SET Asylum

RE: Western Electric 91A SET by Tube Audio Labs

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This Post Has Been Edited by the Author

In Reply to: RE: Western Electric 91A SET by Tube Audio Labs posted by Plinius_Fan on May 11, 2013 at 10:20:23

Sebrof asked for opinions/ comments; I have posted them here because they are relevant to your enquiry.
A lot of people own these amps and most love them; I’ll not argue with them. However, I feel that I should share my experiences and opinions and will try to be brief, balanced and reasonable.. but don't take this as fact.
Caveats: I only have experience with one of his kits and am yet to hear one of his amps. I have viewed closely his photos of builds and have been looking into these types of amps for a while. Make of that what you will.
I was well aware that the “kit” was collection of parts and contained minimal instructions; no problem. The chassis was dreadful: badly burred and out-of-shape holes and a very sub-standard layout. Component quality was concerning: I was not expecting boutique, but reliable tube sockets and appropriate selection of parts that are documented to be important to the overall performance should have been the minimum. Further, some hardware and wire were absent. For me, important requirements were simply not met… to the point I was questioning the long term safety of the amp. I aborted the build and now consider it to have been a great learning experience; I learned a lot and it has forced me to learn more!
I don’t know why Min supplied the kit like this. Many people claim to love the build and sonics of his amps. My guess is that he was busy and took less care than perhaps he should. Still, some of the mistakes would have been obvious to a competent DIYer. Min has performed a lot of builds; perhaps mine was an isolated experience? Perhaps my experience with this kit does not extend to his builds? It is a while since I have looked at the images on of builds on Min's site, but I recall thinking that some aspects of his earlier builds are better than his more recent builds. However, the photos generally do not show layouts I’d be satisfied with and his component selection often leaves much to be desired. Thankfully, Min allows you to specify the components to be used and if he is building.
Which brings me to the things I would ask for if I were requesting a build from him. For simple reliability and safety: do not use the nasty, pin-gouging, Chinese-made ceramic tube sockets (I like the phenolic UX4 and UX6 available for a few bucks each); use grommets around the holes through which wires are routed; and use a suitable location and method for attaching the safety earth-chassis connection (it needs to be a dedicated connection!). Layout and grounding are well beyond the scope of this post, but I’d ask him to use a larger chassis than absolutely required and to lay it out as optimally as he is able, paying particular care to the grounding (rather than just “making it fit”). Important components: a 2uF or greater PIO capacitor for screen-ground bypass; a coupling capacitor that voices the amp to your liking; spend the extra $ on a Yamamoto grid cap for the 6C6; ElectraPrint 3K (primary load) output transformers; and a higher spec the Hammond power PSU (for cooler running). If you wanted to go further, I’d suggest film caps for the PSU and cathode bypasses (you could get away with a cathode bypass of ~ 16 to 33uF for the 6C6, I think).
I have likely missed a few things, but that should get you a reliable and nice-sounding amp, if built well… There is a heap more that could be done to “improve” the circuit, but then it would not be the same amp.
Cheers.
Edits: vastly cleaned up to improve intelligibility.

“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck

Edits: 05/13/13 05/13/13

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