Shannon, ever give any thought to...

[joeriz]

...making a board that will do PPP EL-84s? Maybe with a pair of A-470 OPTs? Yellow_Light_Colorz_PDT_02 Just curious. Seems like it would make a nice addition to the family...

I'm also wondering, anyone here who has made a PPP EL-84 amp before, do they still sound as nice as they do in good old PP?

Thanks,
Joe

[EWBrown]

I've heard other make / brand PPP EL84 amps and they can sound very nice! VTL had a couple models (either as monoblocks or a stereo amp) that uses 12AT7s in teh VA and LTP stages, and PPP EL84s in fixed bias mode, and they could deliver 45WPC in pentode (not UL) mode or 25WPC in "triode" mode. FWIW< Roy Mottram's VTA-70 driver board comes as close to the VTL design as I've seen Yellow_Light_Colorz_PDT_11

There are two slightly unconventional approaches that may be worth trying - I haven't tried either of these, so I will make no claims pro or con...

Approach 1: Use the standard DIY35 board, with a power transformer which has sufficient current handling capability, and mount the extra four EL84s in sockets, off-board.

Approach 2: Use two DIY35 boards, and with a bit of etch cutting and jumping, one VA / PI could drive both sets of EL84s as PPP monoblock or dual-mono. The output pairs could be parallel connected at the terminal blocks and then feed an A-470 or 1773 (4300 ohms CT) OPT.

Somewhat simpler, and fully reversible:

Approach 2A: use two DIY35 boards, and connect the two inputs together, (as was done for mono operation with the ST70) and then parallel-connect both sets of output tubes at the terminal blocks into a suitable (approx 4300 ohm P-P) OPT like the A-470 or 1773s.

Both of these may need some tweeking of the NFB loops in order to not have instability problems. Apparently this was not a problem with the ST70, but once again, YMMV, etc....

/ed B in NH

[Shannon Parks]

I'll think this over.

[mesherm]

http://webpages.charter.net/mesherm/quadel34.jpg

I built a PPP EL84 as shown above using Amplimo toroid OTs and Antek toroid PT. All EL84s are in triode mode. When this photo was taken I had used just a 12BH7 as a VA and Cathodyne PI. I have since added another tube and changed to a 1/2 12AT7 VA with the 12BH7 as an LTP PI.
It sounds better than an ST35.

[joeriz]

Cool ideas. Thanks guys.

Shannon - glad to hear you'll think about it. Yellow_Light_Colorz_PDT_12

Joe