V4B and V4, pair of power tubes, slow red plating

[AMPREPAIRNJ]

Ok, so as I stated before, the one thing both of these amps have in common... is you. Those settings are quite extreme. The V-4, while able to break up, was meant to be a clean tone machine, capable of one of the widest tone shaping preamp abilities in any amp both before it’s time and amazingly well after it’s time. I wouldn’t bother with the bias diode now, knowing the specifics. While the preamp and phase invterter can keep up with the amp cranked to 2-3 O’Clock, the power tubes, at those voltages, can not. These amps were designed to run the original RCA 7027’s, nothing else holds a candle to that tube and the beating it could take while still delivering amazing tones. The Ruby and JJ 7027’s are pale shadows of the original. I would strongly advise you to reinstall the fly back diodes, if you haven’t already, in order to protect your O.T. from that beating it’s getting. I’ve worked on hundreds and hundreds of V-4’s at this point, and I’ve only ever had to change one or two O.T.’s. Now that we have all the info needed, let’s look at the fact of the matter: at least two (non RCA 7027) power tubes red plate when the signal is driven well beyond clipping. The question is why. The fact is the tubes can not handle the task, but that’s an easy answer. How about what’s causing the tube to conduct so critically poorly: the signal it’s being fed. Now, while the “.33” caps may have been changed, that doesn’t mean they’re not the problem, or solution in your case. Those caps are overkill but thought necessary to pass those “Ampeg lows”, but they realistically pass frequencies that we don’t even hear, but the power tube is still working to deliver those frequencies non the less. You should start by dropping those .33 caps to .1’s and see what that gets you. Narrowing the frequency/cutting the excessive lows to the power tubes may relieve the power tubes of enough stress that your extreme clipping won’t drive it into red plating. You should experiment with the tubes you have, if a .1 doesn’t work, try a .01. You should be able to observe a difference in the red plating immediately. Whether it goes away completely will depend on your specific tubes of course. There are other paths to go down, but let’s start there!

If the amp is not red plating in normal playing conditions or at idle, without extreme clipping, then it sounds to me like you’ve got a good working amp.