kv7g@mindspring.com wrote:
> Here is the mod to replace the amplifier keying relay in the TS-940.
It was
> sent to me about 18 years ago I believe by Paul - K4AVU.
> Make this mod at your own risk. I made it and it was not difficult and
> worked great.
> ++++++++++++++++++++++
> Remove RL2 relay mounted on the control board (X53-1420-11)
>
> Take a small drill bit and enlarge the holes where the relay was mounted.
> The holes must be big enough so the leads on the Power Mosfet will
> pass through them.
>
> Mount the Power Mosfet as follows.
>
> Gate to diode D59 (cathode)
>
> Source to ground
>
> Drain to JP17
>
> ++++++++++++++++
> Use an IRF 822 Power Mosfet or equal. I used the only one that Radio
Shack
> sold about 18 years ago but forget the number.
> This mod works great and there is NO noise !!!!
>
> Bud - KV7G - Yuma, AZ
>
> Mailto:kv7g@mindspring.com
> Web Page http://www.qsl.net/kv7g
>
Roger D. Johnson <n1rj@pivot.net> wrote:
subject: Re: [Kenwood] Noisy relay in TS940
> I also added a power FET to do the switching but I added it
> in parallel with the existing relay. I brought the drain of
> the FET out to an unused pin on the REMOTE jack (pin 7). The
> reason I did this is that the FET only allows keying of amps
> with a positive voltage on the keyline. For amps such as the
> SB-220, I could turn the relay back on and use the normal pin
> 4 for keying the linear.
>
> There is another reason for using an FET. Kenwood, for some
> reason, uses a waveform that is delayed 3 ms from key closure
> to drive the relay. This, added to the 2 ms relay actuating time,
> means that the linear relay doesn't get the command until about
> 5 ms after key closure. The 940 starts producing RF at about 6 ms
> after key closure, so the linear relays have no time to switch!
> I drive the gate of the FET through a 2.2k resistor from the TR
> waveform found at JP-26 on the control board. This waveform goes
> positive at key down thereby giving the linear relay(s) 5 or 6 ms
> to switch. This is still not enough time for the old style relays
> but works fine for the vacuum relay QSK system I installed in my
> Drake L-7.
>
>
Looks like there are a couple of options for replacing the amp
relay with a FET. One drives the gate from D59 and the other
from JP-26. The latter has the advantage of being about 3ms
faster, while the former is slightly simpler.
Any thoughts as to which I should chose?
--
cheers, Paul - VA7NT (ex VE7CQK) - email: paule@sfu.ca
"Those who hear not the music, think the dancers mad..."
--
cheers, Paul - VA7NT (ex VE7CQK) - email: paule@sfu.ca
"Those who hear not the music, think the dancers mad..."
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