fender verb circuit with lower supply

Hi tube junkies!

I've cleared out a couple guitar amps, which means time to make another.

I have a cool preamp topology idea I can elaborate on later, but was thinking of PP el84 so my supply voltage would be reduced from typical Fender levels. Anyone have experience with getting the Fender verb sound/mojo at reduced supply voltages?

specifically the transformer loaded at7 with say 250VDC vs ~400

Thanks!

andyfromdenver said:

Hi tube junkies!

I've cleared out a couple guitar amps, which means time to make another.

I have a cool preamp topology idea I can elaborate on later, but was thinking of PP el84 so my supply voltage would be reduced from typical Fender levels. Anyone have experience with getting the Fender verb sound/mojo at reduced supply voltages?

specifically the transformer loaded at7 with say 250VDC vs ~400

Thanks!

Click to expand...

In a Twin-Reverb, B+ is anything from 315 to 410 V . This circuit is extremely tolerant to B+ variations. Do you intend to run your EL84 from only 250V? Blues Jr. runs them at 330V. You may want to adjust the cathode resistor in order to slightly increase the idle current, if the need arises.

abbey road d enfer said:

In a Twin-Reverb, B+ is anything from 315 to 410 V . This circuit is extremely tolerant to B+ variations. Do you intend to run your EL84 from only 250V? Blues Jr. runs them at 330V. You may want to adjust the cathode resistor in order to slightly increase the idle current, if the need arises.

Click to expand...

Thanks for the input!

It's been a while, since I did el84.  I guess 300V is more appropriate range.  I'll sort out this idea a bit more and maybe post for input.

very rough idea: ef86 (Ra 220k, Rk 2.~ master blaster values) -> toggle switch for low cut (coupling cap) send off to fender style reverb, THEN the choice would be either 1/2 tube tremolo too and cathodyne PI to cathode biased el84s, or can skip the trem and do LTP. 
This will go in a chassis with cutouts for 4 pre,fx, and PI tubes and 3 power section tubes (tube rectified).

Another thought was maybe a Princeton reverb with an ef86 and toggle low cut, no treb bass, and Vox Cut. 

I feel like between the coupling cap bass cut and a typical Vox Cut control you have some quality tone shaping.

i'll add a pic of the chassis I am working with, they are basically blank tweed bassman chassis w/ 4 9 pin punch outs.  I've built several types of amps in them as a fun exercise.  I'm about to sell my only ef86 amp and am plotting another.

you can do sooo many designs in this, it's semi-loco.
can't quite do a single channel deluxe reverb unfortch. can't quite do rare fender 6G12A sigle channel vibrato either :-(

andyfromdenver said:

cathodyne PI to cathode biased el84s, or can skip the trem and do LTP. 

Click to expand...

Tube count between cathodyne and LTP is the same, because cathodyne has unity gain, so needs an additional stage before. Cathodyne has the advantage of being better balanced, but has less drive capability and elevated cathode can create issues.

So you've done the Vox thing after 15 ef86?.  The fender verb uses that 3.3 meg with bypass cap with gain stage after.  As you already know ,I'm sure.  So it's the 400 v and the driver transformer that's the problem.  325v is what's on my ac 30 el84s .  I've never ran low volts on my fenders to find out but love where your going.

abbey road d enfer said:

Tube count between cathodyne and LTP is the same, because cathodyne has unity gain, so needs an additional stage before. Cathodyne has the advantage of being better balanced, but has less drive capability and elevated cathode can create issues.

Click to expand...

hahaha!! i'm not sad I threw my spit ball idea out. Good point. That kind of jacks up the add trem idea.


also, Hi Fazer, thank you for chiming in.

alright scratch it all. j/k

new spitball:
ef86 pre- single toggle low cut (no treb bass) princeton verb all else, cept a presence or cut on the back end. maybe no nfb?? argh, i'm losing it... so far from the ef86 ac15...  :

I swore the next one would have verb and trem cause it needs to be awesome for rhodes too.

There's an amp based on the Fender 6G15 (stand alone reverb) and the tremolo circuit from the Fender (Brown face era)… I've seen a schematic some ten years ago but I guess it instill available on the net… that might be something close to what you're looking for?

I vaguely remember people saying they had some oscillation issues building it but that can be fixed from layout I guess.

Best regards

/John

Like this one perhaps?

https://www.tedweber.com/media/kits/5h15_schem.jpg

Hi John, thank you for chiming in.
I actually have been itching to do one of those foreeeever.
I have two more of these chassis to work with, hmmmm. maybe the PT could go on the inside even? i dunno. with careful orientation it could help with keeping the tank interaction under control too. aka, a tighter lil cabinet.
will have to ponder that more, thanks  ;D

I am trying to stay on the mega cheap and do parts on hand, may have most the expensive goods for that.

I am always up for metal fabricating plates and etc. to make it look good. I like your sig! lol reminds me of what i'd need to do to make it look "right".

Andy