[600MRG] MFJ LF Amplifier

[Paul Signorelli]

I have been using my stock MFJ ALS-500M Amplifier on 166.666 kHz for the past few months.

As I mentioned in my previous email (29 Dec. 2016), It was on 480 kHz.

I did get on QRSS3 with some duty cycle adjustments. The internal thermal cut outs maybe set too low.

However with 2 additional fans and the lower duty cycle it is working well.

I built another Butterworth low pass filter for  170 kHz and that keeps my harmonics from jamming the

local airnav beacon on 334 kHz. The driver is an old DX-60 with 2 - 6146's putting out 50W.

The amplifier is drooping a little but the initial power is 500 W.

(I suspect this amplifier would work on 137 kHz.)

My QRSS computer crashed so I am off QRSS for now.

73

Paul   wa2xrm


________________________________
From: Paul Signorelli <w0rw1 at msn.com>
Sent: Thursday, December 29, 2016 2:42 PM
To: 600mrg at w7ekb.com
Subject: MFJ LF Amplifier


I was looking at my MFJ  ALS-500M amplifier circuit the other day and was wondering if

the coupling transformers would work on 480 kHz.

I hooked it up to dummy load and it worked !

This ALS-500M is working with out any modifications, just setting the band switch to 1.8 MHz.

(The MFJ ALS-600 and ALS-1300 probably have similar circuits and would work just the same).

I am driving it with John's (KB5NJD) amplifier at 50W.

The output is about 380W.

I built a W1YD  high power Butterworth low pass filter with cutoff around 600 kHz and it works well.

The MFJ ALS-500M requires additional forced air cooling for beacon operation.

I have not tried any QRSS operation because the FET's used (28C2879) in the MFJ amplifiers are hard to find.

I really don't want to smoke it.

Paul   wa2xrm