[AMRadio] In Defence of Old Buzzard Transmissions

Rob Atkinson ranchorobbo at gmail.com
Mon Oct 12 13:04:05 EDT 2015

On Mon, Oct 12, 2015 at 3:13 AM, Donald Chester <k4kyv at charter.net> wrote:
>> All of the above is probably standard procedure and common knowledge for
> most operators.  It also explains why once I get into transmit I am willing
> to stay there for a while.  Not interested in flipping through all that and
> back again to make a 5 second transmission on a regular basis.
> But if I read that correctly, you only flip one switch, and the sequencer
> takes care of the rest, so you have about a 4/10 second delay.  That
> shouldn't affect your ability to do the fast-break type of QSO if that's
> what you wish.

That's correct, but I don't like repeated toggling from rx to tx
dozens of times during the course of the evening each re-energizing
h.v. transformers; however perhaps I am overly cautious.

 Rob, you remember the
> switch; we found a bunch at Dayton a couple of years ago, where I picked up
> some for  spares. I hate a switch attached to a desk mic almost as much as I
> hate a foot switch (I think a foot switch is just plain silly). My T/R
> switch on the spiral cord works well with my boom-mounted microphone.

I sure remember those switches and I think I got two of them and
they're sitting on my operating table.

What stinks about foot switches (one thing) is the need to keep
constant pressure on them.  Back when I had one I would have to pick
it up off the floor and hold it in my hand to insure it stayed closed.
A hand held toggle switch is much better.

>> If the final comes on, then about 2/10 second later, h.v. comes on for the
> rig's modulator.
> Looks like your sequencer set-up has a total of three-steps.

It's the one you wrote about in the November 2005 ER.  It's only two
steps, but the 3-400 rig has a built-in mod. iron protection circuit,
one of a number of controls in it that the original engineer designer
did in an attempt to make it idiot proof.  It's real nice to have when
there are separate supplies for the final and modulator but it is part
of the rig's mystery I am gradually trying to figure out.  The mod.
delay circuit includes a small rheostat on the rear chassis of the
final that allows for the adjustment of the delay time.  Another
protection that is okay but adds complexity is that the final h.v.
won't come on if there is no grid drive.  I dimly recall that with
3-400 and 3-500, loss of drive isn't a fiasco, but perhaps that is
only if the tube is grounded grid and cathode driven.

 Do you have
> two separate sequencers in tandem, so that step 2 of the first sequencer
> initiates step one of the second, or did you design the sequencer to operate
> in three steps? Mine is two-step. When I first actuate the switch to
> transmit, the antenna change-over relay, the monitor scope and the VFO all
> come on instantly, as the receiver turns off, along with the antenna
> shorting relay I use as an added precaution to protect the receiver's rf
> input coil. In step two following about 2/10  second of delay, the
> transmitter comes on. When I switch back to receive, the whole  process is
> reversed.  One master relay controls power to all the plate transformers in
> the transmitter, so the rf exciter, modulator and final all come on
> simultaneously.  I use arc gaps across the primary of the modulation
> transformer to protect it in case the load is lost as a result of a failure
> associated with the RF final.

I spent an entire day a few years ago experimenting with relays to
come up with a method that would best isolate the rx on transmit and
protect the input coil.   The way I do it now is almost too good
because I can't hear the 122 VFO for spotting on the CW rig.  On the
3-400 rig I spot with both the vfo and driver.   The RCA mod iron in
the rig also has arc gaps.

Like you, I use a  pilot relay to activate the
> big antenna change-over, since its heavy-duty coil is 115 volts a.c. while
> all the rest of my relays run on about 30 volts d.c. The main purpose of my
> sequencer is to avoid  hot-switching the antenna change-over relay, which
> was burning up the contacts.

I put a large P&B 4PDT 24 v. relay in a die cast aluminum box for the
main T/R relay.  It is made with copper arms, silver contacts and
brass/aluminum lugs.  3 poles handle RF; the 4th one is used to short
the rx line to ground on tx.

> Speaking of annoying and chaotic, the very worst has to be to operate AM
> using VOX, particularly making long transmissions with the carrier dropping
> out and back in at every pause in speech.

AM VOX is one thing I have yet to hear (fortunately).


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