Just curious as to why a EF86 pentode driver board is not an option for sale here. I have an old ST-70 that I bought at a good price. I took a tube tester with me, my Sencore MU150. I pulled all of the Mullard xf4 EL34, tested them. All tested ANOS. I also noted the fact that the driver board, while old and dusty, was of the (yellowish/light green/gray) loaded with two Amperex EF86 and what I believe to be a 12AX7? PI. (I managed to break the glass on the US labeled 5U4G) so no great loss. It now has a new Valvo GZ34. It also had metal film resisters and Illinois Capacitors? Yellow like them anyway. The PT looked to be a taller 2 1/8" version and fiber (about the same color as the board) bias point meter probe jacks, in place of the front octals, and the bias ground jack mounted in place of the stereo/mono switch. The chassis was a little corroded, but with all the mods, I couldn't pass on it for the price. Now I was skeptical, because the seller knew nothing about it, not even that it was a Dynaco, no cage.
I bought it brought it home, powered it up (full voltage) with a speaker load. All tubes lit, no smoke, no blown fuse. So it went into the second set of preamp outputs (McIntosh MC20). The first pair are running vintage MC75's. I could not believe what I was hearing, or expecting. The MC75's are driving Belle Klipsch, the ST-70 driving CF4 Klipsch. This system is so well balanced (front and rear stages), I am astounded. Had never heard a
Dynaco before. I am sold on EF86 pentodes, as that is what is our main choice of tube is in guitar amp builds.
So while my son builds custom guitar amps, we are always on the hunt for vintage tubes, old Hammond organ donor amps or anything with good iron and/or tubes. He gets a deal on a stash of NIB audio tubes, some huge
homemade Karlson design speakers and a Dynaco PAS II and one of the cheaper Dyna tuners. So I begin the hunt for a second ST-70, to have a whole complete 2nd Dynaco system.
I had a used Gibson Melody Maker, very little invested in it (for a 1964). And find a ST-70 on one of the better known musical instrument websites. Turned out the seller was in a 100 mile radius of me, he was interested in
my guitar, myself in the ST-70. So a trade was made. (he told me it was working). It looked to be in almost mint condition. Pretty brown cage, perfect label and no corrosion on the chassis.
But this one has issues, so a rebuild is obvious. For starters the stock 7199 board has been jumpered for 6GH8. This one has one weak Sylvania fat bottle welded plate 6CA7. The remaining 3 test good. It also has a lesser
quality new production rectifier tube.
But all of this leads me back to the original question. I am starting to buy parts for this project, but Tubes4hifi does not offer a EF86 driver board. And I know I have already made my first mistake. Ordered the Triode EF86
board w/parts. Is this something that may be offered in the future? People tend to shy away from the EF86, but get good NOS ones, and microphonic and noise does not seem to be a problem.
I bought it brought it home, powered it up (full voltage) with a speaker load. All tubes lit, no smoke, no blown fuse. So it went into the second set of preamp outputs (McIntosh MC20). The first pair are running vintage MC75's. I could not believe what I was hearing, or expecting. The MC75's are driving Belle Klipsch, the ST-70 driving CF4 Klipsch. This system is so well balanced (front and rear stages), I am astounded. Had never heard a
Dynaco before. I am sold on EF86 pentodes, as that is what is our main choice of tube is in guitar amp builds.
So while my son builds custom guitar amps, we are always on the hunt for vintage tubes, old Hammond organ donor amps or anything with good iron and/or tubes. He gets a deal on a stash of NIB audio tubes, some huge
homemade Karlson design speakers and a Dynaco PAS II and one of the cheaper Dyna tuners. So I begin the hunt for a second ST-70, to have a whole complete 2nd Dynaco system.
I had a used Gibson Melody Maker, very little invested in it (for a 1964). And find a ST-70 on one of the better known musical instrument websites. Turned out the seller was in a 100 mile radius of me, he was interested in
my guitar, myself in the ST-70. So a trade was made. (he told me it was working). It looked to be in almost mint condition. Pretty brown cage, perfect label and no corrosion on the chassis.
But this one has issues, so a rebuild is obvious. For starters the stock 7199 board has been jumpered for 6GH8. This one has one weak Sylvania fat bottle welded plate 6CA7. The remaining 3 test good. It also has a lesser
quality new production rectifier tube.
But all of this leads me back to the original question. I am starting to buy parts for this project, but Tubes4hifi does not offer a EF86 driver board. And I know I have already made my first mistake. Ordered the Triode EF86
board w/parts. Is this something that may be offered in the future? People tend to shy away from the EF86, but get good NOS ones, and microphonic and noise does not seem to be a problem.
