PP Amp using 811A

[rwellerson]

Hello

Anyone with exp in this 811A tube in PP for an audio amplifier?
Thanks

Ricardo

[danFrank]

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

[mod_evil]

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.

[jrdmedford]

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

[SY]

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.

[Original Burnedfingers]

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.

[rwellerson]

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

[mod_evil]

Ricardo,

How much are you paying for the 811A in Brazil?

Thanks.

[jrdmedford]

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...

[klm1]

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 !