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Heathkit apache freq. drift




 
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Author Topic: Heathkit apache freq. drift  (Read 5854 times)
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w30kc
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« on: March 16, 2011, 07:40:15 AM »

Has anyone ever heard that the apache has a big problem with freq drift. I know the higher you go in freq the worse it would get, but I read the reviews and never seen any mention of this. I am picking up an apache this weekend and am fearful that I may have made a bad decision by purchasing this rig. Does anybody know if this rig is any worse that the other old boat anchor xmtrs.

Thanks
Steve
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« Reply #1 on: March 16, 2011, 09:13:40 AM »

Steve,
I haven't found it to drift any more than any of the other BA's. I used to let mine warm up about 20 minutes.
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Mike(y)/W3SLK
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« Reply #2 on: March 16, 2011, 09:33:05 AM »

With a little warm up the drift is not too bad and it is on par with most of the other gear of that era.  I have used my Apache for vintage SSB with the SB-10 adapter and even that is very practical.  But don't try this with modern appliance operators.  For AM use in a round table you can either choose another station that is fairly drift free to use as your reference spotting standard or use one of the small modern SW portables to check/adjust your frequency between transmissions.  I now use 3885 crystals in the rigs I use for net control operation but prior to the crystals I kept a Grundig YB-400 receiver on the operating desk and used it to keep the transmitter zero beat on net frequency.

Carefully read the audio setup instructions in the Apache manual.  The control accessible through the key jack sets the modulation level while the front panel gain control acts as a clipping level control.   If you don't have the modulation level control set properly, you will end up with the classic "scratchy Apache" sound from too much clipping.  I think that Heathkit and Johnson had a competition to see who could design an audio control layout most likely to result in operator misuse.  Heathkit hid an important control behind the key jack and glosses over it in the manual while Johnson put both controls on the front panel but has a design where minimum clipping occurs at full clockwise rotation of the control.  Operators who didn't read the manual carefully set the clipping control at what they perceive as minimum (full CCW) which provides around 40 db of clipping and sounds truly horrible.  Both the Apache and Johnson (Valiant and 500) can be adjusted for zero clipping without the need to bypass the clipper circuit.

Don't worry about a little drift, just adjust as needed.  Most of the vintage receivers have a wide passband so a little drift won't bother the other folks.  The bigger problem I have run into is with the modern rigs that only transmit one sideband on AM.  Most of my favorite vintage receivers are selectable sideband on AM so a few times in net operation I will miss one of those stations until someone alerts me to switch sidebands.
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Rodger WQ9E
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« Reply #3 on: March 16, 2011, 09:44:56 AM »

How much drift are you seeing?  Compared to transistor rigs the Apache will drift a lot.  To complicate things if the builder did not assemble to VFO correctly it will compound the problem.  So how much are you seeing on 80 meters and on 40?
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w3jn
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« Reply #4 on: March 16, 2011, 11:51:41 AM »

A good Apache is never a bad decision  Grin

Of course it's gonna drift.  ALL tube stuff drifts - and so does any solid state free-running oscillator.  Turn it on a half hour before you start yakking and you'll hardly notice it.
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Todd, KA1KAQ
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« Reply #5 on: March 16, 2011, 12:30:51 PM »

The Apache is rock-stable compared to the Mohawk.  Wink
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known as The Voice of Vermont in a previous life
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« Reply #6 on: March 16, 2011, 12:53:43 PM »

The Apache is a fine,  good looking rig.  It has good bones,  and you should be very happy with it.  The only thing that I wish it had is 160 Meters.

Have Fun,   Vic
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w30kc
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« Reply #7 on: March 16, 2011, 02:20:50 PM »

Thanks for you your help guys, this is a great forum and I really appreciate your input. I am new to the vintage stuff and am very excited about setting up my station so I really appreciate the help. I am sure you will be hearing from me alot in the future.

Thanks
Steve
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Pete, WA2CWA
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« Reply #8 on: March 16, 2011, 02:33:24 PM »

I've had my Apache in operation since 60 (when I built it). Drift was never a big problem. I did replace the original AC fan in the final cage (set to blow air in) with a DC fan to exhaust heat generated by the finals. Also mounted a second DC fan over the modulator area to exhaust all the heat generated there. The 5R4 HV tubes and the 5V4 LV tube were replaced with homebrew solid-state rectifiers back in the 70's.
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« Reply #9 on: March 16, 2011, 04:55:58 PM »

Todd said:
Quote
The Apache is rock-stable compared to the Mohawk.

You got that right Todd! Damn!
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Mike(y)/W3SLK
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« Reply #10 on: March 16, 2011, 06:16:46 PM »

Heh, and figure this one out: I sold my Apache to a fellow north of here in February because it didn't match up well with the newer Mohawk with the chrome knobs. Translation: I got rid of the one that worked pretty well and kept the one that wanders all over the dial!  Roll Eyes

I'll make good eventually, I promise.
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Don
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« Reply #11 on: March 16, 2011, 09:20:42 PM »

You should have checked both for operation, then put the pretty knobs on the one that worked best and sold the other one.
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Don, K4KYV                                       AMI#5
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« Reply #12 on: March 16, 2011, 09:43:15 PM »

The Mohawk is an interesting beast.  Some of them seem to drift horribly while others are fine.  I am lucky enough to own a pair that are not bad at all but I have a friend who owned one that was a drifting disaster.

The Mohawk front end was a pre-assembled unit that was outsourced by Heathkit.  I have a feeling there was either a lot of quality variance or perhaps a design change sometime during production that results in very different drift performance for different units.  I ran some simple tests on mine after the ER articles came out (I just used an external synthesized receiver tuned to zero beat the HFO and tracked the change by retuning it, not scientific but I didn't feel like hooking up a frequency counter).  One was stable after about 10 minutes on 160-40 (the only bands I was concerned with) and the other was good after 20 minutes.  Warmup drift worse case was about 1.5 Khz (on 15 meters for the slower stabilizing receiver) and I didn't bother trying to temperature compensate them.  Note that both receivers are in a pretty temperature and humidity stabilized basement although each is paired with a transmitter and amp (Apache with a  HA-10 and a Marauder with a KL-1 Chippewa respectively) so there is a significant heat source nearby.

The biggest thing to watch with the Mohawk is to keep the IF gain well retarded.  Heathkit should have put the IF gain adjustment inside the case as an alignment only adjustment like the other communications receivers manufacturers.
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Rodger WQ9E
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« Reply #13 on: March 17, 2011, 08:57:59 AM »

The biggest thing to watch with the Mohawk is to keep the IF gain well retarded.  Heathkit should have put the IF gain adjustment inside the case as an alignment only adjustment like the other communications receivers manufacturers.

For some inexplicable reason, Heathkit only applied AVC to the RF amplifier and one IF amplifier. Adding it to the other two IF amplifiers will make a quantum improvement. Before doing this, I found the front panel manual control necessary. Without it, depending on the setting, the IF would either overload on the lower frequency bands, or there would be insufficient gain on the higher frequency bands.

Darrell, WA5VGO
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« Reply #14 on: March 17, 2011, 04:42:10 PM »

My Mohawk works great and doesn't exhibit the issues complained about by so many.  The front panel IF gain control is hokey and takes some getting used to, but other than that, I like the radio and have used it exetensively on SSB.  On the other hand, my HQ-170A must have been one of the first spread-spectrum radios.  Tearing into that this summer...
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Geoff Fors
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« Reply #15 on: March 17, 2011, 05:35:57 PM »

Before you tear too far into your HQ-170 make sure you use some cleaner on the 6C4 HFO socket and try a couple of different 6C4 tubes.  Problems with this tube are common in the Hammarlund receivers.

My HQ-170A is my favorite "battle conditions" AM receiver but  I have no complaints about my Mohawk either. 
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Rodger WQ9E
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« Reply #16 on: March 18, 2011, 02:18:47 PM »

Heh, and figure this one out: I sold my Apache to a fellow north of here in February because it didn't match up well with the newer Mohawk with the chrome knobs. Translation: I got rid of the one that worked pretty well and kept the one that wanders all over the dial!  Roll Eyes

I'll make good eventually, I promise.

   Maybe the chrome knobs cause the drift ? Have to check with the audiophiles, they make discoveries like that all the time.
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