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Post subject: proreverb issues
Posted: Mon Mar 02, 2015 2:46 pm
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79 proreverb... just had all new tubes, new filter caps, bias, diodes for rectifers put in, worked for a year.... turned it on and the power is gone..... the volume when it is turned up to max produces a distorted sound, mostly low end and bit of the highs, not any midrange, no headroom, is the same on all four inputs..... any ideas.... thanks


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Post subject: Re: proreverb issues
Posted: Mon Mar 02, 2015 3:30 pm
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Welcome to the Forum! :mrgreen:

Try plugging in an extension cab? To rule out problems with onboard speakers.

The amp worked fine after the solid-state rectifier conversion? Were the amp's output tubes re-biased after this mod?

Is the sound distorted in both VIBRATO and NORMAL channels? If so, and the rectifier & speakers are ok --- check the 12AT7 phase inverter tube (V6). Try a known good 12AT7.

Hope these suggestions work. Post your results. Good luck! :D


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Post subject: Re: proreverb issues
Posted: Mon Mar 02, 2015 3:59 pm
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chasingwilma wrote:
79 proreverb... just had all new tubes, new filter caps, bias, diodes for rectifers put in, worked for a year.... turned it on and the power is gone..... the volume when it is turned up to max produces a distorted sound, mostly low end and bit of the highs, not any midrange, no headroom, is the same on all four inputs..... any ideas.... thanks


There are some clues here -- likely, it's not preamp-related which leaves only two major sub-assemblies. 1) the power supply, and 2) the power amp.

I'd start with the P/S but before proceeding, what brand/type of 6L6's were installed in the power amp? Your amp is the ultra-linear variant and these models push very high plate voltages, right at 500VDC. Modestly rated power tubes generally do not fare well in the UL version. If nothing is found to be amiss in the power supply, you may have an issue at the output stage.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: proreverb issues
Posted: Tue Mar 03, 2015 8:13 am
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i appreciate the help here are some answers

BMW2002Ti wrote:
Is the sound distorted in both VIBRATO and NORMAL channels? If so, and the rectifier & speakers are ok --- check the 12AT7 phase inverter tube (V6). Try a known good 12AT7.
the sound is distorted in both channels, the rectfier is good, the speakers are good and the 12at7 is good
Retroverbial wrote:
what brand/type of 6L6's were installed in the power amp?
the tubes are tung-sol

i hope these responses are helpful


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Post subject: Re: proreverb issues
Posted: Tue Mar 03, 2015 8:36 am
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Thanks, for those answers. Looks like you are going to have to check some measurements. Or have a tech check them. Idle current bias of those 6L6GC's and B+ voltage would be good start. Have you worked on amps or any electrical equipment? Need a basic, good DVM and ability to read a schematic.


Image


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Post subject: Re: proreverb issues
Posted: Tue Mar 03, 2015 11:00 am
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From this schematic above, I would also consider the external speaker jack switch might have a problem. It looks like the internal speaker is routed through this jack. If it's dirty, it might cause this kind of problem. You can exercise the switch by plugging into it a few times.
Also, make sure the nuts on both speaker jacks are tight.


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