FT901 preselector

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FT901 preselector

Postby G0GKH » Tue Jul 11, 2017 7:56 pm

Hi



Something a bit odd with the preselector control action on my 901.

On all other bands it works exactly as I would expect from my other similar vintage Yaesus, i.e. it peaks nice and sharply on the scale in the band as marked.

But only on 40m , there seems to be no real distinct peak point in the receiver gain, on tranmit it seems to peak ok, and I can certainly dip ok.

When the rig is on 40,the receive level barely changes over the full travel of the preselector control, right from one end of its complete travel to the other! It seems like there is no actual "peak" going on.

Any suggestions welcomed

Dave, G0GKH
G0GKH
 
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Joined: Wed Oct 17, 2012 6:03 pm

Re: FT901 preselector

Postby N8YX » Fri Jul 14, 2017 7:01 pm

We've chatted a bit about this on the Yahoo reflector.

Next step: Replace the driver tube and see if the condition changes or disappears. That's the "common" in the TX and RX preselector circuitry.
N8YX
 
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Re: FT901 preselector

Postby G0GKH » Mon Jul 17, 2017 4:26 am

Hi Fred,

Thanks for the info on the Yahoo group.

I changed the driver valve for another that I know is ok, re-did the alignment but it's still the same.

It's like the rig is missing some degree of bandpass filtering when on 40m.

When I test it's response with the marker signal, with the receiver on 7.2mhz, the marker signal can be peaked to a displayed S9 +20, (this occurs exactly where the manual says it should at "6.5" on the front panel legend), rotating the preselect control even as far clockwise as it will go (i.e. top of 10m scale), the marker signal still shows S9, when doing this on all other bands it drops away very sharply when the preselect control goes away from its peak.

73, Dave
G0GKH
 
Posts: 8
Joined: Wed Oct 17, 2012 6:03 pm


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