Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mason on May 05, 2021, 09:19:52 am

Title: Reverb Circuit Help
Post by: Mason on May 05, 2021, 09:19:52 am

Hey yall,

I just picked up a 1983 Marshall 2205. The amp has been heavily modded and I'm in the process of undoing all that work to get it back to stock. One of the mods removed the reverb transformer and circuit, so now I need to find a replacement transformer. I've never done reverb in an amp before so I'm not sure what transformer I should get. What would be best for this circuit? https://drtube.com/schematics/marshall/4210.gif

Since the reverb circuit was taken out of this amp I have really no idea how it sounds, are there any potential improvements that could be made to the circuit? It doesn't bother me if the amp isn't completely stock, since enough work has been done to this amp that I would never be able to pass it off as all original anyway. Does anyone have any suggestions?

Thanks!

Title: Re: Reverb Circuit Help
Post by: Bieworm on May 05, 2021, 09:59:14 am

At 18watt.com there is a very good 1 tube reverb. Check the "tremolo TMB reverb"

Title: Re: Reverb Circuit Help
Post by: 2deaf on May 05, 2021, 02:30:19 pm

I measured one of those transformers at 4.75 turns to 1 turn.

The Fender reverb driver uses two 12AT7's that can swing a lot of current and then steps that current up a lot to drive a tank that requires a lot of current.  The Marshall driver uses a single 12AX7 that only swings a little current and steps that current up a little to driver a tank that requires very little current.  The theory is sound, but the end result is something less than impressive for the Marshall version.  IMO, anyways. 

Title: Re: Reverb Circuit Help
Post by: Mason on May 05, 2021, 02:52:50 pm

I was looking at the one tube reverb linked in the all-time great information post here, https://el34world.com/Forum/index.php?topic=7957.0. Would that be a suitable replacement for the reverb in this marshall? The only thing that throws me is the triode labeled Reverb Mix in the marshall schematic. I'm not sure how that works into it.

Title: Re: Reverb Circuit Help
Post by: Bieworm on May 05, 2021, 04:16:25 pm

This is the one tube reverb in my tremolo TMB reverb at 70%

https://www.dropbox.com/s/0n81wlamgt5mrzd/Tremolo%20TMB%20reverb%2036W%20rumble.m4a?dl=0

Title: Re: Reverb Circuit Help
Post by: shooter on May 05, 2021, 04:39:48 pm

Quote

the triode labeled Reverb Mix

quick look appears it should be labeled FX mix or FX/verb mix.   :dontknow: