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Old 12th June 2003, 08:04 PM   #11
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Is there any benefit to the gas-tube rectification besides the 'cool factor' ?

-Maz
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Old 13th June 2003, 02:52 AM   #12
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Old 13th June 2003, 03:03 AM   #13
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Default Question

Wonder how the regulators handle the current and line regulation since the max current is 30 to 40ma, depending on the regulator.
Does AC line variations affect things much?
Any noise problems?

Thanks Guys.
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Old 13th June 2003, 03:27 AM   #14
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James
is there much improvement in doing the cap from B+ to the cathodes of the output tube? parafeed right?
i read somewhere that by doing so reduces the output loop. Lynn Olson's article i think.
and how do we calculate the cap size for this?
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Old 13th June 2003, 07:32 AM   #15
316a is offline 316a  England
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Default Phase Splitter

Hello ,
Are you sure that phase splitter transformer is not overkill ? I would have thought that with driving pentodes , a concertina phase splitter would have been adequate . A phase splitter transformer more costly than the output transformer ? Would there be any advantages ? With a concertina , loop feedback could also be implemented more effectively
Why use the gas regulators ? What do you think will happen to the supply rail when the amp is driven into class B ?

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Old 13th June 2003, 07:48 AM   #16
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Hi NickC,

Quote:
is there much improvement in doing the cap from B+ to the cathodes of the output tube? parafeed right?
I have found a significant improvement in my PP amps by adding this capacitor. IT improved all aspects of the sound, I was quite shocked by it. It is not a parafeed connection but is more akin to the Ultrapath connection. It's purpose is to provide a short high quality signal current return loop to the cathode. A typical value of about 40uF works best - I guess the exact value can be calculated by the incircuit output impedance of the stage and the required lf cutoff frequency. Haven't really thought that through yet. The 1uF is about the highest value the gas regulators will tolerate ... it's better than nothing

EC8010 said:

Quote:
At power-up, when the 6AQ5s are cold, those neon regulators will have to sink a lot of current. Are they up to it?
I hadn't looked at start up conditions - this looks like a problem. How serious would it be? Would delayed B+ solve it?

ciao James
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Old 13th June 2003, 09:11 AM   #17
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james
mix up my words might to say ultrapath. 40 uf is quite big i am using el34s do you think i need that big. might not the have space to fit does big solen's plus the money too.
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Old 13th June 2003, 10:44 AM   #18
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Default Re: A 10W ultralinear amplifier with unique features.

Quote:
Originally posted by Joel
Constructive comments are welcome.
How about replacing the output stage cathode resistor and cap with an *un*-bypassed SS constant current source set at 90-100mA? If the ccs is good eough it will force the output stage to be virtually perfectly balanced because the total cathode current will *always* be 100mA or whatever throughout the whole cycle. Even as the tubes age! It makes the output stage basically a long-tailed pair. Better hum rejection too. If one tube is a bit on the sad side, the drive to the good one is automatically reduced to compensate for it. You could then even earth one of the output tube control grids so that only the other one is driven so you wouldn't need a phase splitting transformer or any kind of phase splitting cct. It then needs double the drive voltage though.

With only one tube appearing to be driven (the "undriven" one is actually driven through it's cathode), instead of earthing it you could apply a small dc offset above or below earth to the undriven tube control grid to make the output stage have perfect dc balance too. The output tranny will love you for this.

It's something I always wanted to do but I don't have a suitable output transformer nowadays. D'oh!
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Old 13th June 2003, 10:50 AM   #19
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Default CCS cathode bias

Been there , done that but the CCS will only force AC to be symetrical . In DC terms a pot between the cathodes would be required to optimise DC balance (and cancel any DC in the core) otherwise variable fixed grid bias will be required . I don't think this is possible with the IT transformer shown , unless it has separate secondary windings .

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Old 13th June 2003, 10:53 AM   #20
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Default ...just another thing

...with a CCS the output stage will only run in class A . Not a bad thing but power will be far less than the original design's 10w and with the output transformer load may not necessarily enable '100%' class A

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