Fisher 500c restore

riglehart

This is my first ever attempt at restoring anything. I've ordered a restore kit from VTV to simplify things. I hope this forum is a good source for advice. If anyone knows of a better place I can go, please advise.

First question...

The 4 little switches on the front panel are very hard to operate (See below). Almost to the point where I'm afraid of breaking them every time I switch them. Do they just need a little DeOxit? If not, are they easy/cheap to replace?

dorokusai

De-Oxit and yes, they are hard to replace. Cali-Lube is nice to have handy as well.

www.fisherdoctor.com

schwarcw

De-Oxit and Cali-Lube (both by Caig Chemicals) are the gold standard for restoration. Audiokarma.com is a good Forum for Vintage audio gear. Check out this link: Fisher 500c

schwarcw

Get yourself an ID and password so you can use the search engine. There is a lot of info on Fisher gear, do the search. Good luck!

Carl

mhardy6647

The VTV kit is OK but overpriced (IMNSHO) for the quality of the components they kit up and the meagre documentation they provide. That being said, it sure is convenient... and fortunately the cheap Illinois coupling caps they provide sound good.

The other good news is that the old Fishers are very straightforward to overhaul. Since they are fixed bias, the bias supply isn't too tricky, although it does mean one needs a quad of matched output tubes to get the bias current right for all 4 tubes.

It is well worth (IMNSHO) adding a 10-ohm cathode resistor to each output tube in lieu of the directly grounded cathode in the stock circuit. This not only provides a de facto fuse to protect the output transformers in case one of the output tubes goes south, but it also permits one to actually measure bias currents for the four outputs (based on the voltage drop across each cathode resistor).

EDIT: FWIW, here's the undersides of my own 500C, which was re-hab'bed by Craig "NOSValves" Ostby and Mike "Punker X" Williams (AF and RF, respectively).




If I may say so... you might want to look at the thread on re-hab'bing the very similar Fisher 400 that I started at Audiokarma. You may need to be a registered member to see the photos.
http://audiokarma.org/forums/showthread.php

schwarcw

Thanks for posting Mr. Hardy! You've always got some good info on vintage gear. Nice job on your 400!

Carl

mhardy6647

My pleasure -- but neither of the 400's I showed in the AK thread were mine :-(
(and, as I said above, I didn't do the re-hab on the 500C that I DO own)

The 400 is a heck of a nice package, IMNSHO.

riglehart

mhardy6647 wrote:

The VTV kit is OK but overpriced (IMNSHO) for the quality of the components they kit up and the meagre documentation they provide.

I have gotten the rectifier, power supply caps, and the FEDREDs replaced so far. I'll attach a picture. I'm pretty proud of myself since I have never cracked open anything and soldered inside it before.

I got a bag of parts and a schematic from VTV without any indication as to where the parts should go. I can read a schematic and find the parts, but I'm not sure WHICH 47uf caps should be replaced, etc... I got 4 "expensive" sequa caps, and I now know where those need to be. But the rest I'm not sure of. I asked him for a list of which parts this "grab bag" replaced, since all parts are clearly labeled in the service manual. Basically I got a condesending reply about the kit not being for a novice. Which I admit I am. However, I can read a schematic and find parts just fine.

Anyway, I noticed the person at www.antiqueradio.org mention "four safety resistors installed on the cathodes of the 7591 output tubes" on an 800c job. Sounds like this is an important mod, now that I've ran into it twice. Thanks for that input.

How the heck do you get the chassis so shined up? Is it just patience with a Q-tip and metal polish, or is there a quicker method?

mhardy6647

I was really surprised at the lack of specific info in the VTV kit. IMNSHO there is no reason to pay a premium for a bag of parts without some documentation!

Your bias rebuild looks fine at a quick glance. I like to tie down the new caps with a cable tie so they can't jiggle around.

There some folks with way more patience than I in terms of cleaning and shining those old (cadmium-plated?) chassis! I don't think there's any quick way out; although a Dremel and buffing disks might improve the kinetics. One'd also run the risk of making a mess...

The cathode resistors "mod" is controversial. Personally, I think it is all up-side and I recommend adding them. That being said, I am NO expert. (EDIT: oops, I already said all that, didn't I?)

riglehart

I tied down the caps.

Question. My left channel wasn't working when the FM was in Stereo mode. It worked in mono. After analyzing things and studying the schematic for a while I decided to look into the "Multiplex Section". Is that an old term for "FM"? Anyways, the first thing I tried was swapping the 3 tubes around you see below. They are all identical 12ax7. Problem seems to be solved.

My question is, is there any reason you can't swap tubes around like that, or does this cause problems if there is a bias adjustment? I noticed a pot on this subassembly but am not sure what it is for. Biasing maybe?

mhardy6647

The multiplex (MPX) section is the circuitry that recovers (demultiplexes!) the stereo channel information from the multiplexed mono-compatible stereo FM signal. Swapping the tubes is fine if it cures the problem! What you've (probably) done is re-aligned the MPX adaptor! The variable transformers or inductors precision tune parts of the circuit for the specific characteristics of the exact tubes (and passive components) present when they were originally aligned. The tubes and everything else ages... you may have just been lucky enough to pull the circuit back into tolerance by swapping around tubes.

or...

it may just be that a dirty tube socket and/or tube pins was "fixed" by removing and reseating.

Generally speaking, though, any time you remove a tuner tube, you want to be careful to put it back into the exact socket from whence it came. Stereo FM receiver alignment is not for the inexperienced.

EDIT: No, don't muck about with any of the adjustments! :-)

riglehart

More progress. Put the main caps in tonight. See before/after pics below.

Can anyone confirm these are in the right orientation? The schematic doesn't specify any polarity (like it does on the electrolytics), but the VTV doc says that the cheaper caps they ship go in this way based on the writing on them. The old caps had a stripe on them.

It sounds fine!

schwarcw

Nice looking job! Give the caps a while to burn in, then give us your impressions of the sound of that vintage tube tuner.

Crispycircuit

The signal/coupling caps do NOT have a polarity. You are fine. The caps with the stripe indicate which side of the cap have the outside foil winding. In some very sensitive circuits this would be oriented a certain way. For audio it's moot and these are on mostly old caps that have much more ESR to them. Hey, nice clean soldering mounting job. Some RTV is quick and dirty way to mount parts.

riglehart

I'm slowly but surely getting this done. Can anyone help with some general questions.

VTV sent me a bunch of reisistors with no indication what they should replace. I have severaly types...

1)Brown hour glass shaped
2)Brown with square shoulders (straight cylinder instead of hourglass)
3)Bigger Green

See picture below. Is there are certain type of these that are problematic that I should just replace as many as I can?

BTW. I am very dissappointed in VTV (Vacuum tube valley). They are in the business to throw parts in a bag and make a quick buck. Their documentation gives no specific help for the peice of equipment the kit is for. They assume you already know what you are going to do. I'm getting this done, no thanks to them. Don't buy from them if you are expecting much help. It's too bad, all they'd need to do is circle the parts on the schematic that they are sending. The guy wants to charge me extra for this "service".

schwarcw

Hi Rob! have you tried testing any of the resistors with a multi meter? Compare the measured value with the stated value?

I wouldn't mess with the resistors unless there was a problem. Caps are another story, and you've been replacing some of those.

Maybe Mr Hardy willchime in!:)

Carl

riglehart

Yes. I have tested a couple. I don't suspect anything wrong with any of them, but would like to avoid future problems if there is anything I can do while I'm in it. I have noticed a very small "pinhole" in a couple resisters near where the wire comes out. Is that a potential problem?

I have been replacing quite a few caps. Basically, anything that says "Mylar" on the parts list. I have one extra electrolytic that I can't find a spot for, and a couple that I never got replacements for in the kit.

Also, there are some mylar caps in the multiplex section. Should I just leave well enough alone in this part of the reciever? I don't want to throw FM out of whack.

grahamrunsran

I have a Fisher 400 I'm restoring. I've heard these kits suck too, I don't want to spend 80 or a 100 bucks on 25 dollars worth of parts, can anyone out there tell me what parts to get? espetially for the rectifier section? I know how to wire up a new bridge, but I hear the quick recovery ones are way better? What part should i get, and what size resistor should I add to lower the voltage and compensate for the increased efficiency of the new rectifier? anyone know from experiance? thanks!

mhardy6647

The kits don't suck, they're just 'spensive.
I don't know of anyone who's done a complete BOM (bill of materials) for a Fisher restore.
The quick recovery diodes are probably 'quieter', but whether it'll really make a difference to you is quesitonable. That said, they're cheap enough!
The voltage adjusting bit is pretty empirical. Get yourself a 25 ohm rheostat rated for a few watts (Radio Shack used to sell 'em, maybe still do), dial in the voltages you need, measure the resistance and sub in a power resistor of the appropriate value.