Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: navdave on July 13, 2010, 10:58:30 pm

Title: Marshall Major phase inverter
Post by: navdave on July 13, 2010, 10:58:30 pm

Does the 1M resistor after the tone stack connect between the 100k and 2.7k junction of the cathodyne PI then to the .047uf cap feeding the buffer or directly to the .047uf cap?

Title: Re: Marshall Major phase inverter
Post by: PRR on July 14, 2010, 12:44:26 am

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Title: Re: Marshall Major phase inverter
Post by: PRR on July 14, 2010, 12:48:49 am

> ....or directly to the .047uf cap?

Then there would be no DC path for the cathodyne grid leakage. And hardly any drive for the lower side of the short-tail pair.

Yes, it does appear to be mis-drawn.

Title: Re: Marshall Major phase inverter
Post by: navdave on July 14, 2010, 01:10:14 am

That's what I thought it was a normal cathodyne setup followed with the buffer/drive stage.
Thanks for the clarification PRR.

Quote from: PRR on July 14, 2010, 12:44:26 am

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Title: Re: Marshall Major phase inverter
Post by: Ritchie200 on July 15, 2010, 04:22:29 am

Navdave,

There are several mistakes on the power supply on that schemo too.  I would also make some suggestions on screen resistors and other items for long(er) life.  This amp morphed several times before its production ended with many things not referenced on any schematics.  Are you researching for giggles or building a clone?

Jim