plate resistance 12x7 12at7 12ay7 12av7? discussion

[SteveinTempe]

I have been experimenting with different triodes
used as power tubes and also
in preamp positions was curious about
swapping differnet tubes in and out of the same circuit
Some folks think you can just swap them no realizing the
plate resistance differences anyone here
Have a list or a chart that compares all these
or have some experience swapping them ?

This is not related to 18watt I acutally took an old
bogen MX6 and converted the 12at7 position to power
tube like configuration and have some interesting results
with a baby output transformer it makes noise..

not bad for a starved power supply

[idiotwithasolderingiron]

steve-

unrelated, please email me - my email link is below...

Thanks

Dave

[loverocker]

Steve - I've not experimented, but I've got to try the 12AU7 as a power tube at some point. The crunchy racket that Doug Hammond gets from his Firefly (1x12AX7 and 1x12AU7) is unbelievable.

[zaphod_phil]

You can often swap 12AT7/ECC81s, 12AU7/ECC82s and similar dual triodes into 12AX7 positions. Two things happen. First you get a bit less gain with the AT7 and a lot less gain than with the AU7. Next the bias/operating point changes, so that they're biased warmer with the same resistor values as the AX7 uses (in the AU7's case a lot warmer). This tends to give a fatter sound. And as the AU7 is a driver, it is like a small power valve and can be used in low power amps as such. I've even heard of someone building an 18W Lite, but with a single AU7 in push-pull instead of the two EL84s. Apparently, it had a great sound, just like a small 18watter - kind of a 1.8watter!

[SteveinTempe]

Thanks dudes I dont mean to be so far off topic but I like this Idea of a 1.8 watter!

I have one thats makes noise but it sure needs a bigger power tranny
its kinda compressed and even cuts out because the power supply just cannot deliver..

the 12bh7 tries to suck even more out of the thing..
also gets louder if you match the output 3.2 ohms..

kinda fun at 1:00 AM

[Plexi]

Yep what Phil said.. alot just look at the gain..you can look at the tube data pages,and see how things change with different voltage ranges..
And the difference in dissapation of the tubes.. theres more to it than gain of the tubes. The tube data usually shows and tell alot..

theres also a few good books on tube data, types etc.. One i like is Tube Lore..very informative book.
Richie

[zaphod_phil]

I dont mean to be so far off topic but I like this Idea of a 1.8 watter!

So did I! I think maybe it was someone on the old Yahoo-hosted 18W group, but I'm not certain, as it was quite some time ago. But it did make me think it would be nice to make a home-practice version of an 18watter that way, or even add an extra 1.8W output channel to a regular 18watter for home/ apartment use.

[SteveinTempe]

Thats It I'm leavin' town I off to 1.8watt.com!!