Friday, April 13, 2012
Resuscitating a Peavey Valveking 212
This Valve King 212 arrived here completely defunct with a blown power tube.
This amp is one of a series of amps that Peavey, formerly doing its assembly in the US, farmed out to the Chinese. As these things go it is only a shadow of the old Peavey amps that were made in the seventies and eighties in Meridian. The cabinet's MDF fiberboard, and the amp itself is lightly built with spindly circuit boards.
It's got a major design flaw and thereby hangs a tale. The tube filament supply and the low voltage supply for the solid state devices and channel switching relays is part and parcel of the same circuit. When (not if) there are problems in the power tube end of things it's likely to affect everything else in that part of the neighborhood because they're plumbed directly into this one circuit.
And, the fuses are pigtail types soldered to the circuit board.
It's a shitty way of doing things for reasons that are now to be revealed.
When one of the power tubes in this amp erupted, before the fuse had a chance to react (I'm theorizing a bit here) the voltage and current surge took out the filament diode bridge and a bunch of other things downstream including several other diodes, a transistor, a pair of JFET switches and the main relay itself. When the amp is powered up this relay is energized and stays that way. Until it gets toasted.
So the first adventure was to restore the filament and mains voltage and get a set of functioning tubes installed-which I did, which is when I found out that the channel switching was defunct. Several hours of troubleshooting various components led me to use a bench power supply to put 12v on the relays which is how I found the bad one.
Then it was off to spending a couple hours finding a data sheet for the existing off brand relay, and then finding something that did the same thing-that's two hours of my life I'll never get back. At the same time I ordered Q101, 102 and 103, as well as a socket and a dual op amp for the reverb side.
When all these things-diodes, transistors, switches and relay were installed, then and only then could I discover that the reverb was inoperative.
After further testing this morning I discovered that D118 had been fried in the general uproar. Replacing that got the whole rig operational, bias looks good, and I hope to hell the effects switching is OK because that's plumbed into it as well with a dual transistor I don't have at the moment.
When it was all assembled, it sounded like what it is-a three hundred dollar Chinese amp, thin, nasally and uninspiring.
Best bet? Save your amp money for something more inspirational.