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Re: Restoring a Traynor YBA-1A: EL34's @ 560Va 535Vg2 ?!?!?!

Those old Bassmasters are killers! I have a YBA-1 (not the 'a', that runs lower voltages) and I won't part with it. I sold off most of my guitar amp collection a few years ago, including a few that I really miss, but that's one of the ones that I won't sell.

Anyway, one thing that I have done to lower the B+ in a couple of old amps is to add a big honking, stud mount zener between the power transformer center tap and ground. Some of the Traynors used a bridge rectifier, but the zener should still work between the bridge and ground.

I did a little search to figure out which part I used... Must have been from the NTE line that Allied offers (link to data sheet below.) You would want one with the cathode connected to the stud, so it would have a 'K' at the end. Allied doesn't stock them all, but they will get whatever you want pretty quickly. For some reason that I have not figured out (and haven't thought about in a log time) the drop in B+ is somewhat larger that the actual zener voltage. A 56V zener will drop B+ something like 65 or 75 volts, which should be about right.

Also, there were quite a few different Bassmasters. Some of the later ones had creative circuits, but most of the earlier ones (most of the ones I've seen) were actually pretty similar to early Marshall / tweed Bassman, meaning that the hi and low range extender controls were really just mid and presence controls. I think they actually sound pretty good the way they are, but don't let me stop you from experimenting.

One thing that they started leaving out was a choke in the power supply. The chassis's are huge, so there's plenty of room to replace the 470 ohm (or whatever) resistor that they started using instead. You don't need much, just a couple of henries at 100mA or so.

As for the single shared screen resistor, I like them. You could try replacing it with a separate resistor at each screen, but I think the common one contributes to the sound of these amps. 10W Mills should work very well either way. Could probably get away with 5W.

-- Dave

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