What to you valve tech thinks of this .......

Heath

found this , and wondering what you valve gurus think of this , will it actually work ....... basically a 12ax7 preamp .....

http://www.sugardas.lt/~igoramps/tomato_preamp.htm

Bob-Dubery

Unless I've forgotten how to read a circuit diagram that pre-amp has TWO valves.

inflames

I'm with Bob, there is 2 valves. Can someone explain?

Heath

the 12ax7 is essentially 2 valves

Bob-Dubery

Tailon. wrote: the 12ax7 is essentially 2 valves

I thought about that. For about 2 seconds. Then I decided that it couldn't be because how, in a single glass tube, do you keep the two signals separate.

But the 12ax7 is a dual triode package.

So I'll just shut up now and go sit in that corner over there....

inflames

Did not know that, thanks Tailon ?

aja

X-rated Bob wrote:
Tailon. wrote: the 12ax7 is essentially 2 valves
I thought about that. For about 2 seconds. Then I decided that it couldn't be because how, in a single glass tube, do you keep the two signals separate.

But the 12ax7 is a dual triode package.

So I'll just shut up now and go sit in that corner over there....

Thank goodness there is no "dunce cap" button! ?

A lot of us would be in the corner then....

AlanRatcliffe

Can't speak to this one, but I built a couple of these a few years ago and they were pretty cool:
http://www.paia.com/proddetail.asp?prod=9305HSRP

Heath

thats not a bad price ..... looks interesting

matta

Yes it is ONE Valve, a 12AX7 is a DUAL TRIODE, 2 Valve in a single tube, each acting independently of each other. It is a 9 pin tube, the pin-out's I've posted below, it will explain things a bit better.

One tube that has my fancy of late is the 12DW7/ECC832, it is also a dual triode, one half 12AX7 the other 12AU7, it SHOULD yield some cool results as preamp valve if biased correctly, more headroom at lower volumes, it is even pin compatible, but a re-bias for optimal performance is needed.

Back on topic, the design looks ok, seen better ones, the B+ is fairly low on the plates, most are almost double that.... still interesting to proto, though there are couple better options around.

Cheers

Matt

TomCat

While on the subject of ECC83's.......

For the filament wiring does one only use pin 4 and 5...or does one wire 4/5 together and also use pin-9?

Valie

The ECC83/12AX7 valve has got 2 filaments. It can work on 6.3 volt or 12v. For 6v operation you connect point 4 and 5 together and use point 9 as the other connection point.For 12v operation you would only use points 4 and 5 (series) Point 9 is the middle tap.

Gearhead

Edit: Valie beat me to this one, but note:
You can put 12.6V floating between 4 and 5 and put 9 to ground through a small value 1/4W or more resistor since the heaters essentially are electron donors.
You can put 6.3V floating between (4 and 5 tied) and 9 but remember to reference as per above. Do not tie directly to ground.

TomCat

@ Gearhead and Valie

Got it....Thanks.......That was how I understood it but I just wanted to make sure...... 8)