JCM 800 2204 PT issue

[Dr.R]

Hello there
I've got from a friend an original JCM800 2204 head amps. It doesn't sound good to me, particularly it's very bright, too harsh and it breaks up quite abruptly at medium to high volumes.
I checked out voltage values and I read 260V across hot wire and CT of PT secondary sets in open circuit mode and with a stable 220V at PT primary. Do you think my PT can have any faults? The PT is an original Drake Transformers 1202-324/2 model and I guess I should have read at least 320V (CT).
Can somebody help me out with that issue or give me some hints?
Thanks a lot!!!
Ciao
R.

[jjman]

260-0-260 sounds low especially in standby mode as you mention. But what is the DC voltage on the CT of the OP tranny with the amp in run mode? I'm guessing an expected voltage of 450-500 or so? I don't see voltages on the scheme I have.

[Dr.R]

Hi
at ct of OT i've a DC value around 360v, it sounds quite low, because of that i measured ac voltage in open circuit at secondary of PT.

Ciao
R.

[jjman]

Sounds low there too. Are both sides of the secondary on the power tranny measuring the same? Do you trust your meter?

[pinkjimiphoton]

also, check the voltage selector switch on the back of the amp...them things fail easily, and can make all kindsa weird stuff happen.

[Zer09]

Originally Posted by Dr.R

Hi
at ct of OT i've a DC value around 360v, it sounds quite low, because of that i measured ac voltage in open circuit at secondary of PT.

Ciao
R.

Dr. R,
If he has one of the original 800's they used a PT with lower voltage secondaries (345). I worked on one recently and there were around 360-370 (original schematic says 365) on the plates so you are right there. They later switched PT's with higher voltage secondaries. For what it's worth, those lower b+ amps are the more desirable 800's.