters in those radios.

I have a small cabinet close by my workbench, and I usually rotate a different cathedral or tombstone in that spot every so often. Right now, my late version 116B is on the cabinet. Next to the cabinet, I have a metal electrical box with a power cord, a dual receptacle, and a bucking transformer inside which drops the 122 volt line here to about 108 volts. Whichever radio I have sitting on the cabinet gets plugged into the bucking transformer box, so it does not get full line voltage while it is in operation. (With many thanks to Ed Locker for the bucking transformer box.)

Tom (TA) - The above may also apply to your AK 92.

[TA Forbes]

I to am using caps from Dave, rated at 450V. In the schematic, it calls for 475V, but even with the higher line V I don't think that it would cause the cap to get that hot and pop as quickly as it did. I am looking in the vic of the cap to trace the issue, but indeed may have to go to a higher rated cap......