I've been trying to understand the details of Thorsten's design as posted in Joelist:
>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>
Here's the schematic I drew from the description:
An externally hosted image should be here but it was not working when we last tested it.
Eric,
Why don't you ask him?
His ID is an open secret...
http://www.diyaudio.com/forums/member.php?s=&action=getinfo&userid=3984
Cheers,
Why don't you ask him?
His ID is an open secret...
http://www.diyaudio.com/forums/member.php?s=&action=getinfo&userid=3984
Cheers,
Hi,
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
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
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
Craig,
dhaen said:Eric,
Why don't you ask him?
His ID is an open secret...
http://www.diyaudio.com/forums/member.php?s=&action=getinfo&userid=3984
Cheers,
THORSTEN.
Hi Craig,
The other one and only,yes.
Cheers,
Hi Craig,
Is KYW TL incognito or something?
The other one and only,yes.
Cheers,
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:
How's this:
An externally hosted image should be here but it was not working when we last tested it.
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.
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.
An externally hosted image should be here but it was not working when we last tested it.
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 )
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 )
Sch3mat1c said: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!
An externally hosted image should be here but it was not working when we last tested it.
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.
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
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
Kuei Yang Wang said: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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