Tom,
At first I wasn't going to respond to your post at all, but decided that
maybe I would try one more time....
It appears to me that the concept of "NO HV on RX" is so utterly alien to
the amateur community that most folks, including you, have jumped to the
wrong conclusion. I have stated that I make mistakes. Maybe I'm wrong again
now, but it really seems to me that people are not reading and
understanding. Let me go through your points one at a time and see if we
can get to some mutual ground.
>I am saying a simple interlock is more reliable than switching the
>HV supply off and on hundreds of times a day or week, and
>expecting something won't eventually fail, and depending on
>complex external wiring to turn off HV for safety.
You know as well as I do that circuits can be designed to rapid cycle
reliably. For instance, pulsed radar, the flashing yellow light at the
intersection down the street, a microwave oven oscillator/PA, and switch
mode power supplies. I have a choke input HV supply that I have used in
this mode for twenty years without a single failure. This new cap input
supply is still in question, I'll get back to you in twenty years.
As for as wiring, it is no more complex that that used to operate the
customary vacuum relays and/or the cutoff bias for the tube. Again, I just
don't see a reliability issue.
>No matter if there is an interlock or not, I always unplug and wait. I
>always check the HV meter, and then crowbar the supply.
Good advice. I never said not to do any of this. I absolutely agree.
>I can't see any safety advantage when depending on a transmitter
>control line to turn off the mains power to the amplifier HV supply.
We have a real problem here. Perhaps it's just semantics. I do not depend
on this feature. It is just one of many redundant things I do to increase
my chances of being around long enough to work another new one on 160.
>As a matter of fact, I consider it a potential hazard. The operator
>might be lulled into a false sense of security... depending on
>station wiring and the rig being in a non-transmit mode to make the
>PA "safe to touch".
A PA is never "safe to touch". At least, one should never consider it to be
so. A foolish person may depend on a single safety feature to "safe" a PA,
I do not. All this not withstanding, on two separate occasions, two
different transmitters, I had the opportunity to get a taste of "old
sparky". Each time I was 110% sure, beyond any doubt, that I had done what
was required and that it was "safe". I submit that, at least in my personal
experience, one more safety device would have been handy.
> Have you
> > figured out how to probe a circuit with all the covers in place?
>
>Sure. I test each component, or disconnect components to isolate
>problems and THEN put the cover back on to see if the fault clears.
OK for stuff as complex as a flashlight. My question assumes you have done
all that was possible with power off and are now faced with the problem of
circuit performance evaluation while under power.
>The only exception is when I have a cover open, and then I go to a
>breaker and turn the PA on while I am across the room. I
>absolutely never get near the PA when HV is accessible and able
>to be turned on.
Unworkable for me. I cannot read the meters, scope, spectrum analyzer, etc,
from across the room without binoculars. Perhaps you are a ballerina on
your night job, but I'm the bull in the china shop. It is necessary for me
to minimize the amount of movement I must do while things are "hot". With
my propensity for clumsiness and mishap, I would trip on a shoelace and
fall face first into the PA. Nope, definitely not a workable solution.
>I have specific covers that allow me to access non-HV areas for
>certain troubleshooting, or I disable the primarys by removing the
>wiring connections at some point before trouble shooting LV
>circuits.
I have found plexiglass covers with holes in strategic spots allow
necessary probing with minimal exposure. Good for production line work, not
easy for home work, but doable.
>
>
>Anyone who does otherwise is a fool, in my opinion. There is
>NEVER a reason to power up a PA and stick one's hands inside
According to Mr. Measures, it is necessary to do that to tune the cathode
networks. I personally do that operation on the workbench, with no power
source in sight. It may take a trip or two back and forth between the amp
rack and the workbench to get it set the way I want, but sure beats
sticking ones hands inside the hot box.
In closing, let me re-iterate a few points.
1) Someone asked about SSR usage and opinions thereof. I replied with my
usage and opinion along with some background for that opinion. The list
went nuts. It's as if I repudiated all conventional safety measures and
demanded that everyone convert to my kind of supply.
2) Never once did I suggest that this approach was appropriate for anyone
but myself.
3) Never once did I even suggest this was a replacement for conventional
safety measures.
4) I don't sell amps or supplies or parts for them. I really don't give a
rip if anybody wants to do what I did or not. My concept (although not
really mine, it's been done before) has been called wacky. You betcha! If I
wanted conventional I would go get an Alpha or a Henry. I homebrew this
stuff because I want it my way. Read that MY WAY, not Rich's way, not Tom's
way, not Mr. DAFfy's way, but MY WAY.
So, somebody, please tell me: What set off all you folks?
73,
Larry - W7IUV
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