HW-101 Survey Question.

[Jim Flanagan]

Hello ..

        I asked this question a week ago and thought I would give it another try.

I am bothered by the obnoxious speaker thump when going from rcv to xmt with my HW-101.  If you turn the audio pot to min audio and key the radio, I hear a loud pulse type thump in the speaker (with headphones on, this is unbearable).  For those individuals who are more on the technical side, there is an RC circuit at the grid circuit of V14A that senses and shapes the negative voltage transient that occurs when the relays are energized.  This shaped pulse is fed into the grid of V14A and this will (supposedly) turn off the audio preamp while the relays are switching from RX to TX.   The problem with this, is that the sudden negative pulse at the grid of V14A will result in a positive pulse at the plate of V14A and this will be heard in the speaker,etc.  I did a SPICE analysis of just the relay/shaping network/V14A circuit and results agree with measured data.  Funny thing, of the few (maybe two) people that I have asked whether they notice this problem, have said that they do not
.

I was always under the belief that the ONLY thing that should be heard when switching from RX to TX is the actual mechanical relays.  Years ago, I remember hearing an SB-102 (same audio circuit) and it was quiet as a mouse between RX & TX.

Therefore, in order to satisfy my curiousity, I am asking owners of HW-101s to test to see if they hear this noise.
The only thing that I have not tried yet is to replace the 6GW8 audio tube, although I don't believe that it will help.

Your responses are appreciated..
Thanks.
Jim
------------------
Jim Flanagan
jflan at ieee.org

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