12AT7 for Reverb Driver & PI

[TheTinMan]

My first build using a 12AT7 was a Blackface Princeton Reverb. I had 3 JAN Phillips 12AT7s and had noise and/or feedback problems with all of them in that circuit. A Groove Tubes 12AT7 from Guitar Center (heaven forbid!) actually worked better.

I'm getting ready to order parts for a BF Super Reverb build and will need two 12AT7s, one for the reverb driver and one for the PI.

Is there a good current production 12AT7?

Is it worth it to buy an NOS Mullard or Siemens 12AT7 for this application?

Thanks in advance for any advice,

Chip

[Bruce / Mission Amps]

I've had good luck using NOS 12AZ7s in that spot and since nobody uses them, they are pretty cheap.

[TheTinMan]

Thanks Bruce! The 12AZ7 looks like a slightly beefier version of the 12AT7 and they are relatively cheap. Should be good for the PI too.

I'll have to try a couple.

Chip

[jazztubes]

Bruce - curious cause the az seems to pull more current than the at, and it doesnt show up as a sub in my old RCA and GE sub guides - are there any draw issues to check first?
thanks

[Rob Mercure]

JT,

Since Bruce hasn't chimed I'll whack at it? As far as current issues go are you referring to the heater current? If so it's only 0.15 amps more and most filament supplies will accomodate this - filament supplies have some reserve built in for heating up a cold tube - the filament resistance is lower when the filament is cold. If, for some reason, you were using a series heater string you'd have to make some allowance for the AZ. As far as sub guides the best one is your own knowledge, experience, and intuition. The poorest only list the very best/easist subs while the best include a range of subs with specific instructions as to how to make a "almost" sub work (such as using the AZ in a series string - paralleling the other tubes heaters with a resistor to allow more current flow. The 6EU7, the 20EZ7, and the 12AX7 are exactly the same tube with different heaters and basing but you'll find very few sub guides that will tell you how to modify for them - the 6GK6 is a 6BQ5 with an pinned out supressor grid (not tied to cathode) but few sub guides will tell you this. I've got a very worn, way out of date, guide from WWII when tubes were scarce and rationed and it describes proceedures for truly amazing subs including replacing triodes with pentodes and pentodes with triodes, etc., in some circuits.

A long answer but Bruce has, if I may speak for him, the knowledge, experience, and intuition to recommend this sub.

Rob

[TheTinMan]

Rob - thanks for the "long" answer. AES has 12AZ7s on sale for $3.15 so I added two to an order. Cheap experiment at worst...

+1 regarding relying on B.C.'s experience & advice!

Chip

[PlinytheWelder]

NOS GE 6201's are a nice PI tube and pretty cheep on ebay.

[TheTinMan]

NOS GE 6201's are a nice PI tube and pretty cheep on ebay.

Interesting - they look very similar to a 12AT7 based on the GE data sheets.

Chip