Clark Beauford makes strange noise

A few things, but I would check that rectifier.

Tube rectifiers are very inefficient, it takes them awhile to supply the power demanded of them when called upon, the more the demand, the harder they have to work. That's the source of "sag." I suspect that your rectifier is buckling under when called to really supply power.

 

agreed. i would try a quality recto tube as my next step.

 

i would visit Clark's site to make certain but i THINK you can.

 

There should be little problems in testing it with the GZ34, but I wouldn't run it in there as a long-term substitute.

Well, if you were using a NOS 5Y3, then a GZ34 will significantly increase B+ voltage and may make the power tubes run too hot. Which could result in other sonic issues that can confuse the issue.

If you've been using a Sovtek 5Y3, then you might as well pop in the GC34, because that's pretty much what you've been running anyway, of course, that could then be part of the problem. Sovtek 5Y3's don't have the same voltage drop as a NOS 5Y3, the Sovteks tend to keep the voltages 40VDC higher, which doesn;t work well with vintage-value cathode bias caps/resistors.

 

taken from the Clark Amp's site:

Voltage corrected power and custom wound output transformer. No harsh high voltages. However, if you want to get the tone of an older overvoltaged 5E3 you can use a 5V4 or 5AR4 rectifier to get the plates up to that level.

 

shouldn't have to rebias as this amp is cathode biased....

 

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It might be bad solder joint at a tube socket. I had the same problem with a 65 Tremolux, especially when hitting low notes. Check that out!