Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Sethyrish on December 15, 2014, 03:25:47 am

Title: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: Sethyrish on December 15, 2014, 03:25:47 am

I've a problem with my revibe build where the sound level drops right off and also distorts. It usually happens when the amp has been on for a couple of hours but I've had a brake in playing for a couple of minutes.  If I thrash out a few chords it seems to come good again after a minute or so. The problem is getting progressively worse though so I’m trying to find the cause.
I did make an initial wiring mistake were I bypassed a resistor (see pink line in image) and left out red link. Could the extra voltage going to pin 6 of the 12AT7 cause damage? The “C” voltage is 258 volts.
If not, does the problem sound familiar to anyone?

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: EL34 on December 15, 2014, 06:10:34 am

Never had that problem on mine


This post will show you how to find the problem, unless it is a tube problem
 http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: sluckey on December 15, 2014, 08:37:48 am

Quote

I did make an initial wiring mistake were I bypassed a resistor (see pink line in image) and left out red link. Could the extra voltage going to pin 6 of the 12AT7 cause damage?

I don't think so. You still had a 68K plate load for the 12AT7. Reverb would not work with that wiring error though.

Does the problem occur with the mix control set to all dry, ie, reverb dialed out?

Disable the reverb and vibrato with the footswitch. Now the signal path is strictly thru V1B and V4 circuitry. Still same problem? Change those tubes first, then check voltages and compare to the schematic. I don't recall if voltages are on that older version of the pdf you have, so if not, download the latest version.

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: terminalgs on December 15, 2014, 10:16:40 am

also, I don't know if its possible to set up the revibe such that you can take voltage readings when the problem occurs.  Maybe upside down on the bench with reverb tank connected?


DC readings on signal tubes at the time of problem might reveal the issue, or at least let you hone in on the problem spot. sudden drop in gain and distortion points me in the direction of VDC issues on plate/grid/cathode.

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: Sethyrish on December 15, 2014, 04:43:01 pm

Thanks for the advice. I'll get it in the bench and go through suggestions.
It's a great addition to my amp so thanks very much for all the info on building it.

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: EL34 on December 15, 2014, 05:00:41 pm

It looks cool

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: Sethyrish on December 17, 2014, 07:37:28 pm

Whoops!
It was the amp not the ReVibe with the intermittent problem. A heater wire must have come loose when I soldered another one over the top.
 I did replace a capacitor that I know I touched with the soldering iron and replaced the RCA plugs that I wasn't happy with. There was also some metal filings that magically appeared so just as well I checked it out. I'd played the amp by itself with no problems so I didn't think to even check it until it went silent!

Title: Re: ReVibe Tore-T Intermittent volume drop and distortion problem
Post by: EL34 on December 17, 2014, 07:43:19 pm

Good deal, glad the Revibe is working ok