Today, I purchased what I believe to be 2 early bottlehead mono amps. Tubes are 3 Dumont and 1 GE 6dn7s. Powered both on ..tubes light up. However after about 5 minutes or so the left side caps on both popped. Is this due to old caps..possibly a couple of bad tubes. Any insight would be helpful...Obvious newby. Thanks.
Original SEX troubleshooting
- Thread starter Hwyers1
- Start date
Paul Joppa
Moderator
That looks like a pair of original S.E.X. amps, with the excellent Magnequest PGPp8.1 power transformer. It probably dates from 1997, a few years before Electronic Tonalities became Bottlehead. Quite a historic find!
If you look over this forum, you will find a subforum called VALVE Archive. It started in 1994 and chronicles the early history of the company. The SEX amp (for Single-Ended eXperimenter's) was the company's first product.
If you plan to bring it to life and listen to it, there are many things that can be done to improve the reliability, performance, and sound.
They are a neat piece of the Bottlehead story and could certainly be made to work, but those original output transformers weren't quite up to the task at hand, so they are somewhat prone to combustion. The traditional remedy for this was fitting the TFA-204. You could likely fit the current SEX iron upgrade onto these to get around that issue as well.
I'm certainly willing to fix them up for you if you want them taken care of, but it's a slippery slope when you'd really want thicker chassis plates, IEC power cord plugs, etc. I do think there would be people online who would pay $300-500 for that pair in unknown working condition.
Paul Joppa
Moderator
For the record, it was the power transformer that would let out the magic smoke ... :^P Dan commisioned a replacement which went into the kit a few months after the first offering. A year or two later we switched to the Magnequest PGP-8.1
The output transformer just rolled off early and needed the feedback to fix that problem. Both transformers were sourced from a surplus store, which made the kit very affordable.
These days there are many SET amps, and this one is not "something special." But back in the day, at the very beginning of SETs in the US, you could hear the SET magic midrange from it, and that was a big deal then.
The output transformer just rolled off early and needed the feedback to fix that problem. Both transformers were sourced from a surplus store, which made the kit very affordable.
These days there are many SET amps, and this one is not "something special." But back in the day, at the very beginning of SETs in the US, you could hear the SET magic midrange from it, and that was a big deal then.
Oh that's interesting, I know that Dan has a pair floating around the house where the output transformer is totally smoked, but that could have happened for a wide variety of other reasons.
I'd say something like this has more historical collector value than hacking value. That original output transformer (and that power switch) dates it as a very early kit and we didn't sell that many of them before we started upping our game with the parallel feed version that PJ worked up. I'd guess that the PGP8.1 might be a retrofit that went in after the original power trans failed. The only gear I hung onto when we sold the business are my current personal system and two sets of S.E.X. amps - my original prototypes and the very first kit we sold, which I reacquired after the original purchaser passed away.
These forums haven’t typically hosted much sales activity. I’m not too eager to start having to moderate transactions. If someone reaches out and wants to make a deal here I’m not going to make a fuss about it, though, since the condition has been pretty well documented. Caveat venditor/emptor.
There are a number of reseller sites (Reverb and eBay come to mind). Many audiophile communities have sales sections.
There are a number of reseller sites (Reverb and eBay come to mind). Many audiophile communities have sales sections.
