6C33C data sheet

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Cressy Snr
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#1 6C33C data sheet

Post by Cressy Snr »

Just thought I'd post this as there seems to be a growing interest in using the 6C33C valve.

I don't know much about these tubes but apparently this is one of the most comprehensive data sheets available for this valve. It is 7 pages long and was compiled by Michael Boele in 2005

http://www.jogis-roehrenbude.de/Russian ... heetMB.pdf

Might be useful

Steve
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Nick
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#2

Post by Nick »

Very useful link Steve, thanks. I had seen that some years ago when I first thought of using them, but lost it since then.

Oddly enough, the 6c33c was the first valve I intended to play with after building the WAD6550, I had all sorts of odd ideas for them suce as a outpout stage using them that was like a SRPP (that was before I discovered OTL circuits), and SET but using a PP transformer with DC on the other leg (thats before I discovered Dave Slagles DC offset experiments).

But before I built anthing I got lucky and was distracted by Darrens 6em7. So went that way.

I say lucy, as since I have been playing with the 6c33c for the past two weeks, I know that all those years ago I would have stood bugger all chance of making sense of it.

I do see now, that trying to use them in SE without cathode bias would be a bad thing without a regulated supply or some OTL type servo, Lamm clearly isn't stupid, just a couple of volts movement in the B+ will cause 30-40ma change in the current, so you would be forever rebiassing them.
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#3

Post by Cressy Snr »

Hi Nick
Glad it was of use.

The bias problem is the same with the 6080/6AS7
They don't recommend fixed biasing that either because of precisely the same thing.

In the OTLs I have seen using 6AS7s they use fixed bias with servos to keep the current constant and very low value cathode resistors (around 2R) to create just enough degeneration to prevent any one valve hogging the current and burning out. So I suppose in very loose terms they use combination bias.

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Nick
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#4

Post by Nick »

They don't recommend fixed biasing that either because of precisely the same thing.
Yes, it seems though by using a regulator, much of that is avoided. The regulator and bias supply both use the same voltage reference, which should further assist the stability of the bias.

I will try running the amp via a variac and see just how stable the bias current is with changing mains.

I do like using fixed bias with this valve though, at 300ma the cathode resistor will be dissapating 15W or so, and the thing produces enough heat from the two valves as it is. (40w for the heater, 55w for the anode, so thats the best part of 200w for each monoblock).
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#5

Post by Nick »

I did the check with varying input voltage. Varying the mains supply between 230-250 only produces less than 10ma change in current, so the regulator is doing its job. I think that the change that I am seeing is due to the different heater current at the different voltages, but I refuse to build a 7A regulator for the heater supply :-).
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#6

Post by Andrew »

Oh go on.......I have a schematics for a 15 amp one somewhere, only 3 LM317s

cheers,

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#7

Post by Nick »

Oh go on
No, bugger off :-)

Hum is down to the 200uv level as it is. The basic hum level is controlled at the moment by the ouput transformer picking up the field from the mains torroide. I have rotated the torroide so its just about nulled (almost like a hum pot). I just have a small earth loop type hum from one chan now to sort out.

Despite the high current through the heaters, the 6c33c seems to be very good at ignoring hum, I guess having the two heaters per valve heaters wired in series may have them out of phase.

Anyway, Simon is poping by tonight, so see what he thinks to them.

I must create a thread in the projects section when I have drawn the circuit out.
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#8

Post by simon »

Looking forward to it Nick. If it's as funkay in the bass as Andrew I's at the last Witham it'll be great :D
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#9

Post by Andrew »

I wish my hum chasing efforts were as sucessful as yours.

The hum on the phono must now be coming from the PSU, though theory says its should be chuff all. Huh, what did theory ever tell us. The hum is getting into into the pentodes, and going through all the gain stages and by the time it leaves the end its loud enough to be very intrusive.

I did find one of the PSU boards misbehaving last night, but not in a way that would cause the hum. I now need to fix the scope to continue.

I'm now thinking the noise could be the zener that bypasses the reg.

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#10

Post by Nick »

I would try and verify that its the PSU before starting on a massive effort (I have been there myself). Add a big as you have electrolytic and a 1k resistor as a RC filter after the reg, if the hum is the same its unlikely to be the reg at fault.
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