new design PT/OT

[lowell]

hello all,
thinking of designing an amp for maximum sag and warm tone. As far in Class A as possible w/o exceeding any pwd and with p/p output. Thinking of using 4 6L6 at low plate voltage w/ high current. I still want enough volume to use this amp in a medium venue setting too. I am curious what anyone might suggest I use for pt and ot on this sort of amp.

[Alex/Tubewonder]

Sag and class A? No can do. In PP class A current draw is constant therefore no sag to speak of. You need to go class AB1 and chose tubes' operating point so it stays in class A up to ca 20% of its max output power.

PT should be properly rated for the current needed but with a tube rectifier and under sized 1st filter cap you'll be getting pretty good power tube compression.

OT: tube data sheets list optimum parameters for OTs

[lowell]

ok... hmmm... then what is it that makes an amp sag or sound squishy? Like an old AC30, or better yet the tone Robben Ford gets on Handful of Blues album... if you're familiar. Tube rectifier plays a part right? I thought that Class A sounds squishy and thus had more sag... any more details on the sag/squish thang?

[pdf64]

http://www.aikenamps.com/Sag.html
see above for sag and squish explainations - Peter

[Wakculloch]

I like the sound of your design idea. Class A does subjectively sound louder than the wattage would indicate. According to my Brimar data book you should be able to get 28 watts from 4 6l6's with a H.T. at 250v. This is very similar to one i built last year that's taken over as my main amp. The only thing that may be a pain is the current for max out is 280mA, which exceeds the max for a 5AR4. I'm wary of exceeding maximum ratings, but others may have knowledge of what, if any, may be the consequences.

[Alex R]

a 5R4 might do it. Drop some volts for you too.