Other two odd tubes - 6DN7 & 12JT6A

[kagliostro]

A friend this evening give me four tubes

one is an used 6DN7 tube a Dissimiliar Dual Triode (General Electric)

one has plate 350v 1W - the other has 550v 10W

http://www.nj7p.org/Tube4.php?tube=6DN7

http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/6DN7.PDF

http://thetubestore.com/nos-6dn7.html = $ 7.95 - not very expensive

to me seems an interesting tube (to me ..............) is it so ?

three are NOS 12JT6A - the 12v version of 6JT6A a Beam Power Pentode (National Electronics)

http://www.nj7p.org/Tube4.php?tube=6JT6A

http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/6JT6-A.PDF

http://thetubestore.com/nos-6jt6.html  = $ 39.95 - an expensive tube (I'll give it back to my friend if I can't use in some way for an amp)

the 12jt6a are same brand but are different each other in their phisical body (two made in Usa one in Japan)

so the only thing I can think is an SE amp with an odd (and maybe in vain expensive) tube

are this tubes 12JT6A & 6DN7 usable ?

if 12JT6A is usable as final tube of an SE amp which will be the OT primary inpedence at the stated (in the datasheet for class A) 250v plate voltage ?

(I really find difficult to understand datasheet and understand which is the right OT impedance if the datasheet don't say it explicitly)

Many thanks

Kagliostro

[PRR]

They are plain old USA TV tubes.

The dual-triode is an earlier Vertical-sweep (frame) driver.

It might be a Fender Reverb Driver. The fat-side will make more spring-shake power than 12AT7, nearly as much as 6F6. Gain is low, the other side can boost gain. But that's an entirely new design, hardly worth the trouble just for one spare tube.

The big pentode is of course the horizontal (line) sweeep.

> which will be the OT primary inpedence at the stated (in the datasheet for class A) 250v plate voltage ?

Start with Pdiss/Vp = current Ip. Then Vp/Ip = approximate good-load impedance.

17W/250V= 0.068a = 68mA
250V/0.068A = 3,676 ohms

However being a SWEEP tube it is made to pass HUGE current at fairly low Screen voltage. 390mA!! A class-A audio amp at 68mA idle needs 116mA peak. 390/116 means the tube can pass THREE TIMES more current than we need. In an ideal world, we would want a 1/3rd-size cathode and 1/3rd the heater power. If this over-fat tube were cheap, maybe we'd use it anyway.

To use it "well": fixed-bias push-pull at fairly low supply voltage. A pair might make as much audio power as a pair of EL34, ~~50W. Lower B+, but custom OT.

[kagliostro]

Many thanks for infos PRR

> which will be the OT primary inpedence at the stated (in the datasheet for class A) 250v plate voltage ?

Start with Pdiss/Vp = current Ip. Then Vp/Ip = approximate good-load impedance.

17W/250V= 0.068a = 68mA
250V/0.068A = 3,676 ohms

this way I obtain the load impedance for a SE right ?

as from your indication those tubes aren't easily usable also if they can be used, more, the 12JT6A are too much expensive and their use will not be justified

Kagliostro

[DummyLoad]

It might be a Fender Reverb Driver.

or a pair for a low watt P-P amp.... or single in SE with a driver... 2 tube amp 6SF5 pushing 6DN7. won't be quite champ gain, but close enough. or 6J7 pushing 6DN7 - that might be interesting...

--DL

[kagliostro]

2 tube amp 6SF5 pushing 6DN7 - or 6J7 pushing 6DN7

Ach ................. 2 or 3 ham fest ago I've seen some 6F5 and may be 6J7

I'll look for that next time

Kagliostro

[darryl]

2 or 3 ham fest ago I've seen some 6F5 and may be 6J7
I'll look for that next time

Kagliostro, there must be a lot of hamfests in your part of the world. 

[kagliostro]

Here around, max 220 Km far

28 august a good one in Cerea (VR)

10 september a very big one in Marzaglia (MO)

24 september a little one in Maserada Sul Piave (TV)

15 october a little one in Bassano del Grappa (VI)

and many others 

Kagliostro