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GK71 Matrix

Posted: Sun Jun 21, 2020 10:08 am
by Paul Barker
I have a few large regrets in life but one was at vsac I was in a small room with a few 2 or 3 stalls and Stephie carried in a big heavy project. Didn’t know who that was at the time. Now I know of course. So I missed my one time opportunity to meet the greatest influence to what little I understand. Apologies Stephie if you lurk here? I didn’t introduce myself, and I bet that was an 813 Matrix!

But at least I achieved sitting for a whole morning listening to every word Bruce Edgar spoke one on one in his room in a slow relaxed drawl. He could have said nothing, his sound in his room spoke loud and clear on his behalf! There was no room on the same level of the motel which didn’t have its sound compromised by Bruces’ new base horn which sounded to me as faithful to 20hz as the Westminster Cathedral organ that day I photographed a Wedding there! All the Thin sounding bass lite Fostex speaker designs of that era were outclassed to say the least!

First good fostex design I-ever heard was after that, Steve Cresswell’s Metronomes. I understand Fostex are better nowadays but the worst part of vsac was Fostex proliferation! Unlike Bruce’s room I wished the music was played less.

I came away thinking US audiophile’s are after a thin bass light sound with nasty unnatural human voicing and no bass or poorly shoe horned in bass help!

But Josh’s speakers, the good old Straight eights and Bruce’s sound saved vsac for me.

Posted: Sun Jun 21, 2020 11:08 pm
by sbench
Indeed, you never know who is going to be lurking on this forum.

Indeed my favorite amplifier is indeed the 813 Matrix. Thank you for the kind words.

Although I still work a full time job, I do not have a full time lab set up at home. In my mid 70's, I've found iron gets heavier every year. :-)

I do have a few things I'll be posting in the "sim city" area as time permits.

Peace,
Stephie

Posted: Mon Jun 22, 2020 2:38 pm
by Paul Barker
Thank you Stephie for you’re reply. I’ve made most of my remarks elsewhere but instead I’ll do so here so you can look if you would enjoy that but no pressure.

I’m too still working and progress will be slow but I’m excited at the same time.

Just quickly GK71 pentode should slot in at 800v 100mA g3 +50v (It’s how all the charts expect it connected) bias -50 should give 90mA anode and 12mA g2 so cathode current should make 100mA but I’ll have minor adjustments for g3 potential and g1 bias, because I may find a sweet spot altering both or either/or. G2 limited to 400v at which official charts look as above so no worries with the lower voltage.

Really marvellous to know you’re alive and working at these times. You are of immense value to me ever since I was a novice on Triodeel. You set me right where needed and I’ve always valued you’re work for us all.

Posted: Mon Jun 22, 2020 3:44 pm
by sbench
Indeed, you never know who is going to be lurking on this forum.

Indeed my favorite amplifier is indeed the 813 Matrix. Thank you for the kind words.

Although I still work a full time job, I do not have a full time lab set up at home. In my mid 70's, I've found iron gets heavier every year. Smile

I do have a few things I'll be posting in the "sim city" area as time permits.

Peace,
Stephie “

On g3 level

“From what I know of those devices, the G3 potential adjustment may very well be important. It controls the "knee" so has the potential to influence distortion a lot. Whether it does so, I don't know.

Good luck on the project.

Stephie“

Posted: Thu Jun 25, 2020 12:36 am
by Paul Barker
Gathering some bits` the Sowter input transformer Im using presently acting unbal to bal for a balanced PP amp. Steve Cresswel’s Barbaric.
ImageImage

Posted: Thu Jun 25, 2020 12:38 am
by Paul Barker
ImageImage All I’m using from the old breadboard are the AE amorphous IT transformers.

Posted: Thu Jun 25, 2020 12:58 am
by Paul Barker
obviously the power transformers for the output stage are over voltage, oh, I need both for the current as Im shunt regulating, I have some 250mA chokes and a 500mA choke, so the supplies will be summed at the entrance to the 500mA choke after hwihc it’s mono. I’m using Stephies capacitorles power supply method, Ive used it two projects and it’s superior sound becons me. So with an LR supply there are quite a few chokes. To loose what else could be a very simple series pass valve. But to refine it down to where I want to be for the shunt regs; I might share the mains with another transformer backwards to end up enough to give me my regulated + 100v. But that will take some experimentation. Probably take some of the ac down for 800v and fine tune with pass valve. Likewise output of series connected mains sharing transformer, better higher, then I can get the extra in the regs.

Posted: Thu Jun 25, 2020 1:07 am
by Paul Barker
Like Stephie I’m not far from finding heavy stuff mor challenging to handle. But I’m cheating my age ta the moment. I’ll module it down. Main B+ is definatly too heavy for carrying so that’smgetting wheels!

Re: GK71 Matrix

Posted: Wed Apr 06, 2022 8:10 am
by Paul Barker
This project stalled a while back. Not sure if and when I’ll pick it up again. Presently listening to pse 801a, quite happily.

Building Raymond Bates 6V6 CF amp full of resistors, no signal caps: to find out how it sounds.

Was planning a GM 70 amp. But probably best admit that’s stalled too.

When you have what you need, soundwise, other needs come forward to push youre obsessions aside for a while.

I was only planning the gm70 amp to make the amp I listen to daily cheaper to maintain, but the 801a amp is that good, what the heck, its worth paying the 801a prices if a valve or two fail before I’m transported away.