I've heard of Dumble super reverb amps with a gazillion tubes in the verb circuit, but can anyone kindly point out whether Mr Dumble ever made an amp using just one tube for the reverb driver and recovery? (i.e. a two-triode, or one triode-one pentode circuit)? And if so what's the circuit/amp called?
I want to build an amp hopefully with one tube only decicated to the 'verb.
I've got a PT with four sec windings, (a 50V bias winding, 300-0-300 150mA HV winding, 6.3-6.3 3A heater, 5 - 5 3A recto). I am hoping to do a low power fixed bias 2 x 6V6Gt PP if I can get away with it> I was thinking of using a 5U4GB rectumfrier, and I was wanting to run three 12AX7 type tubes in a sort of a Princeton 6G2 (can I say that on this forum?) type circuit, with one of those doing the 'verb job.
Sorry that's probably more info that you want to know.
I don't know if Dumble ever did a one tube reverb but I have on mine.Works fine.No need for any fender circuitry.
I can send you rhe schematic if you like.
phsyconoodler wrote:I don't know if Dumble ever did a one tube reverb but I have on mine.Works fine.No need for any fender circuitry.
I can send you rhe schematic if you like.
Look for the single tube reverb in the Dumble files section. There is also an ECL82/86 version if you search the index. Finally, there is an active loop called a Dumbleator designed to handle reverb. You can find schematics to combine the two devices which might be the most useful in this design.
Luthierwnc wrote:Look for the single tube reverb in the Dumble files section. There is also an ECL82/86 version if you search the index. Finally, there is an active loop called a Dumbleator designed to handle reverb. You can find schematics to combine the two devices which might be the most useful in this design.
Welcome aboard, Skip
Thanks Luthierwnc
FWIW I found some used ECL82s at the local junk shop yesterday - they look okay, but I haven't tried them out or tested them in any way. The scheme that I stumbled over in trawling the discussion on this was one Bob-I came up with, albeit that his scheme used an ECL86. There is a difference between max voltages that these two tubes are spec'd to handle.
So using an ECL82 would mean upping the screen and supply resistors somewhat in Bob-I's schematic, but maybe that would be better if the current draw of my PT couldn't handle the higher power tube? (I have a 300-0-300VDC 150mA winding on the PT I had made, and I was hoping to get away with a 5U4GB pusing a pair of 6V6Gts, and two other pre-amp tubes besides this ECL82-86 (if i continue to work with this idea of a modified 6G2 with a 1-hole reverb.)
Still trying to work out what the Zs of the reverb tranny/pan should be for this one. I am not a very experienced tube amp builder - this is only my second build. I live in the tube-amp-making backwater of the world where parts are hard to come by, and I have to get my tranny's hand made by an old fella who lives 500 miles away, and the shops here don't even stock decent high-voltage caps of the right specs etc etc. (Mumble - mumble)
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Last edited by tubeswell on Sat Mar 29, 2008 10:47 pm, edited 3 times in total.
Sorry - for some reason this posted twice - now as a result of trying to delete the second post, I now have the same attachment three times. After I tried to delete the attachment from the second post, I found out that it had deleted from both posts, and then when I added it again to the first post - presto I had three attachments - all the same! Take your pick. Cheers
I really like that reverb. I find it warmer than the 12AX7 type but be careful of the screen current. This had me going for weeks. The reverb would sound great, but crank it and the screen would arc and burn up the socket. I measured the screen current and watched on a scope, no problem according to the specs sheets.
Finally I just upped the screen resistor to the biggest 2 watter I had. No more arcing and the reverb sounded even better.
Good luck with it. I'm sure the tube you found will sound great too.
What were the final values for resistors you used in the 'verb cicuit with the ECL86 BTW?
What voltages on the plate and screen and cathode of the pentode do you get?
What were the Zs of the reverb tranny (primary and secondary) and the pan you used?
Cheers
Not sure I can answer all of these, it's been awhile.
The schem is accurate as for the values of the components. The reverb xformer is a Fender style unit and the pan is a short 3 spring accutronics, med delay I think about 800R input and 2.5K out just like a Fender. I think the pentode plate is about 220V and the screen quite a bit lower, sorry I really can't remember the rest of the readings.
