Dec 31st- and time to Fisher in the New Year and cap off the decade

oneinchside

Openly Baffled
OK, it was a really bad pun

But I do have a Fisher 800c that sounds wonderful that I pulled from service until I could re-cap it. What do I need to know before I dive in?

I can do basic soldering and replacing caps, should I just start with the the electrolytics and give it a listen again? Any advice on which caps to order and other things that should be done at the same time?

I'm sure this has been covered 50 bajillion times, if I've just missed the appropriate thread please don't hesitate to tell me what to go search for.

thanks
Mike
 
Folks more learned than I will jump in, but the power supply caps might be a good place to start. Why did you decide it needed to be recapped? Was it humming? That's power supply caps. It may be worthwhile to try to do them and see what you have. It will make it a much smaller job, and if this is your first time, it will give you something to have success with and make you feel more confidant.

I'd want a schematic if I were going to go any further than that. I haven't done a lot, just recapped a few console amps. But I'd have been dead on my first one without a schematic. I made a small mistake and only going back over everything vs. the schematic found the error.

Take care,

Ed
 
I'd leave the can caps alone for the time being and focus on the bias supply and coupling caps.

Here's the list for a minimal rebuild.

Selenium Rectifer replaced with Silicon Bridge
http://www.mouser.com/Search/ProductDetail.aspx?R=BR36virtualkey58300000virtualkey583-BR36

Replaced the bias filter can cap with (2) 1000uf capshttp://www.mouser.com/Search/Produc...CDvirtualkey64700000virtualkey647-TVX1H102MCD

Replace 100uf electrolytic nearby with thishttp://www.mouser.com/Search/Produc...CDvirtualkey64700000virtualkey647-TPC1H101MCD

Replace the two top hat diodes with thesehttp://www.mouser.com/Search/Produc...3/51virtualkey61370000virtualkey625-1N4007-E3

Replace bias resistor coming off the bias supply can cap with a 10k pot. I used this...http://www.mouser.com/Search/ProductDetail.aspx?R=53C210Kvirtualkey67810000virtualkey785-53C210K

Install 10 ohm resistors on the cathode pin of the output tubes. (I'm at work and don't remember the number off-hand) I used thesehttp://www.mouser.com/Search/Produc...tualkey66000000virtualkey660-MF1/4DCT52R10R0F

Replace 0.047uf coupling caps to output tubes with 0.1uf caps. These will work great. You can also replace coupling caps in the preamp section with these orange drops.
http://www.tubesandmore.com/scripts...&SEARCH_TREE03=716PSERIES&SEARCH_TREE04=0600V

Replaced 330k grid resistors with 200k. I used these...
http://www.mouser.com/Search/Produc...tualkey66000000virtualkey660-MF1/2CCT52R2003F

I'm at work and threw this list together off the top of my head, if I have time later we can get a little more detailed.

I'm sure one of the resident Fisher gurus like audiodon will chime in soon and add/correct my list so far.

-Kory
 
As the 800C is a 500C with AM also, look up 500C rehab's also. Agree with Kory, do the coupling and Bias Supply caps 1st. Then all the others. Can caps last.

Larry
 
Thanks guys, this is an excellent start-- I'm really looking forward to this, although I admit I'm filled with fear and trepidation. Re-cap an old guitar amp? Sure, no problem. Especially the ones I favor (typically the 1960's guitar equivalent of BPC)

But the 800-C? Orders of magnitude in complexity, sound, historical value, and certainly not the least, cash value. I'm sure I can do it, but it does kinda feel like be hired to dust the Mona Lisa.


Couple of questions: if I'm not changing from the (working) original tubes, should I change the grid resistors? (I may be confused, but I thought that was to accommodate newer tubes.)

And a Selenium Rectifier. Great.
Oh well, after I put in the bridge maybe I can drop it into my mother-in-laws coffee. :)

I'm putting together my shopping list, printing schematics and cleaning the workbench.
Onward Ho.
 
Honestly once I started to understand how these tube circuits work, a full restoration is actually pretty simple and straight forward. The key is to take it one step at a time and double and triple check your work.

Also, if you have a digital camera it allows you to take a million before pics to double check any hicups along the way you may have.

There are some real gurus on these forums when it comes to Fishers or tube audio in general. If you ask a question, it will be answered so don't hesitate! :D
 
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Yes the grid resistors should be changed along with the coupling cap value change to .1 from .047. This allows the tubes to run more comfortably (even the NOS ones).

Go over to Jim McShanes TUBE PAGE, and look up the 7591 tube. He has an excellent explanation. If you do go with new output tubes, DON'T GET JJ's. TOO MANY Problems and QC Sucks. The 7591EH by Electroharmonix is an outstanding tube for the 500C/800C. It's a bit large, but will fit. Jim's testing is a lot more indepth that manyof the online shops and his matching is outstanding. Plus his prices are good.

NO AFFILIATION.....VERY SATISFIED REPEAT CUSTOMER.

Larry
 
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