How incredibly rude of "lazy"...I own a 350, love the radio...also own
Icom gear...as for the antenna loading, you need to adjust it while
tuining the radio but with as little power out as possible to save the
finals from going soft on you.

Steve W4SEF


On Wed, 23 Nov 2005 19:26:46 -0500, Chuck Harris
wrote:

I have a silly question about the Swan 350 antenna
loading switch. Did they mean for you to switch it
while the rig was keyed for tuning, or were you
supposed to unkey the rig before switching it?

I've always assumed the later, but...

-Chuck

Hi Steve,

Thanks for the info. The manual was silent on that issue. I was
concerned that there would be arcing at the switch contacts if
you switched live, so I would try one setting, key it, dip, and
adjust the fine loading, unkey, and then try another coarse load
position, wash rinse repeat... until I got the plate current I
was expecting.

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. I wish they would have used 6146's,
but sweep tubes were so plentiful, powerful, and cheap back then that
they probably were as good of a choice as any.

The drifting problems were the result of Swan's using a single conversion
design. They used a band switched HF VFO to feed their first (and only)
mixer. That decision saved them a whole bank full of crystals, and
another conversion stage. It also reduced the number of conversion
products (spurs) that were drifting around in the cabinet. But the cost
was the introduction of that famous Swan drift to the ham bands.

Another cost reducing measure was to exploit the custom of USB on 20,15,
and 10m, and LSB on 80 and 40m. Swan used hi injection for their mixer
on 80 and 40, and low injection for the rest. That allowed them to get
by with a single BFO crystal, and no USB/LSB switch. Hams didn't like
that, so very quickly, Swan introduced a modification to add a third position
to the REC, CW/SSB switch for "opposite sideband", and added a new crystal.

It's an interesting radio. It won't be my favorite, but I was glad to
get a chance to experience it.

-Chuck


Steve Fritts wrote:
How incredibly rude of "lazy"...I own a 350, love the radio...also own
Icom gear...as for the antenna loading, you need to adjust it while
tuining the radio but with as little power out as possible to save the
finals from going soft on you.

Steve W4SEF


On Wed, 23 Nov 2005 19:26:46 -0500, Chuck Harris
wrote:


I have a silly question about the Swan 350 antenna
loading switch. Did they mean for you to switch it
while the rig was keyed for tuning, or were you
supposed to unkey the rig before switching it?

I've always assumed the later, but...

-Chuck

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.