The Fisher 660A console power amp

[Put A Tube In It]

Hello! I JUST joined the diyAudio community. Thank you for having me! I have a couple of projects that I’d like to start, and this seems like the best place online to start some research and ask some questions.

I have an old (1959/60 I believe) Fisher 660A power amp that I acquired years ago that I absolutely love the sound of. I had NorCal tube amp guru Skip Simmons (google him if you don’t know his rep and work, its A+) go through the Fisher unit about eight years ago, and it has been running wonderfully since, powering a variety of vintage KLHs, Advents, And JBLs, as well as some M&K and KRK/Focal passive studio monitors.

Today, I was lucking enough to score an entire old Fisher console for $10 with everything in it, from a second 660A (with all original tubes) to the Garrard turntable. As much as I’d like to restore the entire unit, I’ll at least start with the somewhat simpler task of just the new 660A amp. I’d like to match it as close as possible to my existing 660A in order to use them both together, as either a pair of mono blocks, or as a pair in a bi-amp configuration.

I thought I would post here to see if anyone has any experience working on these power amps, and if they could recommend any possible mods or upgrades to the design or the circuit, perhaps just simple things like upgrading caps, bare wire plugs to bananas, on/off switch, etc. I’m an electronics novice, but I know my way around a soldering iron and schematic well enough to do a bit of audio gear troubleshooting, and have fixed a number of guitar pedals and upgraded a few audio mixing consoles with new transformers, IC chips, caps, etc. Not rocket science by any means, but enough to have some fun, burn some fingers and curse a lot.

Thanks for your time and input!

-Tim

 

[ahankinson]

nice score!

Have you gone through the amplifier to see if the old caps need changing?

 

[Put A Tube In It]

Hi,

I have not done that yet. I just unloaded the console and read through the original manual it came with. It is a Fisher Electra VII, Model E-49. I learned something new according to the original manual. I believe this unit will allow me to use a variety of power tubes. I believe my current model uses 7591A power tubes, however the manual for this model says that it uses EL84 or 7189 power tubes (states that it is auto-bias), but no mention of the 7591A. The goal tomorrow is to pull the power amp out of the cabinet and put the two units side by side to see how close to identical they are. I started Googling this evening, and it may be that these are very similar units, but not identical. If that's true, then the idea of using them as a set of mono-blocks is probably out, but I could still use them as a set of pretty closely matched set of horizontal bi-amps (one used for lows, and one for highs). I guess I'll find out more tomorrow!

-Tim

 

[Tom Bavis]

The Electra VII E49 used the 481 amp, not the 660. This uses 7189s, not 7591s. I wouldn't use modern EL84s in it - voltages are on the high side. Russian 6P14EB (or EL84M) are called for. Other than the output tubes, circuits of the 481 and 660 are quite similar.

Oh yes - manuals here: The Fisher Console and Fisher Audio Website

 

[Duke58]

PATII-- Grew up with a Fisher console and always thought that if the Fisher console could survive my older sister, it has to be a good brand. She would stack records on the turntable and play records all day long, then our mother would come and play her records. I had the chance to buy a KX-200 a few years ago and set about changing the dog turd capacitors and some of the resistors located under the tube sockets. If you check your home electrical voltages, it's most likely around 120 VAC or even higher. When the Fisher amps were sold in the 1960s, most home electrical voltages were right around 117 VAC. Those few volts apparently make the output tubes run hot. Heat is the mortal enemy of tubes and affects tube life. But, we all have to die of something starting the day we are born, so why not give those output tubes some extra life?

 

[PRR]

..... 7591A power tubes, .... EL84 or 7189 power tubes...

Not even in the same league.

If the Fisher was a car, offered with wide choice of engine, the 7591 is "the V-8", the EL84/6BQ5 is "the Four".

EL84 is a very excellent tube. The 7591 goes a bit louder, and the number on the spec-sheet is about double.