Ventura":20b4219k said:
There are a couple of limiting resistors that work with the voltage on tap to the bias trim pot. Hard to explain without a photo but I can post one in the next day or so. One of these 2 resistors modifies the higher limit; and therefore a lower rated resistor can allow for more voltage to be controlled via the trim pot. Of the 73-74 volts on tap in total, the current Rev2 config allows for about 40-45V to the pot (if my memory serves me correct). By replacing said resistor, I upped my voltage available to 60V, thereby allowing the higher draw 6550/KT88 bottles to get enough mA delivered to them (their respective sockets). As mentioned regarding the total voltage available - 60V is still well within safe and reasonable utilization.
Thanks for the info. If you could post a picture that would be awesome. No rush - I'm not planning on doing this immediately (but I do want to get it done eventually - just haven't decided if I want to butcher my Rev 2 or buy another one to experiment on).
Ventura":20b4219k said:
I'm using 6550s and just working through some finishing touches on the preamp glass. What I'm experiencing so far is just flat out balls to the wall MOAR!!!!! It's Rev2 tone just kicked up a notch in the punch and articulation department
If I may offer a suggestion on the preamp tubes. After around a decade of experimentation I have arrived at
v1 = Amperex 12AX7 mC (as in mC2, mC4, mC5, mC6). It's a long plate foil strip D-getter tube. A long plate Mullard works too, especially the mC1, but I find the Amperex to be more harmonically rich. And the high notes on the bridge pickups don't sound harsh at all, even if you crank the treble.
v2-v4 = Mullard 10M 12AX7 gold pin. Really any short plate Mullard 12AX7 works for me but the 10M's - especially the gold pin - have just a touch more definition.
v5-v6 = kinda irrelevant 'cause they don't affect the sound. I have Sylvania 12AX7's in there - just because they are durable and reliable tubes.
These are my personal preferences - not claiming this to be the definitive selection by any means.
Curiously, as much as I love long plate Amperex/Mullards in the v1, when I tried them in the v2, it was not enjoyable.
As far as the power section, my Uber has been outfitted with Mullard Xf2 EL34 OO getter for a decade. I loved the sound of that setup. Of course after 10 years the Xf2's got tired and needed to be replaced (although I must say the amp still sounded great). I just retubed it with Mullard Xf1's (also OO getter) and... I don't love it like I used to. I only played it once so far with the new power tubes and I'm hoping they need time to break in. I'm going to give it a month. If I'm not in love with the sound of the Xf1's I am seriously considering putting in a quad of old stock Genalex KT88's. I loved the way they sounded in my Diezel VH4... until I found out Diezel advising against using KT88's with the VH4. Retubed it with KT77's (also old stock Genalex) and... the magic is gone.
I mean it's still a great sounding amp and super tight in the bass but it just doesn't have what I loved about its sound before. So my guess is I just love the sound of KT88's...