Tweed bassman with verb and trem - Episode 90 million

[tubeswell]

I have too much spare time on my hands and have this monstrosity in my amp cupboard taking up room. It sounds great in the clean channel and the trem is fantastic, but in my quest for surfin' heaven I wonder about the reverb again and again.

I have 2 x pre-amp tubes available for reverb circuitry so I was thinking of putting the reverb circuit after the tone stack. Seeing as how the 5F6A TS is quite lossy, I wondered about using one of the spare stages as a TS recovery stage before the reverb circuit - I would use a kind of BF reverb circuit, but with an Allen old flame recovery TS stage, and then going straight into the PI (instead of using the spare stage to boost the recovery signal). I was hoping to get away with just having a 1M grid load resistor in front of this extra stage (in green) instead of adding another pot, but I'm happy to take suggestions about what to do about the load there (seeing as how its all part of the TS load on the previous DC pair stage). See schematic:

Anyone got any more sensible suggestions about how to accommodate the reverb circuit (apart from throwing it away and starting again)?

TIA

[jimboyogi]

Tubeswell,
I've just recently put together a single tube reverb using a 12DW7, the 12AU7 side directly (no transformer) driving a high impedance tank (~1.5K), the 12AX7 side for recovery. I take the drive signal from before the first vol pot (I only need ~ 16v pp for full drive), so that the drive signal is only attenuated by the guitar vol control, leading to less variation of the drive current. Doing this you don't really need a Dwell control, unless you put a booster in front of the amp and end up overdriving the driver stage. The downside of this is that the reverb volume is independent of the amp's volume setting, so it needs to be adjusted seperately.
My build has no NFB, so I feed the recovery signal straight into the other PI input from the dry signal. I don't know if you could still do this while running NFB in there as well. If you can though you can ditch all that 3M grid stopper and cap, and just use a more conventional grid stop resistance.
Using your 12AX7 PI, I think that you could get plenty of reverb volume and depth using this setup, and still have a tube slot leftover for something else!

[tubeswell]

Thanks jimboy. While you were logged on I was soldering away... (on a mission to get verb into the bassman. This time I think I got much better results than ever before)

Here's the present incarnation schematic with a few sound bytes (gotta love that broadband). This incarnation uses the Old Flame (2007 edition) verb circuitry, where the extra stage is after the recovery insertion point. I figured, what with the lossy tone stack'n'all, that I'd just take the verb off the end of the treble pot, but then boost everything again before the PI.

So now the amp boasts blend-able parallel stages in V1, the old flame verb between the tone stack and the PI, and the AC coupled CF in the LFO circuit, for plenty of woof. Runs into 2 x 25W greenbacks and is powered by 2 x el-cheapo russkie (20W) 6P3Ss idling at 13.6W and sitting at 442 on the plates. The trem is so powerful (not on these recordings) that I can't turn it all the way up. If the vol is on about more than 2 with the verb on, the pan starts to feed back - I've got to biff it in a bag or something.

[Chuck H]

Guys have been trying to put reverb on 5f6a's and Marshall type amps with some degree of eloquence for decades without good results. The brute force method in your OP seems like it should work fine. Kudos on the trem BTW. By the time your done you'll have developed a 5f6a/Marshall type amp with reverb and trem. None too shabby. IMHO the extra tube stage won't add enough noise to matter if it's managed correctly. Series rewsistance is much worse for adding noise IME. You may need to reduce some gain on the stage following the TS in the OP. Perhaps a split load with the reverb driven from the actual plate and the dry off the split. Kind of like a 6g9 I guess. I've done this (but not with a 5f6a) and it works just fine. Much quieter than the huge ass series resistor.

Chuck

[tubeswell]

I got some time to do a 'proper' recording of this amp today (while Mrs tubeswell was out of the house).

Its still bloody loud even with both channel vols on about '2.5', (on lead track - Dwell on 9, verb level on 6, verb tone on 6), treb on 6, mid on 4, bass on 1, speed and depth on about 2-3) Mic'd with SM57 through my desk into garbage band on my mac. At the end I played with the trem depth and speed for a few strums on the lead channel. This amp still has the 2 x greenback G12M 12" (25W). Powered by 2 x Russkie 6P3Se idling at 13.6W. Through my strat on neck 'pup with everything dimed.

Current schematic attached FWIW

[pdf64]

Very cool, both amp and tune.
Have you tried it without the 10pF cap bypassing the 3M3 dry mixer?
Minor schematic error on the reverb recovery, coupling cap to wrong end of plate resistor.
If you like the bass set low, try wiring the mid pot as a variable resistor, like a BF Fender.
Pete.

[tubeswell]

Very cool, both amp and tune.
Have you tried it without the 10pF cap bypassing the 3M3 dry mixer?

I'll pull that 10pF out when I get a moment over the next day or so and let you know

Minor schematic error on the reverb recovery, coupling cap to wrong end of plate resistor.

Fixed

If you like the bass set low, try wiring the mid pot as a variable resistor, like a BF Fender.

Thanks for the suggestion - it has plenty of bass when you wind the bass up.

[Bruce / Mission Amps]

Isn't that actually Man of Mystery?..... The Shadows

[tubeswell]

Yeah actually it is. I forgot what it was called. Shads rule.

[greekie]

Great sounds!

I have the 6P3S-tubes, and I have the problem of a tiny whine through the speakers when the plate voltage are over 400VDC - you aren't having the same problems I guess?

Jake

[tubeswell]

Great sounds!

I have the 6P3S-tubes, and I have the problem of a tiny whine through the speakers when the plate voltage are over 400VDC - you aren't having the same problems I guess?

Jake

Hi Jake

I initially ran 6P3S in there at 400-something volts but found they didn't last long. I changed to 6P3Se (a completely different tube - with the wafer black base) and haven't had any problems.

[jeefberky]

Hi Tubeswell,

This looks like a fantastic project. I'm loving the 5G9 you gave me advice on. Incredible trem! I'm inspired to give this reverb add-on a go in my single-ended build. Just curious how functional the dwell pot is... Can you go from surfin' heaven to a small room reverb?

Space is a bit limited in my design, so if I don't need to figure in an extra knob I won't bother.

Great sound clips too!

[tubeswell]

The dwell pot works fine thanks, and works even better as you wind the V1 stages(s) up.

FWIW as a further refinement, I am now using a 12AT7 in the LTP position (with no circuit changes) for added overall body. This amp does the Clapton JTM45/bluesbreaker sound (e.g.n Hideaway) really well with a LP (I know because one of the guys at the blues club plugged his LP into it last week) - no pedals required (I might add)!

[jeefberky]

Awesome! Didn't mean it in a skeptical way. I always appreciate your input/contributions on the web.

I'll have to use a slide potentiometer to conserve space.

Thanks, Jeff