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eHam Forums => Boat Anchors => Topic started by: N6AF on October 11, 2018, 02:41:05 PM



Title: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 02:41:05 PM
I picked up a swap meet Heathkit AR-3 receiver in very good physical shape.  It works fine in AM mode but when I try CW mode (whereby the reflex BFO oscillator is allowed to run), I get a huge AC hum out of the speaker.  I stuck a scope on the plate of the 12AV6 (pin 7) and it's clean DC in AM mode but has about an 80 Volt p-p 60 Hz AC signal superimposed on the DC when in the CW mode.

I tried the following with no improvement seen:

1) changed out each tube, especially the 12AV6
2) checked for wiring errors in the reflex BFO circuitry
3) checked the BFO tapped inductor and all associated caps and resistors for proper value
4) checked all tube voltages per the suggested troubleshooting section in the manual

I am really at a dead end with this little gremlin.  Fortunately my intent was to just use it with my Viking Ranger on 75 and 40 meter AM nets.  But I'd sure like to see that BFO circuit play right just for completeness.  I repaired my SB-220, HT-37, Viking Ranger and a homebrew tube AM transmitter so this seems extremely trivial but I've run out of ideas.  Anybody ever seen this issue in the good old Heathkit AR-3 receiver?
Thanks!  73  N6AF  Chuck


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 11, 2018, 03:14:13 PM
What does the power supply look like? Is it clean? Are you sure the capacitors are not breaking down when powered up?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 03:29:12 PM
The power supply is clean and confirmed not the issue. Thanks


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 11, 2018, 03:56:31 PM
Have you checked the other tubes? What about the 12BA6 any filament to cathode leakage?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: AC2EU on October 11, 2018, 04:01:07 PM
bypass and resonace caps OK?
paper probably leaky
micas can short


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 11, 2018, 04:38:24 PM
Heath used a lot of WW2 surplus parts in those early days so even mica caps can be leaky or change value.

I thought the AR-3 used a regenerative IF for CW such as in the S-38B and later?

Carl


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 04:45:48 PM
Tubes all confirmed good.
Regarding caps and other components, the crazy thing is that the 12AV6 tube works fine in the AM mode and it is the same tube in use when in CW mode so the tube and its bias is not the problem. If you Google "Heathkit AR-3 manual" you will see the source of my frustration. The
circuit description explains how the reflex BFO is enabled in the 12AV6. Keep in mind that it works great in AM mode. Thanks.

.
  


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 04:53:05 PM
It uses a reflex oscillator in the 12AV6 detector tube when in CW mode. The osc function is disabled in AM mode. It's a true BFO implementation-not regenerative.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 11, 2018, 05:00:18 PM
Thanks, I learned something new! Never bothered with the AR receivers so didnt realize they were ahead of Hallicrafters where only the original S-38 hada real BFO.

Carl


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 11, 2018, 05:10:18 PM
If you turn the RF gain control down do you still have the oscillation? If so why do you try replacing some of the capacitors. As mentioned above even disc ceramic and mica can fail.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 05:32:24 PM
RF gain setting doesn't help. Nearly every cap is in use when it's working in AM mode.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 11, 2018, 05:54:14 PM
OK on the cap replacement suggestion.  The only two caps that are brought into use when switching to CW mode are a 33 pF and a 150 pF in the 455 kHz BFO resonant circuit.  I temporarily replaced each one and it didn't help.  Very strange.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 11, 2018, 08:37:23 PM
You stated you have AC riding on the DC buss when in AM mode, so where is it coming from? Also in the AR-3 manual advises if you have noise and squealing to check the wiring contained in the spiral shielding.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 12, 2018, 06:19:38 AM
Strange because the 60 Hz AC superimposed on the plate of the 12AV6 is only present when the reflex oscillator function of that tube is enabled (during CW mode), yet that same tube is in use in AM mode at which time it works perfectly. Pretty sure it's related to the few passive components that come into play when in CW mode. The schematic shows the situation. The saving grace here is I picked up the AR-3 only for AM receiving anyway but for me I can't stand it when something doesn't fully work. And until I solve it, it's almost an obsession. I know there are far worse afflictions but the XYL sure starts to wonder after I've been hunched over my work bench for hours on end, days in a row.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 12, 2018, 06:27:41 AM
Out of curiosity have you done an alignment on the radio?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: AC2EU on October 12, 2018, 07:50:20 AM
something is wrong with this picture!
Have you verified that it's not oscillating with a scope?
Someone mentioned alignment. If you aligned the bfo to zero beat and left it there, you will effectively have no BFO.
How about the coupling? I once had a radio for repair that destroyed the BFO oscillator tube. Turned out that the previous owner decided  that the wire wrapped around the other should have a direct soldered connection. Direct plate to grid connection is nt good for the grid!
The moral to the story is "ASSUME NOTHING".
There must be a simple but not previously explored answer to this "mystery".


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N2EY on October 12, 2018, 08:56:22 AM
I would re-check the BFO coil, particularly the ground connection. Also all connections to the CW-Standby-PHONE switch

Here's why:

Since you have checked the B+ and it is clean, and it's clean in the AM mode, the only source of 60 Hz hum is the heater supply.

In AM mode, the cathode of the 12AV6 is grounded by the CW-Standby-PHONE switch - but on CW it is grounded through the BFO coil. If the coil is open, or high resistance, or the grounded end isn't really grounded, or anything else is not perfect, heater voltage can get into the circuit and raise heck.

I've never had an AR-3, but my first non-homebrew SW receiver was an AR-2. The AR-2 used a separate BFO tube, which IMHO is a better approach. I think it would not be a big project to convert the AR-3 second detector to the AR-2 circuit.

73 de Jim, N2EY


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 12, 2018, 11:45:52 AM
Quote
The moral to the story is "ASSUME NOTHING".

Aint that the truth. After going to work at National Radio in 63 as a Service Dept Tech, after leaving USN active duty as a ET2, I had that drummed into me by the oldtimers there. Hammy Hambone was alive and well even back then and even long before WW2 as I found out decades later when I got into boatanchors.

Carl


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N6AF on October 13, 2018, 07:04:47 AM
it's aligned on all bands.  Works fine in AM mode on all bands.  The issue is with the BFO circuit.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 13, 2018, 07:20:25 AM
Based on experience start replacing a few parts, even though they check good, you may be surprised results. As mention above It would benefit to redo all the ground connections, including the area where they connect to the chassis. If any of those steps do not work try isolating, half split rule, the BFO and audio section to see if the issue still exist. Best wishes and happy trouble shooting. Sometimes it is harder to find the issue in a simple circuit than it is in a complicated one.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W8RLC on October 13, 2018, 07:42:12 AM
Forgot to mention, did you check the wiring in the sprial springs as suggested in the manual?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: WB6BYU on October 13, 2018, 09:32:01 AM
I used an AR-3 as my Novice receiver.  It as always a bit quirky.  Seems to me
that in CW mode it wouldn't work well unless I set the audio gain to full volume
and used the RF gain to adjust the signal level.  That might have been a problem
with interaction between the BFO and the AGC.

I don't have it any more, but a friend may still have one around if we need to check
it out further.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W0GSQ on October 13, 2018, 12:19:37 PM
Quote from the manual.
"CW Operation:Turn the SELECTOR switch to CW, advance the volume control fully clock-wise and reduce the RF gain, removing AVC and allowing manual control of the sensitivity and therefore, the gain of the receiver.
Adjust the volume level using the RF gain control."

When I do that with mine the loud hum goes away as the volume control is rotated to full volume.

Steve, W0GSQ


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: WW7KE on October 13, 2018, 01:19:17 PM
I used an AR-3 as my Novice receiver.  It as always a bit quirky.  Seems to me that in CW mode it wouldn't work well unless I set the audio gain to full volume and used the RF gain to adjust the signal level.  That might have been a problem with interaction between the BFO and the AGC.

My Hammarlund HQ-145 worked the same way.  With no product detector, it's necessary to do what you had to do.  Receivers with product detectors don't require this, but this was common in low- and mid-priced units back in the day.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 13, 2018, 02:14:35 PM
That was common in most ALL radios into about the mid 50's and some high end radios never got a factory PD such as the HRO-60 except for a special 25 piece (and the LAST run) for Tropical Radio in 1968 which replaced the plug-in NBFM adapter.

Carl
Ham since 1955
National Radio 1963-69.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: AC2EU on October 14, 2018, 08:27:18 AM
I took a look at the schematic. I believe the oscillator type is Hartley.
I can see where there would be a lot of interaction between the BFO ,AGC and audio gain setting.
The OP did not mention if he had a scope or not.
If he does, it would be interesting to monitor the grid for oscillation.
If there is indeed no oscillation , lift the .02 coupling cap to the volume control.

The AR3 does not have a FP adjustable BFO. The OP says he aligned the set.
Did he do that by injection of an IF carrier or just tuning for max audio out?
Did he try adjusting the BFO for a tone while injecting the carrier?
Zero beat = no tone which will make it SEEM like there is no BFO.
A scope would easily verify whether the oscillator is working even if it was zero beat or way out of audio range.
Otherwise, try adjusting the BFO coil on a AM carrier and see if you can get a tone pitch.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: VE3EFJ on October 22, 2018, 01:42:21 PM
Had a lookie at the skemo.

Could it be that the cathode of the 12AV6 is floating in the CW position?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: W1BR on October 22, 2018, 03:32:34 PM
Heater to cathode leakage?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N2EY on October 23, 2018, 09:47:18 AM
I took a look at the schematic. I believe the oscillator type is Hartley.

It is definitely a Hartley oscillator, tapped coil and all.

I can see where there would be a lot of interaction between the BFO ,AGC and audio gain setting.

In the AR-3, for CW/SSB reception, the AGC does not work.

What must be done for any mode that needs the BFO is to turn the AF gain all the way up and control gain with the RF gain control. That's how Heathkit got away with the trick "reflex BFO" circuit, rather than having a separate BFO tube as in the AR-2.




Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 23, 2018, 10:51:28 AM
Quote
n the AR-3, for CW/SSB reception, the AGC does not work.

What must be done for any mode that needs the BFO is to turn the AF gain all the way up and control gain with the RF gain control. That's how Heathkit got away with the trick "reflex BFO" circuit, rather than having a separate BFO tube as in the AR-2.


Already well covered in Post 22 which quoted the manual.

Another thing to consider is that since this is a kit built radio it may have never worked properly and was stored early in its life which could explain the excellent cosmetics.
Also a (or more) ground connection may be loose as I have found while servicing other Heath products.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N2EY on October 23, 2018, 12:11:19 PM
In the AR-3, for CW/SSB reception, the AGC does not work.

What must be done for any mode that needs the BFO is to turn the AF gain all the way up and control gain with the RF gain control. That's how Heathkit got away with the trick "reflex BFO" circuit, rather than having a separate BFO tube as in the AR-2.


Already well covered in Post 22 which quoted the manual.

I replied because AC2EU's post was Post #25. Either he did not read or did not understand Post 22.

Why did you quote what I wrote yet not attribute it to me? Did you not want people to know who you were quoting?

Another thing to consider is that since this is a kit built radio it may have never worked properly and was stored early in its life which could explain the excellent cosmetics.
Also a (or more) ground connection may be loose as I have found while servicing other Heath products.

Any old radio, kit or manufactured, may have all sorts of errors in it, either from original construction or from "fixes". Rarely does one know the provenance of something so old.

Jim, N2EY


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 23, 2018, 12:38:08 PM
Quote
I replied because AC2EU's post was Post #25. Either he did not read or did not understand Post 22.

Why not just direct him to Post 22 instead of making it appear as your idea only?

Quote
Why did you quote what I wrote yet not attribute it to me? Did you not want people to know who you were quoting?

Why is that SO important to you or cant you remember back a few hours?


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N2EY on October 24, 2018, 02:00:16 PM
I replied because AC2EU's post was Post #25. Either he did not read or did not understand Post 22.

Why not just direct him to Post 22 instead of making it appear as your idea only?

It does not appear that it is my idea only.

However, it is clear that AC2EU either did not read or did not understand Post #22. So I wrote a clearer, more complete, easier-to-understand response.

Why does that bother you so much, Carl?

Why did you quote what I wrote yet not attribute it to me? Did you not want people to know who you were quoting?

Why is that SO important to you or cant you remember back a few hours?

It's not "SO important", Carl.

But it is interesting that you sometimes quote people without attribution. Doing so requires more keystrokes and cut/paste than simple quoting. For someone so parsimonious of effort as to not use apostrophes to go to all that trouble indicates that there's a specific reason.

Seems the answer is pretty simple: you quote like that because you don't want the person you are quoting to be notified that you replied.

Why?

Jim, N2EY


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: KM1H on October 24, 2018, 03:20:04 PM
Get a life Jimmy and take your PITA meds....what a dip.

Didnt you get the message from the QRZ owner when you got a good slap a few days ago?

Dont think it was missed by Eham owner and mods.


Title: RE: Heathkit AR-3 Receiver reflex BFO issue
Post by: N2EY on October 26, 2018, 05:24:57 AM
Get a life Jimmy and take your PITA meds....what a dip.

Didnt you get the message from the QRZ owner when you got a good slap a few days ago?

Dont think it was missed by Eham owner and mods.

Carl,

Who are you addressing?

If you mean me, I go by Jim. Not "Jimmy". Your use of diminutives as a way of putting others down is very immature.

You mention "a good slap". Do you mean this post:

https://forums.qrz.com/index.php?threads/jack-andersons-1970s-era-ham-vs-cb-editorial.630616/page-17#post-4836299

??

If so....note that it was addressed to YOU as well. If I was "slapped" - so were you.

What is it you REALLY want, Carl?

Your behavior is very uniform and very predictable. All anyone has to do to get you angry at them is to question or disagree with anything you write. Still worse is if they bring solid facts, references and sound reasoning to a discussion, and in so doing, prove you wrong. Worst of all is if they persist and are not intimidated by you.

It's not me, either - you behave that way towards ANYONE who does the above. Particularly those you consider "inferior" for whatever reason....not being licensed a long time, not having done something or other, whatever.

You accuse others of the very behaviors you demonstrate.

Consider that others don't have to agree with you in order for them to be deserving of respect. Consider that you don't have to put others down to build yourself up. Consider that others will respect you more, not less, if you behave like an adult.

Most of all, consider that there are some folks you just can't intimidate with your bluster and immature behavior - and that they see what's really going on.

Jim, N2EY