sound practices reading club /3

Today as our regular scheduled program we have an early-internet classic, Flesh and Blood from sound practices issue 8, written by Herb Reichert. This article is really a top–down tour of amplifier design, starting off with Herb’s reasons to build it himself and the importance of experience, experimentation and hard work as an intangible component of the final result. Next, there is an outline of Herb’s goals. Then he starts working from the speaker terminals toward the input: the speaker to design for; output transformer; output tube; its operating point. Then the selection of the input/driver stage and—twice as important (in column space)—the power supply design. Then maybe the most notorious part, Herb’s part selection. In the silence after that storm, there is the closing part with the encouragement to become a master yourself.

teaser quote: ‘From the letters and phone calls I receive, I know that many of you believe that if you can get a schematic for a great amp, then go out and buy what you think are some great parts, and put it all together carefully, then you will end up with a great amp. Sorry, it just doesn’t work that way. […] to get a GREAT amp you must suffer.’

my take

This is the article that, once found on the web in 1996, got me hooked on sound practices. I did end up building a copy of the Reichert 300B as my first single ended amp, and moved on from there.

I must have read this article a hundred times over the years. Before re-reading it for this week’s episode, I recalled it as being dominated by the part selection stuff and the ‘do not change any detail or it is not my design’ warnings. I was pleasantly surprised by the top down structure of the whole article, the way it tries to make clear that the order of importance is really the one listed in my overview above: first and foremost your own reason for building it yourself, ending up with the details of the part selection.

With this strict order of importance, it is easy to overlook a theme in the middle section: that the (usually given) speaker + output transformer + output tube + its operating point + the power supply + (the output tube’s biassing + its grid circuit, if I may add so) has to be designed as one single entity. There is no such thing as plug-and-play of these seven ‘components.’ Changing one of them for experimentation’s sake is necessary to gather experience, but if you want to take your amp beyond Frankenstein then you have to sit down with a piece of paper and design the whole entity.

Now about the ‘no changes’ dogma. I can understand that when Herb publishes a how-to-build of what was essentially his commercial product at the time, he would like to be judged on his design, in which he has put all his ‘suffering.’ Not on a knock-off where the builder has got creative with topology, values (‘I had this 3K output transformer on the shelf’) or parts selection. To hear what he believed in you have to build exactly what he was listening to.

The other side of this medal is that with an innocent looking change to the schematic, you are now on your own. And Herb is happy to hand you the steering wheel from there on. Now you can do your own ‘suffering’ for your own benefit.

I used to be pretty proud of how far I went to build ‘his amp’: the exact output transformer; exactly the right tubes, including vintage 300Bs; one-kiloWatt power transformers; 3 Henry, 4 Ohm DCR chokes (OK, 15 Ohm would have been super too); all black gates and jensen caps; all the right component values everywhere. But any time I have told somebody that I built a Reichert 300B they automagically asked about a detail where I had been ‘creative’ myself: kiwame instead of tantalum resistors; no silver wiring; AC on all heaters and filaments; no copper chassis—no chassis at all, really. I guess I never heard what he did and was holding the steering wheel a little sooner than I had planned.

practical note: yes, it says 12K for the plate resistor of the driver 6SN7 in the text and 13k5 in the schematic. As somebody pointed out to me back in those days: both were used by Herb and will work.

bonus tracks

Just for fun, there is on page 28 + 29 of the same issue some pics + info of some inspiring amp projects. And on page 56, next to the masthead, there is an in hindsight amusing advertisement from 1965 lauding those newfangled transistors, which were superseding the those evil tubes and transformers. (update: not on the SP cd, so I scanned it.)

ps: there is quite a bit of extra dope on the F+B amp, between the lines, in Casual Reactions in issue 6.

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