Noise s9 in HQ-170 receiver with antenna dummy load

[ns7h]

I just got an HQ 170 on ebay n very good physical condition which worked first time after a  long Fed Ex trip across country.  Tested the tubes, ordered some new ones, the performance was
 with excellent sensitivity and quiet across bands.  Signal indications and noise seemed near that I saw on my icom 7600.   However,  it has developed an s-9 noise floor that is there regardless of antenna, dummy load, or antenna flat out shorted to ground!  The RF alignment seems to be good and the IF alignment passed the eyeball and signal test advocated by several hams using the calibrator signal and signal deviation through manipulating the sideband and filter functions.  My other receivers go to very quiet with no signal present on the Cantenna dummy load.  As I type, the HQ 170 S meter is reading 8-9 and the dummy load in circuit.   With the antenna terminals shorted, it drops to S3.  The antenna trimmer works to peak the noise signal as before.  With the RF gain totally CCW (0), it drops to 0.  Audio gain all the way up does not indicate hum or any anomaly.  Under chassis inspection revealed nothing out of the ordinary, but I have not checked component values to see if any have changed.

I have checked the tubes and replaced the V1 6ZB6 RF amplifier as a test and no change.  Any folks out there have some troubleshooting hints? It seems the noise (white noise, not periodic or AC rectifier hum) is a signal when going into the antenna and other RF sections.  You can peak the noise reading with the antenna trimmer just like it was an AM or CW signal.   While I have some electronics background in these circuits, troubleshooting something that was working and now isn't is a pain. I would like to get up to speed (by standing on the shoulders of you giants) so I can operate on the air rather than losing the rest of my hair "operating" on a stubborn problem that has a likely solution staring me in the face.

Just did some more checking - seems like the noise is S1 on 160 M, S6 on 80 M, S2 on 40 M, 1/2 S unit on 20M, 1 S unit on 15, and 0 on 10M.  This is with the antenna terminals and ground open and not shorted and with antenna trimmer peaking signal.


Lots of thinking out loud - the last thought is the depressing one if I have to locate and replace transformers....

Thanks for any help - NS7H Bob

[KA2DZT]

Since the noise is greatest on 80M, try pulling the tubes one at a time starting with the 1st. RF with 80M.  Should be able to tell what stage is causing the noise.  Problem could be an open ground somewhere in the input coils or maybe switch contacts in the input circuits.

Fred

[WA4WAX]

Bob:

Make sure all of the IF can shields are properly bonded to chassis.  Carefully look for cold solder joints, etc.

Here is an idea: Get some chiller spray.  I think there was something on the market called cold shot, or something like that.  Go around chilling suspected resistors and caps.  When you chill the offender, noise will likely go way down.

You could also pull the RF tube, and inject IF into the 1st, second, etc.  That might locate it for you.

Is it there on all modes?

Another thought:

My HQ-180AX was getting HORRIBLE noise on all bands at times.  I could not figure out why.

Well, the front porch light is one of those motion sensor jobs.  One day, the noise was there.  I noticed that the light was on.  I turned the light off...............GONE!

Put it on an isolation transformer.  Have a friend switch off breakers in your place one by one.  You never know!

Matt

[WA4WAX]

K7PP has many videos on the 170 and the 180 up on YouTube.

He would be my go to guy if I could not resolve the issue.

Matt

[WD4DMZ]

My HQ-180AX was getting HORRIBLE noise on all bands at times.  I could not figure out why.

Well, the front porch light is one of those motion sensor jobs.  One day, the noise was there.  I noticed that the light was on.  I turned the light off...............GONE!

Similar situation with an HQ180. It was not a motion sensor but an electric eye sensor on a garage door lamp that made the noise, mostly on 80 meters. Took it away and all was well. Some of the LED bulbs have switching power supplies in the base and will make rf noise as well.

Rich

[ns7h]

Thanks all for the info, guidance, and support.  Here's what I know now - 1.  background noise (broadband, white noise - bad band condx) was high with dummy load or antenna terminals shorted 2) band conditions have been bad at s 9 on 40 meters in my Idaho residence - which is far from most adjacent human noise sources 3) Shorting wires  were 6 inches in length to antenna terminals with alligator clips " is this an antenna?", 4) noise background went to below 1 s unit on all bands when I removed shorting wires on antenna terminals ( all terminals were an open circuit) and installed receiver into its metal cabinet with good grounding.  The resulting background level was less than one S unit with open antenna connections - With any connection at all (dummy load, short wire, etc) on the antenna terminals, I got a good background noise.  With the antenna (OCF dipole) on the Icom 7600, the background is about   S 5-7.  This is consistent with background noise in the HQ-170 with the same antenna configuration. 

The signal level for received stations on the HQ 170 compares favorably with that heard on the Icom 7600.  The difference being that the noise level drops to near zero on the Icom 7600 when switched to the dummy load.  The signal drops on the HQ 170 when switching to the dummy load, but a significant background signal persists - a drop of 2-3 s units from an S 5-9 with the antenna.

I have concluded that the noise is not being internally generated by the HQ 170 since a nominal zero signal level (with audio max and RF max and with little discernible signal heard) exists with an open antenna  input.  With the OCF dipole antenna as input, signal levels and noise background to the HQ 170 are comparable to that perceived listening to the same configuration and stations with the IC 7600.  This is consistent across the 80-10 meter bands.

I have not got my test configuration set up to test sensitivity of the receiver yet, but it appears the broad spectrum noise is the current band condition and the receiver is very sensitive to all signals including the noise with minimum receiver antenna needed.  Signals above noise levels= is also near that perceived with the IC 7600.

Thus, I think I had an initial experience with the radio in the time frame where band conditions had a low noise - good propagation period then changed dramatically to the current high band noise conditions. My current test configuration (open antenna terminals, receiver in enclosure with ground) repeatably demonstrates that the receiver has very low to no internally induced  background noise. Any attempt to physically ground the antenna terminals together provides enough antenna impedance to provide a broadband noise path.

Posts and videos on the HQ 170 indicate that it does have a high sensitivity with a general guidance to use the RF gain control as the volume gain adjust.  While I had a receiver like this as a new general in 1963, it has been a long time to remember its operating uniqueness's.  I am working toward doing a sensitivity test (build attenuator for test configuration used with signal generator/scope, etc) and see what gives.  U tube calibration testing show a much higher sensitivity figure for this receiver than is quoted in the manual.

I think the receiver is working to spec and I just needed to work it out a bit with you all.  I will respond with any results of the sensitivity tests.  The surprise to me is that a few inches of wire (alligator clip connecting wires) and/or a coaxial connection to a 50 ohm dummy load provided enough of an antenna to bring the noise level up as much as it does (almost as much as the antenna connected)l.  However, actual signals always stayed above the noise as also was observed with the IC 7600 with the same configuration.

I appreciate this forum more than you know. 

Bob, NS7H

[KA2DZT]

Bob,

Good clear report.  Yes, a short piece of wire shorting the antenna terminals could be enough to pick up noise.  Short the terminals with a 1" piece of wire.  The HQ-170 is a very sensitive receiver with those two RF stages.  I've had a lot of HQs over the past 56 years, including a 170.  I'm down to just a HQ-110.

One of the big problems with The HQ receivers is the IF cans going bad.  Years back you could order new ones, not so anymore.  Now you have to operate on the bad IF can and try to fix it.

Fred

[WD4DMZ]

I had an NC300 and still have an NC303 that both have a very high noise floor. Using the RF gain control was required to quiet them down. Just the nature of the receivers.

Rich

[WZ1M]

I have a bunch of IF cans for the 170/180. Email me for the list.
Regards,
TRS
Gary

[WA2SQQ]

I also have a nearly complete HQ-180 chassis for parts. If anyone needs anything specific, let me know. Clock, case, front panel and notch control are gone.