[Drake] AM Filter Advice for TR-7

[Jim DiMauro]

Hi All:

Here's an update on the filter situation.  First, I fixed all of the loose
shield screws by very slightly crimping the stamped screw sockets on the
vertical shields.  Now things are nice and tight all around.  A check of
radio performance revealed that there was no difference in AM filter
performance, nor was there a reduction in the birdie at 14.340 that I
reported some time ago (around S-5 with dummy load).  I could still hear CHU
faintly as far away as the upper portion of 40 Meters, no change.

I pulled the IF filter board and discovered that the "faux" AM filter wasn't
the 390 Ohm resistor that seems to be a common mod, but instead there were
three resistors: a 100 Ohm between the input and output terminals, shunted
to ground at each end by a 1200 Ohm resistor.  A little web research
revealed that this mod is shown on the Drake Virtual Museum website.  Until
now, I was only aware of the 390 Ohm mod.  I removed the three resistors and
replaced them with a single 390 Ohm resistor.  No more CHU!  Tightened up
selectivity considerably.  AM "filter" performance is now what I would
expect it to be.  Many thanks for all your suggestions.  You saved me around
$100.  Also, thanx to all for filter supplier recommendations.  I'm not
going to need them after all.

73 to all,
Jim
WA2MER

-----Original Message-----
From: drake-bounces at mailman.qth.net
[mailto:drake-bounces at mailman.qth.net]On Behalf Of Bob Camp
Sent: Saturday, January 01, 2005 4:30 PM
To: jfd at warwick.net; drake at mailman.qth.net
Subject: Re: [Drake] AM Filter Advice for TR-7


Hi

I agree that simply using the roofing filter for AM (the resistor mod)
does not do a good job on the ham bands. I gave it a try back when the
TR-7 was new. Next day I went out and got an AM filter.

Finding a original AM filter for the TR-7 may be a tough thing to do.
Finding one that is still in good shape and not installed in a radio
may take quite a while.

There are several outfits that do filters these days. Certainly
Sherwood is one of them. You might get in touch with each of them and
see what they would recommend. Often they have stuff sitting on the
shelf that is not in their catalogs.

	Take Care!

		Bob Camp
		KB8TQ



On Jan 1, 2005, at 3:55 PM, Jim DiMauro wrote:

> Hi All:
>
> I have a TR-7 that I'd like to use on AM every so often.  The trouble
> is
> that the radio doesn't have an AM filter.  A previous owner had
> installed
> the resistor mod that's supposed to act like an AM filter, but the
> result is
> far too wide to be useful.  For example, if I'm listening to a QSO on
> 7290,
> I can hear CHU on 7335.  Now that's wide!
>
> I'm looking for recommendations on AM filters, specifically which ones
> perform well.  Should I look for an original Network Sciences SL-6000
> that
> Drake supplied, or are the better options out there like Sherwood and
> Kiwa?
> All input will be appreciated.
>
> Thanx & 73,
> Jim
> WA2MER
>
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