Fisher 404 help needed, bad module

[tcdriver]

I recently acquired a Fisher 404 2 / 4 channel receiver circa 1972. It has a bad output module. The module indicates it is a "The Fisher PA 500 Hybrid-IC Power Amplifier Module". I have not been able to find any information about this module on the web. I would appreciate it if someone could point me in the right direction for getting a replacement. Thanks.

 

[tcdriver]

Pa 500

I added a photo.

 

[Paul C]

Peel off the Fisher sticker and tell us what the SANYO number is under it.

Looking at the picture, the parts on the board the modules are plugged into, I would guess it is probably a Sanyo STK-082, STK-083, STK-084, STK-085, or STK-086. If any of these you can replace it with the same, or any of the higher numbers. That is, an 084 will sub for an 082, etc.

 

[tcdriver]

Stk

Paul C,

Thanks for the suggestion. I just returned from a weekend trip home. I will take a look at it tomorrow.

tc

 

[tcdriver]

Amplifier Module

I peeled the Fisher label off and found no other label underneath. I checked the pinouts of the STK-08X series amplifier modules and they are quite different from the pinout of the Fisher PA 500. Pinout for the PA 500 is:

1. - Supply (-27V)
2. Output to speaker
3. + Supply (+27V)
4. ?
5. ?
6. ?
7. ?
8. Input
9. Ground
0. ?

 

[Paul C]

That info is very helpful.

My best guess, based on your pin out, is STK-032 or STK032.

If this is it, the body should measure 3.07" (78mm) across (point to point) x 1.733" high (44mm). Screw holes, center to center, 2.756" (70mm). .315" thick (8mm).

Leads are

1 = -V
2 = Output
3 = +V
4 = bootstrap
5 = n/c
6 = n/c
7 = negative feedback (resistors can cap coming back from pin 2)
8 = input
9 = ground (by input)
10 = n/c

Description is Mod-Hybrid 25 w (minimum) audio amp, and max voltage +/- 32v.

 

[tcdriver]

Paul C,

Thank you so much for your thoughtful follow through. Since writing my post, earlier this evening, I discovered, by looking in an old SK Replacement Guide, that the module I am looking for is most probably a STK-032. The SK replacement was the SK3291 and the ECG replacement was the ECG1090. I have downloaded a datasheet from the web.

I have found one place that appears to have a STK-032 but I am continuing to look for other places. Do you know of a good, reliable source for these types of modules? If you do, I would appreciate that information. Again, thank you for your thoughtful help. I would really like to get the Fisher up an running on all four channels once again.

Sincerely yours,

tc

 

[Paul C]

The STK032 is pretty old. The one site where I think I might find it won't come up (Audio Lab of Georgia).

Anybody else know of a souce?

 

[Paul C]

I had a freaky idea... if you absolutely can't find STK032...

There are some little boards you can buy, or make yourself, for STK082, 083, 084, 085, 086. You could replace those old STK032's and board with a pair of 082's-084's, and those small boards.

Or, I have some artwork here for a small board for the LM3886. You could make a couple of those. Only connections to the board are what you have in that photo, Input, Ground, Output, +V, -V. And the LM3886 will run very well on +/-27v.

 

[rca2000]

I THINK I have a chassis from a receiver with those........

I had it at the fest, thinking someone would want it, but no one seemed interested... it has 2 modules with a "PA" number on them, and other parts.but is FAR from being complete. (missing the front panel

I can check for you, if you want. I do NOT know if they are good or not.

 

[tcdriver]

Stk-032

I also had thought about modifying the unit to fit a later, more obtainable module. I want to do some additional searching before I take that approach.

It may be that the STK-025 will also work in this application and I may have a source.

It may be that this is a project that is not worth fixing. If I do decide to part out the unit, I will have three good STK-032's that may be of use to someone else. Indeed, they may be more valuable than a completely working unit.

Another option is to convert it to a tuner/preamp to be used with outboard power amplifiers.

At this point, I have not given up finding a replacement module. Thanks for the suggestions.

tc

 

[tcdriver]

Stk-032

I just bought a STK-032 through the popular internet auction site. Thanks for all your help and suggestions.

 

[tcdriver]

It works!

This is just a follow up to let all those who helped me on this project know how it turned out. I received and installed the STK-032 replacement module and that fixed that problem. I then discovered an intermittent problem in the same channel and tracked that down to a broken solder joint on a connector pin. With that fixed, I have been burning in the unit and cleaning the front panel. I am well on my way to some happy listening.

Thank you to all for the helpful advice that you gave me. A special thank you to Paul C for his additional suggestions and encouragement through the private mail system.