I am working on this Bogen Challenger RC412 (tube receiver from about 1960) that has a few problems, one of which is a blown line choke at the AC in. According to the schematic it is 1.9uH, I have not been able to find a replacement.
Any ideas?
See attached pics.
Any ideas?
See attached pics.
The first thing to do is find out what caused it to burn out. Something is loading the power transformer. The rectifiers, filter capacitors or something downstream. (If not the tranny itself) Putting little RF filters in the AC line was popular in the sixties to filter stuff that the transformers probably wouldn't even pass. I'd be temped to leave the coils out along with the two death caps (C61 & 62). Or I would just rewind the one assuming the form is still solid. I count about 19 or 20 turns of coated magnet wire of perhaps #18 or 20 gauge. Or make one from scratch with a plastic rod or resistor. The actual coil value is not critical. And do yourself (or your customer) a favor and install a fuse in the tranny's primary. Just a standard 3AG 1½ or 2 amp fast blow should be about right.
Yeah I know I need to find the cause, and I thought about just leaving them out (I actually have them bypassed so I could troubleshoot) and I might if the guy that owns it is ok with it, I am working on it as a favor really.
He had just got this and the the tubes did not light up, he tested them and bought replacements for several bad ones. Powered it up, he said the tubes lit up but nothing happened. All of this without speakers or a load connected.
One channel is working now and I am tracing the fault in the bad channel. Just thought I would ask about the chokes.
A fuse is a good idea.
He had just got this and the the tubes did not light up, he tested them and bought replacements for several bad ones. Powered it up, he said the tubes lit up but nothing happened. All of this without speakers or a load connected.
One channel is working now and I am tracing the fault in the bad channel. Just thought I would ask about the chokes.
A fuse is a good idea.
Use a high ohm resistor and put the right number of enameled wire around it. The number of turns is not very critical. It’s just a simple mains filter after all.
After fixing a few dodgy connection I have both channels working.
All of the voltages are within 5v of spec except for the voltage on pin 1 of both ECC832 tubes (7247 on the schematic. It is one of those weird dual triodes with 2 different triodes in it.
Pin one is supposed to be 45vdc according to the schematic but I am getting 60-63vdc. All other voltages are within 5v or less.
I checked the dropping resistors (R45/R52) one is 220k the other 240k.
I wonder if I should change the dropping resistors or let it be, it could be a typo I guess.
What do you guys think?
All of the voltages are within 5v of spec except for the voltage on pin 1 of both ECC832 tubes (7247 on the schematic. It is one of those weird dual triodes with 2 different triodes in it.
Pin one is supposed to be 45vdc according to the schematic but I am getting 60-63vdc. All other voltages are within 5v or less.
I checked the dropping resistors (R45/R52) one is 220k the other 240k.
I wonder if I should change the dropping resistors or let it be, it could be a typo I guess.
What do you guys think?
The chokes are to isolate the power transformer at RF frequency, so that the power cord an serve as an FM antenna. As mentioned, you can wind your own, using a resistor as the coil form. And while you're at it, install a fuse. 1 to 1 1/2A slow-blow should be about right. And 60V on the plate is fine.
How fresh are the tubes? Old tubes may have lost some juice, drawing lower current compared to new ones.