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Old 31st January 2003, 07:01 PM   #11
Serow is offline Serow  Canada
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I wish more people would put the current flowing through the different paths in tube amp schematics. It really helped me to understand Thorsten's 45 Monkey schematic.

How's this:

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Old 2nd February 2003, 02:37 AM   #12
Serow is offline Serow  Canada
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Now for the real question... Will the following work? I read in TubeCad something to the effect that regulating the g2 of a pentode is nearly as good as a regulated supply. The OC3 should give a nice stable voltage.

However, is this going to result in the world's most expensive relaxation oscillator (reg. tube and capacitor in parallel)? There are two parallel capacitor paths for the OC3 that I can see: 22 uF + series 100 Ohm and 22 uF + series 11 kOhm. I don't know enough to determine theoretically whether this will oscillate or just plain blow up .

Thanks for your help.


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Old 2nd February 2003, 03:12 AM   #13
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Replace the 22uF g2-k bypass with the 0C3.

Alternately, you might try two in series, one to the screen, one to the 2A3's cathode (pulling the 22uF and 6.8uF bypasses). This would cause a mild upset in the 235V at the cathode, but nothing Mr. Ohm can't tell you how to design around.
Last possible regulative addition I can think of would be a 3-4V zener in the cathode of, or fixed bias to the 6BQ5. Note this would be detrimental, as no tube will be exactly to spec, causing a different plate current to flow, and hence screwing with the 2A3's bias.

Tim (not like I care, I would never insult the GOT with so much wasted voltage )
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Old 2nd February 2003, 05:50 AM   #14
Serow is offline Serow  Canada
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Quote:
Originally posted by Sch3mat1c
I would never insult the GOT with so much wasted voltage
Thanks Tim. The God of Triodes?

I will eventually get around to trying this version out. I figure that it's like anything containing chocolate, caramel and pecans: if I can't make a good sounding amp using an EL84 with a 2A3, I might as well give up!


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Old 2nd February 2003, 11:26 AM   #15
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Hi,

Quote:
Now for the real question... Will the following work? I read in TubeCad something to the effect that regulating the g2 of a pentode is nearly as good as a regulated supply. The OC3 should give a nice stable voltage.
As others mentioned, the OC3 would have to substitute for the for the 22uF capacitor.

HOWEVER, I would STRONGLY advise against doing this. The circuit as shown with the resistor divider includes a negative feedback loop, though only at DC and extremely low frequencies from the output valve cathode to the screengrid of the Driver pentode.

Most DC coupled amplifiers have not got very good operating point stability and often tend to "run away", sometimes to the point of cherry red anodes in the output valve(s). The DC feedback in the original schematic kills that tendency for good. By "stabilising" the Screengrid Voltage you remove this feedback not only at AC but also at DC.

BTW, under NO conditions try to use a zenner diode in the EL84 Cathode, you need to be able to adjust the voltage there to ensure the Amplifier operates at the correct operating point. Different driver and output valves will bias differently, you need to be able to correct for this.

Sayonara
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Old 2nd February 2003, 05:19 PM   #16
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Exactly (I said it would work, but never said it would work well )

Yes, God Of Triodes.

BTW....you show 57mA coming in the 2A3 anode, and 47mA out the 6BQ5 cathode....ummmmm....

- Looks like a typo adding them above the 100 ohm.

Tim
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Old 3rd February 2003, 02:27 AM   #17
Serow is offline Serow  Canada
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Quote:
Originally posted by Kuei Yang Wang
Hi,



As others mentioned, the OC3 would have to substitute for the for the 22uF capacitor.

HOWEVER, I would STRONGLY advise against doing this. The circuit as shown with the resistor divider includes a negative feedback loop, though only at DC and extremely low frequencies from the output valve cathode to the screengrid of the Driver pentode.

Sayonara
Thanks for the warning guys. I think I'm going through the "a little knowledge is a dangerous thing" stage.

Later,
Eric
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