Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: Ken on May 07, 2022, 04:01:42 PM

Title: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 07, 2022, 04:05:36 PM
Can you post a picture of what you have?
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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.

Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: debk on May 08, 2022, 02:32:04 PM
They sure look nice!
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland 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).
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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?
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken 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.
Title: Beeglow Assembly Instructions
Post by: Ken 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa 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?
Title: Re: Beeglow Assembly Instructions
Post by: Paul Joppa 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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 09, 2022, 05:13:06 AM
The BeeGlow also sort of lacks proper biasing instructions, so you'd need to figure that out as well. 
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 09, 2022, 08:11:01 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?
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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa on May 09, 2022, 01:14:25 PM
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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 09, 2022, 01:46:51 PM
Thank you Paul.  I appreciate this very much.  PM on its way.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Natural Sound on May 09, 2022, 02:59:30 PM
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.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 09, 2022, 03:02:42 PM
@Natural Sound.  Thank you :)  I am completely dependent on Paul J's advice about this.  He did mention a "more recent" C4S but I don't know enough about it to know what that means.  Perhaps he will clarify if/when he sees your post.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa on May 09, 2022, 06:52:38 PM
@Natural Sound -- Are those the older, brown boards? Do you have the original LEDs? (They are in a different format than the current HLMPs.) That would be more authentic than using current production boards!

Alternatively I was thinking  of the v.4.4 green boards, using the trimpot for a cathode resistor and implementing the soft-start function.

The other missing piece is a power switch that fits the old chassis cutout.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 10, 2022, 06:13:45 AM
@Paul Joppa:  Paul, I received your PM and replied (twice) with a notice that the Replies were successfully sent.  However,  those replies are not showing up in my Sent Items folder in Messages, so I don't know if you actually received them.  In case not:

- you can email the manual to [email protected]
- I hear your advice about trying to build the two amps as mirror images; have to reconsider that
- when I'm shopping for the other parts, if I can't find a power switch of suitable size and rating, I can always use a Dremel (or similar) to enlarge the cutout in the chassis
- I will wait to hear further from you about the C4S boards
- great news that the bases are still available; will save a lot of hassle for me.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa on May 10, 2022, 07:08:45 AM
My messages to you should be in your Inbox. Yours to me should be in your Sent Items.

In any case, yes, I got your messages. I'll send the manual scan this afternoon.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 10, 2022, 07:15:18 AM
Thanks.  That's what I figured.  Yours to me are there in my Messages but my replies are not in Sent Items.  Anyway, you received them so all is well.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 13, 2022, 03:05:02 PM
@Natural Sound:  Paul J advised that he's going to come up with some new C4S boards for the Afterglows so I won't need to take you up on your offer.  Thank you though.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 16, 2022, 08:25:08 AM
I now have a parts order pretty much together.  Actually, there aren't that many items missing or lost.  I was able to find most things at Mouser Canada and a few from our esoteria at PartsConnexion here in Canada.  I need advice/input about a couple of things please:

- for the fused IEC receptacle would 5A or 6A rating be appropriate?
- tubes were missing and I have no idea what became of them.  Brent Jessee has a good selection of NOS 5965/6829/12AV7 at reasonable prices but I don't want to pay the price for NOS or premium 2A3 until I have the system up and running.  Any recommendation for decent quality, reasonably priced current production as a place holder for the time being?
- my multimeter also vanished in the haze.  Recommendations for a reasonable quality hobbyist model?

Thank you.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 16, 2022, 08:43:50 AM
No, don't use a 5A fuse. 1-2A is plenty.  Used 5965s on eBay are dirt cheap; just grab some of those!

If you have a Harbor Freight Tools near you, they have a meter that's around $25 that works really well.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 16, 2022, 09:37:34 AM
Thanks Paul.  The 5965s are not a problem, it's the 2A3s that are expensive, even for current production.  Although I did see a couple of places selling Chinese Penta for about $45USD.  How long they might last would be a crap shoot I would imagine.

Harbour Freight is not in Canada.  Would this meter from Mouser suffice as a starter for building this kit (price is in CDN dollars):
https://www.mouser.ca/ProductDetail/Digilent/480-001?qs=s%2FdyVPQMB4xWAQ%252Byz%2FlJpg%3D%3D
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 16, 2022, 10:27:09 AM
How about this?
https://www.canadiantire.ca/en/pdp/autoranging-digital-multimeter-0520052p.html#plp (https://www.canadiantire.ca/en/pdp/autoranging-digital-multimeter-0520052p.html#plp)
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 16, 2022, 10:38:47 AM
There's a Canadian Tire just up the road from me  :) and I did see that meter.  I thought that it only being able to read down to 400R could be a problem.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 16, 2022, 11:13:28 AM
Those are ranges on the meter.  The 400 ohm setting will have three leading digits, a decimal point, then one more digit.  If you're trying to measure a 0.01 ohm resistor (which is extremely difficult to measure anyway), then you'll get a 000.0 on the meter, but it can certainly measure below 400 ohms.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa on May 16, 2022, 11:55:49 AM
For the parts order, add four small resistors for grid stoppers; we've often used 220 ohms but anything from 100 to 500 ohms is good. Carbon or metal film are acceptable; carbon composition is better in theory but tends to be fragile unless you get a premium part.

Also don't forget the 3K power resistors should be rated 20 watts, not 10 as in the parts list. Inexpensive metal-oxide ones are fine, but seem to be out of stock in many places; Ohmite wirewound are good, available, and not too costly:

https://www.mouser.com/ProductDetail/Ohmite/B20J3K0E?qs=%2F%252B4YgdRx4NhlrL7xcy2z3g%3D%3D
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 16, 2022, 01:51:44 PM
I would add to PJ's recommendation not to use the chassis mount type resistors (with the gold heatsinks).  They will only dissipate their rated power if they are mounted to the side of a battleship, and derating them can be tricky.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 16, 2022, 02:50:00 PM
@PaulJ:  I will order the grid stoppers as you said.  I did already find the Ohmite 3K 20W resistor at Mouser.

@PaulB:  that meter I linked at Mouser is less expensive and since they're both likely made in China anyway, would it do the job?  I'm already ordering from Mouser anyway.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 16, 2022, 02:57:44 PM
@PaulJ:  what W rating for the grid stopper resistors?
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 16, 2022, 03:01:21 PM
Grid stoppers handle no current (well, nearly no current), but it's nice to have a reasonably stout part with long leads, so a 1/4W part is a nice idea.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 06:51:23 AM
There are these three resistors on the original parts list.  What voltage rating should I order?  Mouser offers Vishay/Dale in 200, 250, 300, 350 V

249K 1/4W metal film
681 1/4W metal film
182 1/4W metal film
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 17, 2022, 06:53:30 AM
Those all need to be rated for at least 10V.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 06:57:53 AM
Paul, they're rated between 200-350V
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 17, 2022, 07:48:54 AM
That is 20 to 35 times more than they need to be rated for; it's a non-issue for these parts.

Pretty much none of the resistors in the original afterglow circuit gets worked particularly hard in terms of voltage.  The power supply bleeder is going to see close to 500V on start-up, so that's a consideration. 
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 09:19:16 AM
I understand but at 1/4W for the R values listed on the parts sheet, 200V is the lowest that I can see on the Mouser site.  Obviously, they do have some with lower V rating but not corresponding to the other specs we need.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 17, 2022, 09:21:12 AM
You do not need to hunt for a low voltage rating, as any voltage rating is more than enough for these parts. This is a maximum voltage, nothing bad happens if you run a 500V rated resistor at 1V.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 09:33:06 AM
I understand; just trying to keep the cost down by not over-spec'ing what I really need.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 09:42:05 AM
Paul B:  Here are the 270Kohm bleeder resistors that Mouser is showing in carbon film 1/2W.  The max voltage rating offered at these specs is 400V.  I don't understand the difference between the two items listed: one is almost twice the price of the other, at what appears to be the same specs.

https://www.mouser.ca/c/passive-components/resistors/film-resistors/carbon-film-resistors-through-hole/?power%20rating=500%20mW%20%281%2F2%20W%29&resistance=270%20kOhms&voltage%20rating=400%20V
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Joppa on May 17, 2022, 10:41:08 AM
The bleeders dissipate a bit over 0.5 watts. At full rating, inside a tube amp, they will get VERY hot! For reliability, they should be rated for at least three times the actual dissipation - you should use 2-watt resistors. A working voltage of 500v minimum is required, to survive the turn-on transient voltage.   #things_they_don't_tell_you_in_the_specs

The different part numbers indicate how they are packaged, loose individual components, or taped together in reels of 4000 resistors for use in automated insertion machines. See the spec sheet, bottom of the first page.
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Paul Birkeland on May 17, 2022, 10:59:31 AM
Here is the recommended bleeder:
https://www.mouser.ca/ProductDetail/Xicon/294-270K-RC?qs=OFGmc1Cs8YZtYy8epssWyA%3D%3D (https://www.mouser.ca/ProductDetail/Xicon/294-270K-RC?qs=OFGmc1Cs8YZtYy8epssWyA%3D%3D)
Title: Re: S.E.X. > 2A3 Monoblock OPT
Post by: Ken on May 17, 2022, 12:46:52 PM
Paul B:  that resistor shows out of stock at Mouser but I found an equivalent at PartsConnexion for pennies more.

Thanks to both of you for the education :)