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Author Topic: Testing MSR 2000 Final Amplifier  (Read 146 times)

N3AE

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Testing MSR 2000 Final Amplifier
« on: February 21, 2020, 04:37:36 PM »

I have a continuous duty power amplifier (TLD2602A) from a Motorola MSR 2000 that I would like to test by itself (not installed in the MSR chassis).  The plan was to put it on a dummy load, use a HT on low power as an exciter and power it off of a 13.8vdc supply.  What I can't quite figure out is how to key the amplifier.  The 4-wire plug on the unit that goes to the exciter has four wires:

Pin 10 wire labeled TX SW 9.3,
Pin 3 labeled GND,
Pin 15 labeled Control Voltage (which I believe is an ALC line running TO the exciter)
Pin 4  labeled Key A-  or Keyed A- depending on what schematic you look at.

I was thinking that supplying +9.3vdc between Pin 10 and Pin 3 might command the amp into transmit but I'm not sure what Pin 4 is doing.

tnx
N3AE
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K6AER

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Re: Testing MSR 2000 Final Amplifier
« Reply #1 on: February 21, 2020, 05:54:08 PM »

Mot repeater amplifiers are class ā€œCā€. The Vcc voltage is applied all the time. The amplifier will not draw current until a RF signal is applied on the input. There is no T/R application for the RF output goes to a duplexer.
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N2AYM

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Re: Testing MSR 2000 Final Amplifier
« Reply #2 on: February 24, 2020, 08:57:19 AM »

According to the repeater builder msr2000 information page the TLD2602A
amplifier is to be avoided at all cost. Apparently it fails often and the "B"
version is the improved amplifier for the msr2000.

http://www.repeater-builder.com/motorola/msr2000/msr2000-info-page.html
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N3AE

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Re: Testing MSR 2000 Final Amplifier
« Reply #3 on: February 24, 2020, 02:12:15 PM »

Answering my own question in case the information is useful to others.

All it took was hooking pin 4 (keyed A-) on J801 to the A- screw terminal on the PA.  Did not need to supply any voltage to pin 10.  With 300mw from the HT, the PA output was 100w.   One keyed briefly to verify go/no-go for the PA.

Yes, aware of the TLD2602A reliability issues compared to the B version.  But that's what we have at the moment.  We typically run it below its ratings.
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