Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hofenator on November 12, 2014, 03:03:07 pm
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Hello. I am new to the forums but otherwise and old guy with some previous tube experience. I recently built the Hoffman Revibe and have been having reverb issues. The reverb is waaay over the top. When the dwell is at 3 or more the result is "endless dwell" . There are also almost none of the lower frequencies present just the real high treble frequencies. Finally, at any setting over 3 the reverb is very distorted. I tried replacing the pot with an audio taper which helped a little but I need something that helps A LOT.
The amp is otherwise dead quiet and the vibe and other controls function as expected. It is also built to the latest schematic with the Tore mod.Any suggestions? hofenator
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Welcome! :icon_biggrin:
Fender type stand alone reverbs are very strong but they shouldn't have 'endless dwell' or start to distort after any setting above 3. Sounds like something's wired up wrong.
Can you post some hi-res pics of the guts?
Brad :icon_biggrin:
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The reverb is waaay over the top. When the dwell is at 3 or more the result is "endless dwell" . There are also almost none of the lower frequencies present just the real high treble frequencies. ... I tried replacing the pot with an audio taper which helped a little but I need something that helps A LOT.
You turned the Mix control down during this testing? The two go hand-in-hand.
What tank did you use? The schematic says "9AB3C1B" which is a good tank, but has a long dwell. I greatly prefer a 9AB2C1B ("Medium Delay" or "Medium Dwell") for this reason.
The linear-taper for the Dwell control seems wrong to me; all the action of the pot is down at the bottom of the rotation. So a log/audio pot is correct. If that didn't reduce it enough (and turning down the Mix didn't either), then try disconnecting the cathode bypass cap on the first gain stage (C7).
There are also almost none of the lower frequencies present just the real high treble frequencies.
Even when you turn down the Tone control?
In general, the circuit matches the 6G15 Reverb, so too much Dwell or too bright a sound shouldn't be a problem if the Dwell and Mix controls are turned down. Overall, the circuit is designed to reduces lows going into the tank somewhat to avoid muddy reverb, which is very easy to get.
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Have you had any success yet resolving your builds problems?
Brad :dontknow: