JapanAxe

That's just an idealised illustration - I doubt that the filter slopes are really that sharp.

I’m with you on that - tweeters are for adding weight and hiss to your setup!

Thanks @BassmanPaul and @beans-on-toast that's really useful. I built my amp cathode biased so no issue with the bias tap.

Ha ha, yes I know how diodes are oriented! I recently rebuilt a modern Princeton Reverb and it had BYD33V diodes fitted to the rectifier valve in exactly this way. Thanks, I might get some of those.

Lead guitar with a pub covers band (signed up as a dep, now regarded as a member) playing all the usual suspects. We don't do Wonderwall but a group of young people were so insistent that we caved in and busked it to a rapturous reception. Second late night in a row - absolutely Donald Ducked today.

What silicon diodes did you use? On my recent B15-inspired build I had a GZ34 that was arcing. I fitted a new GZ34 and then tried a UF4007 before each anode on the GZ34, but the amp didn't work with the silicon diodes fitted.

Big chain pub with house PA last night. Always a dodgy load in/out requiring us to park on double yellows in the middle of a lights-controlled junction. Mainly young crowd going mad for the usual suspects. My EBS head seemed not to be loud enough at first but then I edged the Drive control up a notch and BOOM there it was - big, fat and furry!

Wear shoes one size smaller than usual - smaller footprint sorted.

Which IR loader do you use?

Yep, this went very well. No bass player, yours truly seen here singing Folsom Prison Blues. Please note I'm the one without a music stand...

My third gig depping on lead guitar with a rock’n’roll band. The dep bass player is ill (don’t ask!) and BL decided to go ahead without bass. I played my Gretsch Duo Jet through my DIY 5E3 and used every opportunity to pick out thumpy bass lines - and it worked. Same again tonight, this time in a pub garden so I’ll also be going DI into the PA.

Update - DIY head based on Ampeg B15.

Fortunately for me I’ve only had to work with 2 singers who were never satisfied with the level of their vocal in their monitor. They both operated on the edge of feedback i.e. as loud as it could practically go. I suspect that the level would never be high enough for them, and that in fact the problem lay elsewhere - most likely in their heads. Neither ever tried IEMs but I do wonder what the outcome would have been. On the topic of using IEMs one-in-one-out, my preferred solution is just to loosen one slightly in my ear (the one furthest from the drums). This allows just enough ambient leakage to overcome any feeling of disconnection.

I enjoy playing different (P-) basses into different heads through my cabs. I can’t see any reason to stick to all the same brand.

Mostly good now. With a 470R cathode resistor, plate dissipation is now just over 46% of max. This is somewhat on the cool side but I'm not hearing any crossover distortion. I'm going to order some 330R and 390R 10W resistors in case I need to warm it up a bit. Having read that current production rectifier valves don't cope as well as they might with reverse voltages, I tried installing some SS diodes in series to protect the GZ34, but the amp didn't seem to like that so I took them out again. Still might try a choke in place of the first dropping resistor, and/or a small dropping resistor before the first node... Here's some nice pictures of the completed amp with its BF playmate.

Well that seems to be sorted. Conclusion - the rectifier valve was the problem. I've now binned it. I've done a quick playing test and confirmed it still sounds just as good. The hum/buzz is still there and persists when the PI valve is pulled, so I'm going to try altering the lead dress around the 6L6s. I'm also going to dial the bias down a bit with a higher-value cathode resistor.

Sorry, no sound samples until I can get this working reliably! I've made some progress this morning - I fitted the new GZ34 and that doesn't blow mains fuses - yay! - but I now have a blown HT fuse (T500mA) so I am working my way through to see whether that was anything more than a fluke. The new GZ34 also produces a slightly higher unloaded B+ at the first node than the old (faulty) one (454V rather than 437V). My filter caps are all rated 500V so that's fine, and it will drop anyway when the other valves go in. Both 6L6 valves still test good. I'll keep y'all posted. Incidentally, I write down everything I do as I'm doing it so I always have a record of what went wrong (or right) and what changes preceded it.

I’ve built valve amps with SS rectifiers but with this one I was trying to recreate the vintage Ampeg as far as possible. The current GZ34 is a JJ that I had as a spare in my gig box for many years. The replacement is a brand new JJ.

A SS rectifier would give a higher B+ but I’m not sure it would help otherwise. I have a full day today but when I next have time my plan is to try the new GZ34. I have heard of rectifier valves developing faults which eventually blow the PT - clearly I don’t want this to happen!

The standby is before the rectifier so not sure whether that would work. Since my last post I remembered I have just got another GZ34 in case that’s the problem - it’s one of the few components between the mains fuse and the HT fuse.

Moving the heater CT didn't fix the problem, in fact switching from standby almost immediately blew the 3A fuse in the mains plug. I'm going to put this to bed for now and come back to it in a day or two, otherwise my sleep will be spoiled by my brain trying to problem-solve when it should be resting!

As per the original schematics, the HT current goes: PT secondary > Standby switch (double pole) > GZ34 rectifier > HT fuse > first filter cap I'm aware of the alternative of the approach of having the standby switch after the first filter cap - there are pros and cons to both approaches. I'm just about to move the heater CT to ground to see what effect that has. Thinking about it, elevating the heater CT is the biggest departure from the original circuit that I have made...

My home studio is built around a Behringer patchbay and Behringer rack mixer. I’m on my second rack mixer because I wore out the switches on the first one, but I recycled it into something else.

I'm still having some issues with this amp on the fuse front. When I switch out of standby, the T2A mains fuse often blows but not the T500mA HT fuse. On one occasion the mains fuse blew some minutes after switch-on, I suspect because it had been weakened. With just the rectifier valve fitted, I tried a (temporary) T4A mains fuse - now when I switch the warmed-up amp out of standby, the mains fuse doesn't blow, but if I do the same thing with the 6L6 valves also installed, the 6.3V pilot dims momentarily but again the mains fuse remains intact. I suspect the problem may be related to one or both of the following: Inrush current to the first filter cap; Sudden flow of current caused by the heater CT being 'elevated' to the output valve cathodes. Any ideas folks?