Diezel VH4 Volume Swell / Intermittent Loss of Gain

[Cro]

Some issues developing with my VH4. Was hoping some of the helpful people in the rig-talk community could assist.

First and foremost, when I turn the amp on, all the channel indicator lights are off and the amp will not produce sound until I select a channel.

To make matters worse, the channels occasionally and unpredictably swell in and out. Channel one goes from ok to inaudible. Channel three never sounds quite right, but gets worse when it loses gain intermittently. When it is not swelling, the amp settles into a significantly less powerful sounding version of itself. The high frequency response disappears, the amp's bite and attack both suffer dramatically.

I checked everything I could check from my end. I've used different cables, different guitars. Still the same problems.

Earlier this year, I noticed that the amp had lost some of it's life. I thought this was a tube issue so I re-tubed the entire thing (both the preamp and power amp sections). This seemed to remedy the issue, but now I feel like it was a temporary fix. I searched this forum and found a thread where someone was suffering from a similar issue. There was no conclusion to the thread, but it was suggested that he plug his guitar directly into the serial return of the head, crank it to the max, and report his results. When I did this, I got a normal, fairly flat, clean guitar sound. I assume this test was done to isolate whether the problem is in the preamp or the power amp section. As a result of my test, I will look into swapping out preamp tubes (V1?) in hope that the amp regains its life.

If anybody out there is familiar with this problem or has suggestions, comments, questions -- please let me know. This is pretty urgent. I know many of you are in Europe so I might be missing out due to time zone conflicts. I hope to hear back from someone soon.

Take care,

Cro

 

[Duolos]

Rotating pre-amp tubes to attempt to find and isolate the problem is the first thing I advise doing. Mark them all before you begin and rotate down the line and see if it changes anything. It could be a simple tube problem however I can not say this for certain. Are you the original owner and what is your serial number please. Has there been any other work ever performed on the amp and if so what was the work performed and by who? Any info will be helpful so we can advise.

 

[Cro]

Rotating pre-amp tubes to attempt to find and isolate the problem is the first thing I advise doing. Mark them all before you begin and rotate down the line and see if it changes anything. It could be a simple tube problem however I can not say this for certain. Are you the original owner and what is your serial number please. Has there been any other work ever performed on the amp and if so what was the work performed and by who? Any info will be helpful so we can advise.

Thanks for the quick response. I am the second owner. Serial number: 0000104. No significant mods done to the amp. When I first received the amp, it had metal harnesses holding the tubes in place. I removed them because they were a pain in the butt. I still have them sitting in a box. That is about the extent of modifications done to the amp. I was planning to get a bias trimmer installed because my amp does not have one. Haven't done this yet. That's about it.

As far as the problem at hand: I replaced V1 with another tube. So far, no swells. However, the amp still lacks the liveliness that it usually has.

 

[Duolos]

What tubes are in the amp (power and pre)? How old are they and what are they biased at?

 

[Cro]

Rotating pre-amp tubes to attempt to find and isolate the problem is the first thing I advise doing. Mark them all before you begin and rotate down the line and see if it changes anything. It could be a simple tube problem however I can not say this for certain. Are you the original owner and what is your serial number please. Has there been any other work ever performed on the amp and if so what was the work performed and by who? Any info will be helpful so we can advise.

Thanks for the quick response. I am the second owner. Serial number: 0000104. No significant mods done to the amp. When I first received the amp, it had metal harnesses holding the tubes in place. I removed them because they were a pain in the butt. I still have them sitting in a box. That is about the extent of modifications done to the amp. I was planning to get a bias trimmer installed because my amp does not have one. Haven't done this yet. That's about it.

As far as the problem at hand: I replaced V1 with another tube. So far, no swells. However, the amp still lacks the liveliness that it usually has.

OK. So after replacing V1 with another preamp tube, I still experienced the gain swelling issue. Pretty frustrating because for a split second it sounded like it was supposed to and then all of the sudden the gain disappears.

I should add that I've owned the amp for over four years with no problems. It was purchased in perfect condition and remains so (with the exception of this unfortunate problem).

 

[Duolos]

Rotating pre-amp tubes to attempt to find and isolate the problem is the first thing I advise doing. Mark them all before you begin and rotate down the line and see if it changes anything. It could be a simple tube problem however I can not say this for certain. Are you the original owner and what is your serial number please. Has there been any other work ever performed on the amp and if so what was the work performed and by who? Any info will be helpful so we can advise.

Thanks for the quick response. I am the second owner. Serial number: 0000104. No significant mods done to the amp. When I first received the amp, it had metal harnesses holding the tubes in place. I removed them because they were a pain in the butt. I still have them sitting in a box. That is about the extent of modifications done to the amp. I was planning to get a bias trimmer installed because my amp does not have one. Haven't done this yet. That's about it.

As far as the problem at hand: I replaced V1 with another tube. So far, no swells. However, the amp still lacks the liveliness that it usually has.

OK. So after replacing V1 with another preamp tube, I still experienced the gain swelling issue. Pretty frustrating because for a split second it sounded like it was supposed to and then all of the sudden the gain disappears.

I should add that I've owned the amp for over four years with no problems. It was purchased in perfect condition and remains so (with the exception of this unfortunate problem).

Have you changed out other pre-amp tubes as well? Are the power amp tubes glowing oddly in any way?

 

[Cro]

What tubes are in the amp (power and pre)? How old are they and what are they biased at?

All the tubes are about two months old having been replaced all at the same time recently.

In the preamp section, V1 is a JJ ECC803S (12AX7), the remaining tubes are Chinese R9 12AX7's.

In the power amp, I have EL34's. The reading on my Weber Bias Rite had a single tube running at around 31ma. I purchased a matched quartet so the rest should be the same. My amp does not have a bias trimmer so I couldn't do anything to adjust the current. Though, if I understand correctly, 31ma is OK for EL34's.

 

[Cro]

Rotating pre-amp tubes to attempt to find and isolate the problem is the first thing I advise doing. Mark them all before you begin and rotate down the line and see if it changes anything. It could be a simple tube problem however I can not say this for certain. Are you the original owner and what is your serial number please. Has there been any other work ever performed on the amp and if so what was the work performed and by who? Any info will be helpful so we can advise.

Thanks for the quick response. I am the second owner. Serial number: 0000104. No significant mods done to the amp. When I first received the amp, it had metal harnesses holding the tubes in place. I removed them because they were a pain in the butt. I still have them sitting in a box. That is about the extent of modifications done to the amp. I was planning to get a bias trimmer installed because my amp does not have one. Haven't done this yet. That's about it.

As far as the problem at hand: I replaced V1 with another tube. So far, no swells. However, the amp still lacks the liveliness that it usually has.

OK. So after replacing V1 with another preamp tube, I still experienced the gain swelling issue. Pretty frustrating because for a split second it sounded like it was supposed to and then all of the sudden the gain disappears.

I should add that I've owned the amp for over four years with no problems. It was purchased in perfect condition and remains so (with the exception of this unfortunate problem).

Have you changed out other pre-amp tubes as well? Are the power amp tubes glowing oddly in any way?

So far the only tube I changed was V1 and I replaced it with one of my old preamp tubes. The issue still persists.

Power tube three has a bit of a blue glow.

 

[Duolos]

There could be your problem....often times when a tube is near failure it will respond like you described in both sound and color. My guess is it is tube related however I can not be certain without the amp in my hands.

These amps need to be maintained and cared for just like a car so they work properly long term. I am not saying you don't take care of your amp, I am saying tube quality can vary and it does need to be looked at and maintained to ensure all is well.

 

[Cro]

There could be your problem....often times when a tube is near failure it will respond like you described in both sound and color. My guess is it is tube related however I can not be certain without the amp in my hands.

These amps need to be maintained and cared for just like a car so they work properly long term. I am not saying you don't take care of your amp, I am saying tube quality can vary and it does need to be looked at and maintained to ensure all is well.

No offense taken. Quite the opposite. I greatly appreciate your assistance. The amp has been an absolute tank since I've owned it (which has been for more than half the amps life). I need to arrange for this amp to be looked at by someone with Diezel. It's due for a tune up.

 

[Duolos]

PM me your number and I will call you Monday and get it in the shop.