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Size Range：OD 5/8"~1 1/2" , WT 1.65mm~2.77mm Min Radio: 29mm ; Max Radio:675.84mmType of End-Finish：PE
ASTM/ASME：A213/SA213 A249/SA249 A268 A312/SA312 A269 A270 A358 A376 A409 A511 A688 A789 A790 A803 A928 A544 A409 A632 A688
A778 A908Materials:304/304L/304H;321/321H;316/316L/316H;316TI;317L;347H;310S; UNS31803 ;UNS32750/U NS08904L,TP410/TP410S;ECT
Tchnical conditions:
Heat treatment:Stress relive annealing of U-tubes after bending
Surface condition Finished U-tubes shall be free of scale, without scratches after bending
Dimensional tolerances U-tubes acc. to TEMA R.C.B.
Length of straight part -0/+5 mm
Flattening (also called “ovality”) at the bend shall not exceed 10% of the nominal tube outside diameter.
Wall thickness in bending part acc. to TEMA RCB 2.31 Minimum tube wall thickness in the bend part (T min)T(min) ≥ (SW × (2×R + D))/( 2× (R+D)where:
SW is smallest wall thickness D Nominal outside diameter R radius
Radius tolerance 1) for R 100 mm +/- 3 mm
2) for R ≥ 100 mm +/- 5 mm
Straightness tolerance max. 1,5 mm per 1 m
U-Tube ends: plain, vertically cut to the tube axis
Repairs by welding: prohibited
Surface condition Finished U-tubes shall be free of scale, without scratches after bending,
Mandatory tests for U-tubes
100 % Dimensional and visual control.
100 % Ball passed test
100 % Hydrostatic test min 10Mpa/ min 10sec.
Coating :Passivation and oiled, Black paint or varnish
Packing:Plastic plugs in both ends, bundles of max. 3,000kg with several steel strips, Two tags on each bundle,
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Mill Test Certificate:EN 10204/3.1B
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811-A amp

Thread starter
john 807

Start date
2005-04-07 5:00 pm

2004-06-28 4:04 pm

Next to an open wormhole NW of Toronto

I have taken a different route, AC heating using 50 KHz filament current. I did some experimenting with this about a year ago and I can tell you that the filament power must be a clean sine wave if this is going to work. Otherwise you will get all sorts of intermodulation products that cloud up the FFT scope, and the sound.

2005-07-14 4:18 pm

West Virginia panhandle

www.tubelab.com

I used a toroid core for the transformer, and a solid state push pull amplifier to drive it. That was driven with an HP audio oscillator. The problem comes from regulating the gain to keep the filament voltage constant, without letting the amplifier clip. Each 811A requires about 25 watts of filament power. The resistance of the filament changes drastically as the tube warms up. Most bipolar transistors tend to melt at this power and frequency. Mosfets work fine.

2004-06-28 4:04 pm

Next to an open wormhole NW of Toronto

I used a toroid core for the transformer, and a solid state push pull amplifier to drive it. That was driven with an HP audio oscillator. The problem comes from regulating the gain to keep the filament voltage constant, without letting the amplifier clip. Each 811A requires about 25 watts of filament power. The resistance of the filament changes drastically as the tube warms up. Most bipolar transistors tend to melt at this power and frequency. Mosfets work fine.

2005-07-14 4:18 pm

West Virginia panhandle

www.tubelab.com

When I have the time to explore this further I will probably resume the sand state experiments, since I have that engineering mentality about choosing the best component for the job.

For those that want to follow the pure tube path, we need to find the schematic for the old Tektronix 504 scope. It used a power supply that derived all of the operating voltages off of a power oscillator operating at an ultrasonic frequency. If my fuzzy memory is correct it used a 6DQ6A. It's been 25 years since I worked on these.

Anyone out there got the diagram?
Hi....
I am New member
we have same problem, because I need Schema Pushpull 811A

regards
BOYTUBE
811 Amp

Hello,
I was looking for an 811 SET circuit to build and it looks like I've found one. Thank you Astouffer.
I also saw the second amp with the transistor (nasty things) in the circuit. But with my heavy towards thermionic emission (an age thing),that one is not for me.

Has anyone got an update or mods to the circuit since 2005?
I noticed some chat about pentodes and bias.... any comments on that??

I did see the "Ganti 811" amp but not keen on the transformer couplings between each stage.

I'm reading that the Svetlana 811 valve is the one to go
for. So I'm looking for a pair if anyone has a vendor.

Thank you for any help.

John
Aug-29-07

2003-10-27 4:07 pm

Upstate New York

I have a couple of 811A's and have been anxious to build something with them. I have a copy of the schematic attached to post #5 of this thread but am having difficulty understanding several things.

If some kind soul would help me, what is the device labeled E202? Also, what voltage/wattage are the zener's?

I just noticed something else, it looks like there is a 100 ohm resistor attached to the paralleled 33 ohm resistors on the cathode of the 811A, but then there is an arrow with 200 ohm/3W in parentheses. Is this a 200 ohm potentiometer?

And finally, the 2SC3783 transistor is hard to source in the U.S.. Can anyone recommend a suitable substitute?

Thanks.

2004-06-02 3:47 am

Pittsburgh, crumbling wasteland

what is the device labeled E202? Also, what voltage/wattage are the zener's?

I just noticed something else, it looks like there is a 100 ohm resistor attached to the paralleled 33 ohm resistors on the cathode of the 811A, but then there is an arrow with 200 ohm/3W in parentheses. Is this a 200 ohm potentiometer?

2003-10-27 4:07 pm

Upstate New York

Thanks very much for the info. Would you have any idea what the appropriate current level from E202 would be?

2004-06-02 3:47 am

Pittsburgh, crumbling wasteland

2003-10-27 4:07 pm

Upstate New York

Thanks once again. From the data sheet you so kindly provided, it looks like a 1N5305 is a suitable substitute. Now I can start collecting all the necessary bits and have a go at building it once the weather turns. (With the price of fuel, I may be spending a lot of time huddled around the amplifier this winter.)
Have you seen this:

811A A2 simple amp

This is the same ckt topology as post #5 with substantially less
complexity and I will argue better performance.

My gripes with post #5 are as follows:
He is forced to use a semiconductor B+ regulator on his driver
stage because he uses a variable-resistor divider network to bias
the EL84 cathode follower at the grid! If, in fact, he used a choke
or resistor to bias the cathode of the EL84, he'd not need this complexity.

He's using feedback from the 811A plate to the 12AX7 cathode.
Gaaaah !!!!

His operating point is too low. At lower B+, the 811A grid is going to produce GOBS of grid current. He's biased the 811A hot at 33V.
The result is you'll get a lower Ra, but also less power and instead
have to dissipate alot of current from the 811A grid. Keep in mind
that grid current is not useable for audio power - it's simply a sunk
cost!

He's using DC filaments but no common mode chokes! I'd not
even bother and use straight AC with a humbucking pot in the
filament circuit to null out hum. If you're going to do DC filaments, do them right - use CMC's. Heck - you can get CMC's in the 6A range upwards of hundred of mH in the Digikey catalogue.

You're better off with slightly higher B+ (400V or alittle more). In
this regime, you'll get MORE plate current and LESS grid current.
You'll get more power. Your driver stage will be alot cleaner.

With my design, I run at 430V, which is a typical, attainable B+ for the kinds of off-the-shelf transformers for guitar amps or the Hammond catalog. The grid is happy at 22-24V (you can go higher if you want). You can use many different tubes on the cathode follower: 6{v,w,y,k}6GT, 6CL6, EL34, 6L6... Finally, since we need to swing 40V, you can use something from the 6SN7 family
as your gain tube. That includes stuff like the 5687, the 6CG7,
12BH7 and all that jazz. Since the gain stage only needs to
develop 40V, the amp is now 2Vp-p input sensitive. This means this
design DOESNT NEED a preamp - you can simply place a 100K stereo attenuator pot on the amp and drive this directly from a D/A converter.

-- Jim

2005-01-14 9:28 pm

South Florida

When I have the time to explore this further I will probably resume the sand state experiments, since I have that engineering mentality about choosing the best component for the job.

For those that want to follow the pure tube path, we need to find the schematic for the old Tektronix 504 scope. It used a power supply that derived all of the operating voltages off of a power oscillator operating at an ultrasonic frequency. If my fuzzy memory is correct it used a 6DQ6A. It's been 25 years since I worked on these.

Anyone out there got the diagram?

2003-10-27 4:07 pm

Upstate New York

Jim,

Thanks very much for your post. I printed out the schematic and will give it a try during the cold months ahead.

I assume you have built this circuit. How would you characterize the sound? Also, the 811A's I have have a radioactivity warning label on the boxes. They were made in 1962. Do these things contain a radioactive isotope or do they generate x-rays in use?

Mike L.

2005-05-06 3:50 am

USA

www.dolphin-hsl.com

Also, the 811A's I have have a radioactivity warning label on the boxes. They were made in 1962. Do these things contain a radioactive isotope or do they generate x-rays in use?

Oh yes, I've built it and it sounds amazing. I was even surprised
at how little I can hear the background AC hum on 98dB eff
speakers. This amp has alot of power (10W) and can drive many
kinds of speakers - not just limited to horns or Klipschen.

As far as radioactivity, the filament is coated with trace amounts of Thorium which enhances the metallurgy and reliability of
the tungsten at hi temp. Natural thorium is weak alpha emitter,
similar to what's in your smoke detector. Thorium is also used
in Coleman lantern mantles, as a catalyst. All DHTs use thorium:
845s, 211s, 572 and the big RF tubes.

The radioactivity labelling on the boxes is more for the benefit
of military cargo handlers.... They like to know if cargo is supposed to be hot so that they dont have to worry if something
(1) got contaminated or (2) a stray nuclear weapons component
has somehow gotten into the regular parts depot shipment for the Signal Corps.

If you follow the news, last year, Minuteman ICBM nosecone parts were accidentally shipped to the Taiwanese army.. They
Taiwanese had ordered batteries for a helicopter, and due to mixups in warehouse, got something for more interesting to play with!

-- Jim

2004-12-05 7:33 am

Dhaka, the capital of Bangladesh

Jim,

I follow your work and I like it. I am thinking of building your 811a circuit. I am unclear about PS though. At idle what load current I should consider while modeling the PS?

I undestand 811/811A ra is high, how 5K OPT behabes then! I do not want the input tube because I will use my AIKIDO pre so how I can go for some feedback If I want to....!!

Pls need your help.

Regards

811s have W/Th filaments, and thorium is indeed radioactive. There really shouldn't be enough thorium in there for this to be a major concern. So far as X-Rays are concerned, the usual operating voltages aren't high enough for this to be a problem.

I realized how old this thread is, but I found it searching 811 power supply info... I started an 811 SE amp last fall when I found some 811s at a meet... It's been thru 4 iterations so far, and the only thing left from the original schem is the 811!!
I'm using a 10A 6.3V FT and a 25A 50VDC bridge with 2x 22000uF caps, which gets it dead quiet, but the voltage is lower than I'd like (5.85VDC)... The amp sounds very good and is running on the breadboard with the last iteration for teh L channel, and the 3rd for the Right... Needed two channels running to load the PS to fine tune it ...
I am considering using a separate FT for each 811 heater, to bring the V up, but not sure if its really necessary, as the Vp is around 390-400V, which is pretty low for this tube... Grid is about 24-26VDC...
Anyone still working with 811s? What did you do to nail down the heater voltage? I'm not too keen on using a lot of SS devices, but open to any input...
Thanks in advance...
Started a new thread after finding this one, since its so old...

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Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.

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Directly heated cathodes, but why?

Thread starter
Hesky

Start date
2004-06-06 6:55 pm

Hi all,

I've been pondering over directly heated triodes, why are most triodes (2A3, 300B, 845 etc...) directly heated and beam tetrodes such as KT88, 6550s indirectly heated? I'm sure there’s a valid reason, but triodes such as the 6C33 with its indirectly heated cathode just confuse me.

Hesky

why are most triodes (2A3, 300B, 845 etc...) directly heated

In that case to me it just seems like it’s a simple case of 'if it works don’t change it'. These said vacuum tubes are antiques but perform well with v low distortion which is an audio requirement as you say. I think that if a company produced an indirectly heated 300B say, it just wouldn’t be accepted not traditional. Might be overall a better valve, but not to everyone’s taste.
Or I could be completely wrong

Hesky

2003-12-28 5:15 pm

Herefordshire

www.borderacoustic.co.uk

I would agree, from a beginners standpoint at least
I've thought about this for a while now, and I really can't think of any technical reason (for audio use at least) why direct heating should be better than indirect heating, though I haven't actively searched for such information yet.
Steve

I've thought about this for a while now, and I really can't think of any technical reason (for audio use at least) why direct heating should be better than indirect heating, though I haven't actively searched for such information yet.

2003-12-28 5:15 pm

Herefordshire

www.borderacoustic.co.uk

Hi Frank,
It would be nice to know though, I guess audio is always going to be a little subjective for science to always have the answer...
Steve

2003-01-09 5:42 am

Sweden

qtron.se

One reason to use directly heated cathodes are that they are more efficient , (higher cathode saturation current for same heater power) Most high power transmitting tubes are directly heated due to this reason otherwise thay would consume even more heater power than they already do.

For a cylindric, elliptic or rektangular tube structure it is possible to show theoretically that linearity will be better the smaller physical surface the cathode has, a directly heated cathode have smaller surface area for same emission than an indirectly heated one , that is one reason why tubes like 2A3, 300B and similar are very linear. Theory regarding effects on linearity by different tube structures was well known before 1940.

Tubes with indirectly heated cathodes can be made with similar linearity by using other tube structures, (non-cylindric). So it would probably be possible to make a indirectly heated tube with similar linearity as a 300B.

Regards Hans

So it would probably be possible to make a indirectly heated tube with similar linearity as a 300B.

guess audio is always going to be a little subjective for science to always have the answer...

2003-12-28 5:15 pm

Herefordshire

www.borderacoustic.co.uk

It certainly is possible and some triode connected penthodes have curves that show very similar linearity to DHTs.

2003-01-27 2:45 pm

Milwaukee, WI

www.seventransistorlabs.com

Can't say I have a SEDHT amp but I suspect a lot of it is money and psychoacoustics... you know, how cables 'work'... For i
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