Thorsten's Chokeless Monkey 2a3 - diyAudio
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Old 31st January 2003, 06:29 AM   #1
Serow is offline Serow  Canada
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Default Thorsten's Chokeless Monkey 2a3

I've been trying to understand the details of Thorsten's design as posted in Joelist:

Quote:
>right. as i alluded to on wedneday. using the cathode for B+.

Yup, and to supply the Screen Grid via a Voltage Divider, also adding full
DC Feedback to the circuit.....

>however, the choke inductance requirement is a tough one.
>seems you'd need several hundred henries.

This Monkey is a "Chokeless Monkey".... The penthode likes to see a LOW
impedance load, not a high Impedance one for best linearity.... So, with one
of my favourite EL84 Operating Points as Voltage Amp we get:

Va 190V (total +B must be raised to 490V here)
Vg2 100V
Ia 12mA

Anode Load 3k9

So, 3K9 from Cathode to Grid of the 2A3, the EL84 Anode gets connected to
the 2A3 Grid.....

The 2A3 Cathode will be at 235V, so a Voltage Divider for the Screen runs of
the Cathode of the 2A3. I'd like to have a reasonable DC impedance here, so
we'll draw another 12mA there (about 2mA of which go into the screen). The
Lower Resistor will be 10k, the Upper (to the Cathode of the 2A3) around
11k. From G2 we take a 22uF Cap to the EL84 Cathode.

Now, the resistors from the G2 Voltage Divider, the additional appx. 6K8 2A3
Cathode Resistor and the G2 Bypass Cap meet at the EL84 Cathode, the
resistor from there to ground Biases the Valve at about 3 - 4V (needs to be
determined), so around 100 Ohm Adjustable will do. Again, the Cathode
Resistor will not be bypassed....

Voila, a Driverstage with very low Drive Impedance, pleanty of gain and
linearity. Only Class A2 Swing is a no-no....

Still, this one with an EL84 and a 2A3 (or 45 with recalculated Resistors)
will give a great and cheap amp....

Rather amazing all this Monkey-Business, isn't it....

Later T
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Date: Fri, 09 Jun 2000 14:36:24 GMT
From: "T. Loesch" <ezee_e@hotmail.com>
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Old 31st January 2003, 06:30 AM   #2
Serow is offline Serow  Canada
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Here's the schematic I drew from the description:

Click the image to open in full size.
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Old 31st January 2003, 06:33 AM   #3
Serow is offline Serow  Canada
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Isn't 23 mA pretty low current for a 2a3? The similar 45 amp he posted earlier is run at 34 mA.

Thorsten mentions something about a 6K8 anode resistor for the 2a3, after describing it as 11K earlier. Perhaps this causes my confusion.

Thanks for your help.

Eric Sampson
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Old 31st January 2003, 01:57 PM   #4
dhaen is offline dhaen  Europe
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Eric,

Why don't you ask him?
His ID is an open secret...
http://www.diyaudio.com/forums/membe...fo&userid=3984

Cheers,
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Old 31st January 2003, 05:10 PM   #5
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Thorsten's Chokeless Monkey 2a3

Hi,

Quote:
I've been trying to understand the details of Thorsten's design as posted in Joelist:
The 6K8 Resistor is in ADDITION to the 11k and 10k Resistor. At the appx. 230V across it a further 34mA are drawn, giving us a total of 58mA current. The rest looks fine, except the 4k3 OPT.

Ciao T
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Old 31st January 2003, 05:18 PM   #6
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Default Huh?

sign off above:
Quote:
Ciao T???
CRyder
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Old 31st January 2003, 05:21 PM   #7
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Default T.

Hi,

Craig,

T. stands for Torsten.

Ciao,

F.
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Old 31st January 2003, 05:27 PM   #8
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Quote:
T. stands for Torsten
Hi Frank.
Ya..You mean Thorsten. I got that part.

Is KYW TL incognito or something? That is how T always signs off. I don't get the sign off.


Cheers
CRyder
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Old 31st January 2003, 05:29 PM   #9
dhaen is offline dhaen  Europe
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Craig,

Quote:
Originally posted by dhaen
Eric,

Why don't you ask him?
His ID is an open secret...
http://www.diyaudio.com/forums/membe...mp;userid=3984

Cheers,
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Old 31st January 2003, 05:29 PM   #10
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Default THORSTEN.

Hi Craig,

Quote:
Is KYW TL incognito or something?
The other one and only,yes.

Cheers,
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