EL34 driver for PT15

[The Shadow]

To the Panel,

The only reason I'm asking this is because the EL34 is all I've got at the 'mo and I'd like to experment with pentode drivers. Also I'm aware the EL34 is not ideal distortion wise

However:
Can it be used to drive a PT15?

Below are a couple of crazy op points worked out from the loadlines with g2 at 250V and an HT of 150V.

The RL = 330R one in particular seems to give a distortion figure of about 0.3% 2nd harmonic if I've read Morgan Jones correctly.

It'll only swing about 20V either side of 100V but it'll push plenty of clean current into the PT15's grid.

Now all this is pure learning again for me so I'm hoping I've got the maths right.

For example, do the same loadline methods work for power valves or am I completely at the wrong end of the stick.

If so i'll get a proper pair of high gm small signal pentodes and abandon this silly idea. But it would be nice to have a go.

I'm also looking at a DHT old Brit simple preamp with valves courtesy of Steve S, but that's another story.

Steve

Edit: here's a circuit I worked out too.

[pre65]

Hi-as the ECL82 is such a super valve could that be used to drive a PT15.I have just ordered 4 (2 for the ECL82 project)and have 2 spare for the Rankin 45 (DC CC) which uses them.

Philip

[The Shadow]

OOPS
Those yellow op pints should be on the 10v line

[James D]

Umm from the persepective of an academic exercise you are spot on with the load line, etc.

but you will be using three times as much current ish in the driver as you will in the output valve

Now thats really pushing the envelope!!!!

[The Shadow]

Oh Well!

Never mind

I'll get some proper valves.

At least I've learned how to work out pentodes now

Steve

[IslandPink]

Steve,

An EL84 would be more worthwhile and well worth a go ....
If you have any - that's where I started on the VV32 SE amp .

Mark

[The Shadow]

Thanks Mark

I might investigate these on a breadboard to get a feel for pentode drive.

Can anyone sugest a nice, cheap, easily obtainable highish Gm octal small signal pentode I could use as I have octal sized holes in the current PT15 6J5 driven amp.

With the PT15 could I even get away with EF37As or is that just going to the opposite extreme of not enough current drive.

Steve

[James D]

Locktals sockets fit octal holes and a C3g is as good as it gets

[Pedro]

Steve,

I got my C3g's and C3m's from ebay from audiotubes.de - good price and fast delivery.

He has the loctal sockets as well.

Rgds
Pete

[Corne]

The Shadow wrote:
Can anyone sugest a nice, cheap, easily obtainable highish Gm octal small signal pentode I could use as I have octal sized holes in the current PT15 6J5 driven amp.

Steve,

I don't know about the easily obtainable and cheap part but the 6AC7/1852 (Gm=9mA/V, Pa=3W) might be an option.

The EF37 looks to weak, the Japanese design I've seen use Ra=82k with a 200k grid resistor on the PT15 (Cin=160pF), this results in a -3db at about 17kHz.


Corne