ECL80 question.

[Zoe_N_Iain]

I'm wondering whether it's possible to use a pair of ECL80 pentodes in push pull, while using their triode sections as the phase inverter?

The triode and pentode sections have a shared cathode, which obviously doesn't make it a straightforward process, but is there any reason why it definitely wouldn't work?

My thinking at the moment is that if we use the triode from valve A to drive the pentode from valve B, and vice versa:

a) The cathode resistor for each side can be made correct for the bias needs of the triode stage.

b) The bias to the pentode can be 'corrected' using a fixed bias voltage.

Is there any gotcha? It's not something I've ever considered before but the ECL80 sounds nice in SE and it would be good to try it in push-pull.

[Ray Ivers]

Z/I,

Well... one way might be to run both the triode and pentode sections fixed-bias, with grounded cathodes. You could have separate bias controls for driver and output stages, and run the triodes as a diff amp preceded by a concertina PI or whatever.


Ray

[Zoe_N_Iain]

Thanks, Ray. I'd thought of the fixed bias thing, now you mention it.

Don't quite get what you mean about the differential amp driven by a concertina, though. Can you elaborate? I often need the 'large print, lotsa pictures' explanation cos my brain is small and inefficient

Long time, no chat, btw. How you keepin?

[Ray Ivers]

Oh, not bad - and yourself?

Re the concertina thing - grounding the triode cathodes rules out using a LTP-type PI, so you're left with either using some version of paraphase (cascaded gain stages separated by a voltage divider) or a separate PI preceding the triodes, which function like driver stages instead of a phase inverter/driver.

Below is a link to the Marshall Major schematic, which shows the concertina/diff-amp circuit in detail:

http://www.schematicheaven.com/marsh..._lead_200w.pdf

Ray

[Zoe_N_Iain]

Ah, I get you now. I've looked at the Marshall Major before but didn't cotton on about what you meant until I looked at the link.

Seems straightforward enough, then. Cheers Ray. Just need to think of what preamp I'd want to put in front. Maybe 6SL7 triode > 6SJ7 pentode > 6SL7 triode cathodyne, just to be perverse and have octals driving novals

Yeah, we ain't too bad. Don't know whether you'd seen the thread on AX84 but we've had a bit of storm damage to the roof this week, which has put a damper on things. Not a big deal, though. Just have to go up and fix it when we get a day without rain and wind.

Other than that, all fine, really. Haven't really done much amp-building for the last month or so, other than tinkering. Cash has been a bit tight with Christmas and everything.

We want to replace the windows and do some home improvements this year, so we'll probably only have time and cash to finish off existing projects, like that SC120 that's still gathering dust under the bench, and build a few things with parts we already have to hand.

[Ray Ivers]

One thing about the schematic I posted... the 1M, 2.7K, and 100K resistors on the PI - along with the bottom .047 cap - all connect together at a single point. The schematic shows the 1M connecting directly to the cap and 'jumping over' the 2.7K/100K junction, which isn't right.

Ah yes, roof leaks - doesn't get much better than that. It's happened to me twice, and the second time I got plastic sheeting down over the leak right away to get a little breathing room to effect permanent repairs. There's nothing quite like two-handed work on a pitched roof, in the rain - especially putting down a large sheet in heavy wind.

The 6SL7/6SJ7/6SL7 preamp sounds cool!

Ray

[Zoe_N_Iain]

Thanks for the heads-up on the mistake.

Really looking forward to doing that roof repair! It's not working at height that bothers me, it's the thought of the 42 foot fall to the pavement below But, what the hell! I'll stick my hand into a metal box with 5 or 600 volts floating about, so what's a little fall to a squishy death?

Looks like we might get a few hours of decent weather over the next few days, though, so shouldn't be that bad. If I can just get all the slates back on, I'll be happy. I'll stick some self-adhesive 'flashing' over the gap where the ridge tiles blew off and cement new ones on when the weather improves a bit. Be Ok as long as it's watertight, I reckon.

Main problem is going to be fixing the loose but still present slates to GET to the middle part where everything has blown off. If I don't get to it soon, we'll be in 'need a totally new roof' territory, so...

[Satamax]

Hi Guys!

Majorwise, i like this one

http://www.schematicheaven.com/marsh...major_200w.pdf

[parcgwyn]

The ECL80 is a very underated valve the following link provides a nice amp:

www.parcgwyn.talktalk.net

Regards
Dave