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Heath Apache TX-1 bias adjustments




 
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wa6lzh
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« on: May 17, 2020, 08:28:14 PM »

My head was locked on needing to do a second adjustment for CW/AM. Of course SSB bias is on the same pot hahah I went to the voltage chart and checked things out that way and finished the other adjustments now it all comes together with 250  (I like 240 as a precaution who can tell the difference) with 4-5 ma grid current and tested the clamp tube works very well.

This may be a second response so I won't elaborate. Does a posting take some time to "Post"? 73 and thanks one million times. I will read the posts to see if I can help or I can learn.

Who is "Mike" above the microphone connector?   hihihihi Must ber a 60's thing.

73 am'ers BCNU.


Tony
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« Reply #1 on: May 17, 2020, 09:12:19 PM »

Horrible manual scans out there; you should get a real manual  Cheesy

All testing and adjustments start on page 91.
Follow the instructions carefully.
Make sure all the linkage is working properly.
Keep grid current to 6 ma
Actual audio gain control is behind the key jack. Have to insert screwdriver through key jack. Front panel "audio gain" control is the clipper.

Great transmitter. I built mine in 1960 and still use it today.
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« Reply #2 on: May 17, 2020, 11:31:52 PM »

Open the case and remove chassis and check the circuitry against the manual's schematic. Very important first step.

I assume you're going to be AMing with this rig so here is my abbreviated procedure:

After circuit check-out, power up and make sure all filaments are lit and fan is turning.

In Phone Mode:

With a DMM check Pin 5,6 of 6CA7 for a negative voltage (bias) of about -35V. We need bias before we ever think about Keydown.

With a DMM check Pin 5 of 6146 for a negative voltage (bias) of about -50V.

Check right side of L24 (LV PS choke) for 350V.

Set VFO to 40 meters at about 7.2 MHz and RF drive pot to zero.

With dummy load and RF Wattmeter, Keydown and slowly increase RF drive while keeping grid current below 6 ma and do multiple plate dip and loads up to about 50 Watts output. Keep an eye on Grid current.

Using an insulated screwdriver for all adjustments, place a DMM probe at Final's screen, Pin 3, and at Keydown adjusting the Clamp tube pot for an initial 160 volts.

Increase drive for 90 Watts output while keeping grid current at or below 6 ma. Do multiple plate dip and loads as necessary.

Readjust Clamp Tube for Final screen voltage (Pin 3) of about 175 volts. Multiple plate dip and loads may be necessary.

BTW, I still have my TX-1/RX-1 twins.

i strongly advise that after checkout, a new, low profile 110V muffin fan of at least 35 cfm be installed atop the RF cage to suck out hot air.

Phil - AC0OB


* Apache TX-1 Left Side.jpg (1470.08 KB, 3872x2592 - viewed 19 times.)

* Heathkit Twins.jpg (3555.86 KB, 3872x2592 - viewed 19 times.)
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« Reply #3 on: May 18, 2020, 08:59:30 PM »

Tony,

Congrats on getting an Apache. I've been using mine on AM since about 2013.

Phil & Pete,

Is your fan drawing out air through the factory perforations in the RF cage cover? I have a new lower profile fan on order after breaking the plastic flange on the stock fan again.

Also, the CW signal is jumping frequency a few hundred Hertz up and down keying the VFO. The problem is in the VFO stage, not the buffer/multiplier, and the crystal oscillator is stable. I've tightened every screw I can reach, reheated all soldered connections inside the VFO enclosure, swapped tubes, and cleaned the band switch contacts. Maybe some crud on the variable cap wiper I missed?  Have you experienced this sort of thing?

Brad K4RT
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« Reply #4 on: May 18, 2020, 11:57:38 PM »


Is your fan drawing out air through the factory perforations in the RF cage cover? I have a new lower profile fan on order after breaking the plastic flange on the stock fan again.

I removed the top cage cover and mounted a suck out fan in the opening with a couple of brackets. The fan now is a 24 v dc fan operating at roughly 18 volts. I also rigged the same type of suck out fan over the modulator section with some brackets. Keeps the entire area cool.

Quote
Also, the CW signal is jumping frequency a few hundred Hertz up and down keying the VFO. The problem is in the VFO stage, not the buffer/multiplier, and the crystal oscillator is stable. I've tightened every screw I can reach, reheated all soldered connections inside the VFO enclosure, swapped tubes, and cleaned the band switch contacts. Maybe some crud on the variable cap wiper I missed?  Have you experienced this sort of thing?
Brad K4RT

Over the years I've had two occasions of jumping frequency. The first time was a bad NE-2 in the time sequence keying. The second time, a few years later, it seemed to be originating in the VFO compartment. Rather then trying to determine the actual culprit, I removed the VFO, opened it up, and replaced all the resistors and capacitors. Problem went away.
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« Reply #5 on: May 19, 2020, 12:10:30 AM »

Pete,

Thanks. Once the new fan is delivered I'll take a closer look at where to mount it.

I forgot to mention that I replaced the NE-2 and reheated the solder connections in the vicinity. I may have to replace the caps and resistor as you did.

Brad
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« Reply #6 on: May 19, 2020, 06:24:48 PM »

Tony,

Congrats on getting an Apache. I've been using mine on AM since about 2013.

Phil & Pete,

Is your fan drawing out air through the factory perforations in the RF cage cover? I have a new lower profile fan on order after breaking the plastic flange on the stock fan again.

Also, the CW signal is jumping frequency a few hundred Hertz up and down keying the VFO. The problem is in the VFO stage, not the buffer/multiplier, and the crystal oscillator is stable. I've tightened every screw I can reach, reheated all soldered connections inside the VFO enclosure, swapped tubes, and cleaned the band switch contacts. Maybe some crud on the variable cap wiper I missed?  Have you experienced this sort of thing?

Brad K4RT

I mounted the fan atop the RF cage to suck out air and placed aluminized Ducting tape on the cage top and upper sides so air gets sucked only into the bottom and out the top.

Make sure the 0A2 is functioning and pin 6 of the Osc. socket has about 115V on it.

Replace the 6AU6 with a 6AH6 in the VFO Osc. stage.

Phil


* Apache TX-1 Top View.jpg (1686.82 KB, 3872x2592 - viewed 34 times.)
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wa6lzh
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« Reply #7 on: May 21, 2020, 02:46:25 AM »

Thanks to all that replied. For some reason I got lost in the adjustment section. It seemed a bit scattered to me but with your clarifications I'm ready to go. The adjustments I thought were necessary as it's been sitting for about ten years. The lockdown brought it back up! The procedures had me going between the Notes, steps and locations and spun my head around a bit.

The muffin fan is at the top of my list. It doesn't seem to move much air but the final cage doesn't get too warm. We live in a coastal climate and it never gets too warm either! New filter caps are in the making but the old ones seem to be holding their own.

Thanks for providing this resource and help. After the adjustments and cleanup I'll come back and let you know how it went.

73 for now and have a happy holiday weekend.

Cheers Tony WA6LZH
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« Reply #8 on: May 21, 2020, 11:21:11 AM »

I looked at my notes and the fan is a 65cfm fan.

After Modifications here was the Measured Data:

Power Out at Keydown* in AM Mode (120VAC input) 120W
Final Vp* = 730V
Final Ip* = 250 mA
Final Icg* = 3.8 mA
Final Grid Bias* = -78V (Measured at junction of R20, L15)
Final Screen Voltage* = 175V (Measured on Blue-Green Screen Voltage wire going into RF cage)
Modulator Screen Voltage Vmsg* = 355V
Modulator Grid Bias* = -35 volts
 
Tube Complement:  Finals WestingHouse 6146B
Modulator Svetlana EL34
Speech Amplifier 12AX7A
Audio Driver 12BY7A
VFO - 6AH6
Osc/buffer - 6CL6
Buffer/Multiplier 5763
Clamp Tube 6AQ5  
LV Rectifier 5V4 (Solid Stated)
HV Rectifier 5R4WGB
 
 
Phil
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« Reply #9 on: May 21, 2020, 02:10:11 PM »

Grid current should to be set to no more then 6 ma for two parallel 6146's.
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« Reply #10 on: May 21, 2020, 02:23:54 PM »

Grid current should to be set to no more then 6 ma for two parallel 6146's.

Yes, you have mentioned that twice.

If you are referring to my post in reply #8 above that was the actual  grid current with 120 Watts carrier for the dual 6146's.


Phil
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« Reply #11 on: May 21, 2020, 04:44:36 PM »

Actually it good to mention it several times since I think it's important to proper operation of the finals. Less obvious is the actual gird shunt resistor which is 5.55 ohms at +/-1%. Of course the +/-1% was when manufactured back in the middle to late 50's if still original. Aging and use, after 60 years, could have moved the actual resistance beyond tolerance causing the actual grid current meter reading to be something different then what it shows.
It's not good to fry your grids and it's equally not good to starve them. Grin

For more pain, bring on those Apache singing cats:

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wa6lzh
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« Reply #12 on: May 22, 2020, 01:53:33 AM »

Phil,

Not to be a nit but I went through everything in the manual concerning adjustment and I could not find anything regarding the AM/CW bias adjustment. Can I assume this should be at zero ma with the operate switch thrown or should I just measure the grid and set for -50v or should the transmitter be loaded up to full input while setting the bias? SSB, MOD went fine. Seems to me I should know what the resting plate current should be for the proper bias with no excitation? If my memory serves me a class C amp should be zero current at rest with no excitation.

Thanks,

Tony
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« Reply #13 on: May 22, 2020, 03:06:48 PM »

Tony,

You may have seen this already, but in case not or for others searching this thread for information, on pg. 94 of the manual, the second sub-paragraph covers bias control adjustment and the third sub-paragraph covers clamp adjustment.  Pete already mentioned that the mic gain adjustment is behind the key jack.

Brad
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« Reply #14 on: May 22, 2020, 03:57:02 PM »

Phil,

Not to be a nit but I went through everything in the manual concerning adjustment and I could not find anything regarding the AM/CW bias adjustment. Can I assume this should be at zero ma with the operate switch thrown or should I just measure the grid and set for -50v or should the transmitter be loaded up to full input while setting the bias? SSB, MOD went fine. Seems to me I should know what the resting plate current should be for the proper bias with no excitation? If my memory serves me a class C amp should be zero current at rest with no excitation.

Thanks,

Tony



I will only add to what Brad has already stated about Page 94 of the manual.

My original tune-up procedure was to make sure you at first measured Final control grid and modulator bias before beginning any tuneup in order to not stress those tubes.

The best place to measure actual control grid bias voltage is at the junction of C43, R20, point "B."

With B+ on the final's, a certain amount of protective bias, and RF excitation, plate current is going to flow so we cannot assume zero plate current at Keydown.

From page 94 the idling current will be about 50 mA with no modulation and this is assuming proper plate dip and tune and your control grid current is less than or equal to 6 mA.

Tweaking of R5 is only necessary if excessive Downward Modulation is seen.

Page 100 is a good reference for checking "ballpark" voltages.

BTW, later on you will want to rid this unit of the clipper circuits. The clipper circuit does not do what is was designed to do and just adds harmonics and distortion.


Phil
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« Reply #15 on: May 22, 2020, 04:35:04 PM »

Phil,

Thanks for posting the pic of your Apache fan configuration. I received the fan I ordered, which is similar to your fan. I might order a second one for the back of the DX-100B.

Tony, stock, my Apache had clean audio with the mic gain and clipper adjusted correctly.  However, I removed the clipper circuit and essentially converted the speech amp to that of the DX-100 with changes to the inter-stage cap values. Conservative changes that sound good with a standard D-104 mic. I also moved the mic gain to the front panel GAIN position and I think I put the bias pot behind the  key jack.

Brad
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« Reply #16 on: Yesterday at 01:47:24 AM »


Phil,

My thick skull finally saw what I was doing. In my defense I think it is very, very odd that they explain the ssb bias adjustment but not the AM bias adjustment. I realized it had already been done as there is only one adjust at all. I used the tube socket voltage chart and all bias voltages were correct for all the modes. I'll attach the tuner/power meter tomorrow but tuneup readings are lookin good. 240 ma with about 5ma of grid current and modulation kicks up nice and easy as well as tested clamp action by turning the driver off with the drive control goes to zero. Looks good on the scope even with the low impedance mike I was using. I have a hi impedance dynamic and it looks good too but I just turn the gain down. I monitored on another receiver with a small wire attached and audio sound pretty good but some years age I installed increased capacitance on the "Three bad boy" caps in the mic amp don't recall the values but on the air test showed up well.

One anomaly I'm sure you know about: The microphone jack is labeled "Mike"! hihi Maybe that was the thing in the 60's.

Thanks again all the help was invaluable. I'll probably do an on the air test in a few days but
I have to pair it up with my R-388 which I love as an am an cw receiver.

73   Tony

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« Reply #17 on: Yesterday at 04:57:01 PM »

Tony,

Good to see you got your Apache adjusted.  Yes, the "Mike" label, it's the same on my DX-100B.  Maybe Mike worked in Heath's screen printing shop. Smiley

73,
Brad K4RT
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« Reply #18 on: Yesterday at 06:50:26 PM »

"MIKE" not really uncommon label back in the "good old days"

Typical Boatanchor Examples:

Hallicrafters HT-32, Gonset GSB-100, Lafayette KT-390



* ht32-1.jpg (48.53 KB, 804x342 - viewed 12 times.)

* gonsetGSB100-1.jpg (20.26 KB, 263x188 - viewed 13 times.)

* Laf-KT390.jpg (31.85 KB, 501x306 - viewed 11 times.)
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« Reply #19 on: Yesterday at 07:50:32 PM »

Both of my Allied Knight's simply had "MIC."

Phil


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« Reply #20 on: Yesterday at 08:52:07 PM »

More "Mike"

Elmac:



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wa6lzh
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« Reply #21 on: Today at 01:40:00 AM »

Thanks again Phil. I pulled the 6al5 "Clipper" a long time ago. I think I'll jumper that audio band pass filter as well. After I resolve the hum issue. Scope says the ac ripple is extremely low less that 1%
I'm still looking for a 120  volt fan in my junk box. I have a hum issue but after pulling all the audio tubes it's still there. I think I have a ground loop or two as I have about a dozen plugged into the same circuit and antenna panel. I'll check it with a battery portable tomorrow.


Tony
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« Reply #22 on: Today at 02:55:31 AM »

Years ago I moved the audio level control (pot behind the key jack) to the position held by the Clipper pot. I then added a Tone control to the position behind the key jack with a phenolic rod extension through the key jack along with some tacked "tone" circuitry. I did it for fun and giggles but it worked so well I just left it in place. Of course, now I can't plug a key into the key jack.
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« Reply #23 on: Today at 01:39:27 PM »

Years ago I moved the audio level control (pot behind the key jack) to the position held by the Clipper pot. I then added a Tone control to the position behind the key jack with a phenolic rod extension through the key jack along with some tacked "tone" circuitry. I did it for fun and giggles but it worked so well I just left it in place. Of course, now I can't plug a key into the key jack.

...Of course, now I can't plug a key into the key jack.

I used a long-barreled Amphenol mic jack to cure that problem.

If you're into modifying the Apache's circuitry for improved audio here are my latest mods:


Phil

* Apache Modificatiions for AMphone.pdf (335.53 KB - downloaded 1 times.)
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« Reply #24 on: Today at 04:06:03 PM »

Years ago I moved the audio level control (pot behind the key jack) to the position held by the Clipper pot. I then added a Tone control to the position behind the key jack with a phenolic rod extension through the key jack along with some tacked "tone" circuitry. I did it for fun and giggles but it worked so well I just left it in place. Of course, now I can't plug a key into the key jack.

...Of course, now I can't plug a key into the key jack.
I used a long-barreled Amphenol mic jack to cure that problem.
Phil
I don't get the connection between my running a phoenolic rod through the key jack ( so I can turn my tone control pot) and a long barreled Amphenol mic jack.
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