sex amps original 300b conversion.

[najo49]

Paul, while I await the critical valve archive. Can you give me a head start with a little info. I think that i will need a set tfa 204s but what about other trans now offered atmagnaquest site Bh-5 for example. And i will be removeing one of dh 7s. I hope to use the c4s I made for the sex. but with some resistor changes. will this mod be a parafeed output design? So as much as you can tell me I can make ready the amps, for the mod. Which I hope will be reveled by doc sometime soon. thanks Jan Olsen

[Paul Joppa]

Hmm ... the article is now 15 years old, I had to look it up to see.

Yes, it is designed for the TFA-204 series feed output transformer. This was done before we got into parallel feed. The original SEX chassis had mounting holes suitable for the TFA-204 pre-drilled, as it was used for the AfterGlow as well.

"And i will be removeing one of dh 7s" - Sorry, I don't follow you. What is a dh 7?

The article shows a mu-follower with a 6SN7; I chose cathode resistors that would allow the substitution of a 6SL7 to compare them. In the end I converted my amps to a 6J5 with C4S - actually, Doc B took them from me and made the conversion to prove it sounded better; he was right so it has stayed ever since. <<long pause>> OK I pulled the old amps from storage and I see I used 110 ohms for R1 and 220K for R2.

Note that I used the original SEX kit power transformer, some of which had reliability problems. I never experienced those problems, but I later converted to the replacement made by deYoung. This new one had a different arrangement for powering the 300B filament.

[najo49]

Thanks paul, I was thinking one of the 6dn7 tubes was used but i see the driver is a 6sl 7. and the finished amp uses the original trans and chock. I think I will leave it an Original collectors item which I think sound wonderful. And build a parafeed 300b after another design. Using a transformer like the tfa2004. I sold my 300b amp a dared which was my first set. but it never snded very good to me so I am happy to be rid of it.But I did save the tubes looking towards the future. sorry to put u to all the trouble. jan O.

[Paul Joppa]

No problem. Perhaps you are confusing the "original-SEX to 300B conversion" with the "shunt regged 45 conversion from Paramour II", another oddball of which there are only a few around.

[najo49]

Paul, I just found a pic in the valve arcive with a build of your  300b conversion, and it clearly show one 6dn7 which is the driver for the 300b. This must be a 6sl7 or 6sn7 right? This is the conversion I am inter ested in.Is this the conversion in the missing valve mag?

[Paul Joppa]

Hard to say, without seeing the picture and its context. I have reminded Doc B to post the issue - that should answer your question!

[Doc B.]

Here you go -

http://www.bottlehead.com/VALVEarchive/1997/va111997.pdf

[najo49]

Doc, thanks so very much. I know how busy you are. Thanks to you and Paul.