PP 2.5k primary Output Transformer

[walkman]

Hi,

Can any one suggest a tube line up for an output Transformer i aquired.

its marked 2500 to 4 ohms, it is push pull as far as im aware

attached is a picture.

The power transformer on the same chassis puts out 285v.

it has octal sockets.

any help would be great.

[Bruce / Mission Amps]

I can't tell how big it is... 10watts 20watts 60 watts 100 watts?
Nobody will be able to tell you what set of tubes to use unless you can identify how muchg power it can handle.
All you'll get is something like, these tube typically see around 2000 to 3200 ohms four 6L6s, two EL34s, two 6V6s in parallel... etc etc...

[Rob Mercure]

Like Bruce noted the power capacity is important. I've got a "15W" Stancor that will go down to 20 Hz that would probably be good for twice that in a guitar amp. So I've thought a bit about output tubes that would work into such a low impedance and the 7695/7754 would probably work well in PPP. AES has the 7695 for quite cheap but these bottles have 50 V heaters. I'm comfortable running them from the mains - this is what they were intended for and the heater to cathode insulation is quite robust - but if you're not comfortable an isolation tranny is easy to wire up.

And there are some other tubes - 6Y6s I believe, etc. Just go to Duncan's site and start searching through the TDSL - that's what I did!

Rob

[walkman]

Hi Bruce,

Heres some pics .... let me know what you think be best

Thanks

Walkman

[Chuck H]

What about...

I might be neglecting part of the requirements here, but is there any reason he can't just run an 8 ohm speaker load for a 5k reflected primary impedance and use a pair of almost anything (el34, 6l6, 6v6, etc.)?

Chuck

[Bruce / Mission Amps]

It looks like about a 35 to 50 watter to me.
If its 5K with 8 ohms then, yes you can run just about any tube but I'd guess at it making the most amount of power with a pair of 6L6GCs ar around 450vdc.

[Amp Kat]

I certainly agree with the above but do you have any idea what it came out of ?

[walkman]

I got a reply somewhere else, that for the these transformers

5k plate-plate to 8 ohms, or 10kp-p to 16 ohms, would be ok

and that a pair of 6L6's with a 10 henry choke-input

filter from the power supply transformer,

should suit the below conditions.

Push-pull AB1
Plate voltage Vp 350V
Vg2 270V
Rk 250 ohms
V(g1-g1)pk 57V
Ip0 88mA
ipmax 100mA
Ig20 5mA
ig2max 17mA
Rl(p-p) 9000 ohms
THD 4%
Pomax 24.5W

it was suggested that the heater current for the power transformer, would limit, the possibility of using 4 output tubes.

i guess by th size of the OT , 24 watts would be a conservative rating anyway.

what do you think? Would it be worth sourcing another power supply?

if so suggestions for a 240v Tranny?

thanks you, Rob and Bruce for your input.


As yet i'm still very much on the drawing boards...

i'm sure to be asking more questions along

the way as it gets going ...

cheers

walkman

[Chuck H]

You should be able to get 350+vp from the power tranny you have. And since your OT is only 25 watts (give or take) you won't be using four output tubes anyway so the heater current restriction is moot. Using Duncan PSU for a quick mockup (285-0-285, 1n4007 bridge recto, 40uf first filter, 100ma current tap) your PT should put out about 375vp.

HTH
Chuck