audio-talk

Probably why ultra-linear is popular as a "best of both worlds" ~ it's also a form of NFB (tap a percentage of the primary Volts back into screen grid) Yeah that's why he gets away with no overt feedback network as he uses the UL operation on the simple EL84. The problem for me is, he the...

Hi Al Looking at the simple EL84 circuit, unless I'm missing something, it does not appear to use any feedback. The trouble with pentodes that don't use feedback is that you get a number of unpleasant problems. The first is that the output resistance goes up, so the output stage's ability to control...

I christened this "Son of The Strident One" in honour of Mr I's creation. It's taken me two days to sort out a layout. This is on the chassis of the first Rocky build I did. http://web.me.com/scress1958/Pictures/el509layout.jpg It's a brash, brutish bugger, but the cage will hide all the g...

Yep, they are very nice, but try and keep Va below 300v with them (IME) Hi Nick, agreed on that one. Mine run at 275Va so they should be fine. I know the music shops don't recommend and won't guarantee them in VOX AC30 amps as these run at 15W dissipation. The Genalex is a 12W dissipation valve app...

Just received a pair of these valves this morning.

Made by the Electro-Harmonix factory. Very very good indeed.

They are more expensive than other new production EL84
but IMO worth every penny.

Not many on here use EL84s but they are worth mentioning nevertheless.

Steve

Mike H wrote:SEP EL84 as a driver for something else?

Got something in mind Mike?

yes well as I said earlier I don't see how el509s will be happy with those output transformers but then you probably know something I don't? They certainly wouldn't be happy on the end of a screen-driven EL509, which would need 5K. With pure pentode push-pull amps such as Bruce Rozenblit's 150W EL5...

Pity, I thought that was a keeper Well to be quite honest so did I. The 13E1 is a beautiful looking valve with a powerful sound, but when something becomes that unstable that it threatens to destroy 250 quids worth of output transformer and another 250 quids worth of mains transformers and chokes, ...

Not really an overreaction Mike.
I just have a very short attention span when it comes to flogging dead horses

I'll take what I've learned with the 13E1, particularly the knowledge gained about valve voltage regulators and use it all in the next amplifier.

Hi mike

Too late now I'm afraid

It's been torn down

Well after much havering and looking at various datasheets, it looks as if my 1K25 output transformers will come in useful after all. Remembering I still have a big 625VA toroidal transformer that was specced for the infamous OTL, I've decided to revive the EL509s as single-ended pentodes. Mounted o...

Yep +7V builds up on the grid before I have to switch the thing off, which means there is 3 and-a-bit mA of grid current flowing. Looking at the pentode curves for the valve, at that amount of positive grid voltage there is a terrifying amount of current going through the valve itself; at least 2.5A...

HI Paul Thanks for the advice as always. Thing is this amp has been working perfectly in its various guises for over 12 months with no trouble whatsoever. It was at the last Owston in its breadboard form and latterly was at the Eggborough do we had after the Owston venue was destroyed. There has nev...

Yes that's it

Touching the meter probe to the plate end of the primary winding on either TX results in lots of sparks. Now that shouldn't be happening. Is that with the meter between there and ground? What sort of meter? Yes the meter is between plate and ground and is just yer average digital multimeter. Well t...