• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

fisher x100a

draget

Member
2005-06-11 2:21 pm
WA
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

Member
2002-01-07 6:02 pm
draget said:
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.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
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

Member
2005-06-11 2:21 pm
WA
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
 

Tekko

Banned
2005-01-01 3:33 pm
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.
 
Looks like the output transformers are not original either - is anything original? :)

draget said:
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
 
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. :smash:
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
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