New Power Transformer Install Help JTM30

[amearse]

Hi There, I just got a Mercury Magnetics P30 JT for my Marshall JTM 30. I'm trying to install it and I want to be sure that my wiring is correct. I tried to follow the diagram as attached, and as it was previously wired. Can anybody check my current setup as in the picture and advise?

The schematics are here:

http://www.drtube.com/schematics/mar...jtm3-60-02.pdf
http://www.drtube.com/schematics/mar...jtm3-61-02.pdf

[oc disorder]

If I were doing it I would check the voltages on the transformer
and make sure the connectors I pushed on went to the right spot.
Assuming the mains side is correct you should be able to measure
the voltages on the secondary which will be a bit higher with nothing connected.
I am not familiar with the Mercury Magnetics P30 JT so I don't know if the terminals correspond with the original.
25 volts AC to W5 W6 ( pre amp board connections )
6.3 volts AC to W114 ,W113
if those 2 are correct theres no need to measure the last one
which is 325 volts AC and goes to W105 ,W103.

I worked on one a long while ago make sure the bias voltage is present
before plugging in the output valves. Should be approx -40v dc.

Think I altered one of the zener diodes to a higher value as the one I had
was biased way too hot which eventually lead to a blown transformer
(wrong value fuses were fitted).

Hope that is some help and not too late...!

[amearse]

Power transformer working fine

I've go the power transformer running correctly with the stock tubes. I just put some new Electro Harmonix 12ax7s and 6L6s wtihout biasing and now it sounds like the amp is cutting out, as if there were a gate on it or something. They are also running very hot. Any suggestions?

[stokes]

Bias the power tubes,sounds like they could be running into "cut-off",running too hot.

[oc disorder]

You need to check what the bias is.
Just a voltage reading will do for starters.
Pin 5 of the output valve or R106 or R105 you should get aprox 40 volts.
Unfortunatly this does not have a bias adjustment trim pot.
I would be inclined to replace C127 a Class X 47n 250volt capacitor and check R107 is still a 4k7 value.
These "tap off" the 325 volt tapping to eventually be rectified and held at
39.1 volts (40volts) by two 15 volt zeners and one 9.1volt zener.
As I said earlier I recall having to up the value to either 12 or 15v of the 9.1 zener (ie replace it) so the valves were not biased so hot.
But first check and see what is the voltage actually is.
There must have been a drastic fault to destroy the original transformer.
The same thing could happen again so be cautious !