diytube.com

Roy Mottram brought to my attention last night that his Poseidon board upgrade didn't sound right. He reversed the connections at 'F' & 'G' and things cleaned up nicely. Could you please post if you remember switching these two when you built yours? Basically, I'd like to know how you have F & G wired up stock or swapped and what output transformer you have (Z-216 or A-431, Dynaco or Dynaclone). This should help sort out if there are differences between them or if I just have a huge bug in the manual. All the testing was done on my friend's MKIII with Z-216 (I'll have to contact him). Hammond testing was done on another friend's MKIII with 1650Ns.

I remember swapping phases on the ST70 board, so I *thought* I paid extra attention to the Poseidon. I'm surprised it just doesn't oscillate like a sonuvabuck.

Thanks guys!

--Shannon

I wonder if maybe the Poseidon feedback tuning puts the "sqeal" above audible range? My Poseidons sounded excellent, clear as a bell and earth shaking bass! The difference in mine was I used ST70 boards cut to fit the MK-3 chassis, long before the Poseidons came out.

A few years ago I threw together an Eico HF89 driver circuit into a ST70, feedback was reversed, and I pissed off every cat within a 5 mile radius!

Pics before I swapped to the Ike circuit

Here's how mine is wired. The outputs are original cloth lead Dynaco. The wiring should be exactly as per the manual.

I used new DynaClone transformers, maybe they are wired different than originals? I actually used Ty's photo as one of two I found, to see whether the phase was correct or reversed as per the manual, which says to wire F to the tube with the blue wire on the plate, and G to the tube with blue/white on the plate. Doing that made the wires crossed, but I've seen that on other MK3 mods so it didn't bother me, until I powered up the amp and all the usual bad sounds associated with incorrect phase.
After checking the photos on this website, I uncrossed the wires, and hooked up F to the tube with blue/white on the plate, and G to the tube with blue on the plate, and then all was well and perfect.
Roy

Thanks a lot, gents. I'm always wary when hooking up feedback. Even when I think I have it sussed out correctly, I still have a 50/50 chance of having an oscillator on my hands. I *do* think that transformer manufacturers - past and present - can accidentally swap colors and phases. I'll guess they are Hipot tested and ratio tested but not phase tested.

Ultimately, I do first power ups without the negative feedback attached, and will even then use a pair of alligator clips to test for oscillation with a temporary feedback hookup. Maybe I should add something like that to the manual. Indeed, the Poseidon manual could use some fattening up, and it is that time of year.

--Shannon

I think I've figured out what happened, I was wiring up 6 different MK3 amps with Triode-Pentode switches added, and I believe now that ONE of the 6 amps I accidently wired one switch with the polarity on the switch reversed. As luck would have it, that's the one I first wired the Poseidon board into. After looking at the photos and replys on this topic, I see that the manual actually was correct, as were the transformers I had.
So I guess everyone eventually makes a mistake to keep us on our toes and keep us humble !! Thanks to Shannon and this forum for it's support.

No problem at all!

--Shannon