taking the blanket off a Valveking...

[bobshbob1]

I've owned a Peavey Valveking head for about 4 years now, it was my first tube amp and for a while I loved it. Then I picked up one of the early 80s Butchers, which I played almost exclusively for a while. I am starting to use the Valveking again after a long hiatus, although it's been played by other people pretty regularly during that time.

Maybe it's just me being used to the super-aggressive Butcher, but the Valveking is starting to sound like it has that blanket-over-amp syndrome. Note definition and clarity are not nearly as good as I remember, and it seems to have some "sag" on heavy chords, especially at high volume and high gain.

I've tried running it through a better cab and jumpering the effects loop, both of which helped but not very much. The output tubes were also replaced pretty recently, like within the last two months, with JJ 6L6s.

Is there anything else I could try to brighten up the sound of this amp (some simple mod even)? Possibly new preamp tubes? and if so what brands/types would you suggest for a high-gain/metal sound?

[Chuck H]

The first thing that comes to my mind is that the power supply is probably due for a rebuild. The filter caps do go bad with age and can detriment fidelity. I would also consider the bias. Was it set for the new tubes or were they simply installed ithout re biasing?

If the above criteria are already met it could simply be perception. Any amp can be adjusted. It will help if you can locate a schematic and post it here.

[J M Fahey]

You already have the solution before you.
*If* tube brand influences sound, just use the same tube brand you use on your super-aggressive Butcher.

[bobshbob1]

Hmm, I hadn't thought about the power supply going bad since the amp is fairly new; I thought filter caps would go bad after like 10-15 years. It's cathode biased so I'm pretty sure the amp was not re-biased when the output tubes were changed. Is there some simple way to check and adjust the bias, like a resistor that can be changed to a pot perhaps?

Also, it has the same output tubes as the Butcher, but I'm not sure on the preamp tubes...I think the Butcher has EH's like the Valveking but I'd have to double check.

I found a schematic that had been posted on here, in case it helps.

peavey_valveking_100_212.pdf

[Chuck H]

I didn't realize that was such a new model. So your correct that it probably isn't the power supply. But the amp IS fixed bias in the schematic. if yours is cathode biased it differs from the schem. If the amp is biased too hot at idle it will play and sound less dynamic than if biased cooler. The bias supply isn't variable but that doesn't mean it's not adjustable. Check current on the tubes before troubling with bias any further though. Until then there is a substantial bleeder cap late in the preamp. Try lifting one end of C-149. As long as the amp doesn't oscillate you should notice an increase in top end. If the amp does oscillate you can try using a smaller value cap and/or a series resistor with that cap to reduce it's effect on the top end. There are a couple of other bleeder circuits elsewhere but the cap values are so small you probably wouldn't even notice if you removed them.

[bobshbob1]

Thanks a bunch for the help. I tried removing C149, and the difference in high end clarity was immediately noticeable. In fact, there's almost too much high end now; I may end up putting a smaller cap in there instead. But it's a step in the right direction.

Apparently I misunderstood the difference between fixed vs. cathode bias. I thought fixed bias amps were ones that had an adjustable bias pot, and cathode biased amps did not. I'll look into how to check and adjust the bias on this amp; at the very least it would be a good thing to learn how to do. I know the Butcher (which I'm kind of using as a reference point for "my ideal sound at the moment") is said to be biased very cold...maybe cooling the bias on the VK would tighten it up somewhat? The amp is still has a kind of sagginess to it, but it's improved since removing that cap and hopefully will improve more with a bias adjustment.

[Tony Ramone]

I installed a bias pot on my valveking head and some 1 Ohm resistors to measure the current at the cathode of each tube. I started testing with the bias pot + "safety" resistor set to 39K to see how it was biased from the factory - I was reading 35mA on each tube (roughly). I set it down to about 30 and it did make a difference to the clarity. I also went much lower (down to about 15, checking it at 5mA steps), but I found the best sound (for me) to be around the 30mA mark.
If you son't need huge amounts of gain (although maybe you do), you could also try installing a 5751 in V1 - I much prefer the sound of mine with one of those in there, and I've just got the cheapo sovtek one, I'm sure it would sound much better with the Jan-Phillips, but I haven't had the chance/inclination to spring for one of those yet...