parafeed in original sex mono

[najo49]

I am converting my original sex monos to parafeed. As per the article in valve titled c4sing the sex amp. can I use the plate choke that is in the amp as plate choke or should I use the original opts for that. And from the magnaquest line what parafeed opt trans would be a good choice. And if I bought both new parafeed opts and plate chokes from magnaquest what would be the best choice?lastly I was going to go with the tra 204 upgrade but I thought the parafeed might be just as good. Does anyone have an opinion.

[braubeat]

I guess the paramour iron upgrade from magnequest would be the obvious choice. See if you can get Mike to airgap the plate choke for the exact current(IIRC it was 40 mils). If you are buying lots of new iron anyway you might do what I did when I upgraded mine and get a power transformer with more current capacity and increase the current through the power tubes from 40 mils to 60 mils. This made a nice improvement in the sound of my amps. If you do this then you will need a plate choke with more current capacity also.

Michael

[Paul Birkeland]

Michael has exceptionally good advice!

Replace the power transformers with PT-7's, build essentially the power supply for the new SEX amp.

Use the plate choke and output transformer for the Paramour upgrade iron package (4K for Parallel 6DN7's would be a good thing).

You can leave one of the driver triodes disconnected in your rebuild, or attempt to shunt regulate the driver section (with a soft-start kit + more parts).  This is pretty technical work, I wouldn't recommend it unless you've built Paramounts, an Eros, or a BeePre before.

[Paul Joppa]

The problem with the OriginalSEX is that it's so old, there are too many mods that have been done in the past!

There was a parafeed version for a while, called ParaSEX. It used the original output transformer as plate choke, with the speaker winding as cathode feedback for the paralleled power sections, and a 4K line output (similar to the Speco we later switched to). There was a conversion manual as well.

The other problem is that there were three different power transformers, and they created different voltages. Add in that we revised the currents a bit at some point, and it gets confusing!