JapanAxe

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?

In one of my previous bands I first used a Boss Multi FX, later a board of 3 individual pedals. It was fun but not really necessary, and these days I just use a tuner pedal. I never find myself thinking, ‘I wish I had X pedal for this bit.’ I do still try my bass through pedals for fun at home from time to time though.

PM’d

You can still get them new but you’re looking at nearly £900.

Although I have used Reaper for the last few years, I don’t have an axe to grind about which DAW you should use. I moved to Reaper from a hardware solution (Akai DPS16) and I’ve got used to using it, but if you’re using a particular DAW and it works for you, you may be better off sticking with it rather than taking on the challenge of learning a different one.

No I still like a mid boost for phatness!

Can’t help with this but you have made me nostalgic for my PF-50T!

Mmmm… warm edges!

Never mind the knobs, count the sockets!

Anyone tried turning those knobs?!

I played with the same band again last night, again on lead guitar. I had my amp firing at a lower volume from the side of the stage as a monitor. It was also DI’d into the PA, which worked well. That’s good - looks like I can carry on without going ampless! The bass player had just bought an Aguilar Tone Hammer preamp pedal but tbh it was hard to know whether this improved his bass sound over the simple DI pedal I had seen him with previously. Obviously it gave him a lot more control over his EQ. I am considering a bass EQ/DI pedal build… EDIT: ...for poos and giggles.

The RCD plug is JoJo with 2 sockets which is very handy but I’ve never seen another one like it. Just make sure you get a double pole one - switches off both live an neutral when triggered. The ring main tester is a Rapitest but there are plenty of inexpensive alternatives available.

I always carry an RCD plug and a ring main tester. I rarely have to use the RCD now as most venues have them at the stage socket or on the consumer unit. The ring main tester has occasionally shown up a missing earth connection, the last 2 times being on an outdoor stage and at a rehearsal studio.