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[TenTec] QRP/QRO Switching for the Ten-Tec Scout

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Subject: [TenTec] QRP/QRO Switching for the Ten-Tec Scout
From: wb2vuo@juno.com (William K Hibbert)
Date: Fri, 28 Feb 1997 19:02:52 PST
I hope this isn't a dupe, but I was just told that the address to post to
changed while I was out of town the last couple of weeks... Keith, WB2VUO


After a few questions about the Argo vs the Scout for QRP, I looked in
the manual and think that a mod to make the Scout switchable would
actually be quite simple and elegant...

By comparing the Main Wiring Diagraams for the Scout (Figure 3-23) and
the Argo (Figure 3-24), the only difference is the addition of the 50
watt RF PA, P/N 81643.  With the addition of either a 4PDT switch, or a
couple of small relays, you can switch the PAin & out of the circuit. 
Without having a Scout here in front of me, here's what the diagram

In the Scout, the low-level RF is routed from the LL DRIVER board (81645)
at connector 55.  It goes to the RF PA (81643) at connector 55.  The
output of the RF PA, at connector 61, is  then is routed to the LOW PASS
FILTER PLUG-IN.  In addition, the +13 volts for the RF PA and the DC line
for the base bias are routed from the LL DRIVER board to the RF PA board.

To switch the PA in & out, the switch or relays would break the lines
from connector 55 and connector 61 and route the power from the LL
DRIVER board directly to the LOW PASS FILTER PLUG-IN, and another pole
would disconnect the +13 and the T line to the PA.  This would provide 5
watts out instead of the 50 watts out, and would also disconnect the DC
to the amp thus cutting 300 ma of standby current.

It is VERY important to disconnect BOTH the +13 and the T lines!!!  If
you have biad on the PA, without the Vcc on the collectors, the
transistors will suffer, probably even letting the smoke out!!!  I had
this happe accidentally in a VHF radio when the clooector choke opened,
and it smoked the PA in no time, to the tune of $35 for the transistor

You could, for a FD operation, just unplug the PA module and re-route the
cable from connector 61 to connector 55.  Later on, you could restore the
rig to QRO by reconnecting per Figure 3-23...

NOTE:  The power meter will read low on the Scout, and the SWR bridge won't be 
accurate.  You might have to play with the ALC level, but I would
have to try the conversion to verify this.  Any volunteers out there with a 
Scout that needs to be QRP'd ???

Drop me a line with your results.

72/73, Keith, WB2VUO, QRP-L #582, scQRP 40, Tech Specialist (ARRL/WNY), 
ARRL Life Member, VP/BARK, Beacon Chaircritter, Rochester VHF Group
Trustee, KB2YTW/B 10 Mtr QRPp Beacon (250 mW @ 28.2870 MHz)
"In the Depths of the Great Bergen (NY) Swamp...FN13ac"
Packet - wb2vuo@w2im.#wny.ny.usa.noam
Email  - wb2vuo@juno.com

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