sound practices reading club /31

And now for a bit of short, sharp fun. We are reading A 5 Watt TRIODE Amplifier by Ed Warden, from sound practices issue 3. In two pages, with less than a page of text, Ed explains how to build this 6BX7 amp. You can do it!

teaser quote: ‘For those of you who are thinking of taking the plunge into triode amps, but remain unconvinced of the real world capabilities of low power triode amplifiers, try this one.’

a gift from Joe Roberts, SP editor: from the sound practices CD, here is the original article.

my take

I am truly uplifted by the positive attitude this amp (article) exudes. It seems to be the perfect antidote amp. Antidote to mid-fi, hi-fi, high-end, even snobbish ultra-fi (it’s only push-pull and no DHTs). Certainly a hell of a lot more inspired than building an EL84 PP amp or 300B SE. It is both exotic—all-triode and cannot be bought for any amount of money—and practical to build. The latter because all the iron is relatively easily sourced—the output transformers especially, compared to single-ended units. Build with what you can get your hands on, is the name of the game. Recycle, from old/junky amps and radios, for instance. Ed highlights this for the output iron, but also for the power transformer and PS choke I say: forget what model Ed used specifically and get yourself in the ballpark with what you can get.

Having done that, you are listening to triodes. I am confident it will sound better than 99.9% of store-bought amps. And also you have a fun platform for experimentation. For instance with all the different input and phase splitter topologies that exists. The extra cost for this is of a couple of different resistors and maybe one capacitor. See which topology you like best. Hell, try to make a Sakuma-style 6BX7. In the output stage you can try self-bias and Blumlein garters. See what those do. You will need a higher B+ for that and that can be achieved by converting the PS from choke-input (classy touch, that one) to cap input.

‘Only five measly Watts. Is that flea power territory?’ Well, it is only 1.5dB less than the 7 Watts of a 300B SE amp. So I say quite confidently: the kind of speakers that work for you and a 300B SE, will also work for you with this amp. For instance read again what the Junkyard Dawg said.

practical note: Department of Corrections, SP4 says: ‘’The 6.3 [Volt —ps] filament is shown grounded in two places in the schematic diagram. Choose ONE grounding arrangement.

bonus tracks

Shishido built and published a similar amp using the 12BH7. No choke in the power supply though, now that is a bit too practical.

More experimentation: check out The Ultimate by Rickard Berglund, in sound practices issue 8. Omit the input stage he is showing and concentrate on what is happening in his phase splitter.

Now go and read the article, see you next week.