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Fisher 500b component query

allhartfidelity

allhartfidelity

More gear than sense
Hello all, please bare with the intro, i do get to the question later down the post.

Having recently acquired a 500b, ive gone over it a little. It has a very dark gold plate, lettering and chasis beautiful, stock tubes testing ex. Orig lights still working, pulled from a console and its clear with all of the above it wasnt used much.
Ive i brought it up slow, and monitored current. It draws 1 amp, and the output tubes run about 26 each respectively. Multiplex works very well. I dod research here, and found great threads on restorations but will not do this myself. I had my Scott stuff done by Craig, and looking for advise on who to ship this one to. However, under the bottom cover i see something i recognize as a coil wound variable resistor of sorts. Can someone by chance tell me what this is used for? Has this been bastardized or is this stock? In the restoration threads i did not see anything similar.
Thank you for any assistance you may provide,
Charles20190502_213157.jpg
 
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Interesting--a variable resistor in the B+ supply? Presume the slide over the wire coil is to vary the resistance for the adjustment. Haven't run into one of these so far.
 
I'm pretty sure that is not original.

those were common items a while ago, but more for the experimenter than in commercial use. Its the perfect thing for breadboarding purposes when you aren't sure exactly how much resistance you need to get a circuit working how you need.

It looks to be sitting between the power transformer HV lead and the first filter cap. I'm guessing its being used to drop the high voltage somewhat, but personally I'd put the amp back to stock without that resistor in place. If the incoming voltage is too high, a bucking transformer to drop that is a better idea IMO.
 
I suspect it’s been repaired at some point. That resistor doesn’t look like anything that came from Fisher to me. Nor does that circuit board at the top of the shot. I don’t think I’d call it bastardized though, especially if it sounds good. You’d likely be better off posting this in the Fisher forum. Good luck.
 
It is not stock, but a modification to reduce the B+ as Gadget suggested -- and surely the reason that the output tubes are only drawing 26 mA a piece. I would remove it.

The circuit board appears to be a modification allowing a different mounting style DC Heater/Bias rectifier to be mounted where the old one was while still using the original mounting holes.

Good luck with it!

Dave
 
Yes, 3 tubes at 26 one at 32. Best i can gather folks run these at 36?
The solder work looks very nice. Would you care to take this on for me? Ive got tons of references as a great guy to deal with ;)
dcgillespie said:
It is not stock, but a modification to reduce the B+ as Gadget suggested -- and surely the reason that the output tubes are only drawing 26 mA a piece. I would remove it.

The circuit board appears to be a modification allowing a different mounting style DC Heater/Bias rectifier to be mounted where the old one was while still using the original mounting holes.

Good luck with it!

Dave
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Could you please direct me to the Fisher forum? Is that here on AK?
RUmad said:
I suspect it’s been repaired at some point. That resistor doesn’t look like anything that came from Fisher to me. Nor does that circuit board at the top of the shot. I don’t think I’d call it bastardized though, especially if it sounds good. You’d likely be better off posting this in the Fisher forum. Good luck.
Click to expand...
 
Screen shot of the TOP OF THIS PAGE. Click on the Arrow as shown in the pic, then scroll up or down (I didn't check) until you finder FISHER FORUM. Click on that and you'll be beamed up. The transporter can be skittish at times.

Suggest you PM (New term is conversation......Damned PC Millenials) Ak'er "TINKERBELLE". Ask her to transfer this thread to the FISHER FORUM.



forum change.jpg
 
Thank you, PM request sent to tinkerbelle . Much appreciated
larryderouin said:
Screen shot of the TOP OF THIS PAGE. Click on the Arrow as shown in the pic, then scroll up or down (I didn't check) until you finder FISHER FORUM. Click on that and you'll be beamed up. The transporter can be skittish at times.

Suggest you PM (New term is conversation......Damned PC Millenials) Ak'er "TINKERBELLE". Ask her to transfer this thread to the FISHER FORUM.



View attachment 1498186
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