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Hi all,
Just got my "dream receiver"...SX-115! It is a beautiful receiver inside and out.
After careful power up, no hum, and it works, mostly.
The sole issue signal in the 0.5 kc bandwidth are about 60 dB lower than any other bandwidth. I carefully cleaned the selectivity switch, inspected the associated resistors, (I didn't desolter them and measure R yet) tho.
I've replaced all the .01 uF caps in the selectivity circuit.
Per the manual, in 0.5 kc bw, all resistors are shorted.
That is happening.
So, why would the receiver have an attenuated sig on 0.5 kc only?
Any suggestions? Thanks and 73
Steve
W8tow
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Wow, it has been 50 years since I had an SX-115. Great receiver. The only thing I can think of is that the narrow BW filter is no longer tuned to the 50 KHZ last IF stage. 73 – Mike ? Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 908-902-3831 ?
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From: [email protected] < [email protected]> On Behalf Of Steve Marquie Sent: Friday, October 25, 2024 2:19 PM To: [email protected]Subject: [HallicraftersRadios] SX-115 Low sensitivity .5 kc Selectivity ? Just got my "dream receiver"...SX-115! It is a beautiful receiver inside and out. After careful power up, no hum, and it works, mostly. The sole issue signal in the 0.5 kc bandwidth are about 60 dB lower than any other bandwidth. I carefully cleaned the selectivity switch, inspected the associated resistors, (I didn't desolter them and measure R yet) tho. I've replaced all the .01 uF caps in the selectivity circuit. Per the manual, in 0.5 kc bw, all resistors are shorted. So, why would it have an attenuated sig on 0.5 kc only? Any suggestions? Thanks and 73
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What if the filter is ok but the 50 kHz IF isn't lined up right on 50
kHz so that the narrow filter doesn't coincide with the passband even if
it is still functioning correctly and on frequency? Just guessing here
as I don't have an SX-115 or its schematic.
73,
Maynard
W6PAP
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On 10/25/24 18:23, Mike Feher wrote: Wow, it has been 50 years since I had an SX-115. Great receiver. The
only thing I can think of is that the narrow BW filter is no longer
tuned to the 50 KHZ last IF stage. 73 – Mike
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
908-902-3831
*From:* [email protected] <[email protected]>
*On Behalf Of *Steve Marquie
*Sent:* Friday, October 25, 2024 2:19 PM
*To:* [email protected]
*Subject:* [HallicraftersRadios] SX-115 Low sensitivity .5 kc Selectivity
Hi all,
Just got my "dream receiver"...SX-115! It is a beautiful receiver inside
and out.
After careful power up, no hum, and it works, mostly.
The sole issue signal in the 0.5 kc bandwidth are about 60 dB lower than
any other bandwidth. I carefully cleaned the selectivity switch,
inspected the associated resistors, (I didn't desolter them and measure
R yet) tho.
I've replaced all the .01 uF caps in the selectivity circuit.
Per the manual, in 0.5 kc bw, all resistors are shorted.
That is happening.
So, why would it have an attenuated sig on 0.5 kc only?
Any suggestions? Thanks and 73
Steve
W8tow
<>
Virus-free.www.avast.com
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<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
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Not uncommon for the narrowest filters to have higher attenuation especially from that era but 60 db down does sound excessive. Possibly an alignment issue but I am not familiar with the SX-115 bandwidth method.
Ed, WA9GQK
On Friday, October 25, 2024 at 01:19:20 PM CDT, Steve Marquie <w8tow.sm@...> wrote:
Hi all,
Just got my "dream receiver"...SX-115! It is a beautiful receiver inside and out.
After careful power up, no hum, and it works, mostly.
The sole issue signal in the 0.5 kc bandwidth are about 60 dB lower than any other bandwidth. I carefully cleaned the selectivity switch, inspected the associated resistors, (I didn't desolter them and measure R yet) tho.
I've replaced all the .01 uF caps in the selectivity circuit.
Per the manual, in 0.5 kc bw, all resistors are shorted.
That is happening.
So, why would it have an attenuated sig on 0.5 kc only?
Any suggestions? Thanks and 73
Steve
W8tow
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"Steve Marquie" <w8tow.sm@...> wrote <snip> So, why would it have an attenuated sig on 0.5 kc only? Any suggestions? Thanks and 73 Hi, Steve Did you try shifting the notch filter? In the SX-115, the "off" position of the notch filter isn't really off, it just locates the notch just to one side of the carrier frequency (to increase the unwanted sideband suppression in USB or LSB modes.) The notch might be a bit off in alignment, or knob placement error, so in the "off" position it is actually notching where you want best sensitivity in the 0.5Kc selectivity mode. 73, Ed Knobloch, K4PF
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RE “So, why would it have an attenuated sig on 0.5 kc only?”? I don’t know the receiver, but it looks like the selectivity switch has 6 wafers which set the circuit values for each position. Any one of those wafers could be badly functioning at the .5 Kc position, throwing the circuit out of whack one way or the other. Of course it could be a bad component, but not so likely because in the .5 position there are mostly jumpers {that is how I read it}. ??You might poke with a plastic poker on the contacts, and look for any goobers or previous mucking around and try deoxit contact cleaner ..if you can get in there.? ??And good luck.. I’m envious! ? -- don??? va3drl
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Don, I think you are on the right track. I have trouble following
the schematic from BAMA. I suggest printing out the part with the
selectivity filter and tracing out the 0.5Khz section with a colored
pencil or hi=liter. Make it clear what part of the bandswitch is
involved. The filter is a type Hallicrafters likes using top linked LC
sections to vary the coupling. The selectivity varies non-symmetrically,
as shown in the selectivity graphs. If there is a problem with the
switch, or a bad component, it can be the same as the whole filter being
shorted. 60db is a very large loss, I suspect more than from just tuning
so the switch seems a good suspect. I agrew with poking at it with an
insulated tool, a chop stick works pretty well of one of those extra
large toothpicks made for holding sandwiches together.
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On 10/26/2024 2:35 PM, don Root wrote: RE “So, why would it have an attenuated sig on 0.5 kc only?”
I don’t know the receiver, but it looks like the selectivity switch has
6 wafers which set the circuit values for each position. Any one of
those wafers could be badly functioning at the .5 Kc position, throwing
the circuit out of whack one way or the other. Of course it could be a
bad component, but not so likely because in the .5 position there are
mostly jumpers {that is how I read it}. ??You might poke with a plastic
poker on the contacts, and look for any goobers or previous mucking
around and try deoxit contact cleaner ..if you can get in there.? ??And
good luck.. I’m envious!
--
don??? va3drl
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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Richard ,now I see there is quite a bit of overlap in the BAMA splitting of schematic, so my wafer count was probably wrong. I tried to patch the selectivity area together [see ATTACHED ]. ?I am now cross-eyed, so maybe somebody can check my edit. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard Knoppow
Sent: Saturday, October 26, 2024 6:26 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-115 Low sensitivity .5 kc Selectivity? Don, I think you are on the right track. I have trouble following
the schematic from BAMA. I suggest printing out the part with the
?………………………. ? -- don??? va3drl
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"Don Root" <drootofallevil@...> wrote
So why would it [notch filter] have an effect on 0.5Kc only? <snip>
Hi, Don
The other SX-115 IF selectivity positions are not symmetrical with respect
to the 0.5 Kc curve. Its like one side of all the other
selectivity position curves are anchored to one side of the 0.5 Kc curve.
There's an illustration of this in the SX-115 manual, figure 6, page 8.
The Drake 2B and R4B receivers have a similar set of IF response curves.
My suspicion is that if the notch filter is effectively notching
the 0.5Kc response, it would not be very noticeable on the other
bandwidth positions. The effective bandwidth would be a bit narrower
on them, but you would not see a major sensitivity loss.
73,
Ed Knobloch K4PF
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Ed and all, I’m a bit unsure about who said what to who, and maybe I added some confusion. So to go back, the original post said [in part] “So, why would it have an attenuated sig on 0.5 kc only?”? I assumed that “颈迟” as originally posted was the selectivity filter response or perhaps the receiver response. If indeed the selectivity filter itself has no defect, the notch may well be doing what you say, but I have not thought about this in many years, so I can’t say more about your theory. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of k2orsfan
Sent: Sunday, October 27, 2024 11:27 AM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-115 Low sensitivity .5 kc Selectivity? "Don Root" <drootofallevil@...> wrote
So why would it [notch filter] have an effect on 0.5Kc only? <snip>
Hi, Don
The other SX-115 IF selectivity positions are not symmetrical with respect
to the 0.5 Kc curve. Its like one side of all the other
selectivity position curves are anchored to one side of the 0.5 Kc curve.
There's an illustration of this in the SX-115 manual, figure 6, page 8.
The Drake 2B and R4B receivers have a similar set of IF response curves.
My suspicion is that if the notch filter is effectively notching
the 0.5Kc response, it would not be very noticeable on the other
bandwidth positions. The effective bandwidth would be a bit narrower
on them, but you would not see a major sensitivity loss.
73,
Ed Knobloch K4PF -- don??? va3drl
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Steve Marquie
don Root