Marshall plate voltage low??

[kurtsstuff]

1978 Marshall 2204 50 watter and went to bias it up. With my handy dandy Weber Bias Rite, The amp is apparently low voltage being as my plate reading is only 375 volts.....shouldn't it be around 450 and up?? Any ideas as to why so low?? Thanks!!

[phsyconoodler]

A couple of things can suck down the plate voltage.A bad or failing filter cap and power tubes biased hot.Considering the age of your amp,it is recommended you service it by repacing all the electrolytic capacitors including the ones in the bias supply.They can cause trouble for you too.
You may have one of the lower voltage PT's,but it stillshould be at least 425v or so.

[Cary Chilton]

1978 Marshall 2204 50 watter and went to bias it up. With my handy dandy Weber Bias Rite, The amp is apparently low voltage being as my plate reading is only 375 volts.....shouldn't it be around 450 and up?? Any ideas as to why so low?? Thanks!!

No clue, but definitely join METRO AMP forum and there are at least 10000 ppl there who could walk you through making any marshall or of course, fixing one....

[trey85stang]

wasnt there low voltage ones and high voltage ones? I think I read that somewhere.

[Blue Strat]

Seems low. Replace your Bias Rite battery and try again. Trust me;)

[kurtsstuff]

Seems low. Replace your Bias Rite battery and try again. Trust me;)

First thing I did no change...hehe ;)

[plexi67]

Some of those amps ran low plate voltage.. and depending on how hot your bias is might drop it a few volts on the plate.. But that is in the ballpark for some of those amps..usually around 385 or so, plate volts

[kurtsstuff]

Amp does sound very very good but just seemed odd??

[Brian Wallace]

Voltage seems fine to me. The early 50W amps had a 420VDC range. I think a lot of these amps have the wrong primary tap used in the US and therefore have higher plate voltage than what they really should be.

[cheesey]

picked up a canadian 2204 today , owner said it was an 88 but it has vertical inputs??
got it home played it for 5 minutes sounded great then started making noises. Took the panel off and one of the sovtech el 34s was dead.
I put in 2 new GT el 34m's that i was saving for my shiva, I dont have any bias equipment , should i take it somewhere? I put in some fresh preamp tubes and played it for a good hour and it sounds pretty good.

[samtheman]

Voltage seems fine to me. The early 50W amps had a 420VDC range. I think a lot of these amps have the wrong primary tap used in the US and therefore have higher plate voltage than what they really should be.

+1, I had 50 watter from 79´ and plate was 390V, really nice crunch tones w/o any pedals !

/sam

[Swarty]

375 is right for that era, no question. That is why they are great w/ 6V6s (which bias almost identical to EL34s). I have a couple combos from this era and have serviced/modded scores of heads. I also have a '71 1987 that is under 400V. Replacing the filter caps will often add a few volts.

[RedMan]

I agree, not low at all for that amp.

[kurtsstuff]

Cool....Thanks guys!....The amp does sound killer (hate that word but applies here.. ;)) I've owned alot of these heads and this one just crunches up nice and sweet so...ain't changin a thing....:bow