UltraLinear Output transformer details

[Bob M.]

I'm building myself a new amp and I'd like to try a UL wired output transformer. I like clean amps and I'm trying to squeeze out a couple of extra watts from the circuit I've chosen. I never tried building a UL circuit before and I'm wondering about filtering and the power supply. If anyone has experience with UL circuits I'd appreciate the benefit of your experience in the form of power supply tips, filtering, ect. I'm thinking of using 2x 6550 power tubes, fixed bias. I'm after a clean sound with big bass. Any tips at all on implimenting this will be appreciated.

Thanks in adv.,

Bob M.

[Bruce / Mission Amps]

I'd find a schematic of the 135 watt Fender Twin Reverb with the UL OT and start with that...

http://www.ampwares.com/ffg/schem/tw..._135_schem.jpg

then buck up the power supply with larger filter caps and use a big PT.
I'd be looking for a PT with at least 375vac@350ma to 500ma and of course solid state rectifier diodes.
As far as the OT for two 6550s, look at Hammond for a big one rated at over 100 watts.

[TD_Madden]

I was going to suggest the 135-watt Bassman (for simplicity's sake).....

[bob p]

Part of the problem of using 6550 in Class AB is that the power supply demands can be HUGE -- there aren't a lot of great off-the-shelf PT options available, and the B+ rail is going to sag heavily under full load. If you use the search function, you'll find lots of posts on the topic of UL 6550s. I( think that an UL 6L6 amp would be an easier target to hit, as the PSU needs are a bit less demanding.

HTH.