PPS Blasting a little BLONDIE thru 70 year old triodes to test the Drum Kit.
Disco + Talent + COCAINE = Clem Burke
Yowza. Not wall-thumping bass, but what's there is crisp & clear. Surprising.
Not the preferred music for this amp. but it's holding it's own...
"WHEN I met you in the restaurant YOU could tell I was no Debutante..."
NB shop speakers are open-baffle BOXES (old kitchen cabinets) with Eminence Beta-LTAs (12" 97.quelquechose dBA/W) with little fostex horn tweeters crossed at 7K, HOWEVER, they're up in the corner between wall and cathedral ceiling (covered with homosote, so well damped). YMMV.
Disco + Talent + COCAINE = Clem Burke
Yowza. Not wall-thumping bass, but what's there is crisp & clear. Surprising.
Not the preferred music for this amp. but it's holding it's own...
"WHEN I met you in the restaurant YOU could tell I was no Debutante..."
NB shop speakers are open-baffle BOXES (old kitchen cabinets) with Eminence Beta-LTAs (12" 97.quelquechose dBA/W) with little fostex horn tweeters crossed at 7K, HOWEVER, they're up in the corner between wall and cathedral ceiling (covered with homosote, so well damped). YMMV.
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What should I do with my 4th TSE-II board??
Very happy with my TSE-II builds so far (2x 300B monoblocks and 1 x 45 stereo). Surprisingly, if I HAD built the 45 version first, though, I'm doubting I would have built the 300Bs; just sayin'.
I have ONE more TSE-II board in stock.
I have most parts to build a 2A3 stereo version:
4 x 2A3 of uncertain age & parentage somewhere
6K7 PST I'm pretty sure. Alternately, some NOS vintage iron.
Chokes. Many Chokes.
2x Transcendar 3K:8ohm OPTs
Most, if not all, parts to populate the board
What are people's experience with 2A3 TSE-IIs?
I've built several 2A3 amps previously (hence the pairs of 2A3s lurking around here somewhere) but never been impressed. The Power Drive does appear to be a game-changer, however, so I'm optimistic.
I'm thinking I should get a separate FILAMENT transformer (Triad 6.3V 8A are $18 at Mouser. Good idea?
Alternately, I do have a bunch of 71A/171A NOS tubes. The B+ and the power output are SO LOW, however, that I'm not sure it's worth the effort. Plus I would have to scrounge-up some more 5K SE OPTs. I'm leaning towards trying the 71As in a UD DHT P-P, as I have some PMillett filament power supplies that would work great. Sorry, just doing a little DHT RIFFING...
Very happy with my TSE-II builds so far (2x 300B monoblocks and 1 x 45 stereo). Surprisingly, if I HAD built the 45 version first, though, I'm doubting I would have built the 300Bs; just sayin'.
I have ONE more TSE-II board in stock.
I have most parts to build a 2A3 stereo version:
4 x 2A3 of uncertain age & parentage somewhere
6K7 PST I'm pretty sure. Alternately, some NOS vintage iron.
Chokes. Many Chokes.
2x Transcendar 3K:8ohm OPTs
Most, if not all, parts to populate the board
What are people's experience with 2A3 TSE-IIs?
I've built several 2A3 amps previously (hence the pairs of 2A3s lurking around here somewhere) but never been impressed. The Power Drive does appear to be a game-changer, however, so I'm optimistic.
I'm thinking I should get a separate FILAMENT transformer (Triad 6.3V 8A are $18 at Mouser. Good idea?
Alternately, I do have a bunch of 71A/171A NOS tubes. The B+ and the power output are SO LOW, however, that I'm not sure it's worth the effort. Plus I would have to scrounge-up some more 5K SE OPTs. I'm leaning towards trying the 71As in a UD DHT P-P, as I have some PMillett filament power supplies that would work great. Sorry, just doing a little DHT RIFFING...
Have not tried 2A3's but regarding the filament supply, each 2A3 is 2.5A and 5842 is 0.3A.
Together 5.6A AC
If I'm not mistaken, the transformer should be rated 2X if using DC supplies.
So I think at least 10A rated transformer. (unless the manufacturer rating is in DC already)
I did not consider this when my building my own TSE's and I think that may have put stressed the transformers.
Together 5.6A AC
If I'm not mistaken, the transformer should be rated 2X if using DC supplies.
So I think at least 10A rated transformer. (unless the manufacturer rating is in DC already)
I did not consider this when my building my own TSE's and I think that may have put stressed the transformers.
I don't know if its overkill.. the experts seem to think otherwise:
From Pete Millett's regulated filament page: Regulated DC filament supply
Valve Wizard Page: The Valve Wizard
That said some manufactures list the rating as DC and some as AC so this becomes a bit confusing
From Pete Millett's regulated filament page: Regulated DC filament supply
Valve Wizard Page: The Valve Wizard
That said some manufactures list the rating as DC and some as AC so this becomes a bit confusing
Hot Transformers
Roger that on Pete Millett's recommendations.
I have about half a dozen of his regulated filament supplies (with the common-mode choke).
Transformers in TubeLabLand are rarely treated this gingerly.
Note what George regularly does to his 6V7VG Allied PSTs.
I certainly understand your point; one of the reasons I made TSE-II 300B MONO-BLOCKS is to reduce the load on the poor 6V7VG PST (well, and I had two of them in stock; probably wouldn't have been so prissy if I had had to buy them new at current prices).
However, in my experience, George has been more right about over-loading power transformers than not. As long as the winding insulation is intact, and you can tolerate that "old electronics smell" (as the Chief Cook & Bottle Washer calls it), I can't see any reason not to push the limits. Provided that you keep the smoke in, of course.
I'm not sure what the exact failure mode would be for a modern power transformer; (1) liquified varnish (2) shorted windings (3) blown fuse?
NB I regularly use ANTIQUE iron (Stancor, Thordarson, UTC. Heathkit, etc).
I try hard to keep the loads within specs on those old puppies, but I would guess that using an 80-90 year-old NOS PST within specs is probably more dangerous than using a modern PST at 125-150% of rated load. Sure smells like it. I do make an effort to insure that the sheet-metal on these old clams is well-grounded; I'd prefer that a short doesn't find its way to ground THROUGH me.
PS Frankly I am more worried about exceeding the amperage limits of the voltage regulator. The failure mode of sand, in my experience, is not gentle. IIRC 5A is right at the data sheet limit for the regulator. Which reminds me to study heat sink requirements for a 2A3 build...
PPS I used to engineer offshore drilling vessels. We used gangs of ~1000 hp GE 752 (originally locomotive) DC drive motors, then later gigantic VFDs for Variable Speed AC motors. I generally don't get excited about Back EMF/Power Factor Correction below about 1000 HP, but that's the Oilfield Trash talking.
Roger that on Pete Millett's recommendations.
I have about half a dozen of his regulated filament supplies (with the common-mode choke).
Transformers in TubeLabLand are rarely treated this gingerly.
Note what George regularly does to his 6V7VG Allied PSTs.
I certainly understand your point; one of the reasons I made TSE-II 300B MONO-BLOCKS is to reduce the load on the poor 6V7VG PST (well, and I had two of them in stock; probably wouldn't have been so prissy if I had had to buy them new at current prices).
However, in my experience, George has been more right about over-loading power transformers than not. As long as the winding insulation is intact, and you can tolerate that "old electronics smell" (as the Chief Cook & Bottle Washer calls it), I can't see any reason not to push the limits. Provided that you keep the smoke in, of course.
I'm not sure what the exact failure mode would be for a modern power transformer; (1) liquified varnish (2) shorted windings (3) blown fuse?
NB I regularly use ANTIQUE iron (Stancor, Thordarson, UTC. Heathkit, etc).
I try hard to keep the loads within specs on those old puppies, but I would guess that using an 80-90 year-old NOS PST within specs is probably more dangerous than using a modern PST at 125-150% of rated load. Sure smells like it. I do make an effort to insure that the sheet-metal on these old clams is well-grounded; I'd prefer that a short doesn't find its way to ground THROUGH me.
PS Frankly I am more worried about exceeding the amperage limits of the voltage regulator. The failure mode of sand, in my experience, is not gentle. IIRC 5A is right at the data sheet limit for the regulator. Which reminds me to study heat sink requirements for a 2A3 build...
PPS I used to engineer offshore drilling vessels. We used gangs of ~1000 hp GE 752 (originally locomotive) DC drive motors, then later gigantic VFDs for Variable Speed AC motors. I generally don't get excited about Back EMF/Power Factor Correction below about 1000 HP, but that's the Oilfield Trash talking.
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On my TSE ( original ) 2A3 setup, I resorted to putting a small RF type heatsink on the filament regulator, with a small 12 volt muffin fan drawing air through the heatsink, same being run at 6.3 volts to keep the noise quiet. This ran cool and quiet, but I had a small amount of hum audible up close on 96 dB speakers because the regulator was running flat out.
Later, when I switched to 801A's, I ditched the filament regulator and used a $6 dollar ish "Tusotek" 5 amp buck / boost regulator to run the filaments and this worked spectacularly well. I also used the Tusotek with 2A3's and it worked very well - it struggled for a few seconds with the cold current surge of the 2A3's, but once it got some heat ( and resistance ) in them, it lit them right up with no trace of audible hum.
I am not an audiophile, but, that said, if I go with DC on the filaments of another amp ( hint SV811 or SV572 ) , I would not hesitate to use a buck / boost convertor in place of a linear chip. I cannot hear any artifacts associated with the use of these devices for filament / heaters.
As for the 2A3, generally, I'm not really a fan. They just sound kind of meh to me. My favorite sounding is the 5930, but they are tough to come by these days. The 5930 is two Sylvania 45's ( literally ) in the same bottle, in parallel. I occasionally see that arrangement in regular 2A3's.
Again, that said, the vanilla hamfest special RCA 2A3 with 12AT7 drive actually works pretty well in the DHT SSE. I was able to get 4 watts out of it with a 5K load before it showed any flattening of a 1 KHz sine wave. I grew to more or less like the sound of it - no real incentive to have torn it down other than to try the plastic chassis thing and make an easy beginner DH amp that anyone can build without having to destructively hack a board.
edit: I ONLY use the old stock, well used, hamfest or eBay type $1 - 10 dollar ish power transformers and chokes because like most hams, I'm super cheap with my hobby stuff. I have never burned one up and I have tried pretty hard, or at least been super cavalier about it. Do I advocate doing this? No, but it's what I do.
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"Meh"
W5JAG said: "As for the 2A3, generally, I'm not really a fan. They just sound kind of meh to me."
PRECISELY what I'm concerned about; this has been exactly my experience with 2A3s in a BUNCH of different circuits.
Really don't want to go through all that work and end-up with a "meh".
If I do a 2A3, I think I would use one of my PMillett fils boards mounted off-board (and vertically), but I would still really need a separate fils transformer...
Alternately, I could splurge on new production single plate 2A3s, BUT from what I can suss-out, they are really just 300B structure with rewired filaments, so...
Perhaps a STEREO 300B; I have those 3K Transcendars, plus a spare set of 300Bs, AND my SIL (the fireman) is clamoring to "borrow" a tube amp. I generally like higher loads (e.g. 5K on 300B and say KT-88s in the SSE) but I have high dB speakers; 3K load on 300Bs might work good for the SIL.
Re: Muffin Fans
I did a similar thing, except using a 120V fan with speed controller mounted in a ply bottom plate (see attached). With speed turned-down real low it's only audible within about a meter...I don't use it on the 300B monoblocks since I relocated the big 10K resistor (R29?) off the board (and increased to 25W heat-sink type). Would work good on a stereo 300B, I think.
PS Still SHOCKED SHOCKED by the noises coming-out of the 45 TSE-II.
Now playing Lou Reed "Walk on the Wild Side". Spectacular bass, and the horns are IN THE ROOM; where the hell is that coming-from? Oh, yeah, MOSFETS!
I feel like a Single Ended REFUGEE who just got rescued by the Coast Guard after many years adrift, given a warm blankie & hot cocoa. And a Sea Nurse who looks like Kate Upton. Needless to say, my ears are toasty.
W5JAG said: "As for the 2A3, generally, I'm not really a fan. They just sound kind of meh to me."
PRECISELY what I'm concerned about; this has been exactly my experience with 2A3s in a BUNCH of different circuits.
Really don't want to go through all that work and end-up with a "meh".
If I do a 2A3, I think I would use one of my PMillett fils boards mounted off-board (and vertically), but I would still really need a separate fils transformer...
Alternately, I could splurge on new production single plate 2A3s, BUT from what I can suss-out, they are really just 300B structure with rewired filaments, so...
Perhaps a STEREO 300B; I have those 3K Transcendars, plus a spare set of 300Bs, AND my SIL (the fireman) is clamoring to "borrow" a tube amp. I generally like higher loads (e.g. 5K on 300B and say KT-88s in the SSE) but I have high dB speakers; 3K load on 300Bs might work good for the SIL.
Re: Muffin Fans
I did a similar thing, except using a 120V fan with speed controller mounted in a ply bottom plate (see attached). With speed turned-down real low it's only audible within about a meter...I don't use it on the 300B monoblocks since I relocated the big 10K resistor (R29?) off the board (and increased to 25W heat-sink type). Would work good on a stereo 300B, I think.
PS Still SHOCKED SHOCKED by the noises coming-out of the 45 TSE-II.
Now playing Lou Reed "Walk on the Wild Side". Spectacular bass, and the horns are IN THE ROOM; where the hell is that coming-from? Oh, yeah, MOSFETS!
I feel like a Single Ended REFUGEE who just got rescued by the Coast Guard after many years adrift, given a warm blankie & hot cocoa. And a Sea Nurse who looks like Kate Upton. Needless to say, my ears are toasty.
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5V CT & Star-Grounding
A 5V center tap is not only UNNECESSARY, but there's no place for it on the board.
If you have a CT lead, suggest coiling & zip-tying it, cutting the end flush AND putting a piece of heat-shrink on there (squeeze the hot end with pliers). Don't use electrical tape, as it's hot under there.
I suppose you COULD ground it, but personally I am religious about avoiding possible ground loops, so I keep the board insulated from the chassis and bring only ONE ground wire (from the red-yellow HT CT) to the star-ground point.
At star-ground I have:
(1) PST ground wire
(2) A/C ground
(3) board ground
Input jacks are isolated from the chassis, and grounded back through the board ground-plane to the star-ground.
At star-ground, don't forget to scrape-off any finish on the chassis.
A 5V center tap is not only UNNECESSARY, but there's no place for it on the board.
If you have a CT lead, suggest coiling & zip-tying it, cutting the end flush AND putting a piece of heat-shrink on there (squeeze the hot end with pliers). Don't use electrical tape, as it's hot under there.
I suppose you COULD ground it, but personally I am religious about avoiding possible ground loops, so I keep the board insulated from the chassis and bring only ONE ground wire (from the red-yellow HT CT) to the star-ground point.
At star-ground I have:
(1) PST ground wire
(2) A/C ground
(3) board ground
Input jacks are isolated from the chassis, and grounded back through the board ground-plane to the star-ground.
At star-ground, don't forget to scrape-off any finish on the chassis.
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A Redundant Tautology: Cheap Hams
This reminds me that I do still have the FrankenAmp (Poor Man's TubeLab prototyping board) which could make a "DHT SSE". PLUS I could change the driver tube(s) too.
Let's see: 2A3s with RCA Red 6SL7s under a CCS, maybe with NiMH battery bias....SOMEBODY STOP ME...
Re: Ham Iron
The advantage to being super cheap is that the same meager $$ makes a pretty good inventory after a few decades.
Haven't been to a HamFest in years, but stocks are running low AND Texas Is Open for Business...
de K5HAR
This reminds me that I do still have the FrankenAmp (Poor Man's TubeLab prototyping board) which could make a "DHT SSE". PLUS I could change the driver tube(s) too.
Let's see: 2A3s with RCA Red 6SL7s under a CCS, maybe with NiMH battery bias....SOMEBODY STOP ME...
Re: Ham Iron
The advantage to being super cheap is that the same meager $$ makes a pretty good inventory after a few decades.
Haven't been to a HamFest in years, but stocks are running low AND Texas Is Open for Business...
de K5HAR
I was actually going to be able to do some hamfesting this spring, for the first time in almost a decade, but
Green Country ( Tulsa ) - cancelled
Ham Com - cancelled FOREVER. No more Dallas Hamfest unless someone steps up to the plate to start a new one.
Dayton ( or wherever it is now ) - cancelled for 2021.
I hear Belton is good - I've never been. Maybe I can make that if they have it.
Green Country ( Tulsa ) - cancelled
Ham Com - cancelled FOREVER. No more Dallas Hamfest unless someone steps up to the plate to start a new one.
Dayton ( or wherever it is now ) - cancelled for 2021.
I hear Belton is good - I've never been. Maybe I can make that if they have it.
Rats. Turns-out that entire too many of us are turning-up as Silent Keys (SK).
For the uninitiated (and therefore rational) Rest of You, “Silent Key” is the Amateur Radio euphemism for deceased.
Should have seen this coming. QST looks increasingly like a newsletter from a nerdy old-folks home…
For the uninitiated (and therefore rational) Rest of You, “Silent Key” is the Amateur Radio euphemism for deceased.
Should have seen this coming. QST looks increasingly like a newsletter from a nerdy old-folks home…
Point being that aging hams (my 68-yo self included) are right in COVID-19’s wheelhouse.
OTOH, at least in Texas, anybody over 65 has had access to a vaccine for several months; IF they want it, that is…
Plus, mandated restrictions have been lifted in Texas AND we gots lots of that SUNSHINE/ Vitamin D goin’ on.
Further, the COVID doesn’t explain the END of the Dallas Hamfest. That’s down to (a) dwindling market, and (b) nobody feeling spry enuf to take it on.
OTOH, at least in Texas, anybody over 65 has had access to a vaccine for several months; IF they want it, that is…
Plus, mandated restrictions have been lifted in Texas AND we gots lots of that SUNSHINE/ Vitamin D goin’ on.
Further, the COVID doesn’t explain the END of the Dallas Hamfest. That’s down to (a) dwindling market, and (b) nobody feeling spry enuf to take it on.
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Still finding stuff.. PAIR of UNOPENED 182-B DHTs
Still cleaning-up the recesses of the shop, one year after LAY-OFF, I mean Retirement. Came across these (!)
5v 1.25A filaments
250V “tension plaque”
-60V “tension grille”
30mA “courant plaque”
5K ohm “impedance de charge”
1.8 W “puissance module”
CLOSE to a 5v 45, but lower Vp max, and at 250Vp, SLIGHTLY higher Rp and Mu…
https://frank.pocnet.net/sheets/121/1/182B.pdf
I assume that they are ST bottles, not globes…haven’t opened ‘em yet.
Anybody have a fluoroscope they can lend me?
EDIT: couldn’t stand the suspense. They are indeed STs, with sumptuous getter.
See photo.
FleaBay prices seem slightly higher than 45s, but not egregious.
Seem to be equivalent to 483s (I think George has UX-483s IIRC)
Unless I SELL’em, I guess I know what I’ll do with that last TSE-II board…
Unless of course y’all talk me OUT OF IT.
Still cleaning-up the recesses of the shop, one year after LAY-OFF, I mean Retirement. Came across these (!)
5v 1.25A filaments
250V “tension plaque”
-60V “tension grille”
30mA “courant plaque”
5K ohm “impedance de charge”
1.8 W “puissance module”
CLOSE to a 5v 45, but lower Vp max, and at 250Vp, SLIGHTLY higher Rp and Mu…
https://frank.pocnet.net/sheets/121/1/182B.pdf
I assume that they are ST bottles, not globes…haven’t opened ‘em yet.
Anybody have a fluoroscope they can lend me?
EDIT: couldn’t stand the suspense. They are indeed STs, with sumptuous getter.
See photo.
FleaBay prices seem slightly higher than 45s, but not egregious.
Seem to be equivalent to 483s (I think George has UX-483s IIRC)
Unless I SELL’em, I guess I know what I’ll do with that last TSE-II board…
Unless of course y’all talk me OUT OF IT.
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On paper you do need a 8 to 10 amp 6.3 volt winding for 2A3's. In practice you aren't going to fine one on a single power transformer that runs the whole amp. If you are using a separate 6.3 volt transformer, then 10 amps is a good choice. My 2A3 amp uses a Hammond 372HX. This force feeds the tubes over 350 volts of B+ so it shouldn't be used, but my amp works fine and the transformer does not get hot. I have tried cheap dual plate Chinese 2A3's and Sovtek single plate 2A3's. Neither seem to mind the over voltage, but then I feed my 45's 320 volts.
Do NOT ground the CT on the 5 volt winding. This will short B+ to ground making for a short unhappy life for the rectifier tube and possibly frying some other parts. The CT on the 6.3 volt winding should be connected to it's terminal on the board. The jumper will decide if it gets grounded or not.
I have been to Dayton every year since 2009. It's still called "Dayton" even though it's now in Xenia a few miles southeast of the old Hara Arena site. 2019 saw a claimed 25,000 people show up. I know it was crowded, but they started giving free admission to the general public on Sundays, probably to inflate the attendance numbers. I had paid for swap spaces for 2020 which were held until 2021, which are now supposed to be held for 2022. I went to every south Florida hamfest since the late 60's. That used to be maybe 6 or 7 per year plus Orlando. All of the larger ones are gone except for Orlando and Dayton, both are on indefinite virus hold.
Many hamfests have died for a variety of reasons. Ebay put a dent in the swap meets and some of the forums were just boring, or trying to appeal to too broad of an audience. Miami was struggling when Evelyn got ill and passed, but the real death knell for Miami was the NFL. Hotel rooms in Miami in February are NOT cheap, but when the NFL extended their season to put Super Bowl Sunday in hamfest weekend, and the game just happened to be in Miami that year, nobody could afford the trip, especially when Orlando was one weekend later. Orlando was still booming as was Dayton before Covid. Even with Florida's permissive attitude toward Covid, the organizers did not want to be the purveyors of the virus. Orlando went "virtual" this year, whatever that meant. I might have gone to sell stuff outdoors, I would not have set up inside those super crowded buildings.
The Shelby NC hamfest promises a decision on 2021 sometime this month.
The 182 is the little brother to the 183. The 183 IS a 5 volt 45. I have a pair of 92 year old NX-483's (same as a 183) in my original TSE. I run them at 320 volts and 30 mA and they are still kicking. They drove my 87 dB Yamaha NS-10M's to a decent listening level in my 10 X 10 foot room in Florida. They are nearly useless here in a 2000 square foot basement, so that amp sits on the shelf, lonely and unplugged.
Do NOT ground the CT on the 5 volt winding. This will short B+ to ground making for a short unhappy life for the rectifier tube and possibly frying some other parts. The CT on the 6.3 volt winding should be connected to it's terminal on the board. The jumper will decide if it gets grounded or not.
I have been to Dayton every year since 2009. It's still called "Dayton" even though it's now in Xenia a few miles southeast of the old Hara Arena site. 2019 saw a claimed 25,000 people show up. I know it was crowded, but they started giving free admission to the general public on Sundays, probably to inflate the attendance numbers. I had paid for swap spaces for 2020 which were held until 2021, which are now supposed to be held for 2022. I went to every south Florida hamfest since the late 60's. That used to be maybe 6 or 7 per year plus Orlando. All of the larger ones are gone except for Orlando and Dayton, both are on indefinite virus hold.
Many hamfests have died for a variety of reasons. Ebay put a dent in the swap meets and some of the forums were just boring, or trying to appeal to too broad of an audience. Miami was struggling when Evelyn got ill and passed, but the real death knell for Miami was the NFL. Hotel rooms in Miami in February are NOT cheap, but when the NFL extended their season to put Super Bowl Sunday in hamfest weekend, and the game just happened to be in Miami that year, nobody could afford the trip, especially when Orlando was one weekend later. Orlando was still booming as was Dayton before Covid. Even with Florida's permissive attitude toward Covid, the organizers did not want to be the purveyors of the virus. Orlando went "virtual" this year, whatever that meant. I might have gone to sell stuff outdoors, I would not have set up inside those super crowded buildings.
The Shelby NC hamfest promises a decision on 2021 sometime this month.
The 182 is the little brother to the 183. The 183 IS a 5 volt 45. I have a pair of 92 year old NX-483's (same as a 183) in my original TSE. I run them at 320 volts and 30 mA and they are still kicking. They drove my 87 dB Yamaha NS-10M's to a decent listening level in my 10 X 10 foot room in Florida. They are nearly useless here in a 2000 square foot basement, so that amp sits on the shelf, lonely and unplugged.
This is probably the same 6V6 > 811A circuit that tubelab built LOL. Everyone has tried some variant on this. I remember it pumping out close to 9W at 5% THD mostly all Second. The 811A is pushing 22mA out its grid at idle. This is pure Class A2 - not "pushing it" class A2.
There is a bug in the schematic. The Filament CT goes to ground, not the to the speaker output. No, running 100mA DC through the parafeed output transformer's secondary is not some "trick". It is a mistake in my schematic. You are welcome to try it if you wish. LOL!
It lived on this breadboard for more the 3 months... Which meant is sounded good enough to keep around! Alas, I already had a beautiful 845 amp in a complete custom chassis, so it was time for the 811A to leave the living room. It would otherwise have been a keeper - and likely got more iterations..
I happened to have a Parafeed TX on hand... But I did try the plain old Hammond 1628SE and it did sound fine - so it's a viable starting point. The Parafeed TX was tried, using the Hammond as a big plate choke, to correct for a HF deficiency known in the 1628SE before it was later corrected.
There is a bug in the schematic. The Filament CT goes to ground, not the to the speaker output. No, running 100mA DC through the parafeed output transformer's secondary is not some "trick". It is a mistake in my schematic. You are welcome to try it if you wish. LOL!
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An externally hosted image should be here but it was not working when we last tested it.
It lived on this breadboard for more the 3 months... Which meant is sounded good enough to keep around! Alas, I already had a beautiful 845 amp in a complete custom chassis, so it was time for the 811A to leave the living room. It would otherwise have been a keeper - and likely got more iterations..
I happened to have a Parafeed TX on hand... But I did try the plain old Hammond 1628SE and it did sound fine - so it's a viable starting point. The Parafeed TX was tried, using the Hammond as a big plate choke, to correct for a HF deficiency known in the 1628SE before it was later corrected.
Ham Radio really should only be DIY as far as I am concerned. It's the whole point of the hobby and should be preserved.
One thing I've learned the hard way. If you buy a commercial ham radio product, you might very well discover that the RF Finals semiconductors are unobtainium when you might need them. And for some products, the finals are fragile enough that you, as a beginner, might blow up a new rig in year 3 or 4 of ownership - only to discover that the 4 legged ceramic biscuit used in the Finals section is no longer available... Extremely disappointing.
This seems to be the case with ALL Semiconductor parts.... If you have something that you love, hoard the replacement critical parts!
One thing I've learned the hard way. If you buy a commercial ham radio product, you might very well discover that the RF Finals semiconductors are unobtainium when you might need them. And for some products, the finals are fragile enough that you, as a beginner, might blow up a new rig in year 3 or 4 of ownership - only to discover that the 4 legged ceramic biscuit used in the Finals section is no longer available... Extremely disappointing.
This seems to be the case with ALL Semiconductor parts.... If you have something that you love, hoard the replacement critical parts!