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Model 90 Stuck At One Volume Level
#13

Here's an idea, pepper,

Short the wiper of the regulator to the chassis. If then the volume is still the same.....you know what I mean?

Idea #2: In Det. Amplifier (the tube that has the pot connected to its grid), with the power off, measure the resistance from the Cathode to the Chassis. Should be about 60 Ohms.

(04-14-2012, 05:31 PM)Pepperoni Wrote:  Hello morzh, I've looked at those VC readings and it does do what it's supposed to do. But before I put this set back together I bench tested that volume control. From outer leg to outer leg it reads 250K. Part # on it matches the parts list and a 500K pot is what belongs there. But when I measured from the CT to each outer leg it was an audio taper so not linear and I did see 500K. Kind of confusing I know. Why does it read 250K across it. Don't know. So for sh$#^ts and giggles I slaved in a new 1 meg pot. All I had but it was new. It didn't change what the radio is doing. About 40% or so volume but no control via the VC at all.

So I did start swapping out tubes. No change with the 27's. I didn't have any 24's but I had 3 very good 35/51's. Swapped each tube out (with that gleam in my eye that one of them would cure the problem) and got the same results. Volume with no control over it.

I've taken the schematic and blown it up to 11X17 (4 Copies) for clarity and space and went through the set from the front end to the speaker. No wiring errors, no bad caps or resistors, no solder splash or unwanted shorts etc. etc. When I had it all apart I checked every coil in it for continuity. No real reference to what the resistance should be but all coils were consistent on the primary and secondary sides.

I went over my notes of every wire and part that came out of it along with comparing my 75 pictures I took before I disassembled it. Just nothing wrong.

But something is and it seems as if my problem lies somewhere between the Det. Rect. and Det. Amp. But everything is correct. One thing I didn't get a picture of until I disconnected the wires was the tuning condenser wiring on top of the chassis. Where each wire attaches to the TC from their respective locations inside the chassis. My notes and pictures tell me where they all connected inside the chassis but not on the TC itself. The grounds were simple but they do connect to specific points in the radio. Looking from the front of the radio I have the 1st and 2nd gang "HOT" wires if you will, connected to the front screws on the TC 1st and 2nd gang. The 3rd and 4th gang hot wires are connected to the rear screws on the TC. I believe this is correct because those four screws were backed out from when I disconnected them. But if someone could clarify these connections this would be one more thing that I could eliminate as being the problem.

Also something that doesn't seem right to me but it may be normal... When the radio is playing and I short the fins on any of the gangs the radio goes silent except for one gang. May be normal, I don't know.

Pepper



Messages In This Thread
Model 90 Stuck At One Volume Level - by Pepperoni - 04-12-2012, 03:54 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-12-2012, 09:19 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-14-2012, 02:44 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-14-2012, 02:52 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-14-2012, 06:16 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-14-2012, 08:51 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-15-2012, 12:04 PM
RE: Model 90 Stuck At One Volume Level - by morzh - 04-15-2012, 01:26 PM



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