Rickresource Rickenbacker Forum

If it is a 12AU7, isn't that basically a lower gain version of a 12AX7?

Yes, but there is no need to modify them as 12DW7's are easily available. JJ Tesla makes them at about 7.99 per tube and they work great, quiet. I have 12 of them in three SVT heads. I modified an old SVT once with 12AX7's when 12DW7's weren't available and the sound changed and not for the better.
It probably does need new power tubes as 7027A's (also JJ Tesla I think) were not available for years until recently. If you buy it get the 7027A's as regular 7027's are just 6L6's, the 7027A's handle more plate current which Ampegs need.

The 12DW7 conversion is in Gerald Webbers' book. The 12DW7 is a tetrode(?) and therefore was used to "simplify" the Ampeg circuitry.

Go figure...

Now if I can find a simple 6SL7 conversion.

That conversion was also in the Groove tube book, but they now recommend you buy 12DW7's. tetrode 7 elements I think, 7 pins that do something anyway. triodes, pentodes, etc.
you should still be able to find 6SL7's those were fairly common too. here you go:

http://search.store.yahoo.com/cgi-bin/nsearch?catalog=thetubestore&query=6SL7&.autodone=http%3A%2F%2Fwww.thetubestore.com%2Findex.html

12DW7, 12AX7 etc are twin triodes, each bottle contains two triodes. usually two identical triodes.
as Jared said, a few posts back 12DW7 is a dissimilar double triode. half 12ax7 and half 12au7

6550 is a tetrode, is that what gerald webber was writing about?

(double checked my info in tube amp book)

I wish these new 7027a and 12dw7 had been available when I still had my v4b. I ended up converting it to 6550 (fiddly) and dropping in a 12ax7 instead of 12dw7 (no mod required in v4b)
it served me well for many years after that. I would rather have not had to mod it.

gotta love Ampeg for those wunnerful tube selections!

...the kneebone's connected to the ... thighbone...

I know, they did use some strange tubes, I have a real old Ampeg here that originally used EL37 power tubes which haven't been made for probably 30 years and were never very common in the first place, luckily 6L6's work in it. I think the strange tubes might part of the reason they sound so distinctive though.

yup

I'd like to buy a couple of EL37's they were British hifi tubes but they go for at least $200.00 a pair.

like GEC Golden Lions?

I don't know the brands actually, because they're all NOS, I don't think they'll ever reissue them. I would never spend that kind of money on an amp that sits in my bedroom anyway unless it was a hifi amp. GE NOS matched pairs are close to 200 bucks also, I may try them once in an SVT and see if I hear 400 bucks worth of difference and see if they last a real long time like tubes used to, but I doubt it.

ya know those GE 6550's are BIG time $$$, but worth it. The ValveArt KT88's and Svetlana 6550 are great and the Svetlana (name changed to ???) can take higher plate voltages that the Ampeg and SUNN 2000S puts out.

I have old Svetlana 6550's in all three of my heads and have had no problems at all. I think Svetlana changed to winged SED or something like that.