Marshall 9005 stereo power amp - nice sound, low volume

[Michael m and m]

hey there,
thanks for checking in.

first of all a disclaimer: i know how to handle the life threatening voltages inside the tube amp, and know how to measure voltage and resistors, without risking my life. ; )

my great sounding 9005 stereo power amp, that i bouht used, unfortunately has very low volume. in HIGH mode i run the gain at 12 o'clock, and the volume is room level. not loud.
both channels the exact way. LOW mode also works fine, but low as well.

the amp sounds absolutely fine ... no hum, almost no noise and no crackling, etc.

as the channels both are the same sounding ... is it possible that someone before me has kind of severely reduced the output to speakers, with resistors, etc.?
maybe even for hi--fi use. dont know how many owners this power amp has seen already ... ; )

the big power supply in the middle is for both channels. is it common thst these lose power after 35 years? as it feeds both, channel a and b simultanously.

valve plate voltage and bias is fine ... all tubes are new.

thanks for help
maybe somebody had a similar experience. maybe with a jcm800 in mono! great sound but very low volume.

 

[Dogs of Doom]

to the forum...

what's the tube array?

In my EL34 50/50, there's a single pre-amp tube, the PI & a pair pf power tubes, for each channel.

mine takes:

ECC83 pre-amp
ECC83 PI
EL34 x's 2 (50 watt) power tubes

per channel.

I'm not sure what yours takes, by design, but, maybe they installed lower strength pre-amp tubes?

On my amp, there's only a gain volume & a presence knob (as well as voicing switches). The amp is basically a non-master volume amp. The pre/gain is the volume... If you put a low value signal tube in the circuit, say an ECC82, in place of an ECC83, that's going to give you 20% of the signal +/-... that's an 80% drop in signal

 

[Michael m and m]

hey there,

thanks for the reply, and thanks for the welcome!

well, there are two separate sides ... channel A and B. each having two ECC83s ... one for gain and one for phase inverter. I have changed them all myself before. to new ecc83s, 12ax7s. so this cannot be the reason.

my 9005 seems to been have changed to operate with 5881 power tubes. and I have redone all these changes, as I am using el34s now ...