Hi Dave;
Thanks for the revision - nope 'fraid the pentode takeoff should be after the pi filter. Basically the pi filter and the dropper/decoupler for the triode sections both reside on the PS board and are shared by both valves.
Everything else is spot on, and for anyone who decides to build a 6BM8 using this data, please realise that there's an implicit 19V drop across the OPT's due to their high series resistance. With higher quality iron I'd need to lose that 19V with a droppper resistor. Also, for any first time builders, don't be shy about substituting something for that 110r CC gridstopper - I just used a 110r because I have plenty of 'em. OTOH I'm running short on 100r CC's so I use those sparingly.
Thanks again and all the best,
Morse
Thanks for the revision - nope 'fraid the pentode takeoff should be after the pi filter. Basically the pi filter and the dropper/decoupler for the triode sections both reside on the PS board and are shared by both valves.
Everything else is spot on, and for anyone who decides to build a 6BM8 using this data, please realise that there's an implicit 19V drop across the OPT's due to their high series resistance. With higher quality iron I'd need to lose that 19V with a droppper resistor. Also, for any first time builders, don't be shy about substituting something for that 110r CC gridstopper - I just used a 110r because I have plenty of 'em. OTOH I'm running short on 100r CC's so I use those sparingly.
Thanks again and all the best,
Morse
Just barely adequate.....
It's embarrassing to write this, but I just finished measuring the AC draw at the primary (before I'd been measuring my currents on the secondary legs and adding 'em up) and I'm drawing 45VA with this trafo - still in spec, since the trafo is rated for 50VA (about 25% of that current drawn off the mains ends up as waste heat in the PS trafo - yeesh).
However that's too close for my comfort so I'll go ahead and upgun to a 270DX in a couple of weeks (when cashflow permits); the 269JX'll go on something else - maybe a line amp or that radio I keep meaning to build.
Also, I heartily recommend that anyone building a comparable circuit do the same (I honestly do not like trafos that run hot!!) and go with a more beefy PS trafo with this circuit. There's a little more voltage to drop in the 270DX, so changing the value of the 820r to 1200r is in order - according to my PSUD model this should yield spot on the same voltages and current draws that I've got now.
My bad for posting results before it's passed it's proving run.
Apologies and all the best,
Morse
It's embarrassing to write this, but I just finished measuring the AC draw at the primary (before I'd been measuring my currents on the secondary legs and adding 'em up) and I'm drawing 45VA with this trafo - still in spec, since the trafo is rated for 50VA (about 25% of that current drawn off the mains ends up as waste heat in the PS trafo - yeesh).
However that's too close for my comfort so I'll go ahead and upgun to a 270DX in a couple of weeks (when cashflow permits); the 269JX'll go on something else - maybe a line amp or that radio I keep meaning to build.
Also, I heartily recommend that anyone building a comparable circuit do the same (I honestly do not like trafos that run hot!!) and go with a more beefy PS trafo with this circuit. There's a little more voltage to drop in the 270DX, so changing the value of the 820r to 1200r is in order - according to my PSUD model this should yield spot on the same voltages and current draws that I've got now.
My bad for posting results before it's passed it's proving run.
Apologies and all the best,
Morse
Thanks again Dave;
I was a little worried about a newbie reading this and trying it with even less iron than I used! That revised schematic is spot on, complete with warnings.
You won't be disappointed with the results with this circuit - while my 2A3 has an edge in both overall clarity and bass response to this, I used some premium components in that, including pricey OPT's, Rikens, and a vastly overbuilt PS (the PS trafo stays at a stable 33 degrees C after multiple days of continuous operation!). About the only 'premium' components in this ECL82/6BM8 are a pair of Sprague 716P Orange Drops for coupling.
Anyway, for a small, portable little amp this ECL82/6BM8 is really quite a champ.
FWIW, I was inspired to build mine after seeing one very like it in a Hiroshima department store last December for 29,500 yen (about $250USD if I recall the exchange rate at the time correctly). They had a PS approx the same physical size, and they were also using Ei's.
Hi Rick;
I'm estimating it at a little over 3 watts, based on the literature. That fits with listening experience too - it's not much less powerful than my 2A3. I'm running that one hot for just over 4wrms per channel. This 6BM8 handles my Fostex drivers with almost the authority (not the bass punch though - that's the difference between a $10 cheapie and a $95 Hammond OPT), and it's got the same SET "magic" to it as does my 2A3.
All the best,
Morse
I was a little worried about a newbie reading this and trying it with even less iron than I used! That revised schematic is spot on, complete with warnings.
You won't be disappointed with the results with this circuit - while my 2A3 has an edge in both overall clarity and bass response to this, I used some premium components in that, including pricey OPT's, Rikens, and a vastly overbuilt PS (the PS trafo stays at a stable 33 degrees C after multiple days of continuous operation!). About the only 'premium' components in this ECL82/6BM8 are a pair of Sprague 716P Orange Drops for coupling.
Anyway, for a small, portable little amp this ECL82/6BM8 is really quite a champ.
FWIW, I was inspired to build mine after seeing one very like it in a Hiroshima department store last December for 29,500 yen (about $250USD if I recall the exchange rate at the time correctly). They had a PS approx the same physical size, and they were also using Ei's.
Hi Rick;
I'm estimating it at a little over 3 watts, based on the literature. That fits with listening experience too - it's not much less powerful than my 2A3. I'm running that one hot for just over 4wrms per channel. This 6BM8 handles my Fostex drivers with almost the authority (not the bass punch though - that's the difference between a $10 cheapie and a $95 Hammond OPT), and it's got the same SET "magic" to it as does my 2A3.
All the best,
Morse
Re: POOOFFF...
Frank,
you should have been at the Vintage Anoraks' Fair today at the NEC. I saw things I didn't believe. And I got a few bargains. Mind you, it hurt to turn down a Telequipment transistor curve tracer in excellent condition (£45), and a 6 1/2 digit DVM (volts only) (£50), Nagra IV-S (£250), Elcaset (£110). There were Garrard 301s and 401s galore - some very pretty.
fdegrove said:
Frank,
you should have been at the Vintage Anoraks' Fair today at the NEC. I saw things I didn't believe. And I got a few bargains. Mind you, it hurt to turn down a Telequipment transistor curve tracer in excellent condition (£45), and a 6 1/2 digit DVM (volts only) (£50), Nagra IV-S (£250), Elcaset (£110). There were Garrard 301s and 401s galore - some very pretty.
LES BROCANTES...
Hi,
Hmmm, the Nagra and of course the Garrards would have emptied my wallet...
This kind of fairs are often organised in Brussels as well, although not specifically electronic stuff, you sometimes find Quad ELSs, the odd valve amp and scopes, etc...
I do notice prices have almost doubles over the years though...wish our salaries had too...
Anything you bought?
Cheers,
Hi,
Hmmm, the Nagra and of course the Garrards would have emptied my wallet...
This kind of fairs are often organised in Brussels as well, although not specifically electronic stuff, you sometimes find Quad ELSs, the odd valve amp and scopes, etc...
I do notice prices have almost doubles over the years though...wish our salaries had too...
Anything you bought?
Cheers,
Re: LES BROCANTES...
Books and odds and ends for me, a really clean (inside and out) Rogers Cadet III for a friend, and a bench HT PSU described by the vendor, "You can always use the KT88 in an audio amplifier." It looks like a very useful supply, and will certainly not be scrapped for the KT88.
fdegrove said:
Books and odds and ends for me, a really clean (inside and out) Rogers Cadet III for a friend, and a bench HT PSU described by the vendor, "You can always use the KT88 in an audio amplifier." It looks like a very useful supply, and will certainly not be scrapped for the KT88.
RE:RE:RE:RE:LES BROCANTES...
Hi,
Was afraid of that...one of our members, quite near to you, should still have a trio of those because my bank screwed up the money transfer.
If you need spares, e-mail me for his details, I don't really need them in my application but in the Rogers you don't have much workarounds.
Cheers,
Hi,
Was afraid of that...one of our members, quite near to you, should still have a trio of those because my bank screwed up the money transfer.
If you need spares, e-mail me for his details, I don't really need them in my application but in the Rogers you don't have much workarounds.
Cheers,
Re: BACK TO THE ECL82.
THE ASL Wave 8 is just such an amp.
As i mentioned earlier the iron from the ELL80 amps should work with 6BM8s. So i was planning to try 2 different amps -- 6BM8 PP using the PP iron and a PP amp using 2 SE OPTs in series (there is a thread i started earlier on this subject and since then Decware has released the Torii which does just that -- 2 x SE OPTs/channel -- and it is getting very favorable reviews so it has upped my excitement level.
I was chatting with Bill Perkins the other day and he gave me the clues i needed to finally gel the idea in my head.
To keep things simple, the 1st prototype will be a pr of 50EH5 PP amps. i'll do the phase split at the input with some phase splitting iron from an early Magnavox solid state amp, and probably just wire them in tridode to start (for a blistering 1 W or so).
dave
fdegrove said:
THE ASL Wave 8 is just such an amp.
As i mentioned earlier the iron from the ELL80 amps should work with 6BM8s. So i was planning to try 2 different amps -- 6BM8 PP using the PP iron and a PP amp using 2 SE OPTs in series (there is a thread i started earlier on this subject and since then Decware has released the Torii which does just that -- 2 x SE OPTs/channel -- and it is getting very favorable reviews so it has upped my excitement level.
I was chatting with Bill Perkins the other day and he gave me the clues i needed to finally gel the idea in my head.
To keep things simple, the 1st prototype will be a pr of 50EH5 PP amps. i'll do the phase split at the input with some phase splitting iron from an early Magnavox solid state amp, and probably just wire them in tridode to start (for a blistering 1 W or so).
dave
Re:Re: BACK TO THE ECL82.
Hi,
With my eyes closed, (meaning that I didn't look at the URL posted) wouldn't that make for a PP OPT with an airgap?
I vaguely recall you presented a similar circuit using this back in August last year though.
It could work fine...what I had in mind was a PP amp where one triode was doing the voltage amplification and the other the phase splitting....9/10 just what the Tori circuit is about anyway?
Cheers,
Hi,
With my eyes closed, (meaning that I didn't look at the URL posted) wouldn't that make for a PP OPT with an airgap?
I vaguely recall you presented a similar circuit using this back in August last year though.
It could work fine...what I had in mind was a PP amp where one triode was doing the voltage amplification and the other the phase splitting....9/10 just what the Tori circuit is about anyway?
Cheers,
Hi Dave;
I just realised that there's one other omission on that schemo you posted - that's the 270kr bleeder. I put it across the 22uF decoupling cap for the triode stage.
Many thanks again and my apologies - I wish I could have just posted a copy of my original schematics, but I can't afford a scanner.
One other late development in all this is that the highest temp that the 269JX goes to (and remains stable at after about 8 hours of operation) is 60C. The 269JX has insulation that's supposed to be good to 105C, so while it's marginal, I think it's on the good side of the margin - so long as the chassis design doesn't impede cooling in any way and so long as there are no extra current demands made of it.
All the best,
Morse
I just realised that there's one other omission on that schemo you posted - that's the 270kr bleeder. I put it across the 22uF decoupling cap for the triode stage.
Many thanks again and my apologies - I wish I could have just posted a copy of my original schematics, but I can't afford a scanner.
One other late development in all this is that the highest temp that the 269JX goes to (and remains stable at after about 8 hours of operation) is 60C. The 269JX has insulation that's supposed to be good to 105C, so while it's marginal, I think it's on the good side of the margin - so long as the chassis design doesn't impede cooling in any way and so long as there are no extra current demands made of it.
All the best,
Morse
Hi everyone;
Here's an update on the 6BM8. As of now I've got the 270DX on there and have dropped the B+ back to the levels I had with the 269JX via a 1k5r 25 w resistor in the PS in place of the original 820r 25w (which later went to 1k2r 25w on the original 270DX installation). Only practical problem with this approach is heat management - that CRC dissipates just over 10 watts as heat; on the plus side, the ripple in the raw B+ is now reduced even further (not that there was an audible diff at the output - this amp is QUIET).
What's the difference because of iron and OP's? Well, I think that the 270DX/original (i.e. 269JX) operating point combo sounds better (switching back and forth yesterday) than the higher B+ operating point I've played with. The heftier iron gives better dynamics, which I liked with the original swapout (and diff OP) but the original OP sounds sweeter overall. You put the two together and you get better dynamics and a more musical sound. Also the plate dissipation is brought down a little to just a hair over 7watts (I know, I know 7 watts is the published limit, but the 7.6 watts on the 270DX, high B+ combo didn't make 'em glow red or anything).
Anyway, for anyone who is starting to design/build their own, my advice is to overbuild that PS. I did that on my first amps when cash wasn't so tight, and now that I've tried experimenting with marginal PS's I can tell you that there IS a difference. PS's with some extra current capacity just plain SOUND better (and run cooler, etc). The extra $10 or $20 to get a PS trafo with more current capacity is well spent IMHO.
Sorry about the delay in posting pics. Hopefully I'll have 'em some time this millenium....
All the best,
Morse
Here's an update on the 6BM8. As of now I've got the 270DX on there and have dropped the B+ back to the levels I had with the 269JX via a 1k5r 25 w resistor in the PS in place of the original 820r 25w (which later went to 1k2r 25w on the original 270DX installation). Only practical problem with this approach is heat management - that CRC dissipates just over 10 watts as heat; on the plus side, the ripple in the raw B+ is now reduced even further (not that there was an audible diff at the output - this amp is QUIET).
What's the difference because of iron and OP's? Well, I think that the 270DX/original (i.e. 269JX) operating point combo sounds better (switching back and forth yesterday) than the higher B+ operating point I've played with. The heftier iron gives better dynamics, which I liked with the original swapout (and diff OP) but the original OP sounds sweeter overall. You put the two together and you get better dynamics and a more musical sound. Also the plate dissipation is brought down a little to just a hair over 7watts (I know, I know 7 watts is the published limit, but the 7.6 watts on the 270DX, high B+ combo didn't make 'em glow red or anything).
Anyway, for anyone who is starting to design/build their own, my advice is to overbuild that PS. I did that on my first amps when cash wasn't so tight, and now that I've tried experimenting with marginal PS's I can tell you that there IS a difference. PS's with some extra current capacity just plain SOUND better (and run cooler, etc). The extra $10 or $20 to get a PS trafo with more current capacity is well spent IMHO.
Sorry about the delay in posting pics. Hopefully I'll have 'em some time this millenium....
All the best,
Morse
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