Reverb tube redplating

[beasleybodyshop]

Ok guys, so I just finished recapping my Super Reverb, now the V3 position (Reverb tube) wants to redplate like mad.

So with my meter and the amp on - the cathode voltage starts to climb like crazy - i check resistance from cathode to 2.2K, then 2.2K to ground, no shorts.

I check the green and black wires running from the reverb transformer - im getting like 1 ohm. other side of the transformer is like 1.8K - is this normal?

Im also getting about 450 volts on the plates of V3 - according to the layout this is correct.

Where else should I check?

[pdf64]

Check the grid resistor / grid voltage.
Maybe it's lost its ground reference.
Pete

[beasleybodyshop]

I checked the 1 meg grid leak. Its fine. I suspect that its the tube socket. When i wiggle the tube in the socket, the cathode voltage jumps around back and forth.

[Stevem]

This may or may not be part of the issue, but note that China made preamp tubes have undersized pins and a half gone socket may be all thats needed for a poor connection.

[beasleybodyshop]

This may or may not be part of the issue, but note that China made preamp tubes have undersized pins and a half gone socket may be all thats needed for a poor connection.

I was lucky enough to have a stash of NOS US 12AT7 - no matter the tube it was causing the issue. I wiggle the tube in the socket and it stops redplating! i went ahead and ordered some new micalex sockets. Thanks for the help guys

[Leo_Gnardo]

Sometimes sockets go bad even in ol' reliable Fenders. Swap it out & enjoy life.

The bypass cap across the cathode R may have been damaged in the process, with enough current to red plate. Personally I leave those bypass caps out to tame the drive level to the reverb tank.

[Stevem]

Next time you change your guitar strings save the D string if its wound, they are a great size to run in and out of preamp tube pin sockets to clean and polish them up.
A wound G string from a acoustic set may also work.

[beasleybodyshop]

Thanks for the tips! I took one out of Jim Marshall's book and added tube retainers when i installed new power tube sockets last night:

[Leo_Gnardo]

added tube retainers

So where's the one for the rectifier - he wants one too!

[beasleybodyshop]

er....i missed that one I kept the claw retainer on for that one in case i wanted to use a bigger recto....I wasnt sure if I was gonna pop in one of those big coke bottle shaped bastards in there or not.....well, i digress...