Restoration/Upgrade of pvinyl's Fisher 400

[Leestereo]

Here are some pictures of the restoration/upgrade of pvinyl's Fisher 400. This 400 is in excellent cosmetic shape and in order to keep the stock look intact, all components except for the multi-section can capacitor were installed under the chassis. Pvinyl sourced all of the parts from Jim McShane, except for the capacitors in the doubler circuit and the IBAM which I ordered from Mouser.

 

[Leestereo]

More pictures.

 

[audiodon]

It's always interesting to see how different people approach the same issue.

One question:
Why is IBAM near the power supply and not near the output tubes? You could then shorten those four output leads.
Just curious, not passing judgement.

 

[HVHiFI]

I like how you used the terminal strips to secure the caps from the cans under the chassis. New ideas every day. Thanks for sharing!

 

[Leestereo]

One question:
Why is IBAM near the power supply and not near the output tubes? You could then shorten those four output leads.
Just curious, not passing judgement.

Fair question; I didn't want to drill the chassis, so the IBAM would have to be mounted with an existing ventilation hole. There just wasn't enough space near the output tubes ventilation holes (I will post pictures of the output tube area).

 

[bhamham]

I like it :thmbsp:

Very clever layout and expert workmanship - well done. I like how you used a cardboard tube to insulate that doubler cap, and your placement of the terminal strips. I see you used the G1856 fast diode off the bridge. Would you mind posting an overview shot of the underneath?

 

[Leestereo]

Yet more pictures.

 

[Leestereo]

I like it :thmbsp:

Very clever layout and expert workmanship - well done. I like how you used a cardboard tube to insulate that doubler cap, and your placement of the terminal strips. I see you used the G1856 fast diode off the bridge. Would you mind posting an overview shot of the underneath?

Thanks for the compliments. Due to its smaller chassis size of the Fisher 400, compared to the 500/800, the layout of the power supply had to be carefully planned, much more so than when I work on a 500/800. Unfortunately, I didn't take an overview shot of the underneath (doh!), and the unit is now back with pvinyl.

 

[larryderouin]

Lee. You might want to add a 100ohm 1/4watt resistor at the places marked in green on the picture for the Screens. Helps cut down on the incidence or prevents arcing of the screens.

Details in this thread......http://www.audiokarma.org/forums/showpost.php?p=6480170&postcount=40 and in Dave Gillespies treatise on increasing POWER TUBE LIFE.....http://www.tronola.com/html/maximize_tube_life.html

And how I did it on my old 400 a few years ago.

 

[audiodon]

I appreciate what you're saying.

I did it a little differently, but this was in an amp that already was partially restored so I didn't even use all the components of the ibam circuit. Not better . . . just different.

http://www.audiokarma.org/forums/showpost.php?p=7553461&postcount=21

 

[Leestereo]

Lee. You might want to add a 100ohm 1/4watt resistor at the places marked in green on the picture for the Screens. Helps cut down on the incidence or prevents arcing of the screens.

Details in this thread......http://www.audiokarma.org/forums/showpost.php?p=6480170&postcount=40 and in Dave Gillespies treatise on increasing POWER TUBE LIFE.....http://www.tronola.com/html/maximize_tube_life.html

And how I did it on my old 400 a few years ago.

Thanks for the links Larry, I'll look into it.

 

[Leestereo]

Would you mind posting an overview shot of the underneath?

bhamham: Here is a serial clockwise overview of the underside of the 400.

 

[Leestereo]

More pictures, again.

 

[eduarsan1]

Excelent job done in that fisher!!!! :thmbsp:

FYI take a look in threads 1, 2 and 3, may be you can improve something of this in your amp.

Regards

Luis

 

[bhamham]

bhamham: Here is a serial clockwise overview of the underside of the 400.

Thanks Lee, a lot of food for thought for my next 400

 

[rwj0j0]

Looks like you have a problem... bet you have a little right channel hum
Kind of quoted Dave here -
The 220 ohm heater balancing resistor on the right channel should go to ground.
You did not disconnect that heater balancing resistor from the cathode terminal -- it was originally grounded there -- and you have now installed the current sampling resistor between the cathode terminal and ground, the 60 Hz heater voltage is now modulating the output tube where the resistor is "grounded" at.

 

[Leestereo]

Good eye, there is no right channel hum; the picture was taken before the issue was noticed and corrected.

 

[turnhig]

Great information - thanks.