Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on July 14, 2021, 10:09:26 pm

Title: Reverb driver/recovery
Post by: Leevi on July 14, 2021, 10:09:26 pm

I'm planning to build a Blues Jr. type amp and thought to use 3 preamp tubes which means
that some extra amplification is needed in order to implement one tube reverb.


I thought to implement either the reverb driver or recovery circuit by using LND150 Mosfet.


My question is which one of those is recommended to be implemented with the fet, driver or recovery?


/Leevi

Title: Re: Reverb driver/recovery
Post by: d95err on July 15, 2021, 02:08:31 am

A FET should be ideal for the recovery stage. This is just clean amplification of a very weak signal; no clipping involved. The fet should provide a good low noise amplification.

Title: Re: Reverb driver/recovery
Post by: Leevi on July 15, 2021, 02:32:04 am

Thanks d95err
And it provides more gain.
/Leevi

Title: Re: Reverb driver/recovery
Post by: Bieworm on July 15, 2021, 04:10:26 am

You have to consider the PT for that project too. There should be enough current for the mosfet.

Title: Re: Reverb driver/recovery
Post by: Leevi on July 15, 2021, 06:00:07 am

Quote

You have to consider the PT for that project too. There should be enough current for the mosfet

Good point, it probably takes ~30mA. That can be an issue in the PT I have planned to use.


/Leevi

Title: Re: Reverb driver/recovery
Post by: Soulfetish on July 18, 2021, 12:07:53 am

This is a 1 tube reverb I designed to go in my buddies Silvertone 1474 to give you some ideas. It uses a 6U8A Pentode/Triode tube with the Pentode used as a CCS driver and a hybrid cascode as a really low noise, high gain recovery stage.

Title: Re: Reverb driver/recovery
Post by: tubenit on July 18, 2021, 04:56:14 am

I would love to hear a sound clip or YouTube of that "one tube reverb".  I like innovative ideas and this looks great!


Can you share a sound sample of the reverb, please?


With respect, Tubenit

Title: Re: Reverb driver/recovery
Post by: pdf64 on July 18, 2021, 05:49:01 am

Quote from: Soulfetish on July 18, 2021, 12:07:53 am

This is a 1 tube reverb I designed to go in my buddies Silvertone 1474 to give you some ideas. It uses a 6U8A Pentode/Triode tube with the Pentode used as a CCS driver and a hybrid cascode as a really low noise, high gain recovery stage.

Nice! What spec tank?

Title: Re: Reverb driver/recovery
Post by: Leevi on July 18, 2021, 06:32:33 am

Quote

This is a 1 tube reverb I designed to go in my buddies Silvertone 1474 to give you some ideas. It uses a 6U8A Pentode/Triode tube with the Pentode used as a CCS driver and a hybrid cascode as a really low noise, high gain recovery stage.

Very interesting! The tank should probably have high impedance?


/Leevi

Title: Re: Reverb driver/recovery
Post by: pdf64 on July 18, 2021, 08:24:49 am

Quote from: Leevi on July 18, 2021, 06:32:33 am

…The tank should probably have high impedance?

Yes, I suspect it would work best with the highest impedance drive coil available.

I wonder what the gain of the cascode stage is?

Title: Re: Reverb driver/recovery
Post by: Leevi on July 20, 2021, 05:24:38 am

I used the following setup because of limited resources.
I had 1/2 12AX7 free. It works excellent, very low noise even if the reverb is fully open.

Longer reverb can be reached by changing the 470K resistor from the reverb pot lower e.g. to 220K or 270K.

/Leevi