Bandmaster Reverb VS Twin Reverb -- Question about reverb circuit

[Skeeter_pdx]

I have an acquaintance who brought me a Bandmaster Reverb that was blowing fuses. I got that all sorted out but he was wondering if the reverb circuit could be modified to be as deep and drippy as a Twin he recently played. Comparing the schematics, the circuits look pretty much identical except for one capacitor--a .002uf from the secondary on the reverb transformer to ground on the Bandmaster--and different plate voltages on the triodes in the reverb circuit. Would the slight differences between the circuit cause the difference in the reverb sound, or is it more likely the individual components (reverb tank, drive and recovery tubes) that cause the difference, assuming all other components are the correct values.

Edit: The only other difference I can think of is that the Bandmaster has a tube rectifier and the Twin has a solid state rectifier

Thanks for any input!

[Willabe]

1st, try changing the verb driver tube, then the verb recovery tube next, do them 1 at a time, might be both.

Then put new cathode (K) bypass caps on the verb driver and recovery tube.

And check all the R's to see if they have drifted on the verb driver and recovery.

If still no improvement, get a different tank to try. Might be several of these things.

That cap on the verb OT is get rid of the very high end sizzle/sparkle in the verb. And to get rid of high end hiss.

Some guys like the high end sizzle/sparkle, others don't. 

[Merlin]

Strange, the 200pF cap is normally on the recovery side,  it won't do a great deal on the driver side 

[glass54]

Sorry Merlin, that's actually 2000pF on the Bandmaster (.002)
...and I agree, weird but a fairly substantial cap.
And nothing on recovery side apart from "stray capacitance"
Kind Regards
Mirek

[SEL49]

B+ voltages are considerably higher in the TR than the Bandmaster. Using a 9AB3C1B 3 spring tank (as found in the 6G15) will change the reverb sound considerably.

[ac427v]

I hear large variation in "identical" tanks. Put the amps side-by-side and plug the Twin Reverb tank into the Bandmaster to test tank sound. Then go shopping for a good used Gibbs tank  
The net likes Surfy Bear pans but I've never heard one to see if the hype is true.

[Skeeter_pdx]

I tried new drive and recovery tubes, didnt make much of a difference. The guy didn’t want to pay more for me to take a closer look, and frankly I’m a bit too busy to take a closer look out of curiousity.

The verb sounds pretty great in my opinion, but when I had the amp on just to monitor things I noticed some sound with the reverb turned up that wasn’t just typical quiet hum or hiss. It almost sounded like something picking up a radio signal, but I couldn’t make out anything intelligible and think it was just the reverb tank making a tiny amount of sound on its own. I suspect a leaky cap upstream of the reverb circuit but thats just a guess. I appreciate everybody’s advice!

[stratomaster]

There's a thread over on TDPRI (or perhaps TAG) where the iteration of the recovery circuit that features a 2000pF cap bypassing the 220k grid leak was modeled.  It was found that when accounting for the inductance of tank output transducer that a treble peaking effect was produced similar to a pickup in a guitar.  Commonly this cap is considered to shunt highs to ground, so this finding was intriguing. I don't have enough of an intuition for the response of RLC filters to immediately dismiss the findings and have yet made time to dive deep enough to debunk or confirm them for myself.

All that to say maybe moving that cap could have changed the tone for the better.

As far as the sound you heard, did you happen to take any measurements of the transformer itself?

[Skeeter_pdx]

All that to say maybe moving that cap could have changed the tone for the better.

As far as the sound you heard, did you happen to take any measurements of the transformer itself?

I didn't take measurements of the transformer. I'd be really curious to delve into what was going on, but I simply don't have the free time right now and I wanted to get this guy his amp back. Whoever replaced the electrolytic caps last marked the date in '04 so I suggested replacing them. I figured a shorted cap could have caused the fuse to blow so I swapped those out before playing the amp. I'll wait to hear back from the owner to see if the reverb is any more lively with new capacitors in there.