Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

42-350 Burned Resistor
#9

I think I've made some progress in the power supply, but I'm not listening to the radio yet.

Basically, after I replaced the bad rectifier and oscillator tubes that had internal shorts, I still had too much current through the 1800 ohm resistor I was using to substitute for the field coil. I suspected I had wired the speaker cable wrong, but I found it confusing to trace it down because the tracers were so faded, so I finally decided to replace with new colored wires.

Once that was done, I set the variac at 117 VAC. The DC voltage at the rectifier and B+ at the output tube plate seemed right, and the current was a steady 43 milliamps through the resistor, so I decided to reconnect the speaker. Now I have some AC hum and static noises in the speaker, but no signal. Tuning through the dial makes no difference, but I get a little pop in the speaker when I touch each plate in the signal path with the meter, but not the oscillator.

B+ readings at each plate were all close to right (5 to 10 volts low or high) EXCEPT the oscillator, which was 51 volts instead of 75. Oddly, the high side of resistor #41 (33K ohm) is about 170 volts, which is close to what I think it should be, but the drop across that resistor is much higher than seems right. That makes me think the oscillator plate current is too high.

I ran out of time last night, but when I get back to it I will look at voltage on the high side of resistor #42 (2200 ohm) and replace the oscillator and see what I can see.

Any other suggestions would be welcome.

John Honeycutt


Messages In This Thread
42-350 Burned Resistor - by Raleigh - 08-09-2008, 06:20 PM
[No subject] - by Steve Davis - 08-09-2008, 06:45 PM
[No subject] - by planigan - 08-10-2008, 12:11 AM
[No subject] - by planigan - 08-10-2008, 12:33 AM
[No subject] - by Raleigh - 08-10-2008, 04:53 PM
[No subject] - by Steve Davis - 08-10-2008, 06:07 PM
[No subject] - by Ron Ramirez - 08-10-2008, 06:52 PM
[No subject] - by planigan - 08-10-2008, 10:00 PM
Progress! - by Raleigh - 08-27-2008, 02:09 PM
Re: Progress! - by exray - 08-28-2008, 07:51 AM
Got AM! - by Raleigh - 08-28-2008, 11:03 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Restoration of the Canadian General Electric A-87
Great job on the cabinet. PS. In the US notation, "kenotron" refers to specific type of tubes; we call re...morzh — 08:24 AM
Part numbers to model cross
This document has at least some tables of models and parts used. Example: Choke 32-7572, used in 604 radio. S...morzh — 08:19 AM
Restoration of the Canadian General Electric A-87
I also checked all the radio tubes on my Hickok 530 tube tester. The 5Z3 kenotron turned out to be faulty, all the other...RadioSvit — 08:02 AM
Restoration of the Canadian General Electric A-87
Well... While the varnish is drying up, I started repairing the chassis... Of course I started by replacing the pa...RadioSvit — 07:12 AM
Philco Model 38-7: what caps & resistors do fail typically?
Hello Martin, Welcome aboard our little community what great Model 38-7 Sincerely Richardradiorich — 12:30 AM
Philco Model 38-7: what caps & resistors do fail typically?
Welcome to the Phorum Martin. I count about 9 paper caps, the 3 electrolytic caps and 2-Y2 safety caps to replace th...RodB — 09:44 PM
Part numbers to model cross
Jim, We have this index put together by Dale Cook but I don't think that is quite what you are looking for. The Parts...klondike98 — 09:37 PM
Philco Model 38-7: what caps & resistors do fail typically?
Yep the dim bulb test is OK but I'd definitely replace all those electrolytics before I did it. Since those #47 conden...klondike98 — 09:18 PM
Philco 42-345 Restoration/Repair
The resistor is a 2.2 Meg, it was the last one I hadn't replaced. The broadcast is coming in after replacing it.osanders0311 — 09:09 PM
Philco 42-345 Restoration/Repair
What does the resistor measure? I think it should be 3.3 Meg. If the oscillator coil has continuity and the resistanc...RodB — 09:03 PM

[-]
Who's Online
There are currently 1345 online users. [Complete List]
» 1 Member(s) | 1344 Guest(s)
Avatar

>