Sounds well designed but poorly assembled and tested. I guess it's
reassuring that you still have to do something to be a real ham.
Jim, ac6tk
----- Original Message -----
From: "Ian Roberts" <ITR@Nanoteq.co.za>
Cc: <amps@contesting.com>
Sent: Sunday, January 14, 2001 22:58
Subject: [AMPS] re: TX lock-up in Mirage D-1010-N 100 W 70 cm amp
To round off this discussion:
The amp's biasing was found to be far too high on the bases of the
driver and final stages. This was causing excessive dissipation in
addition to allowing the amp to self-oscillate when the RF-derived PTT
was dropped.
Re-biasing the driver and finals (pots are provided, - hopefully not
into Class C!) solved the problem. The SSB delay, which had to be set to
minimum, is now working fine at maximum. There is less dissipation and
the heatsink is noticably cooler.
There are no RF adjustments, all caps are the fixed metal-clad mica
types so favoured in Motorola design sheets, so input/output impedances
have to be good; my cables/antenna were not adjusted. Antenna SWR is
around 1.05.
8 Watts in provides 80 Watts out at 13.5 V, and this is in accordance
with the spec.
Further info: both PCBs had not been tightened down properly and may not
have made proper grounding to the earth plane. The 170 deg thermal
protection switch was on the point of dropping off the heat sink as it's
fastening screw was half out. Since this switch hangs from the heatsink,
it would not have sensed the heatsink's temperature properly, thus
failing the only protection offered on the amp.
The product is now made in Starkville (MFJ).
Cheers,
Ian ZS6BTE.
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