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Using a standard pentode-tetrode as output "space-charge tube" any ideas-experiences?

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Using a standart pentode-tetrode as output "space-charge tube" any ideas-experiences?

Hi All,
Had anyone experimented with using a standart (or especially TVline) pentode-tetrode as power stage output "space-charge tube" ?
- With a B+ < 35V
- G1(with substential grid current ) & A tied to B+
- signal driving G2

Thx for your ideas.
 
mmmmhmmm I was more thinking about a circuit in wich
G1>10mA @ 25V B+ (why not put a diode to block AC ?)
OT Z<1k tied to anode (for a single tube SE or why not Z=300 headphones?)
small bypassed cathode resistor
I was thincking of a few 5763 i have and I got also a 6DR6 wich tolerate well G1 current (at least a bit)
but my masterword here is low voltage (maybe also it can be interesting to raise filament voltage to achieve better efficiency despite tube life (as do real space-charge tubes))
I hope my english is clear enough.
 
thank you for your answers,
Tom pointed at it, I was looking for a "alternative" to real space charge tubes like the 12k5 that I can't find here in France, My old tube databook list also europeans EF97 & EF98 but I didn't manage to find them either.
I've just found a source of ECC86 (wich is a real space charge tube (from 6V to 30V B+) but not intended for output stages. very funny to play with.
My Idea was to get the same 10-40 mW , from a rugged TV line tube G2 driven, with also 10mA G1 (tied to B+), & maybe 20-100% increased heater voltage. (I got several bunches of those TV tubes so tube life span is not a problem).
Thx Tom for your 12K5 sending proposal, but for now, It will surely be costly to send few of them, I have better to take some more weeks to find space charge substitutes. Anyway if I can't find any, I wil be interested, It's very nice from you, and I'll be glad to send you some tubes you're looking for too ! (any needs ?)

the whole idea is to make distortion (we're not talking HiFi) guitar effect-amp(mW) FOOLPROOFED, as guitarists have often crazy ideas.

Kevin's idea to parallel tubes in a totem pole may help also, but i'm not so familiar with totem poles, could you give me a few datas for the first prototyping approach.(let's say with a typical TV line sweep tube).

Thx again Bembel
 
My two cents:

If you're looking for novel ways to hook up tubes for low-voltage, higher current operation, try Steve Bench's site:
//members.aol.com/sbench101/ specifically his discussion of inverted operation (swapping grid and plate connections). He gives examples using 6AS7 and 5687. The drive voltage requirement is kinda high, and you won't get any voltage gain, but it seems that you can realize substantial "plate" currents at low (<50V) voltages. He also mentions using beam tetrodes in this mode.

When I first read Steve's pages on inverted operation, I was inspired to buy several 12K5's. I thought this might be a good candidate, since the G1 space charge grid is designed to dissipate 1W, as noted above (and they were cheap at the time!). Alas, real life intervened, and the 12K5's have joined their idle comrades in the tube box, awaiting a day when I can come back and play at my workbench for a while (sigh!).

Have fun, and good luck!
Mike
 
12k5 and 12AL8 space charge tubes

I just finished a single 12k5 output tube amp,and im pleased with its sound. I want to get more power and headroom, in a second version, maybe stereo, so, I intend to run at 24 to 30 volts. The 12AL8 tube has also been used for low voltage designs, i may give that one a try also. About cascode circuits, that is something i think is worth a try, i have to find some cascodes close enough to these tube values though. I lost the link for the Pass tube/jfet cascodes, does anyone have them? Ill post all these up when finished and compared in sound. Ill just add that i am enjoying sweet souind out of the little 12k5 as we speak;)
 
Even space charge tubes never were used for anything close to hi-fi. Any tube will work on low voltages, but distortions will be horrible, and output power will be a fraction of what you spend on cathode heating. Take a bunch of JFETs in parallel if you want good sound. However, if the purpose is to experiment, it is a totally different story. You may solder a bunch of 6AK5 in parallel.
 
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