• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

811a Class A2

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fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
811A

Hi,

This tube was mostly used in radio and quite likely run in class B.

From what I found on the net it is still produced by Svetlana.

Yours may come from the Leopoldsburg military base perhaps?

The schematics you point at can be used if you want to build an amp with these.
Be ware of the high voltages though,this is definitely not beginners stuff.

Beringen?
As a student I used to date a beautiful girl from Beringen.


Cheers,;)
 
J

jim

Member
Joined 2002
:cheerful:
Yes, I don't know when you were a student but the
amount of beautiful girls in Beringen is still very high:D

My 811a's are NOS RCA and come from Kleine Brogel Air Force Base

In my job as radio technician I've worked on transmitters using
700V B+ so I'm aware of the risks involved, but thanks for the warning !(een verwittigd man is ......)

Jim
 
H

halojoy

On Hiatus
Joined 2002
SV811 - 20W amplifier - SEBASTIAN

SV811 - 20W amplifier - SEBASTIAN

uses 7247 as input and
811-10 or 572-10 as single output tube. 20W or 35W.
and an Output transformer called LL 9202-S with a primary impedance of 6000 ohms.

I found this when surfing in swedish tube territory.
I saved the link for future use.
I did not know I should get to use it so quick:

SEBASTIAN 20W SV811 - 35W SV572

Sorry to say I do not understand much of this circuit.
But someone else maybe does.

An externally hosted image should be here but it was not working when we last tested it.


/halo - one step ahead
 
J

jim

Member
Joined 2002
First try

Hi all,

This is going to be the (first) tryout for my 811A-class A2 amp.
Any comments are very welcome !!!!

Greetings
Jim
 

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B

bournville

Member
Joined 2003
I think that the problem is probably a mistake on the circuit diagram - it shows Ig at 20-26ma, which implies a voltage of over 660 volts on the grid of the 811A, obviously impossible! With a current of only 1ma passing through the 33k resistor that would give a voltage of 33 on the 811A grid, a much more reasonable figure.
 
Brett

Brett

Member
Joined 2002
Re: Class A2 !!

jim said:
Hi all,

The 20-26mA flows into the grid of the 811A,
just as the arrow indicates.
The anodecurrent of the EL84 splits into 20mA for
the 811A and approx. 1mA for the 33k resistor.

Jim
Click to expand...

When you've got it running, try a CCS as the CF load. I think it's perfect for this application, and will likely result in lower distortion and more stable bias under dynamic conditions. One of Gary Pimm's BBMCCS would be what I'd try.

{added later} Or (read Kimmel's article below, and) run the EL84 as a pentode CF.
http://laplaza.taos.nm.us/~fvuotto/mustage.html

Just a thought.

I'm interested to see how this comes out. The Russian 811A's are reputedly at least as good as the NOS US ones, and are very cheap.
 
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