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

Bendix woes (or "woe is me")
#1

Well sometimes when it rains, it pours. No this time it wasn't the wrong DeOxit that caused the problem....that lesson has been learned!

I finished up a Bendix 55L2 back in March. Total recap, all new resistors, micas, everything. It has a beautiful white Plaskon cabinet but the dial scale was badly chipped. So I ordered a repro from Radio Daze on March 6th, and finally received it on Monday.

In the meantime, I had the radio tucked aside on a shelf awaiting the dial cover so I could put it together. I had it all back together, looking sharp, plugged it in, and no reception. Just a hum. Not even a hint of reception.

So, back out of the cabinet, checked all the tubes, swapped out tubes with known good tested tubes, and still no change. Then I took the bottom cover off and quickly discovered what happened. 

The last time I tried it, I didn't have the metal bottom cover on the chassis, but cut a thin piece of cardstock and glued it to the inside of the cover to prevent anything from shorting against it (I hate metal covers on the bottom of radio chassis for that reason). I bolted the cover on before I set the radio aside to wait for the dial cover and thought nothing of it.

Well there was an original 2.2K, 2 watt resistor that tested fine so I left it in the chassis. I didn't disturb it. Apparently, I should have replaced it if only because of the difference in size to a modern 2 watt resistor. Apparently the bottom cover pushed against the resistor, and its lead, in turn, touched against one of the leads on the OSC coil. The 2.2K resistor goes between the positive of one of the two electrolytics, and the output transformer, so it sent quite a voltage spike to the OSC coil. It's black color gave away the damage. 

I always install a 3.5 mm cable to my radios, just to have the option of listening to something other than what's found on AM radio these days and for better fidelity than I can get from my AM transmitter. Just a simple connection from the high side of the vol. pot to ground. Yes, I know this is a hot chassis set, but I've never gotten a shock using this simple methog, being careful what I'm touching when using a device the cord is plugged into. So I was able to test the audio output section this way and it's perfectly fine. Plays great. So the problem is definitely in the RF stage past the volume control.

I had one of those AES Universal OSC coils on hand, which always worked great in the past, but I'm still not getting any hint of reception with it. I tried reversing the leads on the primary and secondary sides and still nothing. I rechecked all the resistors, and the capacitors and everything is still good. The IF cans both ohm out as they should on the primary and secondary. The tuning capacitor isn't grounding anywhere that I checked with my test light to ground. So I am at a loss as to what other damage that voltage spike through the OSC coil could have caused. Voltage readings for the most part are right where they should be, except for these:

Pin 5 of the 12SA7 reads - .2 VDC, and should be 5 VDC

Pin 8 of the 12SA7 reads -9.8 VDC and should be - .5 VDC

Pin 4 of the 12SK7 reads -5/76 VDC and should be -.5 VDC

Pin 4 of the 12SQ7 reads -.59 and should be -2.3 VDC

These are all measured to B-

Does anyone have any thoughts as to what may be at fault? 

   

Greg V.
West Bend, WI
Member WARCI.org




Users browsing this thread:
[-]
Recent Posts
Philco 42-345 Restoration/Repair
The thrill is gone again, thought I was close to being done with it. Well Friday it was receiving broadcast, Saturday mo...osanders0311 — 07:47 PM
Help with Supreme 599
Iam getting closer to fixing it. I bumped Up the tranny voltage to get 5v on the 80 tube. I gan get the needle to move ...daveone23 — 03:41 PM
Philco 42-345 Restoration/Repair
Hello RodB, Checking my previous post I realized you're the one with the 42-340. I replaced the string for the tuning...osanders0311 — 03:12 PM
5U4 vs 5Z4 tubes
I saw no evidence of anything going wrong. The transformer is fused already which is nice. Interestingly the 5z4 did...bridkarl — 02:37 PM
5U4 vs 5Z4 tubes
I doubt anything cooked in 30 seconds because of the oops! These are very similar tubes, and nothing but transformer re...GarySP — 02:30 PM
Restoration of the Canadian General Electric A-87
Paul Philco322.You will be keeping very busy, you may have to go back to work for a breakIcon_smile. Paul To rel...RadioSvit — 01:57 PM
5U4 vs 5Z4 tubes
I grabbed the wrong tube and put in a 5U4 tube instead of the 5Z4 - I just had the rectifier in with no other tubes. Af...bridkarl — 01:54 PM
Restoration of the Canadian General Electric A-87
After applying the filler to the entire body, I noticed that the shades of the facade and the side and top walls were ve...RadioSvit — 01:49 PM
Restoration of the Canadian General Electric A-87
You will be keeping very busy, you may have to go back to work for a break:). PaulPaul Philco322 — 01:46 PM
Restoration of the Canadian General Electric A-87
After removing the control knobs, chassis, dynamics and scale frame, I first started restoring the torn piece of veneer....RadioSvit — 01:20 PM

[-]
Who's Online
There are currently 877 online users. [Complete List]
» 1 Member(s) | 876 Guest(s)
Avatar

>