Fisher 500-B Restoration Process for The New Guy

Josey,
Its really handy to have your power tube bias adjustments above board vs inside the chassis.
Here is what I did on my 500B:
DSC01122.JPG DSC01124.JPG DSC01123.JPG

Also if you look close you can see where I cut the can cap's when I re-stuffed them.
 
Josey,

I have all the parts on hand to build you a board, so no worry about funds yet - I think shipping will be more than parts. I am going to Florida for Thanksgiving, so it will be after that that I finish it.

Here is the formula I used (Bruce deserves a lot of credit for making the instructions clear enough that I could figure it out without having to ask a bunch of questions) -same parts too: http://audiokarma.org/forums/index.php?threads/show-me-your-ibam-ibba-2016.713900/

And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.
View attachment 1329756

I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.

View attachment 1329758

Awesome! Did you see what 1rebmem did to his? Do you think i could do something like that?
 
I bought the pot's and test jacks on ebay. Then cut and bent the aluminum sheet metal just big enough to mount them.
Search for some 10K trim pots designed for panel mount.
The remaining components are on a board directly under and inside the chassis, the 500B has some open space there.

I had the metal plate bent at work:)
You could do pretty good with a bench vice.

Matt's can cap bias assembly is a sweet setup though!!
 
Since you are adding IBAM (which is a great thing to add) here is a schematic showing IBAM, along with some other mod's. The schematic is for a 500C but it is close enough to the 500B.
I built the IBAM based on this schematic.
Jef
 
‎Josey,
Here is a schematic for a 500C with IBAM and some other mods. The 500B is similar enough so I built my IBAM as shown in the schematic

Edit: I can't figure out how to put the schematic here.
It's in the AK Database.
 
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‎Josey,
Here is a schematic for a 500C with IBAM and some other mods. The 500B is similar enough so I built my IBAM as shown in the schematic

Edit: I can't figure out how to put the schematic here.
It's in the AK Database.
Thank you, I will check that out. The amp came with an 800-C manual and schematic in the box. I'm wondering how different that is.
 
I bought the pot's and test jacks on ebay. Then cut and bent the aluminum sheet metal just big enough to mount them.
Search for some 10K trim pots designed for panel mount.
The remaining components are on a board directly under and inside the chassis, the 500B has some open space there.

I had the metal plate bent at work:)
You could do pretty good with a bench vice.

Matt's can cap bias assembly is a sweet setup though!!
I'm definitely considering the can cap bias too! Oh, the choices! LOL!
 
Absolutely, it depends on the specific tubes and you're right most tube testers will not reveal bias weakness. Most testers apply around 150-180v and are not adequate for real operating conditions like 400v to the plate.

Are your 7591As new production like Tung-Sols or Electro-Harmonix?
The 7591As in question were purchased new in about 1985, installed in my 500-C which was used for a short time and then put in storage. They are reasonably fresh 1985 7591A tubes. They all test strong on the Hickok 6000 tube test and all show low grid 1 leakage.
 
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...Its really handy to have your power tube bias adjustments above board vs inside the chassis....
Brilliant. I really like what you did mounting the test points and trim pots topside where they can easily be adjusted. :thumbsup:
 
‎Josey,
Here is a schematic for a 500C with IBAM and some other mods. The 500B is similar enough so I built my IBAM as shown in the schematic

Edit: I can't figure out how to put the schematic here.
It's in the AK Database.
Thank you! I'll find it i'm sure.
 
Does anyone have any advice on how not to become obsessed with this? I'm already brainstorming a whole vintage audio equipment testing restoration with Oscilloscope, Tube tester and a tube multimeter prior to my 500-B restoration. LOL.
 
Josey,

I have all the parts on hand to build you a board, so no worry about funds yet - I think shipping will be more than parts. I am going to Florida for Thanksgiving, so it will be after that that I finish it.

Here is the formula I used (Bruce deserves a lot of credit for making the instructions clear enough that I could figure it out without having to ask a bunch of questions) -same parts too: http://audiokarma.org/forums/index.php?threads/show-me-your-ibam-ibba-2016.713900/

And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.
View attachment 1329756

I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.

View attachment 1329758
This looks pretty great. I'm not sure which one to go with. This may sound like a dumb question but the can cap that was there, where did it go or does the IBAM replace the can cap? I know I sound stupid here. And enjoy Florida! Thanks.
 
I put a new electrolytic under the hood to replace the can.

I *think* a replacement for the original cap could fit in there with the IBAM board - the new electrolytic is not that big.

Regarding tube tester, oscilloscope etc, you could, but don't need to. I bought a pretty nice Hickok 752 a few years ago on bartertown here. Spent $250. Could probably double my money, and would have tested more than 1000 tubes in the process.

As far as things getting out of control - yeah, for sure! I am starting restoration on a Tektronix 575 curvetracer to modify and use with my tube tester, and a Tektronix 502A for troublesooting, alignments etc. Tektronix stuff really scratches that "I should be working at NASA itch."

I just need a Fisher 300 generator now and I'll be all tooled-up.
 
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