Unusual Output Trannies

[gingertube]

I went looking for an output tranny for my latest PP 6V6 amp build on the weekend and dragged out a pair of trannies which I have had on my parts shelf for 10 years or so.

I was always under the impression that they were 8K Raa from an EL84 HiFi Amp.

I tested them and found that they are in fact 12K Raa to 4 and 8 Ohms (No U/L taps).
Anyone know of tubes which these might suit. I'm aware that old 6K6 like 12K but is there output tube easier to find that I could use them for?

Any advice greatfully received.

Thanks,
Ian

[jazbo8]

What's the planned B+ voltage? Does it have to be an octal tube? If not, the 6AQ5 might work.

[Stevem]

About how much do they weigh, are they like 15 watt or less?

[matt h]

(deleted)

[johnnyreece]

Just to state the obvious-- running a mismatch for 6k is also a pretty good option.

Would the 12k primary work better for triode strapped stuff?

That's exactly (okay, not *exactly*, but close enough) what I was thinking. I think that would be pretty decent for a duet of 6SN7 tubes, if one were interested. If they're really beefy, that might be a waste for a sub-5W amp, but hey, it's better than letting it sit on the shelf!

[Phil_S]

EL95's want to see 10K. These can often be had cheap on eBay. A while back, I bought a lot that had a couple of Telefunken and other old brands for dirt cheap. I'm thinking 10K is close enough that you can draw the load line to make it work. Nice tube, too. Not real loud.

[gingertube]

About how much do they weigh, are they like 15 watt or less?

From the physical size I would say they are around 15 Watt rated.

The 6SN7 option is attractive for a low power amp.

Other triode options I have on the shelf for push pull operation would be ECC99, 6EM7, would need to check load requirements for these.

Otherwise a 4 Ohm speaker on the 8 Ohm tap to reflect 6K would be what I need to do. That opens up a lot of options.

Cheers,
Ian

Edit: Did some more research, looks like they will suit either 6BM8 (ECL82) or 6DX8 (ECL84) - I have stocks of both.

[JMFahey]

People usually mismatch "downwards" in their builds, so they are used to it, but mismatching "upwards " is about the same thing.
12k vs. expected 8k?
No big deal, about as wrong as loading that "8k tube" with 5k3 .

So think "8k" tubes, use those transformers, you'll probably lose 20% expected power (no big deal, usually inaudible difference) and workload for tubes will be easier.

Even old "pulls" will probably be acceptable there.

Why waste time looking for obscure unobtanium tubes to match paper specs?

Here we have common as dirt EL34 tubes, showing how loadlines are grapically calculated using published datasheet curves.

I calculated 3 very different loadlines: the way I prefer and use in my own transformers and amps, plus a "low" one and a "high" one.

This is just a "classroom" example, guitar amps use around 400V screen voltage, not 250V as shown, and that is a game changer, but method is the same.

The red line is the classroom perfect" loadline, usual guitar amps go for the green one , for multiple reasons, one of which being a cheaper, easier to wind transformer (less turns of thicker wire) but see that going higher (blue) is about the same

[gingertube]

Juan,
Thank You - I'll print off some datasheet curves and get out my calculator and pencil and ruler.
Cheers,
Ian

[katopan]

12K is spot on for a pair of Russki 6P1Ps.

[Kagliostro]

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Datasheet
http://www.mif.pg.gda.pl/homepages/fran ... /6V6GT.pdf

PP 13W:

plate 315v
screen 250v
common cathode bias resistor 150ohm
load 12,000ohm

See Radiotron A504 circuit
The two screens are fed through a common 3,000 ohm resistor from the plate supply voltage, a bleed resistor of 15,000 ohm is connected between the screens and the cathodes, screen and cathodes must be bypassed

K