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RE: 4P1L preamp DIY

Hi George,

The designer...Radu has balanced the size / performance / cost relationship pretty well. For example the PSU board in the LV supplies use dual 0.33 ohm Welwyn resistors in the CRC filter. The resistors could be substituted with suitable off-board filament choke's. Lundahl current choke LL2751 in serial / balanced mode would work fine.

The Kathode resistors could be mounted off board with fly leads because they get hot approx 3.5W is dissipated across them.

The LV transformers used is a dual bobbin design made by Triad something which Rod Coleman has proven reduces capacitive coupling ie noise between primary & secondary.

There is a '555' timer on the PSU board that delays the HT for 30 seconds a nice feature.

And yes the Lundahl LL1671 very cost effective but could be substituted with the Amorphous core (AM) but this all comes at a price $

Yep I'm pretty weary of valve amps & pcb's so time will tell.

PS - Kevin Carter of K&K Audio sells a number of discrete DIY boards for the 4P1L pre-amp, similar design to this one.

Cheers Johno

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