VH4 tone/sound cut out issue

[JulianP]

I was playing on channel 4 just now and noticed the treble kind of disappeared.
I tried playing on channel 3 and the sound was almost gone.
Channel 1 and 2 couldn’t be heard at all unless the volume was increased dramatically.

Does anyone know what happened here? I just changed the power and pre amp tubes last week so I hope that didn’t cause any problems, but it was working fine for a while.

I have a .mp4 file that I recorded which could explain the tone/sound issue better.

 

[Peter Diezel]

Please re bend the clamps in the preamp sockets.
Service manual is on the support section at www.diezelamplification.com

Best regards,
Peter

 

[JulianP]

That didn’t seem to help.
I’m trying to find a tech in Toronto to fix the unit. The highs sound very bad, and lows just ok at higher gain. Not sure what to tell him.

 

[boogie1]

That didn’t seem to help.
I’m trying to find a tech in Toronto to fix the unit. The highs sound very bad, and lows just ok at higher gain. Not sure what to tell him.

I'm also looking for a proper Diezel tech in the Toronto area. Please advise.

 

[Peter Diezel]

Where did you buy the amp ?

I have only an address in Winnipeg and it´s an old one.
Please let me know if there is somebody who knows a
good tech in Canada.

Thanks,
Peter

 

[Ultradeaf]

After about 5 years of use, my Channel 4 began to cut out... progressively worse over time. Then it started happening on Channel 3.

Immediate concern was power tubes, tube sockets, or solder joints for the sockets to the PCB. Being an electronics engineer, I was able to troubleshoot it down to the magnetic relays used for channel switching; there is one for each channel. I purchased the replacement parts, removed the suspect parts, and installed the replacements. I only replaced the relays for channels 3 and 4, and not sure if 3 really needed replaced (*I am IPC certified in electronics rework and replacement). I haven't had an issue since.

If you or your tech haven't already: with the amp on, check each relay (you'll have to get into the amp) by gently tapping on them with a non-conductive prod of some sort. If they react microphonic, they MAY be the source of your problem. Fix it soon because like most systems, after the total failure of one component, all of the other items will begin to fail. This cost me $10 and just my time to fix.