Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: luthierwnc on June 03, 2020, 07:18:47 pm

Title: Assessing gain on 5879 morph control?
Post by: luthierwnc on June 03, 2020, 07:18:47 pm

Hi All,  I'm going to try an idea I've had on the back burner for far too long.  It is just a 5F6a Bassman with the Morph control from Merlin Blencowe that Tubeswell and Tubenit did such great work on a few years back.  I'm borrowing Tubeswell's diagram in my attachments. 

I'm curious about the gain levels as we would compare them to a dual triode-preamp tube across the sweep of the 1ma Morph pot.  From what I can tell of the datasheet on the 5879, in triode mode it has an amplification factor of 21 -- the same as a 12AU7.  In pentode mode, my sheet doesn't have an amplification factor and I can't tell from the charts how I would compare the two.
This is not keeping me up at night but I am curious -- and it would help in designing the faceplate -- perhaps using U, Y, T, X and ! instead of numbers.
Thanks for any help, Skip

Title: Re: Assessing gain on 5879 morph control?
Post by: tubeswell on June 03, 2020, 08:22:34 pm

Its about  100 for that circuit IIRC

Title: Re: Assessing gain on 5879 morph control?
Post by: luthierwnc on June 03, 2020, 09:08:10 pm

Thanks!  I've built them with the EF86 too -- probably a bit more, I'm guessing.  Hope your projects are going well.  sh