Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dunner84 on October 21, 2015, 11:24:02 pm

Title: 5f2a layouts
Post by: dunner84 on October 21, 2015, 11:24:02 pm

Hi,

I am about to start my 5f2a build. I am making a few slight changes like an adjustable NFB, and a speaker impedance switch.
I am curious to know what additional changes the Hoffman layout has made to the circuit, other than dropping one input, and combing the filter caps.. I noticed there is an additional 470r resistor and a few other small changes. Does anyone have any insight?

Thanks,

Jd

Title: Re: 5f2a layouts
Post by: sluckey on October 21, 2015, 11:42:11 pm

Looking at the schematics side by side I see that Hoffman has added the 470Ω screen resistor and also a 1.5K grid stopper resistor, both on the 6V6. Filaments are also wired different and have two 100Ω resistors (artificial center tap) across the filament string. The PT primary circuit is wired different. There is a drawing for two input jacks.

That's all the differences I see. All are considered improvements and should not change the operation or sound of the amp.

Title: Re: 5f2a layouts
Post by: dunner84 on October 22, 2015, 12:40:01 am

Thanks for the reply. It was those two resistors I was most interested in knowing about. I wasn't too sure what their purpose was, so thank you for the clarification.