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SRPP/5687 - love it or hate it ?

Posted by RhythMick (A) on December 7, 2007 at 01:43:16

Hi all,

After the mods I've done recently I'm loving my Kit1. The RCA Red Base 5692 sounds great in there.

Part of me thinks I shouldn't love the sound. I've read up (on tubecade.com) about the SRPP and I know it's "kinda" push-pull. I also know the 5687 valve was designed as a computer switching valve and has almost a "step-function" character, which must (I guess) make it high-gain, fast, powerful but also hard and sharp.

That said, the amp sounds like it has the best of the above but not the worst. I'm inclined to leave well alone. I'm also inclined to try a different circuit design, just to see what difference it makes. I was thinking about using a great 9-pin double triode like the 7308 (I have loads of these fantastic valves from when I had an Art Audio amp, the Amperex white label PQ 7308 is head and shoulders above the rest of the 6DJ8/6922/7308 crowd IMO). Anyway I was pondering on the lines of using the 7308 double-triodes in parallel to give the gain with reasonably low plate resistance.

I'm fairly new to thinking circuit design through so I need a little help. The 7308 has a Mu of 33. The 5692 grid receives the input signal more or less direct as I've removed the volume pot. Between the 5692 amplification and the parallel triodes of a 7308 per channel there should be plenty of oomph to give the 300B what it needs at the grid ?

I'd love to hear other people's views on the 5687/SRPP circuit. I'd love to hear what if anything others have tried in it's place. I'd also appreciate any comments about the above.

Cheers

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