Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on November 12, 2021, 09:31:32 am

Title: Marshall Major, too low power
Post by: Leevi on November 12, 2021, 09:31:32 am

I'm working with a Marshall Major UL from late sixties.
https://el34world.com/charts/Schematics/files/Marshall/Marshall_major_1967u_lead_200w.pdf (https://el34world.com/charts/Schematics/files/Marshall/Marshall_major_1967u_lead_200w.pdf)
IMO the amp is not that loud as I expected. I even measured the power which was less than 80W. Plate voltages are on 60%bias setting 595V. Tubes have been measured and they are fine.The OT is huge and I wonder the DC resistance of its primary winding  which is 30 Ohm Plate to Plate i.e 15 Ohm from Plate to CT. UL winding shows 50%of that.

Any ideas what further checks I should do?


Power tubes are 6550.

/Leevi

Title: Re: Marshall Major, too low power
Post by: shooter on November 12, 2021, 11:12:21 am

Quote

Tubes have been measured and they are fine.

gain or just DC values?
how much drive signal is getting to the PA? 


did your try other speakers?


when something doesn't seem "loud enough" and all the DC stuff looks ok, It's time to measure gain.
finding something "normal" to compare against will be the hard part

Title: Re: Marshall Major, too low power
Post by: Leevi on November 12, 2021, 11:46:33 am

The preamp tubes are new. I have tried with two different speakers.
/Leevi