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Topic: Problematic reverb on Vibrosonic |
Steve Blazek
From:
Lincoln, Nebraska, USA
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Posted 24 Mar 2017 5:56 am |
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| Getting a lot of hissing, popping and spring noise when turned up over 3, switched tubes 1 & 3 but no relief. any ideas? |
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J Fletcher
From:
London,Ont,Canada
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Posted 24 Mar 2017 7:33 am
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| The noises suggest that the problem is pre reverb driver tube, as you probably figured. Why not replace V2? Is that not the reverb channel preamp tube? ...Jerry |
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Steven Paris
From:
Los Angeles
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Posted 28 Mar 2017 8:42 pm
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On the VibrOsonic schematic I have seen (http://www.thevintagesound.com/ffg/), the reverb driver is V3 (12AT7) and the reverb recovery is V4a(7025); the input preamp tubes are V1a and V2a, which are both 7025s. The 7025 generally doesn't have the current drive that a 12AT7 will provide, so I wouldn't swap them. Try a new 12AT7 in the V3 position instead. You could swap V1 and V4, as they are both 7025s; to see if it makes any difference.
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Emmons & Peavey |
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Steve Blazek
From:
Lincoln, Nebraska, USA
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Posted 29 Mar 2017 3:38 pm
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| Thanks fellas, i'll give it a go. |
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Jay Ganz
From:
Out Behind The Barn
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Posted 29 Mar 2017 4:36 pm
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| If it's not a tube, then one of the 100K plate load resistors may be the culprit. 🌟 |
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Jerry Jones
From:
Franklin, Tenn.
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Posted 29 Mar 2017 5:38 pm
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Hi Steve,
If this is a "new to you" amp, check that you have the correct reverb pan. I had a similar experience with an older Showman with a mis-matched reverb pan.
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Jerry Jones |
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Steve Blazek
From:
Lincoln, Nebraska, USA
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Posted 31 Mar 2017 9:04 am
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Hey Jerry,
I've had the amp for about ten years, it's always been great until this last outing.
I guess it doesn't like being pulled out of the basement. |
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Ken Fox
From:
Nashville GA USA
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Posted 31 Mar 2017 9:59 am
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First you need to determine where the noise is coming from. At the back of the amp unplug the RCA cable marked input (reverb). That is the cable going from the 12AT7 drive section to the reverb tank input. If the noise now goes away you have isolated the issue to the drive section. Likely culprit would be the 12AT7 tube, reverb transformer or cathode resistor as well as bypass cap at cathode. The plate voltage is derived thru the primary of the reverb transformer.
Note the schematic shows no cathode bypass cap at V3. That is for the 135 watt amp. Worst sounding reverb drive circuit I have ever heard. It also has a 680 ohm cathode resistor and drives V3 way too hard. I always replace that resistor with a 2200 ohm and put in a 25uf/50V cathode bypass cap, as was done on the older amps. Greatly improves the reverb
If the noise is still there leave that cable disconnected and disconnect the RCA cable from the output (that is the cable from the tanks output). If the noise goes away then you have isolated the issue to the tank, cables or connections. If the noise is still there then you have isolated it to the reverb recovery area, prior the the reverb control pot.
That could again be a tube, plate or cathode resistors or a cathode bypass cap. Seen a lot of cathode bypass caps on V4 cause issues in the past, Usually a high pitched feedback sound.
See schematics for earlier silver-face reverb. Much better reverb drive circuit there"
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Steve Blazek
From:
Lincoln, Nebraska, USA
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Posted 4 Apr 2017 10:25 am
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| Thank Ken, you rebuilt this amp for me and it sounds like a million bucks, hope to get it working again. Steve |
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Steve Blazek
From:
Lincoln, Nebraska, USA
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Posted 19 Apr 2017 11:02 am
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| Took Ken's advice, narrowed it down to the reverb pan, took it out fiddled with the jacks and low and behold, good for another 42 years! |
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Ken Fox
From:
Nashville GA USA
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Posted 20 Apr 2017 5:16 am
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| Good job, Steve! I use some of the typical automotive bulb grease on those jacks to help prevent further corrosion. You can get it in small squeeze packs at most auto parts stores. |
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