If memory serves the older non-OTL version had the same tube complement as the current version. If that's the case, you're looking at two EL84's for output and a 12AX7 for a double triode. Currently they are shipping the unit with Sovtek EL84's and a JJ 12AX7. I am not sure if that is what yours has or not - probably.
We recommend the Electro Harmonix EL84 "EH" as an upgrade from the Sovtek's. I think it's a good step up. I have an MG Head at home and use EH's in it - sounds great. The JJ is ok - you can fiddle around with any one of a million 12AX7 replacements if you like. The Sovtek's are a fine choice, and that's what I use.
As for New Old Stock tubes - there's loads of NOS stuff out there and I am sure somebody will recommend the various choices and sources for these guys. I do not sell NOS for a variety of reasons I won't go into, so I only recommended tubes that are currently in production.
You can get the EH and Sovtek brands from New Sensor (www.newsensor.com) for pretty cheap. A matched pair of EH 84's will run you $12.80/ea. The Sovtek 12AX7LPS will run you $15.50.
We recommend the Electro Harmonix EL84 "EH" as an upgrade from the Sovtek's. I think it's a good step up. I have an MG Head at home and use EH's in it - sounds great. The JJ is ok - you can fiddle around with any one of a million 12AX7 replacements if you like. The Sovtek's are a fine choice, and that's what I use.
As for New Old Stock tubes - there's loads of NOS stuff out there and I am sure somebody will recommend the various choices and sources for these guys. I do not sell NOS for a variety of reasons I won't go into, so I only recommended tubes that are currently in production.
You can get the EH and Sovtek brands from New Sensor (www.newsensor.com) for pretty cheap. A matched pair of EH 84's will run you $12.80/ea. The Sovtek 12AX7LPS will run you $15.50.