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Old 4th February 2009, 08:59 PM   #1
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Default running 6S4S/6C4C hot .. calling widowmaker

hi there

i'm messing around with a (dual) 6N6P driven 6C4C SE amp. i see that it's no prob running these quite hot and well above 15W, well no prob 'cept tube life 350V/50mA is where i'm at right now

6N6P is a real sweetie, low Rp and good gain to boot, but i have a hard time wrapping my head around widowmakers plate resistors, they seem to be a factor 10 off?

2A3 SE Amp

to get 11V at the cathode would be quite impossible with a 56K anode resistor, no?

cheers,

mb4b
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Old 4th February 2009, 09:56 PM   #2
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Default Re: running 6S4S/6C4C hot .. calling widowmaker

Quote:
Originally posted by makeb4break
hi there

i'm messing around with a (dual) 6N6P driven 6C4C SE amp. i see that it's no prob running these quite hot and well above 15W, well no prob 'cept tube life 350V/50mA is where i'm at right now


You can do that also with NOS 2A3's.
During the 50's and the 60's many guys where convinced that the double-plate 2A3 was just made of 2x45's in parallel and used to run the tube up to 20-22W.
The life of the tube, as you know, will be pretty short......


I cannot see the point in doing that. You buy one pair of 300B's, run them at the same plate dissipation and they will last for 20 years at least. With 6S4S or 2A3s you need at least 12 pairs for the period.....
It doesn't seem convenient to me... unless you use that amp for some months and then you go for something else.


Quote:
Originally posted by makeb4break


6N6P is a real sweetie, low Rp and good gain to boot, but i have a hard time wrapping my head around widowmakers plate resistors, they seem to be a factor 10 off?

2A3 SE Amp

to get 11V at the cathode would be quite impossible with a 56K anode resistor, no?
Yes, they are a bit to high with those voltage supplies. However it is possible to get 11V on the cathode (approx. 164V anode voltage).
Basically you are throwing away the good characteristics of the tube (i.e. High Gm and low internal resistance, together with some linearity) but you can do it.

45
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Old 4th February 2009, 10:19 PM   #3
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Up to 17W plate dissipation, you can still expect 7-8000 hours (at least) service life from 2A3/6S4S.



45
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Old 5th February 2009, 12:04 AM   #4
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thank you for your reply

well, according to widowmaker running above 15W will still yield some reasonable tube life. anyway, they're cheap - and i got loads

i allready got 300B amps, allthough stocked with chineese versions. they're not so good, imo. cheap though .. (i sell these for a living so i can get them _really_ cheap)

it's time for a 2A3'ish amp for me, i got all the parts. the psu i'm planning to use puts out 350V or there about's, hence my questions

i do switch my amps around a lot, so that's another reason i'm not so concerned about tube life. more intrigued with the notion that the russian 6C4C sound _better_ at 350V and above 15W ...

regarding the 6N6P. with 285V B+, 56K anode resistor, 164V plate voltage you end up at only 2mA and rightfully at 11V. there, they do _not_ sound very nice, imo. at ten times the current they rock

i find that operating point very odd, indeed. 6N6P is one of my favourite tubes and i use it in a bunch of gear (not hifi though), 2mA sounds .. well, 12AU7'ish
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Old 5th February 2009, 12:04 AM   #5
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well, that's quite a lot! widowmaker seems to suggest that the russian versions will tkae abuse more kindly though?
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Old 5th February 2009, 10:58 AM   #6
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Quote:
Originally posted by makeb4break
thank you for your reply

i do switch my amps around a lot, so that's another reason i'm not so concerned about tube life. more intrigued with the notion that the russian 6C4C sound _better_ at 350V and above 15W ...
I can tell that for sure: you still will get a reasonable long service from both 2A3 (good chinese types included) and 6S4S if you run them at 16-17W.

Yes, NOS 6S4S (thanks to its excellent construction) appears to be a bit more linear at higher voltages.
With 2A3's, both NOS and chinese, I always got the best results with 250-270V anode voltage regardless of SE or PP operation.

IMO, the 6S4S requires DC filament supply, unless you like IMD.

The overall result always depends primarily on how you drive and supply them....

Cheers,
45
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Old 5th February 2009, 09:12 PM   #7
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i'll go dc on my heaters then and probably bias them up towards 20W @ 360V

<The overall result always depends primarily on how you drive and supply them....>

have you been talking to my wife?

cheers,

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Old 5th February 2009, 09:15 PM   #8
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what makes the (internal construction of the) 6S4S different from 2A3s?
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Old 5th February 2009, 10:26 PM   #9
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Quote:
Originally posted by makeb4break
what makes the (internal construction of the) 6S4S different from 2A3s?

The 6S4S practically has the same double-plate design of the 2A3 RCA. The first big difference is the filament suspension. Then the tolerances of spacing between the electrodes are reduced (I think this is also one reason for the higher rating of the anode voltage). I still have to see a 6S4S with a (well evident) canted structure and/or glass.

Basically, IMO, the RCA 2A3 during its "cycle" remained practically the same for decades
(because of beam power tubes first and transistors then, which relegated the DH triodes in the class of "obsolete" devices....) while the russian, that came later, took advantage of better technology (better industrialization).

There are however, NOS 2A3s with more elaborated construction but tolerances have never been as tight as in the 6S4S.

I will never understand why the russian developed the Sovtek 2A3 which, I am afraid, is worse than a classical chinese double-plate and did not continue to produce the 2S4S.....

Cheers,
45
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Old 5th February 2009, 10:38 PM   #10
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thanx for the info. off to ebay to stock some more russkies then

what timeline are we talking about here? when did the russian 2A3 hit the market? how long did they produce it? (i'd also like to know that about the RCA 2A3)

did the russians ever do a 300B'ish tube? i haven't really found one

cheers,

comrade mb4b
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