New 500C Owner

ncwalz

Mostly just a lurker
Just acquired a 500c which appears to be in good original condition. Haven't turned it on but the previous owner said it worked well. I checked the underside and all the caps look original along with the selenium rectifier.

I plan on ordering a Jim McShane restoration kit. I understand that while his kits are excellent, one needs to be able to read schematics. I've restored a number of old tube radios so I don't think this would be too much of a problem.

My 500c has a serial number above 61,000. The only service manual I can find only includes model 500c's up to 49,999. Will this present a problem for my restoration?

Thanks

Norman
 
Norman; Welcome to AK and the FISHER Forum specifically. Great bunch of people here and a good amount of talent. Let's hope you hang around awhile with the rest of us. There's plenty of room on the lower branches.

As for the manuals. I've not seen a manual go higher than 49999 for the 500-C. There probably is a higher #'ed on out there but i haven't seen it yet
It shouldn't. Fisher stayed pretty consistant with the 500-/800-C thruout it production run. I would however get the latest manual and go over it and compare it to the unit, noting any discrepancies BEFORE doing any work or ordering any parts. make a list and post it, so we can look at it and comment either positively or negatively. We can probably suggest a best course of action for the discrepancies based on the unit and the manual.

a couple or a few areas you want to check real close.
1.) Transformer part numbers. They are stamped on the side bells. compare any suffix's.
2.) The bias rectifier may be selenium OR Silicon. We do know that FISHER switched to Silicon bridge rectifiers late in the 400 production (question is when did they do it for the 500-C/800C if ever?). Replace the Selenium with a silicon Bridge Rectifier.
3.) Negative feedback circuit.
4.) Output transformer to speaker wiring (including the headphones) did they use the COM lead to ground or the 4ohm lead.

There are some sticky threads at the top of the FISHER forum you should read. One is the COMMON FISHER PARTS. Another is cleaning a tube amp. Then in the General Forum there is the "The Idiot's guide to DeOxit...revisited" This is the 1st thing you should do to rule out any control problems caused by dirt, Oxidation, and environmental pollution (sulfates on the contacts).

Tube Forum has some good info on tubes and tube gear in general in the sticky's.

Take tons of pictures when you do find discrepancies from more than 1 angle. Also take pictures from multiple angles before, while doing the work, and after on each section of the unit. If you forget what you did or didn't do the pictures will help.

DO NOT POWER IT UP WITHOUT A LOAD! Load being either speakers or dummy loads (8ohm 50W resistors) connected to the speaker terminals.

Build a DBT, (Dim Bulb Tester) and use it on the 1st power-up. If the light dims after about 2-3 seconds of bright (the caps need time to charge) when turned on (150W bulb at least) the likely hood of a part failure is remote as the bulb is a current limiter. Go ahead and turn it off, plug it in to the wall, wait 10 minutes or so then turn it on.

While waiting you can connect speakers(if you had dummy loads or expendable test speakers connected), and other sources. Now power it up and let it cook for a 1/4 hour with the Function selector in AUX, Volume down, and no sources active.

Take voltage readings on the BIAS Circuit (most of them will be Negative), and the output tubes. Also Filament voltages of the 12ax7's that are fed off the + side of the Bias Circuit (these are DC powered heaters. Note the Wall Voltage also. This will tell us whether or not a bucking transformer or other solution to drop the wall voltage is necessary. All voltages shoud be within 15% of nominal on wall voltage. With the exception of most of the tube filaments and the primary on the power transformer all voltages will be DC Voltages. Use the chassis as ground.


This I can't stress enough!!! INSULATE ALL BUT THE EXTREME TIP of the Red Meter probe. this lessens the likelyhood of OOOOOPP'Sies if you slip and the attendent 4th of July fireworks and smoke. We've all done it at one time or another. Getting zapped is one thing. Becoming a Human AED is another! If you are inside with a probe, keep the other hand in the rear pocket. We'd rather you be VERTICAL and BREATHING than Horizontal and wondering why your side of the grass is brown. (nothing personal, I do this to most all newbies here, with the meter probe).

Now that I've scared the crap out of ya (figuratively) DIG IN!

Larry
 
Looks like it's in beautiful cosmetic condition though, if that's it in your avatar. Those *00c models have a fantastic-sounding headphone-out, which saves the cost of buying a standalone headphone-amp.

Picked up my first Fisher yesterday as well. An 800c.
 
Yes, that is my 500c in the photo and I think it looks very nice. Just need to make it sing!

Norman
 
Excellent and thorough advice; thank-you.

Norman
Welcome to the Fisher group...and congrats on your new 500C! I recently got one too and I just LOVE IT!!! You will love yours, too! If you get a chance, check out the Fisher Consoles Sticky...Also, there's been a few beautiful consoles posted recently that are noteworthy. Have fun!

John
 
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