kenpeter said:
I've no experience in that regard (and in many others, but I did build an 801 LF and am very pleased with it). Seems like it couldn't hurt. But just as an academic question; would it make much difference? I don't see much of a load to push if we stay out of A2, though I haven't seen grid current curves for the 2A3. Certainly easy to try.
Sheldon
kmaier - sorry I didn't speak up earlier, I would love to see your design if you don't mind. I am always looking for ideas and am still a very young learner.
Thanks Sheldon for the input with the direct coupling. I was also looking over the schematic I have for the Morrison Micro Direct Coupled 2A3, very simple design!
I am interested though, just throwing this out there, would a 27 work? I know it is much lower gain, and even with a CCS or choke load it would drastically change the input sensitivity. Just something I was kicking around, though I want to try to stay with a two tube design. I am thinking it is doable with a interstage but I am trying to avoid that. Not because I don't like them (Quite the opposite actually), but because of cost... a CCS is about $5 to at most about $35 worth of parts.
Direct coupling isn't really all the huge of an issue to me really. I know it gets rid of a cap in the signal path, which I know is a good thing. That is kind of my reasoning too with the CCS, beside better linearity and lower distortion of the driver, getting rid of the Ck hopefully. For now though I am just looking to get something up and working, I can tweak on it later, that is the name of the game in DIY!
Cheers
James
Thanks Sheldon for the input with the direct coupling. I was also looking over the schematic I have for the Morrison Micro Direct Coupled 2A3, very simple design!
I am interested though, just throwing this out there, would a 27 work? I know it is much lower gain, and even with a CCS or choke load it would drastically change the input sensitivity. Just something I was kicking around, though I want to try to stay with a two tube design. I am thinking it is doable with a interstage but I am trying to avoid that. Not because I don't like them (Quite the opposite actually), but because of cost... a CCS is about $5 to at most about $35 worth of parts.
Direct coupling isn't really all the huge of an issue to me really. I know it gets rid of a cap in the signal path, which I know is a good thing. That is kind of my reasoning too with the CCS, beside better linearity and lower distortion of the driver, getting rid of the Ck hopefully. For now though I am just looking to get something up and working, I can tweak on it later, that is the name of the game in DIY!
Cheers
James
JPeitzman said:
Certainly.
As regards the 27; you will need another voltage gain stage. Let's assume you need a minimum of 50Vp swing. The 27 has a maximum gain of 9 (assuming plate load - CCS). To swing 50v peak, means you need an input of 5.6v peak, or 4v RMS. If you are using a preamp with at least 6dB of gain, and your source is 2VRMS output, then you can do it.
A 1:2 interstage step up can also give you 6dB of gain but your current drive is halved - which is tight but maybe still OK. I would think that the problem is going to be finding an interstage which will give good bandwidth driven by the relatively high plate impedance of the 27.
By the way. The Loftin White approach is more than just direct coupling, it also provides for excellent psrr. More to it than meets the eye.
Sheldon
JPeitzman said:
Hi James,
No problem... I can email you a complete set of PDFs and a BOM list for the 45 and 2A3 versions... mono and stereo versions. My email address is "kemaier2 at bellsouth dot net". Same goes for anyone else... the design was done initially for my son but I opted to make it available for the DIYers. It's a very simple design and works extremely well provided you use the proper parts and a clean layout.
As for CCSes... I did a lot of work with these over 20 years ago. They have some advantages, but the only place I really kept one as a permanent design point was for a long-tail pair phase inverter for a P-P design I did back in the 80's.
Good luck in selecting a design for your 2A3 amplifier. It's a great DHT and you can get good NOS tubes still at reasonable prices... sames goes for the 45.
Regards, KM
Helping to stop paralysis by analysis
Heya James! I want to help you get unstuck before you get really stuck. You're semester is about to start, and in a few weeks, you'll be
REALLY busy and will have to turn back into a spectator of other peoples projects rather than a participant in your own. You're also flush with some summer cash, and that will be spent on other things.
It's really easy to get caught up in a year of planning and never get to listen and live with something.
I'm a HUGE fan of iterative development. That means abandon all
plans of a beautiful chassis with premium parts until maybe next summer. For now, its more important to screw things into pre-cut
chunks of plywood from Lowes, wireup and listen.
Let's start with an inventory of parts you have on and to work
with. Do you have a PSU transformer and output transformers ?
If not, we need to end the paralysis by analysis over those.
You're looking at $160 for $180 for a pair of SE output transformers
of reasonable quality. A B+ transformer will be another $60-$70.
$250 for iron will get you in the game to have an amp that you can
enjoy THIS FALL AND WINTER with your friends at school.
The next step is being realistic with the rest of your money... You
know that 300B's are going to add another $250 or so to this budget, not just for the tubes, but the filament transformers and humpots you'll need. 2A3's might be $160, because you still have to buy the filament supply parts for those too.
Let me make a wise suggestion... To keep the hit on your bank account light and get you an AWESOME amp that you'll be able to steal time away to actually built THIS semester, let's go with something far more attainable and cheap: KT88 single ended triode mode with a 6SN7 driver. You can literally wire it up in a weekend and it will be bulletproof. With a RadioShack 100K volume pot, you can directly drive the amp off a CD player or computer D/A.
This is why I like attainable, iterative projects... It's very easy for
you to spend hard earned cash on transformers, and/or 300Bs,
and run out of both time and money to complete a project... You'll
end up feeling unfulfilled and the regret having spent money on
parts that arent being put to use.
-- Jim
Heya James! I want to help you get unstuck before you get really stuck. You're semester is about to start, and in a few weeks, you'll be
REALLY busy and will have to turn back into a spectator of other peoples projects rather than a participant in your own. You're also flush with some summer cash, and that will be spent on other things.
It's really easy to get caught up in a year of planning and never get to listen and live with something.
I'm a HUGE fan of iterative development. That means abandon all
plans of a beautiful chassis with premium parts until maybe next summer. For now, its more important to screw things into pre-cut
chunks of plywood from Lowes, wireup and listen.
Let's start with an inventory of parts you have on and to work
with. Do you have a PSU transformer and output transformers ?
If not, we need to end the paralysis by analysis over those.
You're looking at $160 for $180 for a pair of SE output transformers
of reasonable quality. A B+ transformer will be another $60-$70.
$250 for iron will get you in the game to have an amp that you can
enjoy THIS FALL AND WINTER with your friends at school.
The next step is being realistic with the rest of your money... You
know that 300B's are going to add another $250 or so to this budget, not just for the tubes, but the filament transformers and humpots you'll need. 2A3's might be $160, because you still have to buy the filament supply parts for those too.
Let me make a wise suggestion... To keep the hit on your bank account light and get you an AWESOME amp that you'll be able to steal time away to actually built THIS semester, let's go with something far more attainable and cheap: KT88 single ended triode mode with a 6SN7 driver. You can literally wire it up in a weekend and it will be bulletproof. With a RadioShack 100K volume pot, you can directly drive the amp off a CD player or computer D/A.
This is why I like attainable, iterative projects... It's very easy for
you to spend hard earned cash on transformers, and/or 300Bs,
and run out of both time and money to complete a project... You'll
end up feeling unfulfilled and the regret having spent money on
parts that arent being put to use.
-- Jim
I have a few questions. I have pretty much decided most of the details I think. Feel free though if you see something really stupid or you feel I am going about this all wrong to speak up. I can take the criticism / design ideas / input, even if it is saying that I am "touched" and going about this all wrong 😀 .
I think for now I am going to stick with the 12AT7 as the input. This is mostly because I have a couple sitting on my desk right now, NOS GE. I do however have plenty 6SL7's which I had also considered. I had given some thought to the 6SN7, but it seems that would really change my input sensitivity. For the same reason my beautiful globe 27 mesh plates are out. They would just add complication and expense. After doing some reading and some data sheet looking I have selected 4mA - 5mA @ 180v aprox for the 12AT7, expert opinions? I want to directly couple the 12AT to the 2A3, does this point seem acceptable or do I need to fiddle a little more. This is with a CCS on the anode and by my calculations a aprox 500R resistor on the cathode. Would it be advisable to try a LED here? I hear good and bad with LED's, it seems valve dependent. Again directly coupled on to the 2A3...
The 2A3 is being run at it's "classic" bias point: 250v across the tube, 60mA across the tube, -45v grids so aprox 295v at the plate. This would be with a 750R cathode resistor and a load from 2500R to 3000R. Instead of using a traditional Ck on the 2A3 I would like to implement Ultra-Path. However I do not know how to calculate the value of the Ultra-Path cap. I am searching but if anyone has any information I would accept, otherwise the search will go on, I know it is out there. For now though for ease I will probably go with the simple Ck bypass cap.
My power supply is giving me some hang ups. I am planning on using Hammond iron. Pausing here I wanted to ask if anyone has used Electra-Print's custom power iron? I am interested to see how it is priced compared to the Hammond. I may get a quote from Jack I just wanted to try here first since he is a busy man. It seems I am looking for a B+ anywhere from 300v to 315v or so. I can get this with anywhere from 550vct to 600vct or so. I am looking at the Hammond 372BX... 600vct @ 0.1A. I am worried though for a couple reasons: 1. In the future I would like to try a CCS driven shunt regulator for the front end. 2. I may in the future want to try other drivers, one of which may be the 417A or 6C45. Both of these would put even more load on the PTX pushing it closer to that 0.1A mark. Also if I did decide to use the 417A and the shunt I think it would be to much for the PTX. It seems my options would be to step down to the 370FX, losing some voltage but gaining current; or to move to the 372FX gaining current but at almost $30 more for 50mA more. I could go to the 272DX, both saving money and gaining more current capability. I have read though about the 200 series humming and running very hot, not good in my book. My only other options seem to be: 1. Custom Electra-Print Iron...$$$? 2. Edcor XPWR107... lose the 5v filament tap and I am not sure about the quality of their power iron 3. Magnequest PGP 8.1... even less current but cheaper (availability?) 4. Magnequest R-481-A... Perfect although more expensive and also worried about the availability. Also the R-481-A has a higher voltage at 700vct, not a huge issue but one none the less.
It seems though that after the cost of the filament transformers for the 2A3's and the cost of the choke is considered that all Hammond iron would be almost the same cost as all Magnequest (R-481-A and BCM-19 Choke). It seems however that this will take a little bit of playing in PSUD II to get the B+ just right. I could however go with Magnequest PTX iron and Hammond chokes, there is more of a selection and the reduced cost would allow me to maybe go with a C-L-C-L-C filter. Way to many options as you can tell.
For the output iron I have a few different options:
1. Hammond 1627SEA - $105 each
2. Edcor CXSE25-8-2.5K - $83.50 each
3. Electra-Print 2.5k or 3k @ 65mA - $105 each
4. Magnequest TFA-204 - $125 each
The only thing I am worried about on the last two, the Magnequest especially, is core saturation. They are running close to or at their listed max current. I would love to go Parafeed but I am afraid that would add quite a bit more to the cost, at least $75 more but closer to $125 per amp. Also I am planning on using the 5U4G as the rectifier. I have quite a few NOS RCA's and I love the ST glass to go with the 2A3. However I am not just building for looks, a better option? For this build I would like to stay away from dampener diodes, I am probably going to use them on my 300B when the time comes, and for sure on my slated P/P amplifier years down the road. I have nothing again SS if you guys think it is a better choice, I may try both and see if I can hear any difference. My guess with Ultra-Path coupling at the output and a CCS + eventual shunt on the input I won't hear a difference. The 5U4 will just look cooler, make the PTX run hotter, and wear out faster 🙄 .
That is a lot but that is also all I can think of for now. Sorry I kind of saved up everything, school has kept me busy. However I really have to get to bed now, it is way past my bed time for a school night. Thank you all very much for all you input, and again suggests welcome!
Cheers
James
I think for now I am going to stick with the 12AT7 as the input. This is mostly because I have a couple sitting on my desk right now, NOS GE. I do however have plenty 6SL7's which I had also considered. I had given some thought to the 6SN7, but it seems that would really change my input sensitivity. For the same reason my beautiful globe 27 mesh plates are out. They would just add complication and expense. After doing some reading and some data sheet looking I have selected 4mA - 5mA @ 180v aprox for the 12AT7, expert opinions? I want to directly couple the 12AT to the 2A3, does this point seem acceptable or do I need to fiddle a little more. This is with a CCS on the anode and by my calculations a aprox 500R resistor on the cathode. Would it be advisable to try a LED here? I hear good and bad with LED's, it seems valve dependent. Again directly coupled on to the 2A3...
The 2A3 is being run at it's "classic" bias point: 250v across the tube, 60mA across the tube, -45v grids so aprox 295v at the plate. This would be with a 750R cathode resistor and a load from 2500R to 3000R. Instead of using a traditional Ck on the 2A3 I would like to implement Ultra-Path. However I do not know how to calculate the value of the Ultra-Path cap. I am searching but if anyone has any information I would accept, otherwise the search will go on, I know it is out there. For now though for ease I will probably go with the simple Ck bypass cap.
My power supply is giving me some hang ups. I am planning on using Hammond iron. Pausing here I wanted to ask if anyone has used Electra-Print's custom power iron? I am interested to see how it is priced compared to the Hammond. I may get a quote from Jack I just wanted to try here first since he is a busy man. It seems I am looking for a B+ anywhere from 300v to 315v or so. I can get this with anywhere from 550vct to 600vct or so. I am looking at the Hammond 372BX... 600vct @ 0.1A. I am worried though for a couple reasons: 1. In the future I would like to try a CCS driven shunt regulator for the front end. 2. I may in the future want to try other drivers, one of which may be the 417A or 6C45. Both of these would put even more load on the PTX pushing it closer to that 0.1A mark. Also if I did decide to use the 417A and the shunt I think it would be to much for the PTX. It seems my options would be to step down to the 370FX, losing some voltage but gaining current; or to move to the 372FX gaining current but at almost $30 more for 50mA more. I could go to the 272DX, both saving money and gaining more current capability. I have read though about the 200 series humming and running very hot, not good in my book. My only other options seem to be: 1. Custom Electra-Print Iron...$$$? 2. Edcor XPWR107... lose the 5v filament tap and I am not sure about the quality of their power iron 3. Magnequest PGP 8.1... even less current but cheaper (availability?) 4. Magnequest R-481-A... Perfect although more expensive and also worried about the availability. Also the R-481-A has a higher voltage at 700vct, not a huge issue but one none the less.
It seems though that after the cost of the filament transformers for the 2A3's and the cost of the choke is considered that all Hammond iron would be almost the same cost as all Magnequest (R-481-A and BCM-19 Choke). It seems however that this will take a little bit of playing in PSUD II to get the B+ just right. I could however go with Magnequest PTX iron and Hammond chokes, there is more of a selection and the reduced cost would allow me to maybe go with a C-L-C-L-C filter. Way to many options as you can tell.
For the output iron I have a few different options:
1. Hammond 1627SEA - $105 each
2. Edcor CXSE25-8-2.5K - $83.50 each
3. Electra-Print 2.5k or 3k @ 65mA - $105 each
4. Magnequest TFA-204 - $125 each
The only thing I am worried about on the last two, the Magnequest especially, is core saturation. They are running close to or at their listed max current. I would love to go Parafeed but I am afraid that would add quite a bit more to the cost, at least $75 more but closer to $125 per amp. Also I am planning on using the 5U4G as the rectifier. I have quite a few NOS RCA's and I love the ST glass to go with the 2A3. However I am not just building for looks, a better option? For this build I would like to stay away from dampener diodes, I am probably going to use them on my 300B when the time comes, and for sure on my slated P/P amplifier years down the road. I have nothing again SS if you guys think it is a better choice, I may try both and see if I can hear any difference. My guess with Ultra-Path coupling at the output and a CCS + eventual shunt on the input I won't hear a difference. The 5U4 will just look cooler, make the PTX run hotter, and wear out faster 🙄 .
That is a lot but that is also all I can think of for now. Sorry I kind of saved up everything, school has kept me busy. However I really have to get to bed now, it is way past my bed time for a school night. Thank you all very much for all you input, and again suggests welcome!
Cheers
James
Sorry to double post but I just realized something that may change the output iron decision. Is the 60mA listed on the TFA-204 what it is actually OPTIMIZED for! Because if this is the case this my be my iron of choice. Not that much more than the Hammond but with arguably better sonic's.
Cheers / OK bed time for real now 😀
James
Cheers / OK bed time for real now 😀
James
Any of those OPTs will work splendidly. They are priced as such
because they are a "standard" part for 2A3/300B folks running at
60mA. If you go with the MQ TFA204 - check with Mike about his
thoughts for a future operating point at 80mA for the 300B run hot
and wild.
Re: Custom Iron. Economics would tell me that the winder needs to
pay for his job setup/teardown time to wind, varnish and inspect a special order core. The premium you pay for a customer power TX
is to eliminate a bunch of smaller TX's. Consider this:
Any 2.5, 5 or 6.3VCT off-the-shelf single winding
TX is going to be $20 out of pocket (including shipping). Will jack
charge you $20 for a single 2.5V 4A winding? Probably not. Economics wins.
I'd avoid direct coupling... It's a bitch to get the resistor values
just right. It's also exceptionally easy to blow up a 2A3 or 300B
when trying to direct couple it ; all it takes is a miswire mistake and POOF. Done.
Re: Drivers. There are *SO* many options for you to explore with
an SE 2A3 that I'd not worry... Get a bunch of extra 9-pin sockets.
I'd recommend you try A NUMBER of different driver tubes and
topologies: GE 6201/12AT7, 5842, 6N1P with LC coupling even.
There there's the whole Loftin-White affair and SRPP 6SL7.
-- Jim
because they are a "standard" part for 2A3/300B folks running at
60mA. If you go with the MQ TFA204 - check with Mike about his
thoughts for a future operating point at 80mA for the 300B run hot
and wild.
Re: Custom Iron. Economics would tell me that the winder needs to
pay for his job setup/teardown time to wind, varnish and inspect a special order core. The premium you pay for a customer power TX
is to eliminate a bunch of smaller TX's. Consider this:
Any 2.5, 5 or 6.3VCT off-the-shelf single winding
TX is going to be $20 out of pocket (including shipping). Will jack
charge you $20 for a single 2.5V 4A winding? Probably not. Economics wins.
I'd avoid direct coupling... It's a bitch to get the resistor values
just right. It's also exceptionally easy to blow up a 2A3 or 300B
when trying to direct couple it ; all it takes is a miswire mistake and POOF. Done.
Re: Drivers. There are *SO* many options for you to explore with
an SE 2A3 that I'd not worry... Get a bunch of extra 9-pin sockets.
I'd recommend you try A NUMBER of different driver tubes and
topologies: GE 6201/12AT7, 5842, 6N1P with LC coupling even.
There there's the whole Loftin-White affair and SRPP 6SL7.
-- Jim
Would suggest you consider the Hammond 302AX power transformer. It has a pair 2.5VAC-CT filament windings and is specifically designed for powering a 2A3 amplifier. It also has center-tapped 5V and 6.3V windings and a universal primary, all for $100.
Regards, KM
Regards, KM
Hi there,
If it's not too late you can take in to consideration slightly different project with C3g tube. This is really cheap pentode made exclusively for German post by Siemens. I'm running this amp and I have to admit that this is the best sounding single tube driver for 2A3.
I was trying ECC81, ECC40, 7AF7 and so far the winner is C3g.
PS. This is not my design. I got this schematic from another man.
Regards,
Artur
If it's not too late you can take in to consideration slightly different project with C3g tube. This is really cheap pentode made exclusively for German post by Siemens. I'm running this amp and I have to admit that this is the best sounding single tube driver for 2A3.
I was trying ECC81, ECC40, 7AF7 and so far the winner is C3g.
PS. This is not my design. I got this schematic from another man.
Regards,
Artur
Attachments
Well I'm into this thread a bit late but as you were originally on about 12AT7s and 2A3's it wouldn't do not to mention the 'Baby Ongaku'
Though I've never heard it, one industry guy I know puts it in his top three. Art Dudley in a 2004 Stereophile article put it at number six in his top ten. I assume from this that even with differences in taste everybody would still think it a good amp. Its designer, Gordon Rankin, has got a good name. Worth looking at imho.
Though I've never heard it, one industry guy I know puts it in his top three. Art Dudley in a 2004 Stereophile article put it at number six in his top ten. I assume from this that even with differences in taste everybody would still think it a good amp. Its designer, Gordon Rankin, has got a good name. Worth looking at imho.
Why not DC-couple? With 310vB+ or thereabouts for the 2A3 you can easily DC-couple an EC91 in a very simple and effective circuit. This follows the Loftin-White design, and works well. Amp input sensitivity is a little low - about 1 to 1.2 volts input for a 3.5watt output (depending on the 2A3 and the EC91) but if you have a decent preamp this is no problem at all.
EC91 are relatively cheap (B7G base), NOS only as far as I know, and as long as your 2A3s are stable (don't use early-production Chinese), then it should run and run.
DC or AC filaments on the 2A3 make little difference in output noise - in mine they're AC and the amp is silent into AvantGarde horns (Duos). Component count is low, and amp noise more dependent on power supply quality than boutique components.
Hope this helps.
EC91 are relatively cheap (B7G base), NOS only as far as I know, and as long as your 2A3s are stable (don't use early-production Chinese), then it should run and run.
DC or AC filaments on the 2A3 make little difference in output noise - in mine they're AC and the amp is silent into AvantGarde horns (Duos). Component count is low, and amp noise more dependent on power supply quality than boutique components.
Hope this helps.
essentialy is 3.12K(hand made) to 3.5K(factory) for output transformer
of 22Hy Lp minimum...
*
little bit higher Va of 272V
and 5mA les current...
as I am remember...
*
Maybe the best solution is
loftin-white topology...
but deserves a higher Vb, solid capacitors of higher voltage,
and few powerful resistors...
*
but for the start the simplyest topologu is maybe solution
6J5 + 2A3
(needs a preamp...)
of 22Hy Lp minimum...
*
little bit higher Va of 272V
and 5mA les current...
as I am remember...
*
Maybe the best solution is
loftin-white topology...
but deserves a higher Vb, solid capacitors of higher voltage,
and few powerful resistors...
*
but for the start the simplyest topologu is maybe solution
6J5 + 2A3
(needs a preamp...)
I decided to take the advice of Hearinspace and check out the Baby Ongaku. I have read the article and read a little bit about it using the magic of Google as well. I have heard quite a bit of bickering about the SRPP, I guess though I might as well cut through all the bickering and just build one and listen...form my own opinions. I have decided I think I will give this design a shot, though going against the article I have begun to dig through my junk piles.
I have two GE 12AT7's picked out of the ... two I own 😀 🙁 . The both test perfectly new (past 100 on my Heathkit TC-1), I have yet to plug them into my Hickok, I would guess the same result. BTW, OT, I spent the last weekend restoring the TC-1, it is beautiful now. It still needs a couple of the sockets that are never used cleaned and the scroll in the center needs some attending too...ie, re-rolled, it is starting to get bad. Other than that I waxed it, oiled the wood box, touched up some chips, new cords, and a few things attended to on the underside. It now works good as new and looks like it just rolled out of the factory 😎 .
I will go about ordering here soon, at least passives and output iron. I have a bench supply I can use for now to test it as I bread board. My next real full weekend off will be sept. 19-21, hopefully I can get some work done then, in between work that is. Next weekend my girlfriend is coming for a visit so that weekend is spoken for.
Cheers
James
I have two GE 12AT7's picked out of the ... two I own 😀 🙁 . The both test perfectly new (past 100 on my Heathkit TC-1), I have yet to plug them into my Hickok, I would guess the same result. BTW, OT, I spent the last weekend restoring the TC-1, it is beautiful now. It still needs a couple of the sockets that are never used cleaned and the scroll in the center needs some attending too...ie, re-rolled, it is starting to get bad. Other than that I waxed it, oiled the wood box, touched up some chips, new cords, and a few things attended to on the underside. It now works good as new and looks like it just rolled out of the factory 😎 .
I will go about ordering here soon, at least passives and output iron. I have a bench supply I can use for now to test it as I bread board. My next real full weekend off will be sept. 19-21, hopefully I can get some work done then, in between work that is. Next weekend my girlfriend is coming for a visit so that weekend is spoken for.
Cheers
James
12AT7 (ecc81)
is somehow without the character in sound ?..
You can try better noval 12AY7
with simmilar mu and biasing...
*
but I think that octals 6SN7, 6J5
or if You want more sensitive input 6SL7
are much better
even pentode in triode mode ef86...
*
tip
if You apply two holes for octal and noval tubes for the input,
You will have chance to try muc more tubes?
is somehow without the character in sound ?..
You can try better noval 12AY7
with simmilar mu and biasing...
*
but I think that octals 6SN7, 6J5
or if You want more sensitive input 6SL7
are much better
even pentode in triode mode ef86...
*
tip
if You apply two holes for octal and noval tubes for the input,
You will have chance to try muc more tubes?
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