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6S19P Amplifier

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I bought 10 of this tube because I would like to experiment with triode sound, without shelling out the cash for 300B's or 2A3's or the like. I was browsing some sellers on eBay and came upon this tube, the 6S19P (6C19pi). It has some interesting specifications, one of which is an 11-watt max plate dissipation. I figure that I could have around 15 watts safely with a PP configuration.

Here are some specifications and pictures:

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


http://www.russiantubes.com/prop.php?t=12&p=309
http://www.klausmobile.narod.ru/testerfiles/6s19p.htm

The tube requires a big voltage swing to drive it, as I've learned. Rather than design a very high-powered, more complex driver stage, I'm beginning to consider using an interstage transformer. This one looks like it might work: (http://www.edcorusa.com/classx/matching/xsm/XSM600-10k.htm )
I read of a transformer like this being used to drive a push-pull pair of 2A3's ( http://www.bonavolta.ch/hobby/en/audio/2a3_4.htm ), which could simplify things, but I really don't know how to design a circuit using these transformers. Does anyone have any experience in this?
 
Well, my bundle of 10 of this tube arrived a week or two ago, and I'm still interested in trying my hand at an amp. I'm thinking push-pull into some 2.5K Edcor OPT's, here: http://edcorusa.com/products/transformers/cxpp/cxpp25-8-2_5k.html . Since the plate resistance of the 6P14P is so low, I assume that this is a reasonable primary? I'm thinking about a Williamson topology to drive the tubes, except with some type of 9-pin semi-equivalents, maybe a 12AT7 input and splitter to a 12BH7 driving the 6S19P's? Any thoughts?
 
well, i've hit a couple snags. mostly, it's that this tube requires a lot of voltage swing on the cathode, but at the same time, i'm trying to work with a main B+ of around 280V. it's hard to feed a driver stage 280V or less, assuming more filtering after B+, and expect it to swing that kind of voltage.

For example, I've picked a bias point, given a 280V B+, at 200V and 40mA on the plate, at around the -75V mark. I quartered an 8K a-a output impedance on an output transformer to get 2K, which gave me my slope.

Depending on the power transformer, I might try to run the tubes VERY hot at, say, 60mA and around -55V on the cathode. A big 300-0 300-0 500mA Antek toroid into a 10H 300mA choke might do the trick. In that case, I'd probably only need to swing 65V in order to have decent headroom, which is a bit easier. I'm having trouble figuring out TubeCAD, though. I can arbitrarily set some parameters to get a pretty decent "Vo max" statistic, but what happens if the "calculated part value" for Rk doesn't match the one I have?

The long-tail pair is also pretty difficult to get working in TubeCAD... well, I guess I have plenty of time.

The plate dissipation I calculated (pretty simple, 160V on plates * 60mA current) is 9.6 watts. 19.2 watts of dissipation, but at what efficiency? I've got my eye on a the Edcor XPP15-8-8K, 8K a-a, 15W, at only $19 per :)
 
The thing is, if I use a value of 500 ohms, the slope of the loadline in pure class A is UNBELIEVABLY steep - almost vertical. Imagine this. B+ of 200V, let's say, divided by 500 ohms. Current maximum of 400mA! My _graph_ only goes up to 140mA. What do you suggest I do, in this case? Even 1kOhms is too steep, and 2K is what I found to be comfortable, looking like about -1 for slope.
 
Attached is a barebones schematic showing the 6S19P in PPP. I figure I want some decent output power, the tubes are plentiful, and the halving of plate resistance means a steady 2.5K on each plate, I'm pretty sure.

An externally hosted image should be here but it was not working when we last tested it.


The 100-ohm plate resistors, I hope, help evenly distribute plate current across the two tubes per phase. I figure I'll try to bias the tubes around -60 to -75 volts, hopefully not too much more than 50-55mA per. I'm looking at around 8-9 watts of dissipation per tube, total of around 32-36W per channel, probably under 20W of audio power, right?

Anyway, how does the basic layout look? Sharon at DIYTube suggested using an LM234Z in the LTP due to lower B+ voltage after two filters but I'm not completely positive how to implement it...

http://www.diytube.com/phpBB2/viewtopic.php?p=8019&sid=155955c9d25b01e77b0d8a8aa090c6d1#8019

Thanks!
 
Have you thought about swapping the 6DJ8 and 12AT7? It seems like you would want a beefier final driver tube, something that can swing more current. Maybe a 6BX7 or 12BH7? I tried playing with a 6C19 to drive an 845SE but couldn't get the bias point right.

Instead of the LM234Z current source you can use an IXYS 10M45S. People have reported good results and its very easy to implement.
 
The thing is, if I use a value of 500 ohms, the slope of the loadline in pure class A is UNBELIEVABLY steep - almost vertical. Imagine this. B+ of 200V, let's say, divided by 500 ohms.

2* RP is the rule of thumb for maximum P.O. in an SE triode amp, higher loads will usually give less power and distortion.

You may be better putting your even current sharing efforts into the cathode or bias. Or just drop 2 tubes. :) They should ok with seeing a 1,250 ohm load.

Those resistors are mostly degrading your power supply.

I figure I'll try to bias the tubes around -60 to -75 volts, hopefully not too much more than 50-55mA per. I'm looking at around 8-9 watts of dissipation per tube, total of around 32-36W per channel, probably under 20W of audio power, right?

Be aware the load increases as you depart class A, its a pain to run PP loadlines, but you may not get the power your after.
 
Well I'd like to stay healthily within Class A but am still a bit fuzzy on exactly what that entails in terms of selecting bias points and whatnot. I don't plan on building PPP 6S19P monoblocks any time soon but if I did, I'd want completely clean, Class A sound with no feedback, mostly because the even-order distortion would be taken care of. I chose 6S19P's because they're nowhere near as expensive as the bigger, more famous triodes, but I have faith that they can make some great sound, and some decent power.

I'd definitely consider using a 12BH7 to drive the 6S19P's as they have a much lower plate resistance, and (as the above mentioned) more current handling. Doesn't make much sense to be stingy with current when i'm looking at feeding 200-240mA to those brutes up front...
 
Hi,
2* RP is the rule of thumb for maximum P.O. in an SE triode amp, higher loads will usually give less power and distortion.
Another bonus is that the lower coil ratio is advantageous the OPT's bandwidth as there are less coil and wire induced capacitance.

I'll second the 1250 load, for me, it doesn't matter if you can see it on the graph;)

Another good driver would be 12B4, low rp with sizable current, I don't get the much complained microphonic..

Cheers
 
Update! I'm probably going to use a 50VA, 9V toroidal power transformer as my OPT. The dual 115V primaries will act as a centertapped primary, and using 9V secondaries in parallel should yield me an impedance ratio of ~1306:8 ohms, which is perfect for the very low plate resistance of the 6S19P. A 50VA transformer will probably have pretty good bandwidth on this amp, which, if it stays pure class A, will only have 10 or so watts maximum. I have no funds though so this is on the back burner :)
 
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