Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on August 07, 2012, 07:49:21 pm
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I have the Marshall one tube reverb in my plexi 6V6 amp. Are the reverb and dwell pots Audio or Linear? I used audio. The reverb does not come in until both reverb and dwell pots are near 3/4 CW position. I feel i could maybe use 250K pots here. The cathode caps and resistor values on the schematic sound good. Not to bright or dull. Just nice. Also does the 220k on the reverb input set the grid of VB of the reverb tube? What would raising the grid value from 220k to 470k do for the signal?
Lowering the cat resistor values does not really add much gain so im sticking with the schematic values
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The Fender 6G15 Reverb (http://www.el34world.com/charts/Schematics/files/fender/REVERB_6G15.pdf) linear pots for the Dwell and Reverb controls (and Tone, too).
Also does the 220k on the reverb input set the grid of VB of the reverb tube?
It gives a ground reference for the reverb recovery stage which keeps the tube happy even if the tank is unplugged. It also provides a defined load for the tank to work against.
What would raising the grid value from 220k to 470k do for the signal?
Nothing, really. It would change the roll-off frequency that the 220k and 500pF cap sets.
But it looks like if you used linear pots the reverb level would come back and you wouldn't have to tinker further. Actually, the reverb operation won't change, but the changed taper will make the operation seem different. And better.
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I normally use 1MA pots for dwell and reverb. Dwell is usually set at "5" & reverb is normally at "3-4" because beyond that is waaayyy too
much reverb for me. You could easily use 2.2M for reverb which is what the original Dumblish "one tube reverb" design used. It was too much for me.
I am wondering if your reverb is interactive with the tone stack? IF so, try a 220k resistor between the treble pot and the reverb insertion point.
IF you want a brighter reverb on more of just the highs, use a 500p or 680p or 820p instead of .001 into the dwell & just remove the 500p paralleling the 220k resistor on the reverb return.
With respect, Tubenit
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tubenit it is not interactive with the EQ. I changed the pots out for 250KL and it works much better and is audible from 0-10 CW on reverb and dwell pots. The amount of reverb is perfect and not splashy or to bright. Verb sounds great
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Excellent! Thank you sharing what worked out for you! Good to know.
With respect, Tubenit
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Thanks for all you guys help. This is only the second one tube reverb i have installed. I have also learned that you have to position the reverb tank in a head cab in the right direction or it will hum badly. Im happy! :worthy1: