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Heathkit TX-1 Apache, My Nightmare :)




 
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Author Topic: Heathkit TX-1 Apache, My Nightmare :)  (Read 1827 times)
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KC3GMQ
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« on: March 03, 2017, 11:32:44 AM »

Good day all, thank you for having me,  I am new to this forum,  I am a HAM one year now KC3GMQ and I have taken to the old tube gear.  Also learning electronics.  Im not a total novice but I am learning tubes and radios. I built small Heathkits throughout my younger days, my Grandfather was part owner of a Heathkit Store and did a lot of repair work at home.  I need some help though.  This is long, mainly because I think If i expect help or advice, you need the full story.  So here we go...

So I got this Apache Transmitter literally from a guys wood shed on his farm.  I also got a DX-100 and a Mohawk.  It looked rough but then I picked them up at night.  After a quick clean up they all looked in pretty good shape in good light.  Later that evening I noticed a burnt wire smell, it was coming from the Apache.  I called the guy I got it from and he said he had plugged it in but smoke started coming out. So now I know it had been fried so I took it out of the case and took a look.  What had happened was the indicator lights had been bent up into the chassis and when he turned it on, it shorted.  I repaired the lights and their position and ran new wire to them.  I also had to repair several other wires that had melted together with it.  I used heat shrink.  I checked a few caps and then decided to just replace them all.  I bought a cap kit from Hayseed Hamfest and then replaced the caps. I then checked all the tubes on my Hickock 600A.  All looked good to go.

So now I think I am ready to try it, I got the manual out and checked all the resistance readings and they were all ok.  So I turned it on...no smoke.  I let it warm up for an hour and started the set up procedure.  It didn't go smoothly at all, I had to tweak the pots some to get the indications I needed.  I figured somethings were out of whack because they all should have aligned so to speak from the full counter clockwise position like the book said.

Anyway, all was working until I got to the modulator setup portion.  I got zero indication on the gage or on my Panadapter that it was modulating.  I did have a good 100 watts of carrier on my Palstar turner watt meter.

So another HAM was telling me that as I read thru how the radio works, it has to short the modulator transformer in CW and SSB.  He thought a wire was off or miss attached...and it was.  So I discovered I had an older version of the Apache.  (If you need this versions manual say so and I will send you the PDF.  I made it searchable ,  makes it easier)

After I corrected the mode switch wireing, I still had no luck.  Another HAM walked me thru testing the transformers the best we could and all the resistance readings matched his radio, and some spares he had on the shelf.  So we assume the mod transformer is ok.

So a local ham tried to help me too and had me taking the tube readings,  the 12AU7 (V8) pin 6 was suppose to be 150, but I was getting 300 volts.  Then I noticed that the EL-34 tube socket was half missing, and the other badly cracked.  I replaced both sockets and re wired that area.  I also replaced the coupling caps from the 510 pf to .01 mf.  This time when I got to the modulator part of the set up, it was reading nice on the meter.  So I had modulation out now, but it was very distorted.  I discovered my gain potentiometer on the front panel did not effect the meter until I got 3/4 around on it.  I removed the gain pot and checked it.  It was shot.  I checked all the other pots and 4 of the 5 were bad.  I have replaced them now also.

After replacing the pots, I tried it again.  Things acted a bit different which I expected.  After setting up the modulation I tried again and still had the same distortion.  I rechecked all the tubes and the EL-34's read good in the micromohs setting,  but when reading the GOOD/BAD portion of the tester, one was in the ? zone and the other in the high end of the bad zone.  So I ordered new ones.  I actuall found that on V8, the jumper from PIN 3 to pin 8 was broken in the protective sleeve.  Repaired the wire and modulation is awesome and clear now.

So I think I have this thing licked.  I start going thru the setup again, and when I got to the place where you set up the Bias to 55ma in SSB, it would not come up to 55ma.  So as I am playing with it, the Bias ma started rising, as I backed off the potentiometer, it ran away high, the mode switch arced and the fuse blew.  I pulled the mode switch, cleaned it, got the carbon off, and put some Corona Dope on it to help prevent the arcing.  Tried it again trying to gather more info, and same thing,  low reading and then it comes up and runs away.  Another HAM said it sounded a lot like my tubes (6146) were bad.  I pulled them and sure enough, I had fried them.  (it should be noted, my inexpperience in loading the power I think is the main reason I killed those tubes.  I was doing things totally wrong)

Update today, I have good tubes back in the rig 6146A's.  In the SSB mode to set the bias, a lot more stable now, I can get 55ma right away, but still after some time tries to run away high.  I tried to load the power in both CW and phone, and I have great grid, but the plate barley dips, and I cant get power over about 20 watts.  It should also be noted, I have not set the CLAMP yet, I have tried to jump in there also, but it is not responding right either at this point. So I went from a good working amp section, to whatever I did to mess it up.  Also HV is at aprox 800volts.

This Transmitter in my opinion has never function correctly do to the wiring mistakes I have found.  Anyway, if anyone out there read thru all of this and can lend me a hand, It would be greatly appreciated.  I have several boat anchors , all need fixed, but I am not giving up on this one until I figured it out lol.
.
**  Only tubes that have not been replaced with new are the 5763, 6CL6, 6AL5 but tested good

**  Keep in mind please, if you ask me to check something,  treat me like a 5 year old.  I need to know how to do this stuff safely, and so I don't wipe out my test gear or cause more issue in the transmitter.

**Test gear I have:  Heathkit VOM,  Heathkit MM1, Fluke 79, Signal Generator, 100mhz Oscilloscope , Dummy load, Capacitor checker IT-28.  Still learning the signal generator and scope.

Thank You all 
KC3GMQ Dave
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kb4qaa
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« Reply #1 on: March 03, 2017, 12:25:32 PM »

Welcome aboard, Dave!

You have definitely jumped in with both feet.   I don't have any specific advice with these radios.   Being methodical and patient is often the key to sorting out any radio.  Since these are kits, checking every wire and every solder connection is paramount.   With any old radio I always go through and test every resistor. 

Hang in there, you have made great progress, Bill
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« Reply #2 on: March 03, 2017, 02:22:06 PM »

Make sure you have negative voltage bias througout the RF chain, especially at the choke of the 6146 grids.

That clamp pot needs to be adjusted pronto so the Finals' screen voltages are < 180 volts. If not adjusted properly, the screens heat up and plate current soars. Make sure the 6AQ5 tube is good.


Phil - AC0OB




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KC3GMQ
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« Reply #3 on: March 03, 2017, 06:25:17 PM »

Phil, Thanks for the reply. So let me say, these problems cropped up and the only other thing I had done was fix the choke on the loading capacitor.  The porcelin had been broken and it was not longer attached to the chassis wall.  I put the choke back on the screw best I could, and re attached the connection which is ground.  I may remove it and see if that changes anything.

So I got the book out and checked the 6AQ5 (V4) and the 6146's After tweaking the bias, and the clamp, I could get my readings to match the book.  Also, The book, even though it shows my configuration, in the tube check page (98) it list the newer version of the Apache.  Main difference is the mode switch.  I do not have contact G-23,  that was on a newer version of Apache. I looked at the drawing and used contact position GD-14.

I checked the choke for 6146 choke, and idle current was 3.4 vdc and with it in transmit, 820 volts  I will mention so you know I am not to stupid.  I made the meter connection for the high voltage readings with power off and disconnected, then turned it back on, let it warm up again, and flip the transmit switch for a reading.  You mention negative bias at the coke so I am not sure I took this reading correctly.  I have included pictures of the 6146 choke test locations,  and the loading cap choke I re installed.  Still wont load by the way Smiley  Thanks for the help, it is greatly appreciated.
Dave



* TX-1 6146 Choke.JPG (151.76 KB, 480x640 - viewed 72 times.)

* TX-1 Load Choke.JPG (134.55 KB, 480x640 - viewed 86 times.)
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« Reply #4 on: March 04, 2017, 08:10:36 AM »

I love your blow by blow descriptions and accurate writing of symptoms.
As Phil says, Sounds like rising plate current draw is because bias is rising from nominal negative on the 6146s to more positive as something warms up from excessive cirrent, hence heat. I don't have the schematic but isn't the 6al5 the bias rectifier?  Possibly some resistor in the bias chain. Measure the bias voltage coming from the bias rectifier and also at the 6146 grids to see if the proportional voltage rises agree and stabilize as things warm up.

Is the same 6al5 bias circuit used to feed the modulator tubes? If so, check the components there to see if some of them are sucking down the bias as things warm up., etc. I don't think your miss-loading  caused problem. So much is old, broken and solder crapped on that rig that anything, even fogged solder joints as others have mentioned can be the cause.
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« Reply #5 on: March 04, 2017, 11:34:36 AM »

Don't forget that the front panel control marked "Gain" is actually the clipper control while the mic gain control is hidden behind the key jack and requires a long, thin screwdriver to access it through the jack from the front.
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Geoff Fors
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« Reply #6 on: March 04, 2017, 12:27:43 PM »

when I got to the place where you set up the Bias to 55ma in SSB, it would not come up to 55ma.

It seems like you might have the bias for SSB squared away now, but not sure.  If not, when adjusting bias did you have a jumper wire plugged into the Apache's accessory socket on the rear panel?  The manual for my Apache covers this early in the testing section, but does not mention it later in the step for adjusting bias in SSB mode so if the step referencing the jumper is overlooked, it may not be apparent when following the instruction for adjusting bias.  

I did the W3SCC mod that moves the mic gain to the front panel "Gain" pot.  I also removed the clipper circuit, but I may restore the clipper at some point.  There are advantages to having the clipper and if mic gain & clipper are adjusted properly Apache audio sounds fine.

Good luck!
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Brad K4RT
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« Reply #7 on: March 04, 2017, 03:57:11 PM »

Thanks you all for the advice.  Brad, we had a QSO once and I have been to your web page.   I chose to keep everything stock by the book until I get it ironed out and functioning.  Currently the rig only runs away when in SSB on the mode switch when trying to set bias and clamp.  Yes I did have the jumper installed.

Last time I tired to set up, everything worked as prescribed in the book until I get to the SSB BIAS part.  I tried to set things quick, and then I tried to load the amp in CW and in Phone.  When loading, I get very little DIP but it is there.  I can get things up to about 20/25 watts and then I switch over to operate.  When in operate if I try to load more, I get no dip, and power will not come up at all.

Today Iv been trying to follow the book and take the resistance reading of the grid system.  I have measured from several spots and get 60k Ω,  book says it should be 6K Ω so now I am not sure if the book has an error, or I do have an issue there, or am I taking the reading wrong.  I have checked and re checked all resisters.  Was going to pull the 6146 V5&V6 and sockets to take a look, but that is going to be some job with all the other things it affects.  I will do it, but want to make sure that is needed first.

Just want to point out, I have the modulation section fixed and it works great.  Before I had that fixed, The amp and everything else worked great lol.  All tubes checked good, most have been replaced

Thanks to all who have added recommendations.

Dave  KC3GMQ

 
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Pete, WA2CWA
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« Reply #8 on: March 04, 2017, 05:35:43 PM »


Today Iv been trying to follow the book and take the resistance reading of the grid system.  I have measured from several spots and get 60k Ω,  book says it should be 6K Ω so now I am not sure if the book has an error, or I do have an issue there, or am I taking the reading wrong.  I have checked and re checked all resisters.  Was going to pull the 6146 V5&V6 and sockets to take a look, but that is going to be some job with all the other things it affects.  I will do it, but want to make sure that is needed first.

Dave  KC3GMQ

I don't know of any errors in the manual.

From the chart on page 101, the grid resistance should be roughly, 5K to 7K, depending on the R5 bias setting. After 50+ years, some resistor values may have drifted up or down. Mode switch must in the CW position; resistance is measured from pin 5 of either 6146. Looking at the schematic, you can calculate the series/parallel combination of R22, R23, R24, R5(whether at 0 or 5K) plus the series resistors R20 and R21 going to pin 5 and you get roughly the same number range shown in the chart.
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KC3GMQ
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« Reply #9 on: March 04, 2017, 08:55:52 PM »

Pete,  Took some readings and I attached them,  all look pretty good.  Just seems odd, everything I check seems to be ok, there has to be something someplace thats out ??  Thanks For the help

Dave KC3GMQ

* TX-1 Resistance Readings 3-4-2017.pdf (447.08 KB - downloaded 20 times.)
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« Reply #10 on: March 04, 2017, 10:19:34 PM »


So I got the book out and checked the 6AQ5 (V4) and the 6146's After tweaking the bias, and the clamp, I could get my readings to match the book.  Also, The book, even though it shows my configuration, in the tube check page (98) it list the newer version of the Apache.  Main difference is the mode switch.  I do not have contact G-23,  that was on a newer version of Apache. I looked at the drawing and used contact position GD-14.

Dave

The older Apache had satin type knobs; the newer Apache had chrome-type knobs. There were no circuit differences that I ever heard of.
On the mode switch, there are no wires connected to the GD-23 terminal. I'm not sure if a terminal is actually mounted there. I looked at the original manual for my Apache (satin-type knobs) and there was no GD-23 terminal used on the mode switch. However, on the resistance chart, the references to GD-23 are incorrect. It should be GD-14.
GD-14 should have two wire connections (red wire and blue wire). Red wire connects to terminal strip GB-2 (one end of the 5K 7 watt resistor). This connection also goes to the wiper of the Tune/Operate switch. Blue wire goes through a hole in the chassis and connects to Pin 3 of V5.

Also note that grid current should be set between 5 and 6 ma. Don't go over 6 ma.

If you can get grid drive, screen and plate voltages are in range, the plate tank cap, C51, 500 mmf at 5KV, might be suspect. Also, when you switch bands, various mechanical linkages are engaged to moved switches to their correct positions. Make sure all the switch positions are correct for the band you're testing on. It wouldn't hurt to inspect the various plate tank connections and the plate and loading cap connections.
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« Reply #11 on: March 04, 2017, 11:48:11 PM »


Today Iv been trying to follow the book and take the resistance reading of the grid system.  I have measured from several spots and get 60k Ω,  book says it should be 6K Ω


Dave, yes I remember our QSO now, last fall I think.

Check to make sure your VOM probe is in the right spot.  Per the chart on p. 101 of the manual, resistance from the final screen to ground is 60K, final grid to ground 5K to 7K - mode switch in CW position as Pete said.

It seems that you have RF drive. Are you seeing the low power output, shallow or no Ip dip on all bands?  Is the HV actually present at the 6146 plates?  Are you seeing voltages at or near spec as listed in the voltage chart, manual page 100?  Just a few things that come to mind at the moment that you may have checked already.  Use caution measuring voltages.

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Brad K4RT
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« Reply #12 on: March 05, 2017, 07:45:22 AM »

Morning all, 

Pete, I can get my 5 to 6 grid current easy, and I have been careful not to go over,  but I was when first learning how to setup things.  When I go into transmit with my gage switch in plate, the gage actually shutters now, and barley dips,  it is very sensitive, in transmit, it wont come up or dip at all. As for the books, I too did not think there were differences, but the book I had was not matching my rig.  I started downloading all the books I could find to check, and one day, I found a 1958 version that matched my rig.  I have attached a few pics to show you.  If you would like a copy or either I will gladly send you the one you want.  Looks like the biggest change is the mode switch, in 1961 version of the book, they add GD 23,24, 33 and 34.  Looks like a neutralization upgrade, also shows on the drawing and a few parameters are different, not by much though. In the 1958 version, must have been in a transition, it talks about GD 23 and 24, but does not show them.  Mine had satin knobs, but I polished them Smiley  I will check the 500mmf cap, do you check it as you would any cap?  Wondering if I should pull the sockets for V-5&6 and check out the caps.  It will be a major pain, but I am thinking its next in this endeavor.

Brad K4RT, Checked all resistances, all were good. I am seeing the low power output, shallow or no dip on all bands.  I have measured 810 vdc at the top of the 500 mmf cap. And I am setting up for my High volt readings power off, taking readings, then power off and removing the test gear.

Thanks again all,  attached are the pics of the two different manuals.

73  KC3GMQ  Dave









* pg 2 1961.jpg (3027.48 KB, 2549x3299 - viewed 39 times.)

* pg 2 1958.jpg (2592.84 KB, 2549x3299 - viewed 45 times.)

* pg 36 1958.jpg (4137.22 KB, 2549x3299 - viewed 38 times.)
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KC3GMQ
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« Reply #13 on: March 05, 2017, 07:47:34 AM »

Here are the pics of the different manuals,  last post would not take the last pic

Dave


* pg 36 1961.jpg (4009.34 KB, 2549x3299 - viewed 36 times.)

* pg 36 1958.jpg (4137.22 KB, 2549x3299 - viewed 30 times.)
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KC4VWU
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« Reply #14 on: March 05, 2017, 03:34:14 PM »

I'd bag the SSB mode checks for now and get it stable on AM/CW. Do you have proper bias reading in those modes?

If the plate current metering is showing random shuddering, I'd suspect arcing somewhere. You may want to carefully do some tests in a darkened room and be expedient while looking around in the transmit mode. BTW, I don't believe you ever did mention plate current readings. 

Have you checked the loading capacitor for arced or bent plates, accumulated crud/oxidation, good connections, and most importantly, good grounding? I'd look over the assembly of the entire tank circuit, including the bandswitch, while there as well.

... Phil
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KC3GMQ
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« Reply #15 on: March 05, 2017, 09:00:56 PM »

Well all, time to take a break.  Readings on 6146 pin 3 and 5 are flaky, pin 5 the 150 reading is 170.  Time to rest, regroup and start from the beginning again Smiley  Ill get after it tomorrow again Smiley
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KC3GMQ
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« Reply #16 on: March 06, 2017, 07:17:05 AM »

Is the plate tank cap tested like any other capacitor?
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« Reply #17 on: March 06, 2017, 04:39:38 PM »

I know nothing about the Apache but what about the possibility of a parasitic oscillation? Might explain why this instability just takes off and runs away.  Got the right 6146's in there? 
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« Reply #18 on: March 06, 2017, 06:14:48 PM »

I do have the correct 6146's.  So today,  I have pulled the 2 chokes in the final compartment, checked the 2 caps, and now pulling the 6146 sockets to make sure they are in good shape underneath.  What a job that is.

So I checked continuity on the chokes, the 1 mh 500ma RFC shows no open in the coil, the 2.5 mh choke however reads 43Ω but does not make the fluke 79 DMM beep.  Not to sure on that?

Also not positive how to read the .001 mf 2000 volt cap or the 500 mmf 5000 volt cap?

Dave
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« Reply #19 on: March 06, 2017, 06:39:08 PM »

Dave,
Are you able to measure the values of the chokes and caps rather than just continuity on the chokes and shorts on the caps?
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« Reply #20 on: March 06, 2017, 06:46:06 PM »

I have the heathkit IT-28 cap checker,  and I have a small electronic one that will just tell a value

Dave
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« Reply #21 on: March 06, 2017, 07:47:00 PM »

Dave,

You didn't say if the plate voltage you measured was under load or idle.  800 volts is too high for 6146s on am, and should be 600 volts.  Your apache uses a choke input filter in the high voltage supply, like my home made transmitter.   While operating, my input choke shorted and the plate voltage went very high and fried the finals before I realized what was happening.  Just something to check.  Good luck.
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« Reply #22 on: March 06, 2017, 09:36:11 PM »

I do have the correct 6146's.  So today,  I have pulled the 2 chokes in the final compartment, checked the 2 caps, and now pulling the 6146 sockets to make sure they are in good shape underneath.  What a job that is.

So I checked continuity on the chokes, the 1 mh 500ma RFC shows no open in the coil, the 2.5 mh choke however reads 43Ω but does not make the fluke 79 DMM beep.  Not to sure on that?

Also not positive how to read the .001 mf 2000 volt cap or the 500 mmf 5000 volt cap?

Dave

2.5mh choke will be about 40 ohms.  The 1mh choke should be much lower resistance, not sure exactly what.  The .001 cap, if it is a ceramic cap it is most likely good.  The 500uuf cap should checked for leakage.  Put a high voltage on one side and read any voltage leaking through on the other side.  Leave the sockets alone highly unlikely there is any thing wrong with them.
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« Reply #23 on: March 06, 2017, 11:28:00 PM »

This is a very good and interesting topic and right on time for my education. A friend bought an Apache to get the NOS EL34s that somehow came with it. He considers the rig, sans $$ tubes, to be useless except for a place the tubes were safely stored, and it looks like it may come to me. Might be a good replacement for the TS430-S in all AM needs.
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« Reply #24 on: March 07, 2017, 03:29:24 AM »

What band are you testing on?

Are you using the VFO or crystal control?

When you press the Spotting switch (with the plate switch off) you can adjust the Driver and Drive adjustments for something between 5 and 6 ma.

When press the Spotting Switch, can you hear the signal in an adjacent receiver?

As I said earlier, alignment of the linkages are very important. When you turn the bandswitch, if the switches in the final and driver area are not in alignment, strange things will happen when you try to tune up. You donít want adjacent switch contacts overlapping each other or not quite touching the correct contact.

The 2.5 mh rf choke is really unimportant in the initial working of the rig. My choke cracked in its threaded hole back in the 70ís and I didnít replaced till sometime in the 90ís.

For now you should concentrate your efforts in the CW mode. Put the AM notion aside until you get the main part of the transmitter working. Remember, in the CW mode (with the plate switch on), you need to plug in a key before you can get any RF power out.

I like using a 100 watt lamp for a dummy load. Gives you a great visual indication. Apache using a pi-network so it will work fine.

Loading control should always full counterclockwise when initially tuning up. Adjust the Final knob for an initial dip with the Tune/Operate switch in the Tune position. Then put switch to Operate, increase the loading a bit, then adjust Final for dip, increase loading, dip, etc.

Variations in voltage are normal. Line voltage variations, component aging, meter accuracy would all have to be taken into consideration. As an example, if Heathkitís measurements say were done at 110 volt AC to read 150 volts on the screen, at 122 volts AC, the same voltage would read approximately 166 volts even not considering any other circuit anomalies.

Given your test equipment, thereís no real easy way to test that 500 mmf for failure under the existing operating conditions other than replacing it. I wouldnít do it until youíve exhausted all other physical examinations and circuit testing.

I would also go back and inspect that entire clamp circuit and adjustment. If that adjustment is not done properly, the rig will not put out much power, could get into plate current runaway, and/or blow fuses.
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