All DHT Push-Pull

[Cressy Snr]

Here's the latest hare-brained scheme; an all DHT push-pull amplifier made up of stuff I have doing nowt at the moment. Very simple circuit with transformer phase splitter

Three stages. 26 first stage, choke-loaded 4019A Post Office repeater amplifier valve as low-distortion driver and a pp 2A3 output stage.

No component values yet as it's just the seed of an idea at the moment. I could choke-load the 26 first stage too.

Any comments?



Steve

[andrew Ivimey]

Yep, hare brained - Let's do it!

But why? because you can!

I don't know this 4019 at all. What's its virtue?

What interstage have you (in mind)?

or

its so much easier to do something simpler, say 417 into interstage to 2A3 output pair. I had this rocking a few months ago - wish I'd never started Amity now.

Where does PP really get you apart from WELLY?

ponder/thinks...

[Cressy Snr]

Y

Where does PP really get you apart from WELLY?

ponder/thinks...

Er...... I'm not sure I know anymore, so I'm with you on that one Andrew.

I am very much enjoying the 6336A SE amp at the moment. Every time I put back the push pull amp, fiendishly clever and much sweated over as it is I find there's something missing from the presentation.

When you've worked so damned hard on something, as you and I both have with these pp amps, it gets a bit hard to let go and just stop.

The welly factor is indisputable. PP amps rock like nothing else I've heard. But if you're more of a jazz, blues and soul lover, you don't need that sort of hairy-arsed power. So uncouth doncha know.

So I might just simplify this amp down to a single ended type and see how it goes.

The 4019A is a rare beast with the old tilted plate construction, and uses a 300B sized bayonet socket; a pair of suitably period bakelite ones which Steve S has kindly loaned me.

It has a lovely set of curves

Here's a pic of it. Look very carefully and you can just about make out the tilted plate structure inside the bulb.



Steve

[IslandPink]

Steve,
I'd say an interstage and a pair of 2A3's might be too much for that 4019A , looks like it runs below 10mA with 5k Z-out of so . Try it , but don't be disheartened about PP Class A if it doesn't sound right ...

You can ultrapath the output stage as per the Lynn Olson stuff which will keep the PS even more out of the picture .

Mark

[Cressy Snr]

Hi Mark

Yes... The operating advice on the box gives 130V on the anode 8mA of current at -8 grid volts. So you're right about it not coping with driving a 1:2 interstage and a pair of 2A3s.

OTOH it should manage a single 2A3 using a cap instead.

I've had these valves for a while and am itching to put them to use in something. If Phillip Ramsay can get away with paralleled ecc83s driving 2A3s then I'm reasonably confident the 4019A will be OK.

Is there anything else in the DHT family this valve might be better able to drive as I'm not that well up on DHT power triodes, having only ever used the 2A3

Steve

[andrew Ivimey]

It does look rather nice!

[Dave the bass]

Bah! Light bulb out a Microwave oven innit?

DTB

[steve s]

I'm not sure of the specs for this valve steve
i would guess it has a gain of around 10

if thats correct, for most dht output valves, means you need 3 stages..
cap coupled..

unless you used something like a triode connected kt66/el34 etc which are easily driven...
if you still have rocky.. try clipleading it in as a driver for it.. you will tell the difference
...if you get it right ...

if you dont.. you may get the smoky atmosphere of a jazz club..
as you unplug it fast...

steve

[Will]

It looks like a very nice valve but not knowing
its sound I would put it in the pre position and
use the 26 as it has almost the same sound as a 45
to drive the 2A3 which can have a hard edge.
Talking SE not PP.
and the 26 is easy to use in this position.

[pre65]

Hi-what about the LP2 ?

Amplifcation of 15 with 2v filament.

http://cgi.ebay.co.uk/LP2-CV1166-DRIVER ... m153.l1262

http://www.mif.pg.gda.pl/homepages/fran ... /l/LP2.pdf

[IslandPink]

James is very fond of the P2 and LP2
Gain on the 4017a I think was around 7 from the d/s , yes ?
Will's idea sounds good .

You might need to take some steps to damp vibration if you use it as the imput valve. Looks v.nice though , interesting .

Mark

[Cressy Snr]

Hi Guys and thanks for the tips.

I was debating whether to put the 26 in front of the 2A3 rather than the 4019A and I think that is what I'll do. They are both roughly similar, in terms of gain, but the 26, being susceptible to hum, might be quieter in the driver position.

Steve

[triodeconnected]

Where does PP really get you apart from WELLY?

A better frequency response for a start.
And with triode-strapped KT66s, PX4-quality sounds........

[Nick]

A better frequency response for a start.

Assuming a competently wound and sized transformer in both cases, what is it about push pull that provides a better frequency response?

Given that I don't own any kt88s or px4s I can't comment on the other part.