From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Digital divide by ten, 1949 style
Date: Sun, 15 Sep 2002 22:31:45 GMT
NNTP-Posting-Date: Sun, 15 Sep 2002 15:31:45 PDT
John Woodgate wrote:
> I read in sci.electronics.design that Chuck Simmons
> wrote (in <3D84D4B3.50B511EF@webaccess.net>)
> about 'Digital divide by ten, 1949 style', on Sun, 15 Sep 2002:
> >The 6H6 dual triode dated from the late 1930s and was common in
> >commercial and military equipment but the 5 tube radio of the era was
> >inocent of the beast (if I recall, the 6H6 was a "metal" tube).
> Yes, the plain number, without 'G' or 'GT' mean 'metal tube'. They had a
> thin glass envelope inside the metal can. But the 6H6 was a double
> diode. The earliest double triode appears to be the 6F8G - two 6J5
> triodes in one envelope, with one grid on the top cap, The 6SN7 was the
> single-ended version.
> >"MSI" came to tubes in the 1960s with the introduction of compactrons
> >that might have two triodes and a pentode or some such.
> No, double- and even triple-diode-triodes were around much earlier, as
> well as triode-pentodes and triode-hexodes, like the 6K8 which was in
> almost every US AC mains radio, and plenty of British ones, for many
> years. Even some AC/DC products.
I repaired hundreds of radios from about 1957 until I actually started
working at a radio station in 1963. I never saw a 6K8 in a radio at all.
The All American Five had the 12BE6 mixer, the 12BA6 pentode IF, the
12AV6 diode triode detector-AGC-audio amplifier, the 50C5 beam pentode
audio power amplifier and the 35W4 rectifier. There was an octal tube
complement used in an identical design from the late 1930s until about
1948 when the list above became absolutely universal in low cost AM
radios. The schematic is here:
I can't remember ever seeing a 6K8 in an AM broadcast radio and I fixed
radios that were antiques even in 1957 (TRF recievers that predated the
superheterodyne) - I was able to do that because my father had a lot of
tubes he had collected during the 1930s and 1940s.
I did run across an oddity I had forgotten about. There was an AA5
variant that used a rectifier with a 117 volt filament. The other tubes
had 1 volt filaments. These were rare indeed.
There were a couple of other AA5 variants that existed. Car radios were
essentially the AA5 but the tube numbers all began with 6 and then
latter 12. The plate supply in car radios was derived from a vibrator
and tube rectifier or else a vibrator with synchronous rectifier
No, the 6K8 was almost unknown in broadcast band radios in the US. I
never saw one in a US made radio.
> >I forget any of
> >the numbers of these but in reality, these were like ASICs in that they
> >really were optimized for particular applications in TV recievers. They
> >had little impact on the traditional dual triodes like the 12AX7 and the
> >12AU7 and the garden pentodes such as the 6AU6. Actually, some
> >integration was not obvious. It seems to me the 6BE6 had 5 grids and was
> >ideal as a mixer in superheterodyne recievers such as radios and TVs
> Not for TVs; pentagrid mixers don't do too well even at 50 MHz.
True but the comment was more about the superheterodyne than the 6BE6.
TVs used germanium diode mixers fairly early on. I forget the earliest
tuner I saw that in but it had to be circa 1950 when TV came to the city
in which I lived.
> >(there was a metal tube that was similar dating from the advent of the 5
> >tube radio).
> Many, for sure; even the 1A6 2V filament tube, with a UX-6 base, was a
> >Pin limitations on tubes were important in the 1920s and early 1930s, 6
> >pins was about the limit.
> Not so much in Europe. There was a UX-7 base in USA, but, although I
> can't put exact dates on them, there were bases with up to at least 10
> contacts in use in Europe before 1939. I have a double-tetrode tube LV4
> listed, which I think was a Telefunken product, with a 10-contact base.
> >A very common tube of the time, the 01-A had
> >but 4 pins. Power tubes and some pentodes had the anode brought out
> >through a contact at the top of the tube. The 417 and 723 local
> >oscillator klystrons had the repellor on such a contact.
> The 7193, the VHF/UHF version of the 6J5, had both grid and anode/plate
> as top caps. They were sold off after WW2 in millions in Britain, for
> very attractive prices (equivalent to 4p, but 4p was worth more then!).
There were a few here. I never saw a piece of equipment that used that.
There were quite a few power triodes in use that had the grid on the
side and the plate on top. However, when I was a broadcast engineer from
1963 to 1966, really high power tubes were disk seal. Note the short
broadcast career. It was, on the whole, too much work for too little
money. I got a significant boost when I went from a union (IBEW) job in
TV (technical director) to a non-union job at the University of
California (senior electronic technician).
> >In the 1930s,
> >the octal, 8 pin keyed base, came along. Later power tubes expanded the
> >number of pins with the 826 dual power triode and even later the 829 and
> >3E29 dual pentodes. In this era, miniature tubes had 7 or 9 pins (the
> >classic 12AX7 and 12AU7, still available today in some variant, had 9
> Well, not only power tubes. The EF50 r.f. pentode, which practically won
> the electronic war (with the SP 41 and SP61), had a 9 pin base,
> approximately octal-size. The SP41 and SP61 had Mazda Octal bases -
> superficially like the International Octal but with a bigger key and a
> larger spacing between pins 1 and 8.
I saw almost none of the international stuff back in those days. It was
hardly imported at all in the 1950s and 1960s. It was impossible to deal
with because the parts houses did not have the tubes and they had to be
special ordered. Imagine the response when a 12 year old puts his chin
on the counter of Parts Electronic of Arizona and asks for a Mullard
blah blah blah. The man at the counter asks the 12 year old, "What's
Mullard?" I went through that one. The foreign tubes tubes were
challenging to get in the US in the 1950s. You could completely forget
about getting a schematic for a foreign radio then unless it had
developed enough popularity for Sam's to pick it up.
Curiously, I have a British Enfield 303 rifle that was made in the early
1940s (No. 4 Mk I*). It, however, was made in the US by Savage Arms
rather than by BSA.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org