S.E.X. > 2A3 Monoblock OPT

Ken · 8836

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Offline Ken

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on: May 07, 2022, 04:01:42 PM
From way way back, I have a pair of OPT from the days when, if I recall correctly, Doc was offering some sort of conversion from the basic S.E.X. to 2A3 monoblocks.  My memory is hazy and could be mistaken about how or on what basis I came to acquire them.

In any case, is there anywhere online where I can obtain the specs for those OPTs?  They may be useful somewhere else if I can figure out their characteristics.  Alternatively can I get any useful measurements from them unmounted as they are?  If so, how?  Thanks.

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Paul Birkeland

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Reply #1 on: May 07, 2022, 04:05:36 PM
Can you post a picture of what you have?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Ken

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Reply #2 on: May 07, 2022, 04:51:16 PM
Can you post a picture of what you have?
Sure.  They're mounted on chassis plates right now so I will have to unbolt them.  I'll do that tonight and post pix tomorrow, including the leads.

There's not much to see.  They have a lot of laminations and bell ends which, apparently, I had chromed at some point.  I got these over 20 years ago so my memory is a bit faded.

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Paul Birkeland

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Reply #3 on: May 08, 2022, 04:15:48 AM
Oh you can just take photos of them as they are mounted; that's probably enough to say what they are.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Ken

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Reply #4 on: May 08, 2022, 07:53:28 AM
OK Paul, here are the pix.  Please excuse the reflections in the chrome :)

I went through a very down and dark place back then for about 10 years so my recollection is incomplete and hazy about that period.  I'm pretty sure about this being some sort of conversion to 2A3 that Doc was offering at the time because you see the sockets installed in one of the pics.  Those ceramic and gold sockets came from Michael Percy I think.  I also have a vague recollection of something Magnequest EX "something: but that could be a false association.

I have a matched pair of these that I apparently tarted up with chrome and paint, including both power transformers.  Some but not all of the components are installed.  The others are scattered and lost.  I don't have the original parts list, the assembly instructions nor the wooden bases.  If I could somehow re-assemble those missing items I could now complete this project.  I realize that DocB and his crew have made significant improvements over the years but these little amps would suit my modest purpose if I could complete them.  And since good quality transformers are a big part of the expense of a tube kit, I'm half way there :)

You may recall from my previous thread that I am enamoured of monaural playback.  These little monoblocks would would allow me to experiment with that and if mono turns out to be too much of pain to get quality source material, I would have the two of them for stereo.

Or maybe the whole idea would be more trouble than it's worth?

Your thoughts and guidance would be much appreciated.


"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Ken

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Reply #5 on: May 08, 2022, 11:06:54 AM
I had forgotten the name of this amp but on reading through some of the legacy threads it seems this might have been one of the first iterations of Afterglow.

Even if it would be more trouble and expense than it's worth to try to resurrect this build project, I would still like to learn the specs of the OPT because it might be useful somewhere else.

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline debk

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Reply #6 on: May 08, 2022, 02:32:04 PM
They sure look nice!

Debra K

Eros 2Phono amp
BeePre2, Psvane ACME 300b
Kaiju, Linlai Elite  300b
Monamour 2a3 amps various tubes
Sota Sapphire, Pete Riggle Woody Tonearm, Kiseki Purpleheart Cartridge
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Roon Nucleus
MHDT Labs Orchid DAC
Jager speakers


Offline Paul Birkeland

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Reply #7 on: May 08, 2022, 02:38:12 PM
Those are TFA-204s.  Those could be built as Afterglows or Bee-glows.  I would definitely get some nylon shoulder washers for those TFA-204s to isolate the brass screws from the chromed covers. 

I attached a photo of my pair of Afterglows, which also have the same Deyoung power transformer that yours have (not the Magnequest PGP 8.1).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Ken

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Reply #8 on: May 08, 2022, 03:14:16 PM
Thanks Paul.  So the question is:  is it feasible and practical to assemble the parts AND detailed instructions necessary to complete this project build?  I have built the original S.E.X. kit and tinkered with a few other things but I am essentially a newbie.  If I had a detailed parts list I could hunt down and buy everything but I most definitely would need detailed instructions (and maybe a bit of hand holding along the way).

If that doesn't make sense, then do you (or someone else) have detailed specs for the OPTs?

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Paul Birkeland

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Reply #9 on: May 08, 2022, 03:56:11 PM
I'm not so sure you'll find detailed instructions, and to be honest those top plates we provided are just not thick enough to really be useful and tend to bend very easily if you attempt to ship the amps.  A lot has changed (in a good way) in the 25 years since we shipped that kit. 

The TFA 204 is a 3K series feed output transformer with 0-4-8-16 secondaries.  Yellow is 16, orange is 8, brown is 4, black is common.  The core will (just barely) tolerate 60mA of standing current.  It's a nice sounding output transformer, but it's pretty light on the bottom end and was essentially superseded by the TFA-2004 parallel feed output transformer and EXO-003 plate choke which offered substantial improvement in the bottom end.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Ken

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Reply #10 on: May 08, 2022, 04:23:31 PM
OK, got it.  Can you give a ballpark estimate of how "light' they would be on the bottom if running a 300B?  Say, roughly how far down at 40Hz?  -3dB or -6dB or-19dB

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Ken

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Reply #11 on: May 08, 2022, 05:56:07 PM
Paul, I found the answer to my question about bass extension in another thread here.  In response to someone else you said that the original spec for that OPT was 40Hz.  If it starts rolling off from there down, I can live with that for my listening tastes, room and neighbours.

I'm going to post a new thread here to ask if anyone here knows where I can get access to the parts list and build instructions for the Bee-glow variant.

Thanks for your help thus far, much appreciated.

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Ken

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Reply #12 on: May 08, 2022, 06:10:59 PM
I have an unfinished pair of monoblocks from about 20 years ago that Paul B has helped me to identify as Afterglows with TFA204 OPT and Deyoung PT.  Paul advises that these could also be built as Beeglows.

Some of the components under the chassis have been installed but many have been misplaced or lost.  Most importantly, I do not have the original parts list nor the original assembly instructions.  Does anyone know where I can access them?  Thank you.

"It is not that I am mad; it is just that my head is different from yours" - Diogenes of Sinope


Offline Paul Joppa

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Reply #13 on: May 09, 2022, 04:48:44 AM
My recollection of the designs is that the B-glow is more problematical than the Afterglow, which is probably what you had originally. I'm away from my primary computer this morning, but I'll be back later today. I'll check what manuals I may have and post again. What (if anything) is installed below the chassis plate?

Paul Joppa


Offline Paul Joppa

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Reply #14 on: May 09, 2022, 04:57:55 AM
I posted in the original thread before I saw you had already started this thread. I'll post again here when I get back this evening and can look at my archive of manuals and notes.

Paul Joppa