fisher x100a

[draget]

I have a fisher x100a amp which i got from an old repair shop, i would like to restore it (i am not going to be buying audiophool crap), apparently there is a problem with the plate transformer, i cant seem to find a schematic, and im a newbie to this sort of stuff.

pix etc.

That sorta outlines my problem.


Any ideas would be great!

Thanks,

draget

 

[Brett]

I have a fisher x100a amp which i got from an old repair shop, i would like to restore it (i am not going to be buying audiophool ****), apparently there is a problem with the plate transformer, i cant seem to find a schematic, and im a newbie to this sort of stuff.

Do you mean power transformer?.
I have a schenatic, but it's too big to post. PM me with your email addy and I'll send it out tomorrow.

If your power trans is bung, then you'll need to get it rewound, replace it with something similar (and in this case you can get rid of the poxy doubler circuit) or remove the output transformers and ship them to me.

PS: I can't get your link to load.

 

[draget]

thanks for your reply!

thats weird,

http://draget.net/fisheramp

e-mail addy is:

da@draget.net

i think i'll have a go at rewinding the transformer myself, there is a tutorial by gregg (from geekzone) about doing it.


LOL, "remove the output transformers and ship them to me" you are the third to ask, no, i want them 😛

 

[audiousername]

Re: Re: fisher x100a

PS: I can't get your link to load.

It was broken before, but seems to be working now. Odd.

 

[Brett]

LOL, "remove the output transformers and ship them to me" you are the third to ask, no, i want them 😛

They work well in guitar amps, and I have aproject brewing....

Emails sent.

 

[anatech]

Hi draget,
Have a look at the filter caps and rectifiers before installing your rebuilt power xformer. If you have a selenium rectifier, it should be replaced by silicon diode(s) and a resistor to give the correct voltages again. Grid coupling caps on the outputs could cause excessive current too.
-Chris

 

[draget]

hum, the schems show different output valves to what i have got, and several other differences.

im thinking i might just pull everything out of it and start from scratch using something like this http://www.bonavolta.ch/hobby/en/audio/el84_5.htm

thinking of using 6gh8a as input/phase splitter (else i also have 5x 12ax7 and 1x 6cg7) and either 7189 or 6v6 for power stage.


any comments or ideas would be great!

thanks,

draget

 

[anatech]

Hi draget,
Well, if it's in good shape and you want a Fisher, rebuild it as it is. If not or the unit is in bad shape, reuse some parts and build on a new chassis.

The units I have rebuilt to original spec have not disappointed me.

-Chris

 

[Tekko]

I can see one of the previous owners did replace the power transformer. Replace all caps, by now they are all dried up and wont do their jobs as they should, also change the resistors, they are very old and could have drifted in value enough to cause the amp to malfuction such as blowing fuses, making the output tubes run glowing red or even fry the transformers.

 

[draget]

going to have power transfo rewound, and start from scratch to keep things simple.

should I use:

6gh8a or 12ax7 for drivers
and
6v6 or 7189 for power valves (PP)



thanks,

draget

 

[mcs]

Looks like the output transformers are not original either - is anything original? 🙂

should I use:

6gh8a or 12ax7 for drivers

Use whatever the original was using? I would use the original circuit (if you can find it).

6v6 or 7189 for power valves (PP)

6V6 won't fit, so that choice is easy 😉

Best regards,

Mikkel C. Simonsen

 

[draget]

dont want to use the original as it is very (over) complex and i'm a n00b 😉

As for power valve, of course 6v6 would fit, just gotta change sockets.

thanks,


draget

 

[draget]

having teh transfo rewound is going to be too expensive, i shall have to try myself.

 

[Brett]

Ditch the doubler supply if you replace/rewind the power tx.

 

[SHiFTY]

Rather than rewinding it, why not just ring up a few ham radio guys in your area, ask them if they have a spare transformer? Most have boxes and boxes of them. Then you can rebuild without the nasty voltage doubler.

You would probably need 250-0-250 (500VCT) at 150mA, and 6.3V 4A, and maybe a 5V winding to. Easy to find... Cost you about $10 if that. They might also have some cool other stuff you can get. You could try the aussie newsgroups too.

BTW I would stick with EL84s or 7189s, more powerful and easier to drive. And 12AX7s are easier to connect and a perfect match for EL84s. You might want to consider the Leak Stereo 20 circuit as an easy to build, good sounding starting point. You can easilty modify that later if you want to.

I think you should keep the chassis but build a totally new amplifier on it.

 

[draget]

where would I find numbers for HAMs?

You dont think I should use the 6GH8A, a couple of people said they would be ideal for this PP circuit.

thanks,

draget

 

[anatech]

Hi draget,

Google +hamfest +"your state"

Go to the hamfest and meet people. You may have to wait.

Do the people who like the 6GH8 (TV tube) have a diagram for you? Didn't think so. So build what you know or can easily find. You will find a contradictory opinion on everything. Just build the thing and go from there.

-Chris