Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on November 29, 2025, 06:59:02 am

Title: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: kagliostro on November 29, 2025, 06:59:02 am

I was thinking to us a pair of LND150 as Source Followers in that position but someone explained me that the available current to drive the Power Section will be too low and also in the first approach I put the couplign caps before the PPIMV and that was told me is not a good choice

This is the first approach
(https://i.imgur.com/F3YeWwt.jpeg)

and this is the new version with moved coupling capacitors and new MOSFET, a DN2540
(https://i.imgur.com/M4T5ZTg.jpeg)

I've never seen something like this arrangement with a SF that follows the exit of a Cathodyne PI and feed a PPIMV

Why I've think to this solution ?

The reason is because I don't want to load too much the PI and alter the tone when the Frondelli PPIMV has the shaft rotated near ground and the PPIMV is used because the gm of the 6N6P is near 3 times the gm of the 12BH7 tube that is originally used on the Wangs Mini 5, so it is there to enlarge the possibilities of use of the amp

Need really help to evaluate if this thing will be useful or not

MANY THANKS

Franco

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: Merlin on November 29, 2025, 09:02:22 am

Someone gave you bad advice. Your first schematic makes more sense, and it doesn't even need LND150s, it could use ordinary enhancement MOSFETs. The second schematic will not work at all; it has DC on the pots and positive bias on the output tube grids!

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: pdf64 on November 29, 2025, 09:16:55 am

Quote from: Merlin on November 29, 2025, 09:02:22 am

first schematic makes more sense,

Sorry for a derail, but how are you viewing imgur stuff?

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: Merlin on November 29, 2025, 09:27:56 am

Quote from: pdf64 on November 29, 2025, 09:16:55 am

Sorry for a derail, but how are you viewing imgur stuff?

VPN

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: kagliostro on November 29, 2025, 11:38:42 am

Many thanks Merlin

I surely misunderstand the council it was given to me

I can see what you say

So, I'll maintain the first arrangement and use on it a DN2540, will this MOSFET be adequate or it will be better to use one other one ?

Many Thanks

Franco

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: Merlin on November 29, 2025, 03:02:06 pm

Quote from: kagliostro on November 29, 2025, 11:38:42 am

So, I'll maintain the first arrangement and use on it a DN2540, will this MOSFET be adequate or it will be better to use one other one ?

DN2540 will work, even a classic like the IRF820 will work in that scenario

Title: Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
Post by: kagliostro on November 29, 2025, 03:14:43 pm

Many thanks

Franco