Tweed Bassman / Deluxe w/ reverb. any opinion?

[Victor Denance]

Howdy!

I'd like my next design to be a mix of various amps. Basically:
- 5F6A Bassman preamp (2 gain stages + cathode follower + tone stack)
- BF style reverb (12AT7 driver + 1/2 12AX7 recovery //ed with 2.2M resistor, feeding a gain stage).
- 5E3 Deluxe cathodyne Phase Inverter and cathode biased power amp.

Now I'm wondering where should I stick the verb in this circuit:
- between the Tone stack and PI
- between the 2nd gain stage and CF

Which spot would be the best theoretically?

Also, would you think that design would work? I'm concerned about having way too much gain in the preamp, and wonder if something w/ lower preamp gain in the vein of a cathode biased Princeton Reverb would be any better (then, what should I do w/ the unused triode?)

Thanks a million!!!

Victor

[tubeswell]

BF style reverb (if that's what you want) usually comes between the tone stack/recovery and the driver/PI combination.

However there being no tone stack recovery in the 5F6a, maybe either put one in, or put the 'verb before the tone stack?

[Victor Denance]

Thanks Tubeswell,

That's precisely the dilemna I'm fronting now... guess only the trial error method will tell.
Think I'll do the "GS>Vol>GS>VERB>CF>Tone>GS>PI" first.
It's just a guess there, but looking at the old circuits, it seems like the Reverb likes to have a GS right before, and so does the cathodyne PI. That way of doing it will get me there.

Feel free to chime in folks, and give your opinion!

Thanks!

[MWJB]

If you're tapping the signal for the reverb before the tone stack, you'll probably want a tone control in the reverb circuit for the wet signal.

[txstrat]

Since your're aiming for a 5F6a tone I'd leave the circuit up to the tone stack unaltered and put the verb after the TS.
Put the recovery stage right before the PI and you're there. At least I hope so.
Might be a game of try and error to find out how much of a resistors value you'd have to put in between the driver and recovery stages of the reverb not to attenuate the original signal too much.

[GibsonLover]

You can return the reverb signal on the 'other' side of the PI also. Check the Matchless Chieftain schematic. It works beautifully, and may save you an extra stage.

[tubeswell]

As a further thought on this, I think that if you put the verb between the first and second stage it will work. I am working up a schematic at the mo'.

[tubeswell]

1-ch bassman w/ verb & trem

So bite me (some inspiration from tubenit's CC Plexi - credit where credits due)

[Victor Denance]

Thanks for the drawing Tubeswell, it looks like the perfect Bassman.
The Vibroverb 6G16 style trem is yummy... however, I don't quite get how the reverb works. I was expecting something like the std BF reverb (with the dry signal being lowered with a 3.3M / 10pF pair) but I don't quite understand what I see.

Could you please shed some light on this reverb circuit?

Thanks for the insight!

[tubeswell]

Hi Victor

I borrowed and adapted the reverb scheme from one of tubenits plexi designs. One side of V1 feeds the reverb driver and the other side of V1 offers a 'dry' mix option. However as an afterthought, the switch on the grid on the dry mix side of V1 was a mistake. And you can run the driver and recovery with one tube and save yourself a tube (altho' won't get as much current into the pan as you could with the parallel 12AT7 driver)

[tubeswell]

Revision #2 (with 6BM8 reverb driver/recovery)

Me again

FWIW To try and economise on sockets, I revised the reverb circuit based on a 6BM8 - Svetlana spec is here;
6BM8/ECL82 spec

I ended up with 3.78A heater draw (without factoring in the 6.3V lamp, which is about another .3A), so it might pay to drop the trem if you only have a 4A rated heater winding. I think the pentode driven reverb would be quite intense.

I took out the 500pF cap in front of the reverb 'dwell' pot, and substituted a .002uF coupling cap from the 12AY7, so that it sort of resembles the driver stage and pentode of a 6G15, but I'm not sure whether this would boost the signal enough for the pentode. I guess you could always put a 470R-680R cathode resistor on the pentode to run it a bit hotter to get more current through the reverb tranny.

Also I think the older types of 6BM8 were rated for 250V max plate voltage, so it might pay to drop the plate supply a bit in that case.

Comments/criticisms welcome

[tubeswell]

V3 with PR reverb circuit

I've done a slightly more conventional (or slightly less unconventional?) possibility here. I don't know how well it would work (diverting, as it does, after the post vol mixing resistors). Any thoughts or comments would be most welcome.

Also since it only requires 4 & 1/2 preamp triodes, can I get away with connecting (say) pins 4 and 9 (or pins 5 and 9) (if that's possible?) in order to run the filament in the 1/2 used tube for one cathode only? Or doesn't it work like that? (But if it did, would that tube only draw half the usual heater current (i.e. .15mA instead of .3mA?)

[MWJB]

I'd suggest having the reverb re-injected after the tone stack, but have a tone pot on the reverb circuit, to EQ the wet signal.

A tweed bassman style PT should cope easily with 6 preamp tubes, plus power tubes (4A min on the 6.3VAC secondary, 6A would be good). Wire the half used 12AX7 as normal with regards to the heaters & ground the unused plate, grid & cathode.

[pdf64]

To keep it tweedy, how about sticking a standalone reverb circuit 6G15 in front of the pre-amp. That's how it would have been used in the day. The vibro king uses this idea with a few tweaks. Peter.

[tubeswell]

I'd suggest having the reverb re-injected after the tone stack, but have a tone pot on the reverb circuit, to EQ the wet signal.

A tweed bassman style PT should cope easily with 6 preamp tubes, plus power tubes (4A min on the 6.3VAC secondary, 6A would be good). Wire the half used 12AX7 as normal with regards to the heaters & ground the unused plate, grid & cathode.

Thanks MWJB I'll re-draw it later today. (Have to go to my day-job now)

I already have a Bassman spec PT with a 4A 6.3V winding - That's why I was wondering. AFAICT that gets me to 3.3A plus a lamp (about another .3A).