S.E.X. > 2A3 Monoblock OPT

[Ken]

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.

 

[Paul Birkeland]

Can you post a picture of what you have?

 

[Ken]

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.

 

[Paul Birkeland]

Oh you can just take photos of them as they are mounted; that's probably enough to say what they are.

 

[Ken]

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.

 

[Ken]

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.

 

[debk]

They sure look nice!

 

[Paul Birkeland]

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).

 

[Ken]

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?

 

[Paul Birkeland]

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.

 

[Ken]

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

 

[Ken]

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.

 

[Ken]

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.

 

[Paul Joppa]

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]

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 Birkeland]

The BeeGlow also sort of lacks proper biasing instructions, so you'd need to figure that out as well. 

 

[Ken]

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?

Here's a photo of the underside.  Pretty rag tag - a sign of the mess I was in back then I guess.  It might be better to think in terms of stripping everything from the underside and starting from scratch, which I don't mind at all.
I'm almost positive that I was building the Afterglow variant and I would be completely happy to stick with that if it is less problematic and more easily doable than using 300B.

 

[Paul Joppa]

A few preliminary notes, now that I've checked my files:

* I have an original Afterglow manual. I can't locate a digital copy, but PM me and I'll scan the old manual and email you a copy.

* You are fortunate to have the deYoung power transformer - it was well made and gave the right voltages, but was only used for one year.

* The big cathode resistor (2500 ohms/10 watts) should be replaced with a 3000 ohm, 20+watt resistor. (There was an error in calculating the part value that was not caught at the time.)

* You'll have to use a more recent version of the C4S current source circuit board - we'll work something out.

* The inline fuse is a poor solution and does not allow proper safety grounding. The usual solution is to install an IEC inlet/fuse holder in the wood base.

 

[Ken]

Thank you Paul.  I appreciate this very much.  PM on its way.

 

[Natural Sound]

I may have an old pair of c4s boards that you can have if I can find them. You may need to adjust the resistor values since it was originally setup for a S.E.X. 2.0. The original design that consisted of 2 separate boards. Perfect for a pair of mono blocks. I'll start digging if you are interested.