Advise on HQ 110A problem

[N2IDU]

The reciever only works if I keep my hand on the antenna peaking control or very near it, otherwise it doesn't hear anything but the strongest of signals or it goes into a terrible audio/rf/ squealing or mototboating sound.  All the voltages were tested and found in spec. It has been retubed and the power supply caps are within spec. It did this before it was retubed as well. It does this on all bands.  As long as my hand is near or touching the antenna peaking knob it works great. It would appear nobody altered or even opened up this rx.  I am sure someone out there has expirenced this type of problem.

Thanks,

Peter N2IDU
Old Shincracker, VT.

[W3RSW]

Even though I have an HQ110 this problem may be common to many other receivers. It sounds like your coupling RF signal by hand capacity into the RF input coil but the ant. jack on rear has a broken lead somewhere.

Now looking at the HQ110 schematic, the first suspect if not an actual open lead is the common S6A switch wiper contact, common to all bands. This contact wiper feeds the ant. input to the primary of each band's RF coils.  The ant. peaking is across the secondary of the RF coils along with the RF tuning capacitor.  Your hand is acting as a small (5 to 10pf) antenna feed into the top of an L/C resonant circuit, very much the same as elementary regen. sets in the old days.

Your oscillation/motorboating, etc. may be related due to lack of signal 'loading' down the AVC line, etc. or feedback circuits, or loss of bypasses somewhere, lossy coupling caps in the AF amps, you name it, etc. May or may not be related.  

Open her up and feed your antenna signal directly to, say, the 160 RF coil primary to see if that works.  If so, inspect the wiring and contacts of S6A. Oh, and be sure to make sure you haven't strapped the wrong ant. terminal to ground on the rear panel.

[N2IDU]

Ok Rick,

Thanks for the tips. I'll attempt to do what you suggested. Yes, I did make certain that the antenna was connected correctly. Interestingly, if I disconect the antenna wire and put my finger on the antenna screw in the back and peak it with the other hand, it works just as  well as if it had the long wire on it? It would be kind of tough to operate on the air this way!!
Like you stated, I am sure others have had a similar or same type of issue as well.
Thanks,
Pete

[N2IDU]

Rick,
Well, not much luck on this end. I checked for any open leads on S6A and fed the antenna directly into the primary coil of 160. Checked & traced all the antenna coils both primary and secondaries for open or shorted condition as well. Nothing  obvious found. Could this be an agc problem? Where do I go from here?
Thanks,

Peter N2IDU

[W3SLK]

Peter said:

Well, not much luck on this end. I checked for any open leads on S6A and fed the antenna directly into the primary coil of 160. Checked & traced all the antenna coils both primary and secondaries for open or shorted condition as well. Nothing  obvious found. Could this be an agc problem? Where do I go from here?

Goesintas and goesoutas. Scope or signal tracer. Inject a signal at the antenna input and follow it back to where you lose it. Beware of capacitive coupling since that is what you see when you get near it.

[W3RSW]

Peter, Wow!
Can I hire you for a perfect antenna? 
Kidding!

Just in case, ...not just open lead on S6A but the contact itself.  Is there continuity across the band switch? Did the signal come up when you jumpered out the bandswitch?

Hmmm, if not, I'll continue to peruse the diagramme.
The only other thought I have at the moment, (and given the 'action' on all bands, etc. it's a long shot) is that all the contacts are working but the RF amp is so misstuned that your hand capacity acts to extend the value of the ant. trim cap. to such an extent that signals are now in tune.  Given the small values of the ant. trim cap and any effect of your body that's really a stretch.  But stranger things have happened.  That type of effect should be more pronounced at higher frequencies if at all, given constant cap. values vs. freq.

So yes, as Mikey says, start the trace.  And yes look at resistor and cap values on the AGC line, RF decoupling capacitors on the screen and plate of the RF then IF stages, etc., not just the voltages. 

[W3RSW]

Just for the heck of it, I fired up my HQ-110. The ant. trim seemed to have no effect on sig. strength and signals seemed to be somewhat weak even for day time conditions.  (No hand effect though, sorry.)

 But then I rotated the ant. trim. several times and , voila!, signals came up and peaked properly using it.  So the rotor wiper action of the ant. trim cap. is intermittant.

For casual use on 80/75 etc. I probably never noticed before due to abundance of strong signals on lower freqs.

Interesting.  So there's something else to look at, wiper contacts on ant. trim and RF / osc. tuning caps when restoring receivers.

[W3RSW]

Peter,
Find anything yet?

-Rick

[K9PNP]

Make sure the antenna tuning capacitor shaft is actually grounded.  Saw one that had not been used for some time that had developed some kind of film on the bearing such that the shaft and therefore the rotor plates were just floating electrically.  Looked like somebody at one time had tried to lubricate the shaft with some kind of oil which apparently sat and formed a dielectric film after a while.

[N2IDU]

Hi Rick,

I had many interuptions lately, so I will report back tomorrow and do some more test .
Thanks,

Peter

[N2IDU]

I have performed the following procedures as suggested by the various replies to my 110A problem.
Here are my findings and observations.

(1) There is continuity across the S6A band switch. No difference in signal when jumpered.

(2) The antenna peaking knob  (air variable) is not floating and is grounded correctly.

(3) Using a HP606A I injected a 3.885MHZ signal at the antenna terminal screw on the back. I am running this receiver with a long wire and not in a balanced position. The second terminal antenna screw uses a shorting jack to chassis ground.

The signal appeared at the same amplitude on the primary of the 75/80 meter antenna transformer as it did on the antenna input screw. I obtained the same results on 160 meters and 40 meters as well. This would make switch S6A functional. However, when I go to the secondaries of the 75 meter, 160 meter and 40 meter transformers, the amplitude is about 1/2 the value. I would have guessed that the secondaries would have stepped up the signal not halved it!!! Would this be correct? This reduced amplitude value also shows up on switch S6B where it connects to the antenna trimmer. I noticed that on the secondaries of 20, 15 & 10 meter bands there is a .01 cap across each secondary to ground?  These are not shown on the HQ 110A schematic. They are factory installed and almost impossible to access or remove due to the band switch and support. They are the same sprague caps used throughout the rx.

(4) Placing the long wire directly on the antenna primaries has no effect on rx. However, if I  place the antenna on the trimmer or on S6B where the trimmer coax attaches to the switch, the signals come in strong. If I peak the trimmer it will go into oscillation. There is some but very little handeard the the same hi capacitance at this point.

(5) So I put the rig on 3880, attached the antenna to the trimmer, tuned it so it would go into oscillation, walked across the room and tuned in another receiver and heard the same exact noise in the receiver.  The damn thing was was regenerating. Where to go now??

Thanks Again,

Peter





 

[N0WVA]

Where to go now??

Perhaps an exorcist??? Out, Demons!!! Keep an eye on the thing, it might start foaming at the filter cap!

[N0WVA]

I took my 110 out of the case and am looking at the circuitry. I dont have a manual and I cant seem to get the BAMA downloads to work with adobe reader. I would definately check all the bypass caps. Sure enough the front end is going regenerative. Also if the stage has AGC applied to it, Id check for an aging resistor in that line. Check all the way back to the AGC rectifier. If its going regenerative, then the Ant tune cap will be hyper-sensitive up until oscillation, then it will be weak heterodynes.

[N2IDU]

Directed to N0WVA:
Since you took your 110 out of the cabinet, could you let me know if you find any .01 caps across the 2ndry's of the antenna transformer coils for 20, 15 and 10 meters. As I stated these are not shown on my schematic. You and others suggested to check all the bypass caps!  Did you mean the screen bypass caps?  My problem would appear to be located somewhere between the antenna terminals and the antenna trimmer on the band switch 6SA & 6SB. Also, would anyone know if the antenna transformer coils are step up or step down? If all else fails, I will call an exorcist. The agc works fine.

Thanks for all of your suggestions. I will check all the bypass caps today, if possible and report back.

Peter N2IDU Old Shincracker, Vt.

[K9PNP]

This is wierd.  What you are describing with the 0.01 mf bypass caps is the HQ-100 type front end.  See attached.

[N2IDU]

Correction: The .01 caps that I said were across the 15 and 10 meter 2ndry's( tow of which)  are really the bypass caps for V1. They were bent over and appeared to be attached to the antenna transformers. During daylight I was able to determine this. The caps tested good but there is still a  .01 attached across the 2ndry of the 20 meter antenna transformer. Sorry for the error. Also, The schematic attached to K9PNP's reply is not the same as my 110A I believe his is for the HQ110 as it lacks the circuit for the 50Mc band position but I am not sure.

I have started to test all the bypass caps  and so far  v1-v4 caps are ok. I didn't know when I acquired this rx that it could actually transmit too!!

Thanks Again,

Peter N2IDU

[K9PNP]

Also, The schematic attached to K9PNP's reply is not the same as my 110A I believe his is for the HQ110 as it lacks the circuit for the 50Mc band position but I am not sure.

Just for clarification, the schematic I posted was for the HQ-100 [partial] since it sounded to me that what Peter was describing was a HQ-100 RF coil set with the bypass caps, even though it was in a HQ-110A.  Sorry if I confused anyone.

[N0WVA]

N2IDU: I think it has those capacitors you are mentioning, I am posting pictures of that area. Im not sure about the turns ratio. Wish I could download the manual. Yes, there are some discs on the socket of the RF tube. I doubt they are bad, but its worth a shot checking.Hard to tell what the circuit is exactly without having a schematic.  The squealing points to a problem other than the input coils/trimmer parts unless they are using some sort of unorthodox coupling scheme. Is the AGC applied to the grid or screen? 

[N0WVA]

I checked with my VOM and there is a negative voltage applied to the grid for AGC. There is a 470K coming off the grid then to a .01 cap then to a 100k, a 1meg and on to the detector. The .01 disc capacitor that is between secondary and ground is simply a RF bypass for the grid AGC bias. Jumper this cap with another and see what happens. Let me do some more snooping and maybe Ill have another suggestion or two.

Edit: Looks like manual gain is controlled via the cathode. Can you influence the squealing with the gain control?

[K3ZS]

This is probably unrelated to the problem, but I found the original manual I have for my HQ-110A was wrong.   The pictorial diagram showing where the trimmers and coils are was backwards.   I got this receiver last year and it was totally unaligned.  The poor Cber who owned it probably followed the manual.    I found the problem by tweeking the oscillator coils  and finding which ones were actually correct.   The associated mixer and RF adjustments were backwards also.  After alignment the receiver works just like new.

[W3RSW]

(3) Using a HP606A I injected a 3.885MHZ signal at the antenna terminal screw on the back.will go into oscillation. ....."etc.

Ok, yes the secondaries are much higher impedance and are L/C tuned circuits of Hi Q and are easily loaded down by almost any finite resistance probe so that voltage might appear as 'half.'  Now if you used a high impedance scope probe, even that would de-tune the RF resonant circuit. Are you using a scope probe or just noticing that the signal drops by ear?

But all that aside,  Since you coupled the ant. directly to the output side of S6(B), and all bands came roaring up, I suspect the output wiper of S6B.  Try jumpering that.
Oscillation now may because you're loading up the RF tube grid with the direct antenna load of improper impedance, feedback from the RF tube plate to the length of improperly shielded or placed ant. wire now inside the chassis, etc. 

Of course , once oscillating, you'll hear it in any nearby receiver.
Also check the RF and other IF amp tube sockets for proper ground to the chassis.  They're rivited; you may have to solder them directly.

[N2IDU]

Thanks to all for your input on attempting to solve the issues with the HQ 110A. It is much appreciated. I believe I am getting close to the answer. Ok, here are my latest test: There was a .01 cap across the 2ndry of the 20 meter antenna transformer. It was just touching it and so I moved it.  No difference in performance. This is the same cap you can clearly see in N0WVA picture above. It is a bypass cap related to another tube. Yes, I did jumper the 6SA & 6SB switches with no results. I also used a milliohm meter to confirm that both switches have continuity. Yes, the grids of V1 goes negative on strong signals. Yes the avc is fine too. Yes, to W3RSW, I used a scope probe on the  antenna transformers. Next, I took all the resistance measurements according to the manual and all are withing spec., except for the following on v3.
Pin #1 says it should be 22K mine measured 45K and pin #2 says 1.6 ohms, and mine shows 167 ohms. I believe the manual has a typo as you can see by the schematic it would read what mine says. However, I may be wrong. As stated prior, I also did the voltage test on all the tubes and they were in spec. Yet again, I re- retubed the front end. No improvement. Next, I tested the bypass caps in the front end V1 to V7 I believe. All  appeared not to be shorted. I did not test for open condition as I need to hookup my cap meter. I also jumpered a .01 to all the bypass caps in the front end with no improvement. Bottom line is that this rx works fine from the input or output of band switch 6S(B) it is as if the primaries of the antenna transformers don't exist. (continued on next post)

[N2IDU]

continued from previous post. A short jumper on 6SB on the correct band position or its output makes this rx come alive. Attaching the long wire on the rear antenna screw while the jumper is in place has no effect whatsoever. Also, attaching the long wire direct to the grid of V1 works great too.  I am beginning to believe the primaries may have been nuked by a near lightning strike or something.  Each one shows continuity but rather low. I can report back their readings as I didn't write them down. I believe that none of them showed anything more the 8/10ths of an ohm.
Peter N2IDU

[W3RSW]

wow!
Curiouser & curiouser.
It's almost as though someone selectively zapped each primary, one at a time, on purpose.
Almost has to be that -
... or are all the primariies tied to a common ground which is open?  Possibly all the primaries were always open, even when new? 

I'd check that and if all else fails run a 3 to 30 pf trimmer from the ant. input directly to the top of the ant. trim cap. Set it for max sig. at, say, 10 meters, (the lower freq's usually come in stronger.)

Oh, and have you gotten the oscillation to stop?

[N2IDU]

Answer to W3RSW Rick: Primaries are tied to common ground and they are not open. Ran a 12pf from antenna input to trim cap no improvements. Reheated solder connections  on S6A and S6B to remove all doubt about cold solders. Checked socket rivets for  tightness and ran seperate grounds. No improvement. Removed can from 160 meter antenna transformer and inspected and ran ohm test. Nothing found wrong. So, I think I am running out of stuff to check. This problem would seem simple to fix but it is not.  I am going to give it a rest for a few weeks and try again.

Thanks to all.
Peter N2IDU