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Those who haven't read the description of what I and my techie Bill did to the amps, can read it up over in reviews."Why do you ask, Timbo?"
Well I've been trying to follow the several threads about this over at Tube/Diy, led mostly by Triode/Kingdom and the headroom/overload/recovery issues. And especially bad old Pentode mode!
Way back when, I 'found' four NoS AWV and AWA Aus. mfd 6CG7s in the shelves of my soon to retire old techie and decided that they would make a good replacement for the 4 OEM 12AX7 driver tubes in the two - 2 - LEAK st20s that I'd been 'given.'
And that old techie nodded and agreed, and Bill then suggested a single CCS Fet each and LTP mode for the splitter-drivers. I made the mods because I instinctively? believed a higher-current lower-gain valve would be better in this role and overload more cleanly. And, we could allocate the NFB better - to the OPT stage mostly. There's a low-gain tt input tube as well.
The amps will soon be running from above and below 150Hz (line level crossovers). Still into ~91db/w sensitivity speaker loads.
Sooo, amp two - was used in triode-mode role driving an Fs trap, 3rd order HP crossover from 3.5khz and a big soft-dome tweeter It's now in UL mode (16wpc RMS 20-20khz) - and it will be working a LOT harder? Yes?
Further, the other chassis will be working a lot LESS hard, just from 150 Hz and down only and still in pentode mode (20W RMS 20-20K). Yes? The reflex tuning will still be the same QB3 and Fb @ 38hz. A slow, shallow initial slope. I'll run the two bass spheres in series - 16 ohm load - and change the OPT tap.
(The bass-duty amp will likely also have to drive a high impedance load for an active sub-woofer LP filter. Into a SS power amp and two or more sealed PP subs with LT eq. But it won't even blink at that.)
I've already had Bill put in the PLL 1st order filters on each amp's inputs as well as service them.
Soooo, what kind of tests for overload and recovery can I get Bill to do on the two amps in the workshop OR at home here running at 'turn that down' / 'Are you DEAF!!!!' loud? :-)!
How big's the room? The l-shaped lounge-dining room's longest dimension is ~ 35 feet, and has 8 ft ceilings.
Or do I just stop worrying, and forget about it? ;-)
TIA
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 09/04/14 09/04/14 09/04/14
This post is made possible by the generous support of people like you and our sponsors:
Topic - Behaviour in overload of PP EL84M cathode bias amp? How to examine for that? - Timbo in Oz 16:27:15 09/04/14 (8)
- RE: Behaviour in overload of PP EL84M cathode bias amp? How to examine for that? - Triode_Kingdom 00:05:50 09/06/14 (4)
- i) Have you read the description of the modifications we did?? - Timbo in Oz 04:06:26 09/06/14 (3)
- RE: i) Have you read the description of the modifications we did?? - Triode_Kingdom 08:47:56 09/06/14 (2)
- RE: i) Have you read the description of the modifications we did?? - Timbo in Oz 13:26:42 09/06/14 (1)
- RE: i) Have you read the description of the modifications we did?? - Triode_Kingdom 00:02:58 09/07/14 (0)
- RE: Behaviour in overload of PP EL84M cathode bias amp? How to examine for that? - Caucasian Blackplate 20:45:15 09/04/14 (2)
- Same question as above!? Did you go and read what I wrote about the mods we did - Timbo in Oz 04:23:13 09/06/14 (1)
- RE: Same question as above!? Did you go and read what I wrote about the mods we did - Caucasian Blackplate 10:07:51 09/06/14 (0)
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