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Old 25th August 2003, 05:24 AM   #1
exurbia is offline exurbia  Australia
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Default 6336A valves

I have 6x 6336A valves brand spanking new with special coolers

does anyone have a suggestion as to how i can use them or

should i sell them ? .

thanx in advance
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Old 25th August 2003, 05:33 AM   #2
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Holy CHIT! Sell them and get like $400 (not literally, but they're worth a lot) or use them for an OTL. Each one counts for like, 2x6AS7 so it'll be easy.

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Old 25th August 2003, 06:08 AM   #3
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As Tim mentions they're like a super beefy dual 6AS7/6080 with a 60W (2x30) plate dissipation. Don't seem very linear, but would work in OTLs, SRPP (incl parafeeds) or as pass/shunt elements in active power supplies.

However, they're not worth much. I got a half dozen NIB for less than a couple of pizzas. Prices on ebay are pretty low at the moment too.

What you do with them depends on what you want to accomplish doesn't it? Could be used in a highish power amp, but low impedance OPTs are less common as are higher current PS chokes. Try them and see what you think. The SRPP in particular is easy and may be able to use OPTs from other amps.

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Old 25th August 2003, 07:36 AM   #4
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Really? Guess I better buy some up then..
ISTR them being expensive.. yeah AES has them for $50 each.

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Old 25th August 2003, 12:44 PM   #5
316a is offline 316a  England
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Default Sooper Dooper SRPP

Quote:
Originally posted by exurbia
I have 6x 6336A valves brand spanking new with special coolers

does anyone have a suggestion as to how i can use them or

should i sell them ? .

thanx in advance
Hello ,
6336 would make an excellent stacked SRPP/SEPP (parafeed) output stage Use 1st tube in fixed bias for the lower amplifying stage , use 2nd tube as upper SRPP elements floating the filament to 1/2 B+ . This should make a good sounding output stage , use something like a 20uF parafeed cap and 600/8 ohm output transformer (a 230:12/12 mains toroid would work well for experimenting) . Only trouble with these things is that they're greedy buggers with the filament supply (6.3V 5A) . Have fun !

316a
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Old 25th August 2003, 06:10 PM   #6
PRR is offline PRR  United States
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> I have 6x 6336A valves brand spanking new with special coolers... does anyone have a suggestion as to how i can use them

I've been looking at these for 30 years. As far as I can tell, they are low-gain power-pigs.

Good mostly for the original purpose: massive regulators.

As audio tubes, the cathodes are too big (power hungry) for the output, and the gain is WAY low (Mu=2).

The heavy cathodes mean this is more of a heater than an amplifier.

The low Mu means that you can not build a practical quasi-efficient Audio Amplifier with 6336 unless you use an additional power supply for the driver.

Working at 250V B+, fixed-bias, the peak grid voltage is over 80 volts. So the driver probably needs over 400 volts B+ to run clean.

Fixed-bias is not a good idea on low-Mu triodes working at their ratings: small shifts in the tube can mean large shifts in bias and thus a melt-down. It actually seems to work if you run a 400V B+ and let 100-150 volts drop in a cathode bias resistor. But that means 33% of your power is wasted in the one resistor.

It roughs-out like: 60 watts in two plates, 30 watts in the cathode resistor, 30 watts in the heater == 120 watts of heat pouring out of the chassis, for maybe 20 to 30 watts of audio power.

Working at fairly high plate voltage and high load impedance (much higher than plate resistance) they would be fairly clean and linear. Except the enormous drive voltage often means more distortion in the driver than the output. You may need a quite beefy triode and a high driver supply voltage to get clean grid swings.

Also note that the 6336 grids are leaky, you need a fairly low grid resistor. Specs vary, but unless you have early (1958) TungSol the grid resistor should be 47K per tube. If you parallel a few 6336 to improve the power, the grids may need something like a small guitar amp power stage to whomp them around.

I'm sure it can be done. I may try it some day. Some COLD day when I need the heat.
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Old 25th August 2003, 07:49 PM   #7
DrG is offline DrG  South Africa
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Default not sure I agree entirely...

6336's getting rare and expensive. V-reg application lends specific characteristics (low-mu, high current) eminently suitable for OTL use. PP also possible - see attached circuit by De Haan which looks pretty good to me.

Personally I'm thinking of a hybrid single-ended darlington: 6336 into MJ11015 with current-source load.
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Old 25th August 2003, 08:48 PM   #8
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Hi,

As an example of an OTL amp using four 6336A per channel:

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Old 25th August 2003, 10:05 PM   #9
PRR is offline PRR  United States
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> see attached circuit by De Haan which looks pretty good to me.

Looks fine to me. Is fairly inefficient: 70W B+ and 30W heater == 100 watts in for a claimed 17 watts out. The 17 Watts out looks about right for 8K load and low distortion. With a 4K load it could make 35-40 gross watts at clipping, but distortion would be higher. Taking 100 watts in for 40 watts out, it does not look all that bad! Especially considering it includes heater power.

> OTL amp using four 6336A per channel

Assuming a 16Ω loudspeaker, eight triodes (four 6336), and assuming that you can jam the loadline into the "V" between the zero-bias line and the plate power limit: this gives 20 watts out for probably over 200 watts of heat. Also the driver tube is really working too hard to whomp those grids around, even though it is fed +490V.

The actual condition with 160V per tube suggests a 200Ω loadline per pair, or 50Ω for four bottles (eight triodes).

(Assuming it was designed to respect the 30W plate limit. Actually in speech/music it could swing far above the plate dissipation limit on peaks, and maybe even on 1KHz test tones. Sustained 16Hz might show a flickering red glow and eventual plate cracking.)

Witihin ratings, that gives about 16 watts per pair, 64 watts for the whole rig, IF you have a 50Ω speaker. In 16Ω it would be 21 watts, in 8Ω only 11 watts. Or you could stack a dozen bottles per channel and drive maybe 150 watts into 16Ω. However that's over 1,000 watts of heat rising off the bottles! (and your electric bill)

Ignoring the plate rating, it may make a whole lot more power, though with some doubt about tube longevity if you use that power a lot.

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Old 25th August 2003, 10:41 PM   #10
PRR is offline PRR  United States
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For audio, a more interesting tube might be 6528.

http://www.tube.be/6528.html

http://www.pentalaboratories.com/pro...dept%5Fid=1381

This is apparently a 6336 (same heater and plate ratings) but with Mu=9! The ideal Mu for a tube with driver running on the same supply is about 5: any less, and the driver can't swing the grid, any more and the perveance and thus the peak current drops. In this series of tube, when aiming for low distortion and high efficiency, the perveance is not so important and a Mu of 9 means easy driving.

In a 6336 circuit: reduce the bias and you don't need so much drive. It may work with 320 volts on the plate and only 25-30 volts bias and drive, a radical reduction from the 114 volts the 6336 needs in a similar situation. Power output is similar, unless 6336 output was limited by lack of drive, or you were wasting a ton of B+ in a bias resistor and can handle more tube-volt and plate swing.

They get the high Mu not by forcing plate resistance up, but by increasing transconductance (to 37,000 µMho!).

One disadvantage: the 6528 is a rare bird. It was apparently used only in one model of radio transmitter. And the Gm suggests it is not an easy tube to build. PentaLabs above lists it at $85, but uncertain availability ("Call").
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