ST70 upgrade to VTA70 tube information needed

by McGar Tue Jun 09, 2015 11:04 am

McGar: Posts : 9
Join date : 2015-05-29

Post n°1

ST70 upgrade to VTA70 tube information needed

by McGar Tue Jun 09, 2015 11:04 am

First time poster here.

I am upgrading my original ST70 to the VTA board I just ordered from tubes4hifi, along with the triode/pentode switches. It calls for the 12au7 tubes. I have been reading lots of great info on this forum for the past couple of weeks and have learned A LOT!

My question: I am seeing a lot of organ tubes for sale (baldwin, conn) and military spec tubes for sale on that auction site. Can anyone give me any advice regarding these (what to avoid or what to look for)? Also, do I want a matched triplet, or just a matched pair and one odd tube?

Thanks. I am sure I will have some more questions later.

by **Bob Latino** Tue Jun 09, 2015 12:16 pm

Bob Latino

Bob Latino: Admin; Posts : 3262
Join date : 2008-11-26
Location : Massachusetts

Post n°2

Re: ST70 upgrade to VTA70 tube information needed

by Bob Latino Tue Jun 09, 2015 12:16 pm

In the VTA ST-70 CCS driver circuit you can use any 12AU7, 12BH7, 5963, 5814, 6189 or the Mullard CV4003. The last 4 tubes mentioned are military/industrial versions of a 12AU7. All those Conn, Baldwin etc. are 12AU7 tubes that are "rebadged" and made by RCA, GE or Sylvania. They are ALL excellent tubes and much better than any modern Chinese made 12AU7.

Most tubes made by RCA, GE or Sylvania have the two triode sections on each tube fairly well matched. In general, you don't really need all three of those driver tubes "matched". If you want to buy one tube that has matched sections, use it in the center voltage amplifier position on the ST-70.

Bob

by kaner Tue Jun 09, 2015 10:22 pm

kaner

kaner: Posts : 93
Join date : 2011-09-20

Post n°3

Re: ST70 upgrade to VTA70 tube information needed

by kaner Tue Jun 09, 2015 10:22 pm

I have had excellent luck with the rebadged tubes. I run green label "Baldwin" 12ax7's in my guitar amps that are Sylvania's. They replaced some JJ's that were ok, but just couldn't keep up.