marshall jcm 800 2204 homemade build

[lu.diabla]

Hi, I am making jcm 800 2204 and I have a problem with voltage on both EL34s on pin 3. I canīt get 435V. There is only 15V. Can you help me, please?

[Jazz P Bass]

JCM 800

Both EL34 pin #3 are connected to the output transformer primary.
The center tap of the output transformer primary should be connected to B+ Vdc.
If the CT is connected to B+ & you have low voltage at EL34 pin #3, then your output transformer is shorted.
Have a look at this link.
JCM800 2204

[lu.diabla]

I think I removed the short-circuit the OT. I can clock up around 425V, but when I connect all tubes, voltage on pin 3 on EL34s fall on 92V.What may be the problem?

[Jazz P Bass]

EL 34 Pin #3

EL34 Pin #3 gets its voltage from the output transformer.

[lu.diabla]

Yes, I understand.But I donīt know why the voltage fall down from 450v to 92V. I have this OT:OTR-60W-1 - GES-ELECTRONICS.

[Jazz P Bass]

Ultralinear transformer

English link:http://www.google.com/search?hl=en&s...&aqi=&aql=&oq=

[lu.diabla]

yes,this is it.

[Jazz P Bass]

Transformer wiring

How do you have the transformer wired to the amp?
It appears to be:
12-Pin #3 EL34
14- B+
16-Pin #3 EL34
13 & 15 are for ultralinear screen tap?
Measure the resistance from 12 to 14 & 16 to 14.

[Steve Conner]

Looks like you have a mistake in your power supply...

Tell us more about the power supply? What transformer, rectifier, etc are you using? Double check that everything is wired up right.

I like to use two 240V, 40W lamps in series to test the power supply. In 120V countries you'll need four in series.

[lu.diabla]

Power transformer is right and rectifier too.But I havenīt got any voltage on one from three ECC83 tubes.