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Old 30th October 2003, 12:30 AM   #11
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Quote:
You mean to say reliability...(fiablite being a french word).
Sorry!!...thanks for the correction...


Quote:
Separate cathode resistors can be better still...sonically
That's to subjectif for me...what is good for one people can be the worst for other people...

Knowing that...i never enter in subjectif discussions about sound quality....sorry,one more time...
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No argument from me there...saudade!
Saudade ...du chocolat de la Grand Place de Bruxelles!!!
A bientot!
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Old 30th October 2003, 12:44 AM   #12
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Default Re: cathode bypass in PP output stage?

Quote:
Originally posted by RichJones
Best option:

A) common cathode resistor bypassed
B) common cathode resistor unbypassed
C) choke
D) solid state CCS

This is for 2 6B4G's (Sovtek) running at 398v 60mA each 62v bias through a common 470 ohm resistor.

Thoughts???
CCS. Based not on theorising but having done it with both DHT's (47, GM70, 813) and IHT's (6V6, EL84, EL34, KT88). But this of course limits you to class A.

Rather than repeat all the arguments again here, go to Audio Asylum Tube DIY, and read the last two or three weeks of threads, it's been a hot topic.

As for which one sounds the best, well that's up to you. I've tried them all and know what I prefer.
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Old 30th October 2003, 12:58 AM   #13
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Hi,

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As for which one sounds the best, well that's up to you. I've tried them all and know what I prefer.
He's a dedicated follower of constant current source...give that man his CCS.

Many a road leads to the mountain top.....

Bom dia, Brett.

Kidding agian folk...

Cheers,
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Old 30th October 2003, 01:08 AM   #14
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Quote:
Originally posted by fdegrove
He's a dedicated follower of constant current source...give that man his CCS.
Not always, but there are a number of performance advantages with it here and it's far, far, far from a subtle strain-like-you're-constipated-trying-to-hear-it difference.
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Old 30th October 2003, 01:24 AM   #15
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Hi,

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Not always, but there are a number of performance advantages with it here and it's far, far, far from a subtle strain-like-you're-constipated-trying-to-hear-it difference.
Sure enough, but, as usual, it takes some intelligence to use the darn things in the appropriate places...

You just can lift a newbie from zero to a hundred...it takes some steps IME.

Sayonara,
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Old 30th October 2003, 04:42 AM   #16
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I go with CCS too. but again as mention limits to class A. Another term for CCS is also a current limiter. It would limit the amount of current to its set value. This could help in limiting the extra amount of current flowing thru your tube when something goes wrong.
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Old 30th October 2003, 09:23 AM   #17
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Default Re: cathode bypass in PP output stage?

Quote:
Originally posted by RichJones
Best option:

A) common cathode resistor bypassed
B) common cathode resistor unbypassed
C) choke
D) solid state CCS
E) fixed bias
or separate catode resistors bypassed

Quote:

This is for 2 6B4G's (Sovtek) running at 398v 60mA each 62v bias through a common 470 ohm resistor.
398V are plate-to-catode or plate-to-ground?
i.e. 23.88W or 20.16W on plate?
Sovtek 6B4G are 15W max, as far as I remember
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Old 30th October 2003, 09:56 AM   #18
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Hi,

Quote:
398V are plate-to-catode or plate-to-ground?
Maybe someone's building an amp to put under the x-mass tree?

You're quite right that's way too high one way or the other...

Cheers,
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Old 30th October 2003, 04:11 PM   #19
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6B4-G Sovtek This new monoplate 6B4 looks like a baby 300B! Biases just a hair less than the old US ones, which should make it a bit easier to drive. Looks like just the ticket for people who'd like to experiment with using 6B4 in amps that have 6L6, etc, but don't want to try higher plate voltages with NOS tubes... these have a plate voltage rating of 450V and can be used at a plate dissipation of up to 30W.
I have run them at around 24W with no problems. They sound pretty good at these higher levels too

Tom
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Old 30th October 2003, 05:34 PM   #20
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Default Re: cathode bypass in PP output stage?

Konnichiwa,

Quote:
Originally posted by RichJones
Best option:

A) common cathode resistor bypassed
B) common cathode resistor unbypassed
C) choke
D) solid state CCS

I know plenty of people like the CCS, but it is not always the best solution. Worth trying though. one of the biggest problems with the CCS will be the impedance to ground which may track hum into the circuit. Also, you need a way of balancing the Valves current with ANY form of common cathode ballast. The way I do this is shown in the attached Circuits one for semi-fixed bias (also easily adapted for fixed bias) and the other for self bias.

To measure the current balance I simply make sure that the two halves of the transformer have the same DCR (if not simply add a suitable resistor to balance the DCR) and measure the voltage on the two anodes of the Valves via a pair of 1M "safety" resistors. If there is no voltage difference, then the two valves draw identical current.

I personally would likely tend most towards a choke BTW and seperate, capacitive bypassed cathode resistors is definitly the worst sounding solution....

Sayonara

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