Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: macula56 on December 05, 2011, 11:14:54 am

Title: Hoffman/Randall 50 watt schematic
Post by: macula56 on December 05, 2011, 11:14:54 am

I was scrolling thru the schematic section looking for cool stuff when i saw this.
it is using half of a 12ax7 before the PI. is this for a volume boost?

Title: Re: Hoffman/Randall 50 watt schematic
Post by: Willabe on December 05, 2011, 04:14:20 pm

I wonder if it's more for recovery for the FX loop?


               Brad            :dontknow:

Title: Re: Hoffman/Randall 50 watt schematic
Post by: macula56 on December 05, 2011, 04:27:19 pm

i wondered about that as well.

Title: Re: Hoffman/Randall 50 watt schematic
Post by: DummyLoad on December 05, 2011, 05:35:40 pm

i'm wonderin' what happened to the potatoes....  :dontknow:

Title: Re: Hoffman/Randall 50 watt schematic
Post by: alerich on December 05, 2011, 09:20:20 pm

Seems to me that it does both. It provides amplification/recovery for the effects loop return but if no effects are plugged in (with no subsequent loss from that area) then it is providing a bit of gain.

Title: Re: Hoffman/Randall 50 watt schematic
Post by: Willabe on December 05, 2011, 09:54:06 pm

Quote from: DummyLoad on December 05, 2011, 05:35:40 pm

i'm wonderin' what happened to the potatoes....  :dontknow:

Yeah, it's got the Gravy switch, where's the Potatoes?   



                  Brad          :laugh:

Title: Re: Hoffman/Randall 50 watt schematic
Post by: PRR on December 06, 2011, 08:36:37 pm

The 220K:22K before FX Send knocks the signal down 11:1.

The added stage has 220K:100, 3:1 loss, and gain of ~~25; net gain near 8.

This part alone, it has less gain than a stock 5F6A. 8:11 or 0.72.

However the direct path omits the channel mixer, so gain is 2X higher than stock. 1.4 times stock gain. No big difference, but enough to ensure no disappointment.

The add-in V1B and the huge Meat pot kick it up a considerable notch past 5F6A gain.

Title: Re: Hoffman/Randall 50 watt schematic
Post by: EL34 on December 06, 2011, 08:46:19 pm

It's for recovery after returning from a line level effect

Got to get the level back up a bit before you send it to the phase inverter