Thursday, July 14, 2016

Brook Electronics 10C3 and 12A3 Advert

Very cool Brook ad. Posting this in anticipation of the clones.

I would love to have a copy of the free technical bulletin and distortion analysis..


  1. The Brook was the only production pure triode amplifier commercially made after WWII for home audio use and was designed by Lincoln Walsh, whose radio writings go back before WWII and whose Ohm speaker driver was his last product.

    There was one model that was even designed so that it could be used with the WE300B, which was not available for consumer use at that time. Before the patents on most tubes ran out, WE tubes were licensed for use in broadcasting equipment and cinema use only so manufacturers were not supposed to use them in consumer equipment. Graybar would sell anyone with cash the tubes, but it was a violation for manufacturers to "misuse" them.

    The cult of triode goes back to WWII, but it was a small minority by 1955. Curtis Schafer wrote DIY articles on building triode power amps, but the Brook was the only commercial unit. It had direct filament triodes, but was push pull and used feedback across the output transformer. (Even WE amps almost all had feedback after 1935, because anti-feedback is a code word for anti-fidelity, but they did not have feedback across the output transformer.)

    The triode cult became big in Japan by 1970 or so, but aside from the rantings of Robert Fulton, a man who had a diagnosed mental illness that made him "see color" when certain frequencies were sounded, it was not rediscovered until Alan Douglas published an article in one of Ed Dell's magazines about 1986 or so on what was happening in Japan.

    1. That is very interesting I did not know about the 300B version...

      I am going to build Stock Brook 12A clones really soon. Then I am going to see if any improvements can be made. I am very excited about it.

      If you have any advice I would be very interested.

      I will look up the writers you mention.


    2. To clone the Brook requires the transformers, or rather the output transformer and the center tapped driver choke, and neither are off the shelf items as far as I know.Newell (1954) talks about these quite a bit.

      No Brook amp came with 300Bs. The 300B is a similar tube to the 2A3, but it has a 5 volt filament rather than the 2.5V of the 2A3. I think there is an unused 5 volt winding on one of the Brooks but I do not know if Brook ever endorsed or planned for this to be used to convert the amp to 300Bs.

      As the commenter says, WE tubes were never used in commercially made equipment except for some use of WWII surplus tubes by various companies. Some WE tubes were cognates of commercial types or could be interchanged, i.e., 350Bs for 6L6 class tubes. But WE tubes were quite expensive as well as the license issue, which became moot sometime in the fifties, but before WWII and after for a few years was a serious issue. All tube makers pooled their patents with WE being a significant contributor as well as having an immense physical plant as compared to other electronics companies, especially before the industry expanded greatly due to TV manufacture. Antitrust was a serious matter and had WE been seen as actively selling to consumers there would have been fuel on the break-up-Bell fire.

      Also, WE tubes were not necessarily superior to commercial tubes for entertainment purposes. They were controlled manufacture for parameters that did not matter in entertainment circuits...a concept audiophiles sometimes just can't get. Telephone repeater circuits required stability of DC parameters over thousands of hours, but that would make no difference whatever in RC or transformer coupled audio circuits. The WE300 was originally designed for WE ERPI sound reinforcement unit, but had it been only used for that production would have stopped in the forties, not the eighties. It was in use as a DC pass tube in the Nike Zeus/Nike Hercules ground radar system and for certain telemetry applications, and for that, mu mattered little within a broad range-so postwar 300Bs are not especially tightly controlled for that, contrary to audiophile sacred writ.

    3. Thank you so much for the detailed information.. Good stuff!.

      The transformers, center tapped choke, and outputs have already been specd to Heyboer. They are custom order under these part numbers.
      Most of the guys cloning these have stayed close to original footprint etc. I'm using motor runs for power supply caps and a bunch of those russian caps everywhere else. The footprint will be bigger but will stay stock for the first build. Then maybe a few mods. I'm curious what folks will recommend.

      I'm going to start soon on this project.

      Thank you

    4. Assuming the transformers are accurately produced you should have a really good amplifier. Now if we could get reasonably priced single plate 2A3s...

    5. Fortunately two others have already built with the transformers and they are good.

      Single plate 2A3's.... Woo... I don't have that but do have access to good ole NOS 2A3s.

    6. The We 350B was very popular for use in certain Seeburg (I think) jukeboxes, which had a fast warmup circuit that slammed the heaters with 9 volts for several seconds before dropping back to 6.3 for running, just like the starters on old cars that bypassed the coil resistor for an extra hot spark. This was a poor design but the 350B had a super tough heater that would last for a longer time under such operations. In most bigger cities all jukeboxes except those in private clubs, or cop bars were mob owned and the mob wasn't known for electronics skills, so using the 350B was the workaround. (There was a published fix and a kit from the jukebox operator to change the circuit, and then a later kit to put in a solid state amp,those were commonly implemented when secondary operators bought them used and put them in non mob areas, like small towns where the mob did not want to bother.) Graybar did a lot of business with these guys, which had a sort of irony to it....Graybar would sell WE tubes to anyone from the forties on, and there were homebrew 300B amp designs in hi fi magazines up to the very late 50s. There were large WE transmitting tubes used in prewar WE transmitters that often stayed in backup use in small town or religious broadcast stations, and there were a couple of WE microwave types that hams used for UHF work;you could order them from any Graybar up until the seventies or early eighties.

      In general though, the availability or existence of WE tubes was not well known among tube users. They were expensive. And also WE made it a point to stay below the radar in terms of outright sale of anything except to the Bells or the government, because they were deathly afraid of antitrust, as the previous poster said.

      My grandfather worked for Graybar in the fifties and sixties, which is how I know much of this. He was an avid ham and something of an audiophile as well, although he did not cotton to anything but classical music in his house. Apparently he had built some sort of tube amplifier at one time, but by the time I was old enough to be curious he had gotten rid of all tube audio equipment, and much of his ham gear save the linear amplifiers. He thought my interest in tube audio gear was foolish and the audio business intrinsically crooked.

    7. Yeah, the old guys thought the "kids" in the 70s-90s (we are all over 50 now) who were wanting to get back to tube signal chains and efficient speakers were nuts. They had been raised to believe that newer was better, and when they were kids, it was. A 1935 radio or car was better than a 1925 one, and a 1955 one better than that, and so on.