Greetings all...
I've been following this thread with much interest as I received two TL-922A
amps from the MARS program. While these amps had very little time on them,
one of the amps had significant damage to the bandswitch. These amps were
used in a controlled environment by only one or two individuals from the
local air base. Bottom line is that they were used in strict accordance
with the owner's manual and yet one of the amps destroyed it's respective
bandswitch.
After I received the amps and before applying power, I searched the web for
"tl-922" and found several sites, including AG6K's. I had never been on
this reflector before, nor had I heard of Rich, Tom, et. al., before coming
to this reflector. So, I read Rich's TL-922 modifications from an unbiased
standpoint, and quite frankly, they made a lot of sense to little old me,
and I found them to be well thought out. I thought his findings were very
sound. I'm not a rocket scientist, but I do possess a BSEE, MSEE, and soon
to be Ph.D. in EE (RF).
I was quite surprised to find out that Kenwood really missed the boat on the
little things too, such as inrush current and filament voltage. A few more
minutes of design work, or perhaps keeping the marketing folks out of the
engineering, and Kenwood would probably still be in the HF amplifier market
today...
I guess the bottom line here is that for less than the cost of a new
bandswitch, the TL-922 can be made very reliable, and much more pleasant to
operate (quieter T/R change-over). I can't say for certain exactly why the
bandswitch failed, but it did. Since making the mods, I haven't had any
problem with either of these amps. I can highly recommend to owners of
non-modified TL-922s to consider making these mods to their amps.
I have since gone back and dug out Rich's article, "Parasitics Revisited",
and it is well worth reading. I can't prove whether it was parasitics,
parasitic paranoia, or "little green men" that damaged the amp, but it did
happen. I particularly enjoy this reflector when the discourse is more
technical, but I find the thinly veiled personal attacks to be rather petty.
If you don't agree, with someone, please provide sound engineering
data/practice to argue your points.
I'll step off the soap-box now...
Thanks, and 73 de Don (kiss)
-----Original Message-----
From: Tom Rauch [mailto:w8ji@contesting.com]
Sent: Monday, June 07, 1999 8:27 AM
To: Jon Ogden; amps@contesting.com
Subject: Re: [AMPS] TL-922 Filament Transformer Protection
Come on Rich, use your head.
The low pass system on the input of the amp virtually guaranties
the rise time of any pulse is about the same as the rise time of the
desired signal. That's very well known!
As for the relay cathode return closure causing a transient, that
assumption is silly beyond belief! When the relay closes in the
cathode, the bypass capacitors--filament transformer---filament
choke---etc etc all slow the transition down. The slope of the
transient must be less than high audio frequencies after passing
through all that stuff.
I'm amazed you try to propagate such BS in order to explain
something so easily understood.
> >>This (VHF) ringing occurs whenever there
> >>is a transient in anode-current. I contend that RF input contact arcing
> >> (hotswitching) during relay closure will produce transients in
> >>anode-current -- and that the resultant ringing in the anode circuit
> >>will be fed back by the feedback C of the amplifier tube. .
> >
> >HOW?
Good question, now look at Rich's reply......
> ? A spark is reliable producer of wide-band feculence.
As Rich is also!
> >How does closing a relay wether it is a hot closure or not produce a
> >transient in anode current?
> >
> ? hotswitching causes a spark.
So does flint. I guess than means Zippo lighters have parasitics.
> >I always thought anode current (other than bias current) was produce by a
> > driving signal.
>
> ? The spark is connected to a wire that connects to the input of the
> tube.
Through a low pass filter that prevents any transcients faster than
the signal frequency from passing....
> > Hot switching is not good, but I don't think it is a
> >cause of anode current transients.
>
> ? When I was on 1296MHz, I could hear spark-plug interference from
> automobiles 400m distant.
I can hear thunderstorms from Boston on frequencies that will pass
through the input circuit. Thunderstorms must also trigger
parasitics.
73, Tom W8JI
w8ji@contesting.com
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