Chuck Harris wrote:

The Swan design was very competent, but very much driven by cost.
That said, it is sort of odd that they used the fancy, but expensive,
7360 balanced modulator tube.

That's the sheet-beam tube? Those things actually reduced the cost of
a design because they eliminated a whole slew of parts. Later on there
were a bunch of cheap ones designed for chroma detectors in TV sets, but
at first there was only one.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
Chuck Harris wrote:

The Swan design was very competent, but very much driven by cost.
That said, it is sort of odd that they used the fancy, but expensive,
7360 balanced modulator tube.


That's the sheet-beam tube? Those things actually reduced the cost of
a design because they eliminated a whole slew of parts. Later on there
were a bunch of cheap ones designed for chroma detectors in TV sets, but
at first there was only one.
--scott


I've only heard of them being used because of their extremely good
carrier suppression. They provide on the order of 60dB of carrier
suppression, as compared to a typical balanced modulator which gives
only 30dB. When used in conjunction with a crystal, or mechanical
filter, the 7360 can achieve 80dB of carrier suppression.

I can see that they would provide some reduction in parts, they are
capable of oscillating, but Swan didn't use it that way. I think
they could have achieved a greater cost savings using 4 matched
diodes in a ring modulator configuration.

-Chuck

it is sort of odd that they used the fancy, but expensive,
7360 balanced modulator tube.

That was an extremely common choice for not only for not only
transmitter balanced modulators but also for receiver mixers and
product detectors in the 50's and 60's. I think it must've been the
case that one early ham article used it and everyone else copied it.
Certainly it was not a common junkbox part...

Tim.

wrote:
it is sort of odd that they used the fancy, but expensive,
7360 balanced modulator tube.


That was an extremely common choice for not only for not only
transmitter balanced modulators but also for receiver mixers and
product detectors in the 50's and 60's. I think it must've been the
case that one early ham article used it and everyone else copied it.
Certainly it was not a common junkbox part...

Tim.

Hi Tim,

ARRL published a circuit using it in many of their handbooks from the
'60s. And I have heard that it was used in TV applications, but the
part that surprises me is I have only seen one type, the 7360. If it
was such a commonly used tube, it surely would exist in a non industrial
numbered version (eg. 6ZZ9, or some such).

The reasons for wanting such a tube are easy to figure out. It can
easily give 60dB of carrier rejection... add a xtal filter, and 80db
is easily achieved. Compare that to a diode dbm, and its 30db, and
50db capabilities.

-Chuck

In article ,
Chuck Harris wrote:

ARRL published a circuit using it in many of their handbooks from the
'60s. And I have heard that it was used in TV applications, but the
part that surprises me is I have only seen one type, the 7360. If it
was such a commonly used tube, it surely would exist in a non industrial
numbered version (eg. 6ZZ9, or some such).

Chuck,
There was never a pin-for-pin "entertainment" version of the 7360,
but there were a few functionally-equivalent types, the 6AR8, 6JH8,
and maybe another (6M-something) I can't remember. They could be
used in the same circuits as the 7360, and they were cheaper
as they were made in much larger numbers (Zenith used the 6JH8 in
color-TV demodulator circuits). And they were used in ham gear
too -- my old Swan 260 "Cygnet" used a 6JH8 as the balanced mod.
These tubes did make great balanced modulators, and nice receiver
mixers too.

Ted Zateslo, W1XO

Ted Zateslo wrote:
In article ,
Chuck Harris wrote:

ARRL published a circuit using it in many of their handbooks from the
'60s. And I have heard that it was used in TV applications, but the
part that surprises me is I have only seen one type, the 7360. If it
was such a commonly used tube, it surely would exist in a non industrial
numbered version (eg. 6ZZ9, or some such).


Chuck,
There was never a pin-for-pin "entertainment" version of the 7360,
but there were a few functionally-equivalent types, the 6AR8, 6JH8,
and maybe another (6M-something) I can't remember. They could be
used in the same circuits as the 7360, and they were cheaper
as they were made in much larger numbers (Zenith used the 6JH8 in
color-TV demodulator circuits). And they were used in ham gear
too -- my old Swan 260 "Cygnet" used a 6JH8 as the balanced mod.
These tubes did make great balanced modulators, and nice receiver
mixers too.

Ted Zateslo, W1XO

Hi Ted,

Thanks for the info. I thought I knew my old RCA RC-25 tube manual
pretty well; I bought it new, and the binding has all fallen apart,
but there they were just like you said.

I must have stopped mucking around with tube color tv's before they
became popular.

-Chuck

[7360 tubes for balanced modulators and mixers]
Chuck wrote:
ARRL published a circuit using it in many of their
handbooks from the '60s.

I just pulled out my '65 ARRL handbook and there are two SSB exciters,
each of which uses TWO 7360's.

And there are two not-awfully-fancy receivers, each of which uses a
7360 in the mixer.

Man, somebody in the ARRL must've owned stock in that tube company :-).

Tim.