Marshall JMP Plate Voltage

[louderock]

Just finished re-tubing and re-filter-capping (is that a word?) my 1974 Marshall 50 watt. I'm getting a plate voltage reading of 375V. Is that a little low? What factors determine this and what effect does + or - have on the amp's sound?

[V846]

PT will determine the voltage, what is the p/n of the PT?

example here

http://www.marstran.com/164.htm

[louderock]

PT will determine the voltage, what is the p/n of the PT?

example here

http://www.marstran.com/164.htm

Already put it back together but it looks like the transformer on the link you provided puts out 370v to the plates. Just wondering what the optimal plate voltage is??

[V846]

Looks like the 1202-164 PT was introduced in 74 which IIRC puts out less voltage than its predecessor the 1202-118.

Most likely the 1202-164 is what is in your amp though p/n not verified, so that plate voltage would be correct for that year amp give or take some for wall voltage.

http://www.kbapps.com/audio/schematics/tubeamps/marshall/ampchart.html

more info
http://marstran.com/74%206624FAN>.htm (http://marstran.com/74%206624F.htm)

http://marstran.com/Historic%20Data%20Base.htm (http://marstran.com/Historic%20Data%20Base.htm)

[louderock]

Thanks for the info. It's sounding good biased close to 70%.

[Mr. SD-1]

That plate voltage seems normal. My '73 runs at 365VDC and sounds awesome!

[samtheman]

Maybe its *low voltage* 50 watter, i.e. Yngvie amp, not so much headroom, very early break up, me likey :drink

/sam