U R Welcome for the HV Warnings !...1570 is AB2...Needs Power Drive....

Vintage Asylum

Classic gear from yesteryear; vintage audio standing the test of time.

Posted by Interstage Tranny (A) on August 2, 2015 at 09:54:59

In Reply to: RE: Thanks for your warning posted by unclestu on August 1, 2015 at 14:40:54:

The 811s are positively biased; between +1 and +2.2 on the grids in 1570s !
Class A amps are negatively biased and most A1 amps simply require voltage gain. That is why we have seen the rebirth of WE 91A type front ends with pentodes driving triodes. Since the late '80s, French and Asian designers have spoken/written how the distortion products of pentodes are complimentary to the triode opts' distortion. Be that as it may, I favor all triodes....

Power drive is always a good thing; like having "reserve power" for loud passages. Power drive requires low grid impedance; hence cathode followers or interstage trannies with 1:1 or Step-Down Ratios. Have you seen the Japanese MJ or other experimenter books/magazines ? Every issue seems to have had at least one amp, from over a dozen schematics per issue, with a SE triode amp driven by a power tube or a cathode follower. Some have feedback; even around an IT ! Why this topology ? Because these tricks help an opt tube to give a bit more output. When we are dealing with a flea power amp, it can sound better if an extra watt or two can be pushed on signal peaks.

Having tried many topologies for SE or PP, including over a decade with Class A PP triodes using a step-up intertsage tranny, I now have almost two decades using Power Drive with 2A3s or 45s. Just as an aside, the absolute world reference triode amps through the years was/is Brook ! Their supreme 30 Watter uses power drive. The 1950 Peerless A-100 amp that pushes 18W out of back-biased PP 6B4s, also uses power drive; with a pentode as the amp input tube...thumb through those magazines my friend...online research is inadequate...ENJOY !

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Follow Ups Full Thread

Topic - OLD Altec Amp - unclestu 00:04:51 07/30/15 (16)

RE: OLD Altec Amp - unclestu 14:15:46 07/31/15 (4)

RE: OLD Altec Amp - Potato_Head 15:04:17 02/06/17 (0)

OLD Altec Amp = A-255, 256, 1430 or 1530... - Interstage Tranny 14:55:38 07/31/15 (2)

RE: OLD Altec Amp = A-255, 256, 1430 or 1530... - unclestu 15:26:36 07/31/15 (1)

I forgot the most important part - unclestu 15:27:35 07/31/15 (0)

RE: OLD Altec Amp - Awe-d-o-file 16:17:15 07/30/15 (8)

Thanks - unclestu 16:40:17 07/30/15 (7)

RE: Thanks - Awe-d-o-file 17:27:23 07/30/15 (6)

1570s are some of the best...ever seen the 1570A ? Me neither... - Interstage Tranny 15:28:42 07/31/15 (5)

RE: 1570s - unclestu 17:31:05 07/31/15 (4)

1570s - Interstage Tranny 18:15:17 07/31/15 (3)

Thanks for your warning - unclestu 18:57:45 07/31/15 (2)

RE: Thanks for your warning - unclestu 14:40:54 08/01/15 (1)

U R Welcome for the HV Warnings !...1570 is AB2...Needs Power Drive.... - Interstage Tranny 09:54:59 08/02/15 (0)

RE: OLD Altec Amp - Hornlover 07:54:54 07/30/15 (1)

Thanks, but - unclestu 14:27:39 07/30/15 (0)

Follow Ups

U R Welcome for the HV Warnings !...1570 is AB2...Needs Power Drive.... - Interstage Tranny 09:54:59 08/02/15 (0)

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