Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: punkykatt on September 08, 2020, 12:01:04 pm

Title: Question on D`Lite schematic
Post by: punkykatt on September 08, 2020, 12:01:04 pm

Hello all, been looking at a D`Lite schematic and wondering what is the purpose of two 22M resistors and a 0.05 cap all in series between grid pin 7 and plate pin 6 of v-1 on the attached schematic. Any input is much appreciated. Thank you in advance.

Title: Re: Question on D`Lite schematic
Post by: sluckey on September 08, 2020, 12:05:58 pm

It's a very tiny local negative feedback loop.

Title: Re: Question on D`Lite schematic
Post by: punkykatt on September 08, 2020, 12:21:47 pm

Thanks  Steve,  very tiny means hardly any difference at all is what you are saying. Correct?

Title: Re: Question on D`Lite schematic
Post by: shooter on September 08, 2020, 12:34:57 pm

 :laugh:


I got a pretty good scope, pretty sure 44meg will eat any signal I could see short of many VAC

Title: Re: Question on D`Lite schematic
Post by: Sonny ReVerb on September 08, 2020, 03:38:25 pm

Only Howard can hear it!

Title: Re: Question on D`Lite schematic
Post by: sluckey on September 08, 2020, 04:40:23 pm

Quote from: Sonny ReVerb on September 08, 2020, 03:38:25 pm

Only Howard can hear it!

Oh no! He has a cult of followers and they all can hear it too!  :l2:

Title: Re: Question on D`Lite schematic
Post by: tbn on August 08, 2021, 01:11:15 pm

Quote from: punkykatt on September 08, 2020, 12:21:47 pm

Thanks  Steve,  very tiny means hardly any difference at all is what you are saying. Correct?

Sorry, bit late of a reply, but here it goes for the fun of it.

I've built a single ended 6l6 d'lite two years ago, and i wondered the same thing. So I added this local nfb loop on a switch with the following settings:
-off
-full resistance nfb
-nfb with half the resistance (so twice as much feedback)

I was surprised by the effect of flipping the switch.

In normal setting the preamp tightened up considerably, bit less crunch too, compared to the "off setting". In double mode the amp got very tight and clean; too much so imho. So it does have effect.

Unfortunately I don't have the amp anymore, but pictures are still up at ampgarage