Gotham Audio Corp made one to use as a record cutting amp that is a little tricky to build but sounds very nice. Use a 4-5k output transformer. Here's a link to the schematic:
http://www.triodeel.com/gothamp.gif
I have one that I built and I love it; I just never got arount to building a mate to it for stereo.
Daniel
http://www.triodeel.com/gothamp.gif
I have one that I built and I love it; I just never got arount to building a mate to it for stereo.
Daniel
Hi Ricardo,
What you will supply with the 811A?
Can you put in here more informations?
You will supply subwoofers or a full-range speakers?
Thanks,
Felipe.
What you will supply with the 811A?
Can you put in here more informations?
You will supply subwoofers or a full-range speakers?
Thanks,
Felipe.
Class A2 or Class AB2 ??
You can always implement the Altec 1570 topology. MagneQuest
could supply you with the magical centre-tapped choke that
is the essence of the driver stage for PP 811A.
The 1570 will be expensive to implement. It will also deliver a
full 150W and run out at 900V at several hundred mA of current.
You could attempt to implement at lower and saner voltages.
You'd definitely be breaking new ground by doing a PP 811A.
I dont know of anyone whose ever attempted it. The closest I've
seen is a PP SV572-10 that was featured in Glass Audio years back.
811A's are cheap and easy to come by.... You could also use
572Bs. Ask yourself if you really need all this power? A 20W
single ended 845 amp might not only be sufficient, but pleasantly
satisfying. 🙂
-- Jim
You can always implement the Altec 1570 topology. MagneQuest
could supply you with the magical centre-tapped choke that
is the essence of the driver stage for PP 811A.
The 1570 will be expensive to implement. It will also deliver a
full 150W and run out at 900V at several hundred mA of current.
You could attempt to implement at lower and saner voltages.
You'd definitely be breaking new ground by doing a PP 811A.
I dont know of anyone whose ever attempted it. The closest I've
seen is a PP SV572-10 that was featured in Glass Audio years back.
811A's are cheap and easy to come by.... You could also use
572Bs. Ask yourself if you really need all this power? A 20W
single ended 845 amp might not only be sufficient, but pleasantly
satisfying. 🙂
-- Jim
I've done two 811A p-p amps. The first, maybe 25 years ago, was a fairly conventional transformer-coupled p-p. I wasn't happy, mostly because the tubes really wanted to see a higher plate load, and high power 10-15k transformers are not easily available, nor would I expect them to have good bandwidth.
The second, a recent project, was a class B p-p direct drive ESL circuit using a center-tapped choke. That worked very well, but the plate voltage limitations did not allow anything above background music levels.
Class B zero-bias with a nice high current drive seems to be the key.
The second, a recent project, was a class B p-p direct drive ESL circuit using a center-tapped choke. That worked very well, but the plate voltage limitations did not allow anything above background music levels.
Class B zero-bias with a nice high current drive seems to be the key.
I owned several Altec's in the past and was not happy with the bass response. I'm wondering if the driver stage had something to do with it. I also had a 807 PP Bogan with a similar driver stage and lack of bass.
I sure do like the look of the 811's.
I sure do like the look of the 811's.
Thanks a lot folks...
I can see we have some hidden experts in these exoteric 811A matters here!
Well I was wondering about an input signal tube e.g. 12AT7 feeding something like a pair of EL84 or even a pair of EL34 doing the phase splitter to a pair of PP 811A...
I think this is perfectly possible to implement and just imagine a pair of these relatively cheap triodes yelding around 100 to 150w...
What do you think about this approach?
Any ideas about the circuitry?
Power is just like money: it's never enough!
[ ]s
Ricardo
I can see we have some hidden experts in these exoteric 811A matters here!
Well I was wondering about an input signal tube e.g. 12AT7 feeding something like a pair of EL84 or even a pair of EL34 doing the phase splitter to a pair of PP 811A...
I think this is perfectly possible to implement and just imagine a pair of these relatively cheap triodes yelding around 100 to 150w...
What do you think about this approach?
Any ideas about the circuitry?
Power is just like money: it's never enough!
[ ]s
Ricardo
As far as bass response.... I did a Parafeed, single-ended 811A.
I have fantastic bass. In fact, better than my 845 amp. The
PF transformer is rated at 10W and has a nickel core.
I think you run into trouble dealing with high-Z output transformers combined with the high levels of standing current. Further, conditions at the driver (which needs to cope with grid current), might further compound the problem already presented by the DC current in the output transformer...
I have fantastic bass. In fact, better than my 845 amp. The
PF transformer is rated at 10W and has a nickel core.
I think you run into trouble dealing with high-Z output transformers combined with the high levels of standing current. Further, conditions at the driver (which needs to cope with grid current), might further compound the problem already presented by the DC current in the output transformer...
Yeah 811's in ...massively parallel...
Million watt amp!!
sooooo Kewwwwllll!!!!
Ok; check out tubelab.com's site here
for his totally cool 811A project(yew are 'da man, tubelab)
Please, please, please do not miss his safety info; also on our
site here under tubes.
also check out antique radio classified links here 😀
there are some very nice, helpful guys out there-join the club,
get acquainted, take your time, learn some good stuff!
Now, about that massively parallel design
!
Million watt amp!!
sooooo Kewwwwllll!!!!Ok; check out tubelab.com's site here
for his totally cool 811A project(yew are 'da man, tubelab)
Please, please, please do not miss his safety info; also on our
site here under tubes.
also check out antique radio classified links here 😀
there are some very nice, helpful guys out there-join the club,
get acquainted, take your time, learn some good stuff!
Now, about that massively parallel design
!
Seem to recall an extensive thread a month or so back on 811 amps... worth a search
The 1570 needs a few mods to sound reasonable... the short version is this: the output iron is anemic (it was a PA amp), the driver choke sux.
All you need to drive a set of 811s is something like a 6W4 in triode. Or a similar power rated tube (45?). Not more. EL34s as drivers is wasting expensive tubes for no gain.
For the 1570 style driver chokes, take an inexpensive 10watt class output transformer and use the primary. It will give you better results than the silly choke they made (they short out anyhow - major source of failure in the 1570).
Otherwise you'll need a driver transformer to driver those grids, or another means of DC coupling the driver to the grids. You'll need to run in B2 or AB2 (depenging your view on the static bias point on the 811).
Plan on 900v-100vdc on the plates...
Look ma! Zero bias!
I think the plate tranny needs to be ~10k primary... BUT making high power transformers that run on higher B+ AND go high in frequency and have sufficient L to go low = expensive iron, in general.
Otoh, I liked my 1570s a lot lot on my Acoustats after they were modded a little bit.
The 811 is a nice high power tube that will take significant abuse, has a long life, relatively low cost, isn't too huge and sounds ok, fine...
_-_-bear
PS. the driver stage's LF rolloff depends entirely upon the L of the choke and Z related to that circuit. In general, it has better response than a coupling xfrmr, and costs a fraction of the $$. Big L, low power chokes are cheap, so you could get down to <10hz easy.
PPS. at least in the Altec 1570 the limiting LF factor is the output iron which is clearly not rated for the full 175 watts at LF, given that the core size is less than some "60 watt" nominal transformers that I have seen...
The 1570 needs a few mods to sound reasonable... the short version is this: the output iron is anemic (it was a PA amp), the driver choke sux.
All you need to drive a set of 811s is something like a 6W4 in triode. Or a similar power rated tube (45?). Not more. EL34s as drivers is wasting expensive tubes for no gain.
For the 1570 style driver chokes, take an inexpensive 10watt class output transformer and use the primary. It will give you better results than the silly choke they made (they short out anyhow - major source of failure in the 1570).
Otherwise you'll need a driver transformer to driver those grids, or another means of DC coupling the driver to the grids. You'll need to run in B2 or AB2 (depenging your view on the static bias point on the 811).
Plan on 900v-100vdc on the plates...
Look ma! Zero bias!
I think the plate tranny needs to be ~10k primary... BUT making high power transformers that run on higher B+ AND go high in frequency and have sufficient L to go low = expensive iron, in general.
Otoh, I liked my 1570s a lot lot on my Acoustats after they were modded a little bit.
The 811 is a nice high power tube that will take significant abuse, has a long life, relatively low cost, isn't too huge and sounds ok, fine...
_-_-bear
PS. the driver stage's LF rolloff depends entirely upon the L of the choke and Z related to that circuit. In general, it has better response than a coupling xfrmr, and costs a fraction of the $$. Big L, low power chokes are cheap, so you could get down to <10hz easy.
PPS. at least in the Altec 1570 the limiting LF factor is the output iron which is clearly not rated for the full 175 watts at LF, given that the core size is less than some "60 watt" nominal transformers that I have seen...
Used the same setup.
Ran a pair of modified Accoustat III's with 1570's ten years ago. Picked a couple pairs from John Tucker when he was local. They had a Curscio style input stage, 6BL7's for drivers, and power transfomer as the driver chokes. Sounded great.
Sold my last pair to Isreal Blume and he bragged on how well they drove his speakers in the showroom. So, the 811a can work fine, just as the 1570 with some changes.
George
Ran a pair of modified Accoustat III's with 1570's ten years ago. Picked a couple pairs from John Tucker when he was local. They had a Curscio style input stage, 6BL7's for drivers, and power transfomer as the driver chokes. Sounded great.
Sold my last pair to Isreal Blume and he bragged on how well they drove his speakers in the showroom. So, the 811a can work fine, just as the 1570 with some changes.
George
Having had some 1570's a long time ago I may have dismissed them way to early. Having read some articles recently I must admit that my interest has again been perked up. I am in the process of looking for another pair and thought I would open up the thread and see if anyone had any ideas to get rid of the driver choke in favor of something better and incorporate a decent bias setup for the driver tubes and maybe different driver tubes.
Any suggestions for getting rid of the center tapped driver choke and a decent adjustable bias setup?
Any suggestions for getting rid of the center tapped driver choke and a decent adjustable bias setup?
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