Using Hammond 1650N Outputs with the Poseidon Boards

for Dynaco Mark II/III/IV and DIY PP monoblocks

Using Hammond 1650N Outputs with the Poseidon Boards

Postby Shannon Parks » Sat Dec 09, 2006 7:48 am

Some have asked for tips on using the Hammond 1650N output transformer with the Poseidon boards. The Poseidon boards are based on the earlier Eiclone project, itself based on the modified Mullard 5-20 design as used in the Eico HF-87 and HF-89. The stock Ike build did use 1650Ns, and I've always thought they were excellent iron.

Anyhow, I would build according to the Mark III schematic build but make the following changes:

Change R5 to 2k (Mouser PN# 71-RN60D-F-2.0K)
Change C2 to 220pF (Mouser PN# 5982-15-500V220)
Change R7 to 3.3k (Mouser PN# 71-RN60D-F-3.32K)
Change C3 to 470pF (Mouser PN# 5982-19-500V470)
Use the 8 ohm tap for the negative feedback.
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1650N ?

Postby maynard999 » Fri Feb 03, 2012 8:32 pm

I can't find a single difference between the Hammond 1650N and the A431S from Triode everyone else is using with the Poseiden. Why the mods?
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Postby TomMcNally » Fri Feb 03, 2012 11:51 pm

Notice that the post is 5 years old, and the Hammond 1650N of that
day didn't have the new "easy wire" secondary, you couldn't use
the 16 ohm tap for the feedback if you were wired for 8 ohms.
Shannon's notes changed the feedback loop to work with 8 ohms
rather than 16. That may not be necessary with the new style
Hammond 1650NA.

... tom
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Postby Shannon Parks » Sat Feb 04, 2012 10:24 am

In addition to the different tap impedance, every brand and model of transformer is going to need its own unique feedback tuning when negative feedback is applied. Plus you can make adjustments depending on your bandwidth and stability requirements.

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