Fisher 500b restore

calman46

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I have a nice and dirty Fisher 500b was found in an attic.Its missing one output tube and no case or feet and no AC plug (it was in a homemade cab ) . From what I can see its complete and all the tubes are Fisher with one output tube being a Westinghouse .I'm on fact finding mission before I start working on it. I found a few threads and have the SM. What I could use is the Replacement PN# for the selenium rectifier . I noticed there are some resistors mod also. Any info or suggestion would be greatly appreciated . I'm not a tech but can do the work . Thanks
 

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That's a nice attic find. I wish I could find gear like that in attics. I find only scorpions and black widows.

The 7591 in behind the right output transformer has gone to air and isn't good, note the white getter material on the top of the tube.

I use this style of bridge rectifier http://www.alliedelec.com/search/productdetail.aspx?SKU=2660053 They are way over kill on the voltage spec but are roughly the same size as the selenium rectifier many Fishers used. The new bridges have a through hole that can be used for mounting. I bought a bag of 20 at at swap meet for $5

Do a search in this forum on the Fisher grid resistor mod, you'll find everything you need to know. There are a few nicely documented resto threads with pictures that were done within the last year or so.

Check for chassis cleaning threads. There are several methods that work well.

Great receiver for a resto! Keep posting your progress and questions.
 
Great find.
Welcome.
Try the search tools at the upper right of the screen. There's more information on this forum than you can absorb in one setting.
 
The 400V 8A Bridge Rectifier from Radio shack is popular. I have it in all my fisher equipment. It's shaped like a square, with 4 legs, 1 in each corner. It has a mounting hole in the center.

The part number is in a few of my posts, but I can't remember which ones.
http://www.audiokarma.org/forums/showthread.php?t=327561 Rectifier is part #1 on list.
Larry
 
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Needs some love, but should clean up quite nicely. You'll be proud of that 500B every time you fire it up.
 
I see the 400,500, 800 b&c receivers are very similar . I was looking for just the 500b .
 
The 400V 8A Bridge Rectifier from Radio shack is popular. I have it in all my fisher equipment. It's shaped like a square, with 4 legs, 1 in each corner. It has a mounting hole in the center.

The part number is in a few of my posts, but I can't remember which ones.
http://www.audiokarma.org/forums/showthread.php?t=327561 Rectifier is part #1 on list.
Larry

Hi Larry,
Think you're going to have to tatoo this one on the site header, that or some sort of cyber speed dial.

You may even be answering this one enough to justify/copyright your own app! :D

"Selenium Rectifiers, All You Ever Needed to Know According to Larry!" :D

Maybe Rat Shack would cut you in on the action?!

Hope all is well with you and yours.

Thomas
 
I have a nice and dirty Fisher 500b was found in an attic.Its missing one output tube and no case or feet and no AC plug (it was in a homemade cab ) . From what I can see its complete and all the tubes are Fisher with one output tube being a Westinghouse .I'm on fact finding mission before I start working on it. I found a few threads and have the SM. What I could use is the Replacement PN# for the selenium rectifier . I noticed there are some resistors mod also. Any info or suggestion would be greatly appreciated . I'm not a tech but can do the work . Thanks

That white one's history my friend, unless that's white paint.

You'll need at least (2) outputs that work at least to get started.

Mine was dirtier than that; thankfully it was only dirt and not corrosion.

It'll clean up quick and you'll really get into it. The quick gratification from just getting through the top layer will help fuel your momentum.

Have fun!

Thomas
 
Great find but be careful. Not sure if the power cord is cut or removed, but either way it was likely done to stop one from plugging it in! Could be an open OT or something else. Also, this era of Fisher chassis' are cadmium plated - don't want to be breathing that stuff in. Having said that, should be a fun resto, lots of help around here.
 
I'm doing my homework for this now . I need a fuse cap ,power cord ,4 new outputs tubes and cap brights just by looking at it. I looks as if they had added on a length to the power cord and it was in a crappy custom cab I'm told . I'll keep ya posted on what I find.
 
Ok new power cord done ,new fuse holder installed . Should I replace those 0.01uf 600v caps (c91,c92 molded caps)one is from the fuse to GD and the other is from a secondary winding to GD ?
 
Yeh, those are called the death caps.
Sometimes when they go, they blow up with a loud pop and the amp dies.
Replace 'em.
 
Ok I am all most done with the multi value can caps on this 500B. I never powered this unit up and I would like to use a dim light tester to check the power transformer before I continue . So, I should leave all the tubes OUT ? the new rectifier is in circuit is that OK ? Any advise or tips always greatly appreciated. Thanks
 
The 400V 8A Bridge Rectifier from Radio shack is popular. I have it in all my fisher equipment. It's shaped like a square, with 4 legs, 1 in each corner. It has a mounting hole in the center.

I use those for lower-voltage stuff (preamps and tuners), but I bought a bunch of 600V or 1000V (I can't remember which) bridge rectifiers from Mouser to use in power amps.
 
Ok I am all most done with the multi value can caps on this 500B. I never powered this unit up and I would like to use a dim light tester to check the power transformer before I continue . So, I should leave all the tubes OUT ? the new rectifier is in circuit is that OK ? Any advise or tips always greatly appreciated. Thanks

Never start the amp with tubes out. Leaving out tubes changes the loading on the power supply. Great way to burn it out.

The whole purpose of the Bulb tester is to introduce a variable resistance that will bring the voltage up slowly with the load.

The best way to bring one up is with a Variac, the bulb is second best.

Consider adding a thermistor such as an ST-80 to one leg of the incoming AC. That's like having a bulb on every startup.
 
Ok new power cord done ,new fuse holder installed . Should I replace those 0.01uf 600v caps (c91,c92 molded caps)one is from the fuse to GD and the other is from a secondary winding to GD ?

C92 is the death cap, it should be replaced with a AC "X" rated cap. C91 is a snubber for the main diodes. It should be a minimum 600v film cap.
 
C91 &C92 are done I have the restore kit. I like the dim light tester because it will tell right away if there is a short . I didn't want to have to do a full restore to find out the power transformer is toast.
 
C91 &C92 are done I have the restore kit. I like the dim light tester because it will tell right away if there is a short . I didn't want to have to do a full restore to find out the power transformer is toast.

Which restore kit did you go with? I hope you take plenty of pics, it's great fun to watch how everyone does the restore, and a great learning tool for some of us !!

Chuck
 
Ok I am all most done with the multi value can caps on this 500B. I never powered this unit up and I would like to use a dim light tester to check the power transformer before I continue . So, I should leave all the tubes OUT ? the new rectifier is in circuit is that OK ? Any advise or tips always greatly appreciated. Thanks

Probably the only way to test that transformer in situ without powering up is to disconnect the leads and measure resistances. You should get pretty low readings - my guess for the B+ secondary winding would be a bit less than 10 ohms, the others lower.
 
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