[Amps] TL-922A on 17 & 12

[Thomas Walsh]

While it is true that the pi network and/or the input tuning may also be outside optimal
tuning for that band, and both would cause reduced pwr out, mostly via high input swr.
The pi tank on a 160-10m or even an 80-10m design should handle the warc bands, 
of course the tune cap will be outside the normal bands, but the pi tank is continuously variable within the above ranges.

If you smell something burning it almost always is the plate choke having some
resonance at the frequency of operation! And it also starts showing more and more 
pwr loss the closer it is to the resonant freq. of that choke. Needless to say it won't last long. 

An example: On the Alpha 9500 the Plate choke is purposely tuned to 27.1-27.3mhz. 
By doing this, even if the op figures out how to hack the freq. tables to even allow 
the CB band, the plate choke will immediately smoke rather violently if they key up on say 27.185! In that case almost all the rf goes straight to the hvps! Thus the violent
Reaction! These were two methods to disable illegal operation on the CB band.

I've seen plate chokes tuned even 500kc away from the op freq. get so hot they smoked.

So what causes this? The plate choke is supposed to be non-resonant at the 
frequency of operation to block the rf from getting into the hvps, and keep it going toward the pi tank and ultimately the output.

 A partially resonant plate choke passes some of the rf toward the hvps and less to the 
output side, thus the reduced output. This is also why they get very hot!
It is variable and it all depends on how close to the chokes' resonant freq. you are operating at. Always check where the resonances of the plate choke before operating
on bands not designed into the unit. They knew about it but didn't tell you.

A.R.S. W2CO


On Oct 12, 2021, at 11:07 AM, Peter Voelpel <dj7ww at t-online.de> wrote:

It tells me that the pi net is not optimized for those bands and efficiency
dropped for that reason and the input filters are not wide enough for those
bands as well and drive power is less.

There is no such thing as RF power being send back to the power supply!

73
Peter

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Thomas
Sent: Dienstag, 12. Oktober 2021 16:06
To: Victor Rosenthal; Dick NY1E
Cc: Amps reflector
Subject: Re: [Amps] TL-922A on 17 & 12

This tells me 100-200w are being sent back to the PS by a partially 
resonant choke, thus the "brown spots".
You need to use an accurate grid dip meter with the choke in circuit to 
measure for any resonances near the
freqs you plan on using. If you make any changes like adding or removing 
windings, you would need to check
all the bands again! If the choke opens and unwinds during operation, it 
could short the B+ to ground! Bang!
73
de W2CO


> On 10/11/21 8:50 PM, Victor Rosenthal wrote:
> Yes, it does work, although output is slightly lower than other bands. I
> use my tl922 on the WARC bands as follows:
> 30m - bandswitch on 20
> 17m - bs on 15
> 12m - bs on 10
> Power output is 1 - 1.1 kW compared to 1.2 - 1.3 kW on non-WARC bands.
> 
> Victor 4X6GP
> 
>> On Tue, Oct 12, 2021, 05:12 Dick NY1E <dick at ny1e.com> wrote:
>> 
>> I don't want to find out the hard way, does the plate choke on a TL-922A
>> work on 17 & 12 meters? 12 meters is really coming to life and I get
>> temped...de Dick NY1E
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