Fisher X-100

[Modegard]

I picked up a Fisher X-100, tube rectified 6bq5 amp from 1962 or so. It seems a prior owner replaced the power transformer with one much larger than stock. It's so big that it won't slide into the wood sleeve that came with it. Does anyone have a schematic or a part number or transformer specs? I have a Fisher 400 power transformer. Would that work? Thanks.

 

[doucanoe]

I picked up a Fisher X-100, tube rectified 6bq5 amp from 1962 or so. It seems a prior owner replaced the power transformer with one much larger than stock. It's so big that it won't slide into the wood sleeve that came with it. Does anyone have a schematic or a part number or transformer specs? I have a Fisher 400 power transformer. Would that work? Thanks.

I might have the schematic on that one Mark. Let me check and I will get back to you.

How ya been? Haven't heard from you for a while.

RC

 

[doucanoe]

Mark,
I haven't dug through them yet but in looking at a spread sheet I put together for on hand schematic and service manuals, it looks like I have the X-100-2 and X-100-a.

Either of those help you out?

RC

 

[Dadbar]

Your Fisher 400 power tranny won't have a 5 volt filament winding for the tube rectifier. It was also meant to be used with a diode-based voltage doubler power supply which your X100 doesn't use so the voltages will be annoying to match up. You might be better off waiting to get something else....like the power tranny from one of the more similar 7189-based HH Scott 299A/B or 222 series amps....or have someone like Heyboer make up something suitable for your unit.

 

[Modegard]

Mark,
I haven't dug through them yet but in looking at a spread sheet I put together for on hand schematic and service manuals, it looks like I have the X-100-2 and X-100-a.

Either of those help you out?

RC

Thanks for checking. I think those are different animals - solid state and with 7868 tubes, if I remember right. Been pretty busy at work. In times like this it's good to be wanted. Take care. I'll catch up with you.

Mark

 

[Modegard]

Your Fisher 400 power tranny won't have a 5 volt filament winding for the tube rectifier. It was also meant to be used with a diode-based voltage doubler power supply which your X100 doesn't use so the voltages will be annoying to match up. You might be better off waiting to get something else....like the power tranny from one of the more similar 7189-based HH Scott 299A/B or 222 series amps....or have someone like Heyboer make up something suitable for your unit.

Great points. I'll see if I can find the specs. Thank you.

Mark

 

[Tom Bavis]

I have a schematic for the X-100, and it shows the transformer as 360-0-360 at 160 mA, 5V @ 2A, 6.3V @ 4.5A. You could go as low as 330V if you eliminate the dropping resistors after the 5AR4.

 

[Modegard]

I have a schematic for the X-100, and it shows the transformer as 360-0-360 at 160 mA, 5V @ 2A, 6.3V @ 4.5A. You could go as low as 330V if you eliminate the dropping resistors after the 5AR4.

Thanks for the information. I really appreciate it.

Mark

 

[Modegard]

I have a schematic for the X-100, and it shows the transformer as 360-0-360 at 160 mA, 5V @ 2A, 6.3V @ 4.5A. You could go as low as 330V if you eliminate the dropping resistors after the 5AR4.

Tom, I found a replacement transformer from a very cosmetically challenged (rusty) Fisher X-101 B or C - 7591 outputs with a 5AR4 rectifier. It should work. I've also picked up two X-100 parts units. Both of these had fried power transformers. Did Fisher under spec power transformers in the first series of X-100? Or was there some design flaw in these? Thanks for any information you may have.

 

[Dadbar]

IIRC....The design of that X100 uses the 4 filaments of the 12AX7's to serve as the cathode bias resistor....so you need to be running ~250ma of idle current to run through 4 EL84 tubes to power those filaments (~60ma per tube at idle). That's pretty hot....and at 380V on the plate/320V screen, the amp should eat EL84's for breakfast. You should have better luck with the X101 tranny which probably has a bit more gas in the tank to power 7591's. I would suggest running huskier tubes than the EL84's that Fisher originally specified.....like the 6P14P-EV's (EL84M/7189)

 

[Modegard]

IIRC....The design of that X100 uses the 4 filaments of the 12AX7's to serve as the cathode bias resistor....so you need to be running ~250ma of idle current to run through 4 EL84 tubes to power those filaments (~60ma per tube at idle). That's pretty hot....and at 380V on the plate/320V screen, the amp should eat EL84's for breakfast. You should have better luck with the X101 tranny which probably has a bit more gas in the tank to power 7591's. I would suggest running huskier tubes than the EL84's that Fisher originally specified.....like the 6P14P-EV's (EL84M/7189)

I've got a matched quad of those output tubes on order. Thanks for the suggestion. Apparently, Fisher was aware of the issue since they recommended the beefier output transformer as a replacement.

 

[Dadbar]

Make sure you use high quality, reliable 12AX7 tubes for your entire heater string. Don't put crap tubes into the phono section just because you don't listen to vinyl. Any filament failure (or short) in any of those tubes will totally throw off the value of your cathode bias...which may have led to the destruction of your power tranny in the first place.