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Author Topic: Heathkit AR-3 Receiver reflex BFO issue  (Read 2239 times)
AC2EU
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« Reply #15 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".
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N2EY
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« Reply #16 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
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KM1H
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« Reply #17 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
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N6AF
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« Reply #18 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.
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W8RLC
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« Reply #19 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.
« Last Edit: October 13, 2018, 07:29:55 AM by W8RLC » Logged
W8RLC
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« Reply #20 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?
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WB6BYU
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« Reply #21 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.
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W0GSQ
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« Reply #22 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
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WW7KE
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« Reply #23 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.
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He speaks fluent PSK31, in FT8...  One QSO with him earns you 5BDXCC...  His Wouff Hong has two Wouffs... Hiram Percy Maxim called HIM "The Old Man..."  He is... The Most Interesting Ham In The World!
KM1H
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« Reply #24 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.
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AC2EU
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« Reply #25 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.
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VE3EFJ
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« Reply #26 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?
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W1BR
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« Reply #27 on: October 22, 2018, 03:32:34 PM »

Heater to cathode leakage?
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N2EY
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« Reply #28 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.


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KM1H
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« Reply #29 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.
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