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CR420/CR66ll Lights

Fhamre

Fhamre

Super Member
Picked up a nice little CR66ll. Needed a little attention.
Looking at some great older posts I repaired a very stiff tuning shaft. Replaced the lights with LEDs.
I found the DC offset to be about -95mv /channel.
So I put a 1k trimmer in place of R407 and R408.That allowed me to get to 0mv easily.
So while I was patting myself on the back I noticed that I no longer had my lights. Was a bit of work to do a nice job putting them in. But I have since taken them out and checked each one,again. No luck.
I am getting 39V at L1,L2,L4. 6V at L3.
Any suggestions?

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This probably isn't the technical response you are looking for, but I don't have that expertise...

However I do remember somebody here telling me when I had my CR-420, that the lighting circuit was really sensitive to tapping around in there and bulbs would blow out for no apparent reason. I believed it after going in to tighten up the tuning string and suddenly all the lights were dead. I put new bulbs in and it was fine after that, but I was dealing with regular incandescent bulbs and not LEDs.
 
Yes I am aware they are in series. Thx. Strange that the three LEDs worked fine until it seems I addressed the DC offset. Although that could be just a coincidence.
 
I think I see whats going on. To get your DC offset under control.Your probably going to have to replace the long tailed pairs.(Diff pair) TR403/405 or TR404/406 with Hfe matched transistors. Any who, the trimmers are loading down the regulated power supply.
 
The unit has been performing fine. It was a freebie that I plan to pass on to my daughters room mate whom expressed interest in a vintage piece. The gist, I wasn't planning to recap it if I didn't need to.
What would be good subs for those transistors?
Maybe I could try increasing the DC offset to say 35mv or so.
 
Fhamre said:
The unit has been performing fine. It was a freebie that I plan to pass on to my daughters room mate whom expressed interest in a vintage piece. The gist, I wasn't planning to recap it if I didn't need to.
What would be good subs for those transistors?
Maybe I could try increasing the DC offset to say 35mv or so.
Click to expand...
See what happens.
 
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