The postman brought me a nice little gift yesterday:
Btw, for the European guys in search of transformers at a reasonable price, the pair cost me 30€ shipped, from Don-Audio. It took about 5-6 weeks to get it. Looks like a good time to thank the Torpedo team for specifying a now easy to get parafeed transformer.
Since tinkering is a never-ending pleasure, I thought I might repurpose my current amp into a very simple parafeed one, with one tube per channel. It's currently an OTL µ-follower with ecl85/mosfet. The power supply has a regulated 280VDC@60ma B+ and a 12.6VDC/1A heaters supply (could be upped to 15V). The µ-follower mosfet section is on its own pcb and can be used as a gyrator easily, by taking the output from the anode of the tubes. Only the tubes themselves, the output caps have to be changed (the ecl85 really have too low a µ for an output transformer).
So what tubes ? We need something with rp under 4k, better yet under 3K, which can stand a 200Vdc Va at a decent current and has a µ above 25 or so. It's best if it doesn't break the bank too. All data following is from Tom Schlangen.
- As an obvious first choice, I was thinking about the ecl84/pcl84 (pentode, triode strapped). With a µ of 31, rp of 3K and Pd of 4W, it's roughly similar to two 6J6 sections in //. Bonus being I've got a quad home.
- A second possible choice from my parts box is the ef184. Triode strapped, µ of 55, rp of 3K7 and Pd of 2.5W. µ is a bit high, power dissipation a bit low... I've got a few on hand though.
- A third tube that looks interesting on paper is the 7ky6-9kx6. But it's very uncommon in Europe, let's forget about it.
- Fourth tube that looks interesting is the 6ag7 (or the equivalent 6p9 in Russia). Triode strapped, we get a µ of 25, rp of 2k2, Pd of 9W.
- And as a fifth, there's the el83/pl83. Again triode strapped, µ of 25, rp of 1k8, Pd of 9W. It could push the 7K tap easily...
Any other candidates I'm missing ? There's always the 6922 (in //) I guess.
Edited by 00940 - 2/18/14 at 2:19pm