HW-12A Issues

[ve3fwf]

Kent:

There is no service manual per se other than service bulletins.

Based on your E-mail, I assume that the receiver is working just fine.  So 
try the following:

1. Check for B+ . You can do this from the top of chassis near the left 
front where the RF choke resides. Careful here, 800V !  Make sure that the 
power supply is not sagging under load. You may have bad electrolytics in 
the power supply.
2. Also check the screen voltage. Best to use the voltage reference table in 
the manual at this point and check all voltages around the finals and the 
driver both in RX and TX mode.
3. If 1. and 2. are OK, swap the TX mixer tube with another similar tube in 
the radio.
4. If still no joy, then I would use a scope and find out where the RF is 
falling off. You should have about 50 volts PP on the grids of the finals. 
There are some signal levels in the manual.

Take your time and use a "lab book" to write down what you do so that you 
can restart your work without having to perform steps previously completed 
and verified.

Good luck

73, Bernie, Ottawa, Canada


----- Original Message ----- 
From: "Kent Kressenberg" <krkress at BELLSOUTH.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Tuesday, February 13, 2007 4:48 PM
Subject: Re: [HEATH-TEMPE] HW-12A Issues


Hello,

    I am happy to be in on this forum. I own a HW-12A, working well until a 
few weeks ago, when I experienced a rapid loss of RF output power... down to 
10 watts or less.
    I assumed I had lost the PA tubes, so I replaced the finals and driver. 
This had NO effect whatsoever, so there is another problem, perhaps loss of 
HV or B+??
    I have the manual, but it does not include much service/trouble-shooting 
information. Is there a separate "service" manual for these radios? Can 
someone suggest diagnostic procedures for this problem? I have built kits 
before, even built a couple of my earlier radios from scratch, and can use 
basic test gear with facility...
    Would greatly appreciate any assistance members could give on this 
problem.

73 de WB4SYU,

Kent Kressenberg
Chattanooga, TN.

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Products bought, sold or traded here is the responsibility of the
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