Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ernie_jr on January 23, 2014, 06:19:34 am

Title: Fisher 500
Post by: ernie_jr on January 23, 2014, 06:19:34 am

Anyone have any experience restoring one of these? I got one from my dad's estate. Powers up but now sound. I am sure it needs a cap job and replacement of the selenium rectifier. Any other hints or advice?
Thanks,
Ernie

Title: Re: Fisher 500
Post by: jjasilli on January 23, 2014, 07:30:59 am

Great amp.  Lot's of info on the web.

Title: Re: Fisher 500
Post by: stratele52 on January 23, 2014, 08:06:04 am

Quote from: ernie_jr on January 23, 2014, 06:19:34 am

I am sure it needs a cap job and replacement of the selenium rectifier. Any other hints or advice?
Thanks,
Ernie

Why you say that , What are voltage reading ?

I never see an amp with old or bad filter caps with no sound . Bad filter caps will hum but you have sound .
Better to fix why you don't have any sound before put new parts you don't need for now.

All Fisher service manual and schematic here;

www.vintageshifi.com/repertoire-pdf/Fisher.php (http://www.vintageshifi.com/repertoire-pdf/Fisher.php)

Title: Re: Fisher 500
Post by: ernie_jr on January 23, 2014, 08:10:43 am

Caps are over 40 yrs old, and there is a bad hum but did not leave it on long due to age of the caps.
Ernie

Title: Re: Fisher 500
Post by: eleventeen on January 23, 2014, 12:58:32 pm

Those are great amps. One nice forum I have found that deals with these things is diyaudio.com. I am sure you could find several others, but I know that one to be a good one. Most likely, it probably just needs the standard electrolytic cap job to kill the hum, maybe a few other things to really tune it up, but no doubt the e-caps need replacing and you have to do that to get to the finer details. It is also a near-commandment to replace any selenium rectifiers with silicon ones because seleniums generate toxic fumes should they burn. Cheap fix.

Additionally, you may wish to build a "light-bulb limiter" thingy to test the thing out when you first power it up. 

You do not need to use "can" type electrolytics as replacements, you can use axial or radial ones.

Of course, I am assuming you have reasonable electronic skills and at least a meter and some tools and soldering gear. The standard "lethal voltages" warning should be given as well.

Title: Re: Fisher 500
Post by: stratele52 on January 23, 2014, 03:48:28 pm

Quote from: ernie_jr on January 23, 2014, 08:10:43 am

Caps are over 40 yrs old, and there is a bad hum but did not leave it on long due to age of the caps.
Ernie

You write " no sound " . IMO hum is a sound . Yes need new filter caps