Tubes-What do?

[diemilchmann]

Hey,
I have some very old tubes i pulled from my grandma's garage, and i have found no reference to them, other than old data sheets online. I also have some random sub minis. Without buying too many other tubes, is there some kind of small, tube amp project that could be done, possibly just with some rewiring of pins? Something like Frequency Central's Murder One or something.

5840W  x2
5702WB
5744WB

12AB5  x2
35W4
12AV6
50DC4
12X4

I also have a bunch 12AX7 and 12AU7.

Thanks!
Julian

[PRR]

> old tubes i pulled from my grandma's garage

With rare exceptions, garage-tubes are oddball radio/TV tubes, and very often the "DEAD" ones pulled out in a repair. And you mostly can't tell by looking.

Many radio/TV tubes can be perfectly good audio tubes, but if you have to ask, then you don't have the skill to adapt to them.

> Without buying too many other tubes

There's tons of fun in $5 tubes. Tube-cost is rarely any large part of total tube-job assembly. Did you get sockets? Coupling caps? (Are they good?) Hi-volt power transformers? (Documented?)

The amp I built a few years back cost well over $500 and used $70 of new tubes. The one I am dreaming of tonight needs a $100-$200 tube plus $400-$800 of transformers plus a chassis large and stiff enough to support a large glass jar and two dumbbells (what this tube and transformers amount to). And arc-welder filter-caps. The $200 made me gasp, because I knew that would be one of the smaller chunks of making a Whole Amplifier.

5840W, 5702WB, 5744WB - Ignore the W/WB codes. These subminiatures are semi-popular, although the overall size of a tube amp is hardly reduced with smaller tubes (there's SO many other components and too-tight construction is usually a mistake).

12AB5  - 12V version of 6V6, a classic audio tube. Cool, except 98% of the power transformers for 6V6-like amps have 6V heater windings, so you have to cobble a 12V heater supply (added expense).

12AV6 - half a 12AX7 plus some diodes needed for a radio but nobody finds a use for them in an amplifier. Super convenient for a radio. Amplifiers will need more than one such triode and the twin-triodes are more convenient.

35W4, 50DC4 - rectifiers for large transformerless radios. Useless even if new.

12X4 - rectifier, suitable for a couple 12AB5, can eat the same 12V, but a couple 40-cent 1N4007s work better.

12AB5. 12V B+. (Use 12V wart to power both heater and plate-circuit). Triode-strapped. 1K cathode resistor, 5K plate resistor. No input cap needed, use 0.1u 50V output cap. In a pedal. Should give significant boost and distortion. Much tweaking needed.

[lowend]

I'm no expert but I'm pretty sure the 12AX7 and or 12AU7 would get you 5 or ten W of distorting guitar amp. But like the man said, it's all the rest that costs the bigger amount so unless you actually wanted a 5W guitar amp you wouldn't bother.

[diydave]

I thought a 12ax7 and even a 12au7 can produce 1w max  . 
According to datasheets, that is.

[maarten]

Not Murder One, but Frequency Central's 5840 Boost:
http://www.diystompboxes.com/smfforum/index.php?topic=76356.0

Maarten

[lowend]

I thought a 12ax7 and even a 12au7 can produce 1w max  . 
According to datasheets, that is.

I was reading yesterday an old pdf from Philips, 1954, that said a 12AU7 amp circuit will make 5W, amongst a lot of other stuff that I don't understand.

I had a wee looksee at google and they use EL84 in the power stage for a lot of those 5Wers, but the 12au7 etc in preamp stage. Oh well, at least half the valves are free.

[phector2004]

Not Murder One, but Frequency Central's 5840 Boost:
http://www.diystompboxes.com/smfforum/index.php?topic=76356.0

Maarten

Also check "Le Craquement Thermionique"
Gotta build myself one, sometime

[PRR]

> I thought a 12ax7 and even a 12au7 can produce 1w max  . 
According to datasheets, that is.

No, a 12AX7 can _DISSIPATE_ 1 Watt.

A 100W incandescent lamp will dissipate 100 Watts. But it _produces_ 2 or 3 watts of actual LIGHT output (and 97 Watts of instant heat).

Unless specially made for Power Amplifier use, a triode in audio service will rarely output even 25% of its power dissipation rating.

The first good loudspeaker amplifier used a type 10 tube dissipating 8 Watts to deliver 1.1 Watts to the speaker. The 12AU7 is very much a small type 10.

There are better tubes. 2A3 dissipating 12.5 Watts will output 3.5 Watts.

Push-pull can do some better. Pair of 2A3 dissipating 24 Watts will output 15 Watts. But bias and drive requirements are non-trivial.

Look at "real" amps. 10W-20W DeLuxe uses two 12W dissipation tubes. A 40 Watt 5F6A uses two 23-watt dissipation tubes; its 60W upgrade uses two 30W Pd tubes. It isn't true that output equals dissipation. Two 350W tubes can churn 1,700 Watts into a load. But lesser tubes suffer many small losses which make it hard for sine output to be much larger than dissipation. And 2-watt tubes fall even shorter.

> Philips, 1954, that said a 12AU7 amp circuit will make 5W

This one?
http://www.drtube.com/datasheets/ecc82-philips1954.pdf

Does not give _any_ power-output conditions or results.

When you do find push-pull 12AU7 it is usually about 1 Watt output. Using a sharper pencil, I figure 1.6 Watts.... but going somewhat past ratings (WTH, 12AU7 are cheap) and using an unusually high impedance winding which will probably have high transformer loss and narrow bandwidth.

Oh, you could call 1.3 clean Watts "2 Watts!!" in the guitar market. What-ever.

> 12AX7 and or 12AU7 would get you 5 or ten W of distorting guitar amp

No. The grossly-distorted power output is twice the nearly-clean output. (Difference between the customary Sine and the clipped Square-wave.) 12AU7 is unlikely to make an honest 3 Watts of gross overdrive power. 12AX7 is 5 or 10 times less suitable for "large" power.

There IS a "small" twin-triode with a 10 whopping Watt output rating.

6A6/6N7 http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6N7.pdf

But it does the 10W only in class B2. The "2" means grid current, and lots of it. That means you need another power tube to drive the power tube (another 6N7). And a grid transformer as well as your output transformer. There was a time when this made sense. But a pair of 6V6 can be wired into the two 6N7 sockets, use the same power and OT, lose the grid transformer.

[Ronsonic]

Has anybody tried using the diode in a 12AV6 in clipping circuits?

Could be convenient.

Ron

[merlinb]

Has anybody tried using the diode in a 12AV6 in clipping circuits?

Not the 12AV6, but I have used other valve diodes- works like magic if you lower the heater voltage a little. You don't have to use 'proper' diodes either, you can just use the grid-cathode connections of any valve. Plus you can play with the anode voltage to change the 'diode' characteristics on the fly!