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1-10 of 14 messages
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HW-101 S Meter Question
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by KI6YFQ on July 1, 2009
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Hi,
I just inherited an HW-101 and I have a question regarding the S meter operation.
When in receive mode and the meter switch is set to ALC the S meter doesn't seem to register the signal strengthen unless a REALLY STRONG signal hits the antenna input like about 30mv using a generator (the S Meter reads 1 at 30mv milli volts, NOT micro volts) OR you tune into a REALLY STRONG birdie then the S Meter will go as high as S5 or S6.
I thought maybe the RF amp was weak being it takes about 30mv to open up the receiver BUT once you get the receiver to open up you can turn the generator down to about 3mv and you can still hear the signal then below 3mv your lose the signal and have to go back to 30mv. THAT makes me STILL think the RF amp is weak BUT I can hear other hams with just a 30 foot random wire antenna connected so the receiver seems to working. Just how good I am NOT sure. NO S METER READING EVEN WHEN I HEAR OTHER HAMS.
I suspected my RF Gen was just low BUT my RF voltmeter, scope both and RF counter all say the RF Gen is putting out a solid, clean signal at the correct level at the correct freq.
ALSO at NO TIME does the s meter move unless a 30mv signal or greater is present then you might get a reading of S1 to S3 depending on how strong of a signal you hit it with.
AND if I turn the RF Gain down (starting at full clockwise) the S Meter goes UP with or without a signal applied. Have no idea if that is is normal or not being I never used an HW-101 before. I can't imagine it being normal, or am I chasing my tail?
THOSE are the first set of problems I'd like to fix. The other may or may not be related. But I think I have a bad filter. Something is intermittently changing the sound of speech for normal to tinny and back just by rapping lightly in the area of the filters. IF I want to bypass these filters temporarily as a trouble shooting method would I just use a .01pf cap across it or something else.
THANKS in advance for any thoughts or ideas!!!
Russ
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RE: HW-101 S Meter Question
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by K4TLJ on July 1, 2009
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First, it is normal for the meter to read higher as the RF gain is decreased. Working as designed.
Likely one or both 6AU6 IF tubes are weak or have grid emission causing the S meter to not work correctly. Align the IF transformers if the IF tubes are replaced. There is the possibility also of having a cold solder joint as you say the tapping changes the sound.
The carrier oscillator 12AU7 load resistors are known to increase in value causing poor performance on both send and receive. These are 33K half watt resistors and should be replaced with 33K one or two watt resistors.
Proper alignment may be needed.
Many other possibilities but this should get you started.
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RE: HW-101 S Meter Question
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by KI6YFQ on July 1, 2009
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Thanks for the info. I was afraid I was chasing my tail on the S Meter going
up as the gain is turned down. Just seems strange through! WHY would they do
that? Just a design flaw???
I have been reflowing and touching up every solder joint I can find. Did
find the "neutralizing wire" broken off from the tuning capacitor C421B that
goes through hole "W".
I DID realign the receiver each time I moved tubes around too. The alignment
didn't change very much though. I seem to find good, clean, solid peaks each
time. Did find a cracked slug but I had a spare board with a good coil and
slug I used.
I found a schematic that has a signal injection chart on it and I am no
tracing the signal back through the receiver in the order the chart shows.
Back as far as inject point 7 (3.9mhz at 30mv) everything seems to work as
it should including the S Meter (S meter seems to work TOO good in fact
almost pegs out). When I get to inject point 8 (3.9mhz at 30mv) the signal
seems to be shapely attenuated and the S meter barely moves (yes I peaked
the preselecter, missed that the first time though, didn't make much
difference). That is where I left off for the night.
Tomorrow is another day.
I will check the items you suggested! I DID run ALL the tubes through my K&K
700 tube tester and they "appear" to be fine. I even tried swapping the
various 6AU6 tubes around to see if the S Meter problem changed or the
problem moved. It didn't. I have some brand new 6AU6 tubes I'll try in the
morning too.
THANKS.
Russ
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RE: HW-101 S Meter Question
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by KA5N on July 2, 2009
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You really need to do some studying on how receivers work.
The S-meter does not read the signal strength directly. When a signal is received a voltage is developed (AGC: automatic gain control. Used to be called AVC: automatic volume control. AGC and AVC are the same thing). This voltage controls the gain of the RF amplifiers and IF amplifiers to maintain a more or less constant audio level. The manual RF gain control allows you to "mess" with the AGC. The S-meter reading should increase as the manual gain is decreased.
In all probability the strange meter reading (too low with readable signals) is due to aging resistors in the AGC circuit. The type of resistors used in older gear tend to increase in resistance as they age and heat up and cool. While tubes and alignment are important, out of tolerance components are a major source of problems in older gear. So troubleshooting is in order. A first step would be to measure the resistance of all resistors in the AGC and IF circuits with particular attention to high meg values.
Good luck
Allen
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RE: HW-101 S Meter Question
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by G3RZP on July 2, 2009
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The S meter circuitry is actuated by the AGC line, and the RF gain control applies bias to the gain control line in the same way as the AGC. It's almost usual these days (well, after about 1970)for the S meter to go up as the RF gain is backed off. The one rig I know that didn't used an RF attenuator as the gain control, not, I may say, totally successfully.
Tube rigs that used a separate tube as a DC amplifier for the S meter, and di RF/IF gain control by varying the reistance in the cathode ciruit didn't exhibit this effect, but it needed at least one extra triode, and a wirewound pot in the cathodes for gain control. Generally, it was a bit harder to get a decent signal to noise improvement ratio with varying gain control using that method.
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RE: HW-101 S Meter Question
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by W6OU on July 2, 2009
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On a HW-101 you should be able to hear a 1 microvolt signal easily and if you strain your ears you should be able to hear a 0.1 microvolt signal. There are so many things that can go wrong to reduce sensitivity. Do you have an oscilloscope with a 10X probe? That plus a good signal generator could help troubleshoot receiving problems.
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RE: HW-101 S Meter Question
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by KG6YV on July 9, 2009
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I would agree with previous comments regarding the need to verify resistance values. I check any resistor over 100K on older rigs. Anything 1 meg or over I simply replace. I have seen 1meg resistors that have aged to over 3 megs....
Actually if you have a voltmeter and the Heathkit voltage charts from the HW101 manual it is fairly quick to check the voltages on the receive tubes at each pin. Anything more than 10-15% different from the chart indicates possibility a resistor has gone high.
Gud luck, you are learning,
Greg
KG6YV
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RE: HW-101 S Meter Question
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by KZ1X on July 10, 2009
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I am a 30-year-plus HW101 owner and fan. You may find that your restoration efforts would be a lot more definitive if you had a calibrated RF signal source to see if the thing is working well or not. Fortunately, Elecraft sells their XG2 kit that does just that. No need for a big-$$ signal generator.
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RE: HW-101 S Meter Question
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by KI6YFQ on July 10, 2009
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THANKS EVERYONE,
Problem turned out to multiple problems;
1) Initial builder had problems with mini shielded cables. Shortened the shields and re-solder. re-flowed every solder joint I could find on the boards, controls and other connections. This took care of MANY intermittent problems.
2) Had to literally rebuild the VFO section including re-soldering the coil connections inside the cans, including HOT GLUING components down to keep them from wiggling around to get the VFO to quit being phono! Now it is rock solid.
Using a signal generator, RF probe and scope and the levels found on a chart from the schematic I managed to work from the audio section back to the antenna one stage at a time, JUST LIKE THE CHART SAYS TO DO and found;
3) Found several broken slugs in the oscillator coils, grid coils and plate coils and because the slugs were jammed the coils had broken loose from their mounts so I had to reattach the coil forms to their mounts (HOT GLUE) and repair the coil connections which were tore loose.
This got me a "decent" signal from the ant to the speaker BUT still had poor S Meter action and it took to much signal, 30mv not 30uV, to open hear a signal.
4) More signal tracing and I found L801's coil tore loose from the solder connections because the coild fomr had broken loose from its mount (more hot glue).
5) STILL poor receive level and poor S Meter Action. So I started replacing tubes ONE AT A TIME and when I replaced BOTH 6HS6 tubes (which checked 85% gm on a tube tester) with JAN 6AU6 (which also checked 85% gm) as called for in a Heathkit SB. Suddenly the signal got better, still poor but better, and still poor S METER action.
When I replaced the 6BN6 tube (2 sections checked 100% gm and the third section showed 75% gm, when HOT no short but when COLD shorted!) the signal level jumped WAY up and the S Meter started working GREAT! Now it only takes .1uV to get a CLEAR signal from the antenna to the speaker and less then .5uv for 20 db quieting and less then 30uV for S9!
With NO antenna (just a random 40 foot wire) I listened to almost everyone on the SB Net role call last night! Only a few were too far north to hear. those beyond Fresno as far as I could tell although i heard Frisco fine.
NEXT, transmitter overhaul then build a stealth/attic antenna then FINALLY make my FIRST ever transmission as a HAM!
THANKS again everyone!
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