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[AMPS] re: TX lock-up in Mirage D-1010-N 100 W 70 cm amp

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Subject: [AMPS] re: TX lock-up in Mirage D-1010-N 100 W 70 cm amp
From: ac6tk@cybertime.net (J. Bradshaw)
Date: Mon, 15 Jan 2001 08:29:19 -0800
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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