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Fisher 500B.

Freddie73

Freddie73

Active Member
I purchased this clean but “As Is!” Not tested 500B a while back. I cleaned it up physically, replaced the dial glass weatherstripping. Cleaned all the switches, potentiometers, and tube sockets. Cleaned the dial glass and put it up. Never turning it on.
The power cord was broken and the low filter switch brown button is broken off.
I don’t know if it works or not but physically it’s very clean and the price was right.
 

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I’ve cut the damaged part of the power cord out ( only lost about 8”) and installed a CL-80 thermistor. Changed out the molded capacitors and installed a safety cap. Put in a silicon bridge rectifier. Changed out the 2 acorn diodes. Installed 10ohm cathode resistors and K40-y9 coupling capacitors.
I bought the Hayseed Hamfest Can Capacitor kit with the 1000-1000uf 50 volt Can that goes on top. After I install it I will slowly bring it up on my Variac and dim bulb tester.
 
I will, if it plays, change out the other Can Capacitors on top as well as the other electrolytics . I will also replace the remaining Mylar capacitors.
I just thought I’d change out the coupling capacitors,the bias Can capacitor, and a few other safety things first before I brought it up slowly.
The on/off , volume switch clicks loudly and feels smooth but who knows.
I hope it goes well but physically it’s beautiful.
 
Yes. I was able to find a couple of original switches. I’ve slowly been gathering all I need, if nothing major is broken. So hopefully all will go well and a nonfunctional Fisher will be playing again.
 
I think I’ve replaced enough to add all the tubes and slowly bring it up.
Might have to wait until the weekend. Nothing looks burnt, charred or broken.
 

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Slowly bringing it up. Hopefully no sparks or smoke.
 

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Pulled it up slowly on the Variac. Non eventful. Dim bulb worked as it should. Disconnected the dim bulb tester. Brand new matched quad of Tung-Sol 7591’s. Using a trimmer potentiometer to control all 4 at once and they measure 342-359ma’s. Unit not running hot.
I am getting nothing from the left channel in anything. FM, Tape, auxiliary. Right channel playing great.
Any ideas? Anyone seen before? Hopefully something small.
 
First things I try: check the U-shaped jumpers on the IN/OUT jacks. Manys the time one jumper got pushed in too far. Next I would poke around the output tubes with a wooden popsicle stick and the unit playing to make sure I didn't short out a wire while installing those new coupling caps. I've done that before. If no joy, then try the standard stuff next, swap tubes between channels, check pots, slider switches.
 
Will do.
Since the 10ohm resistor blew I pulled the new 7591’s to check them to make sure they were OK. None had red platted and all were just warm to the touch almost immediately after I turned the 500B off.
I hadn’t used my tube tester in a couple of weeks and when I tested the first tube for shorts in position 5 the needle rose about 1/8 inch. Two of 4 did this. Reading about the Hickok 800 the needle has to go all the way to the asterisk to be a bad tube, about 1/3 of the gauge. Then testing again all pegged the meter in positions 1-4 but not 5. Then a known good 12ax7 did the same then another 12ax7. “When it rains it pours.”
I read it’s probably a problem with the shorts circuit. I didn’t want to have to repair my tube tester and don’t know if I can.
I took the tester out of its case and used Deoxit 100 on every contact of the shorts/leakage section the rinsed with 91% isopropyl alcohol no loose or broken wires or burnt resistors. Dried with a blow dryer.
No improvement with or without tubes in position 1-4 the needle pegged but action is much smoother.
Then I pushed and released all the test buttons P1tru P7 then, “Magic fix,”
Now my tester is back to normal and the tubes are good and test new.
Time to step back and think.
I hooked up my Fisher 400 and it’s playing great.
I will go thru the 500 as thoroughly as possible and hopefully get it sorted out.
I appreciate everyone’s help. Thanks Steve.
Physically the 500B is excellent. And Vusually I see nothing burnt or disconnected ( yet ) except the 10 ohm resistor.
 
Ok. Working on the 500B again. I changed out the K40-y9s (because I was afraid one might be leaking ) to new orange drops. Changed out the 330k and 1k resistor going to the power tubes. Replaced the blown 10ohm safety resistor on V14.
Replaced the 2 phono .022uf resistors. Everything was within 10-15% except…….
The tone control .047uf capacitors . One measured .053uf, the other was dead. It measured .04nf which is .00004uf. I think I have found the reason for no left channel.
I have time this week so I think I’m going to do a few more Can Capacitors before I try again bringing it up.IMG_5875.jpegIMG_5874.jpeg
 
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