The AM Forum

This TX-1 Apache powers up, filaments glow, and no hum nor smoke.  But when switching to the transmit position, the fuse pops and there is an arc flash at what I think is the plate relay  I'm guessing this is a HV short, bad caps, resistors...

Can you help this old appliance op by walking me through the obvious checkpoints.  Have a VOM and lots of ambition to get this rig on Ya AM.

Russ
WA1JFX

First thing is to visually inspect all connections from hi voltage rectifiers, filter caps, bleeder,  lead from power suplply, feed thru insulators, to where the HV is feed to  to modulator, and final.
If you don't see anything that has  arced to ground,  Pull the final/mod tubes and fire up. And see if it still arcs.
If so keep pulling all tubes, even the rectifiers and see if it still blows the fuse..

Let us know what you find..

GL Chuck

I'd work it the other way.

Unplug the rig.
Take your voltmeter and make sure there is NO HV on the plate caps.
Remove ALL the large tubes - that's the mod tubes and the output tubes.
(open cage top for access.)
Identify the HV rectifier, and the LV rectifier.

Replace the fuse.
Remove the rig from cabinet.

Download manual from BAMA (amfone main page upper buttons, click)
Open schematic.

Identify convenient test points for:
1. LV B+ after filter cap
2. LV B+ after rectifier tube, before filter
3. HV B+ after filter cap/pi filter
4. HV B+ after rectifier tube, before filter

A. Fire up AC with NO rectifiers in place - check AC voltages going to the sockets of the rectifier tubes - can be done from the top into the tube sockets.

B. plug in LV rectifier, fire up rig with meter attached to the test point 1.
C. plug in HV rectifier, fire up rig - you may or may not need to key the transmitter to actuate the B+, see schematic, meter per 3.

IF the fuse blows at either point, then you've almost certainly got a shorted filter cap - very common.

With the AC unplugged, check the filter caps with your ohmeter, after checking them with DC VOLTMETER to be sure they are discharged fully. IF they read ZERO or some constant low impedance, they are bad. Replace.

Or remove lead to suspicious cap/filter assembly and test per 2 or 4, as depending on which ur testing.

Most likely a bad filter cap.
Less likely a shorted transformer - like the power iron or mod iron.
On occasion you get a short in a choke - sometimes you can get away with just lifting the choke above ground, if it is a short to the core. BUT YOU MUST LABEL IT CLEARLY AS BEING B+ HOT - and preferably install an insulated shield to prevent inadvertent contact. Best to replace though...

If the power is all good, then suspect a shorted tube.
Plug them in one at a time and see what happens...  ;D

Report back.  ;D

         _-_-WBear2GCR

In addition to the excellent advice you have received so far, take a very close look at your 5R4 sockets and the base of the 5R4 tubes themselves.  I have repaired several rigs using 5R4's that had "carbon tracks" on the sockets and tube bases causing fireworks and fuse blowing when the plate supply is activated.  The physical layout of the 5R4 makes it and its socket particularly prone to this given a little bit of dirt and debris getting where it shouldn't.

Rodger WQ9E

Much obliged, Chuck, Bear and Rodger.

The rectifier tubes have been replaced with top hats.  Should I unsolder the two red leads on both legs as well as the middle black connection, then measure AC HV?

Removed finals and modulation tubes and still blows fuse.

Russ

Hi Russ,

Before you start disconnecting wires, pull the power plug, HV rectifier replacements, temporarily short pin 2 of one of the 5R4 sockets to ground (to make sure the filter caps are discharged) and check resistance to ground from pin 2 of one of the 5R4 sockets (after removing temporary short)-you should measure around 30K.  Have you been trying to start the HV in the CW or AM position?  If in AM and you think the arc is coming from the plate relay then switch the mode to CW and (with power plug pulled) measure resistance from pin 4 of one of the 6CA7 sockets to ground, should be near infinity.  The relay switches the screen voltage to the modulator and a tube problem or a problem with the modulator screen bypass, C-55 would cause this problem. 

Rodger WQ9E

Rodger, I removed both legs of the tophats (1N549s x 3 each).  Then with power up, I switched HV on without blowing a fuse.  Voltage check showed over 1KV on each red lead from xfmr (my VOM only goes to 1000 volts).

I checked each leg of tophats and found one leg of 3 has 2 that show no resistance.  The other leg of 3 has equal readings across each tophat (with resistor and cap).

Russ

Hi Russ,

OK, I am not quite sure about the exact nature of the replacements in your TX-1.  Does each 5R4 socket have 2 strings each of the 3 1N549 diodes?  When you say no resistance across some of the diodes are they measuring zero ohms or infinity?  In any case, I believe these are likely to be pretty old units and the reliability is far less than the more modern rectifier diodes.  I would seriously consider rebuilding these with modern rectifier diodes such as using 1N5408 units (3 amp, 1KV rating) and available from Mouser at 10 for $1.60.  The 5R4 tube sockets are in parallel so you could make just a single plug in unit using 4 1N5408's in series for each section (a total of 8 ) and leave the second socket empty.  This will give you plenty of current capacity and you shouldn't add any resistors or capacitors in parallel with these rectifier diodes.

Since you are using SS rectifiers you can also disconnect the filament leads from pins 2 and 8 of the 5R4 sockets,  just make sure that the common cathode connection of the two rectifier strings attach to whichever pin (2 or 8 ) that is connected to L-30 (the HV filter choke).  This will keep the high voltage off of the LV transformer 5 volt winding which is a fairly common source of failure in some transmitters (the Halli HT-32/37 series for example).

Although these rectifier replacements may not be the only (or main) problem given their age and the "odd" resistance measurement I would replace them before you go any further.  Of course if you have a pair of 5R4 tubes around you could test it with those.

Rodger

Note to self, do not put a closed parentheses immediately after the number 8 or the BB software converts it to a smiley face.  That definitely changes the meaning of a post.

Rodger

Hi again, Rodger and AMfone gang.

Diodes that are bad read full scale continuity (0 ohms?).  There are two strings of 3.

You say no resistors and caps are necessary for the 1N5408 diode strings.  Are the new diodes nowadays a self-contained device with built-in resistors and caps?

The 5R4 sockets had been removed previously.  There is a 3-lug strip with a yellow and a gray wire and no other connections; 6 volts across the lugs, so this must be the filament power for pins 2 and 8 you refer to; or, should I look for the secondary winding filament leads.

I don't see the L30 choke.  Looks like it was removed.

Will order diodes and a choke from Mouser and go from there.

In inspecting solder joints and bare wires in proximity to ground, there have been several that were found.  One wire to the mode switch was broken completly off.

Man oh man, this is great to have superlative advice; thanks!

Russ

Some other advice from a Apache owner. Try it in the CW position. This eliminates the mod and drive transformers. Also, I would work in the 'Tune' position instead of 'Operate' until you figure it out. Saves wear and tear. Gud luck.

Thank you, SLK.  That helps me understand.

Russ

What is the rating of L30?  Mouser part #?

Russ

Hi Russ,

I imagine L-30 is still there as it is a BIG piece of iron mounted on the chassis top, it is the input choke for the plate supply and there should be a lead going to it from the cathode end of the currently installed rectifier strings.  I don't have the manual with me here at work but it is one of the enclosed large metal units on the chassis top.

If those diodes are reading zero ohms on a low range (RX1) then they are likely shorted, if it it is on a higher range then they may be OK but the one reading different is then open.  In any case, they should be replaced as according to the specs I have they are only rated for 300 mils at 1,200 volts and they are being run right at their current limit in a TX-1 (for comparison the 5R4 tube rectifiers were designed for about 250 mils per section, per tube into a choke input and with 2 tubes in parallel they were rated for 500 mils).  Since they are in a full wave center tap design theoretically you can draw 600 mils continuous from these SS replacement units but that leaves no safety margin for surge and temperature de-rating.

Modern rectifiers from the same batch have very similar characteristics and they should not need any extra components hung on to compensate for differences in switching time or reverse resistance.  Using 4 in series for each string gives you plenty of safety factor for the PIV rating.

If the various electrolytics have not been replaced yet then you might want to add those to your order for Mouser to avoid future failures.  Modern units will be considerably smaller and some of the standard values have changed so for example 47 uf will be the closest to the old 40 uf value.  You can safely go up a bit in microfarad rating to the current standard value; particularly with choke input filters.  You can also safely go higher with voltage ratings.

Rodger

Your right, Rodger, replacing paper caps is going to be another task.  How about ceramic caps and resistors?

What do you recommend for replacements for the 125 uf @ 450VDC and 20-20-20 @ 450 VDC filter caps? 

I looked on Mouser to find info on the 20-20-20 can but didn't have any luck.  Apparently, my terminology of the part name and what's in their database didn't match. 
Found the 1N5408 in their catalog with no problem.  Good looking company with lots of inventory; I've got their catalog ordered.

The old diodes must have broken down.  There were 3 readings: 2; 6K; 200K ohms.  I measured +-/_+ across each.

Thank you.

Russ

Bear, you had mentioned the following:

Identify convenient test points for:
1. LV B+ after filter cap
2. LV B+ after rectifier tube, before filter
3. HV B+ after filter cap/pi filter
4. HV B+ after rectifier tube, before filter

According to the schematic, the TX-1has a HV xfmr with a secondary of 1600VCT @ 800ma.  There are 3 leads: 2 red, 1 black.  Which is B+, B-, etc.?

Russ

Hi Russ,

For the 125 @ 450 volt capacitors I would go with Mouser part# 140-ls121m2w-2240 which are 120 uf @ 450 volt Xicon brand units for $3.14 each.  You will have to be a little creative in mounting these but that should not be a problem, do be careful where the units are in series to keep the capacitor case which floats above ground well insulated from ground (this is capacitor C-1 which is connected directly to the output of the HV choke L-30; the other filter caps (C-2, C-3 have one side connected to ground so that isn't a concern with them).

 I don't know of any new manufacture HV triple capacitor units so you could just use 3 discrete 22 uf @450 volt units to replace the triple.  There should be plenty of room to mount them below chassis and I have used a lot of the Xicon brand units (which are around 60 cents each) with no problems.  I believe there may be some people (Frontier rings a bell) who make "new" multi section units by stuffing discrete caps into old units.  I bought some similar items when I restored my  Collins S line and KWM-2 but for most rigs I generally leave the old unit mounted in place on the chassis for looks and replace the caps below chassis using a terminal strip.

Do be careful replacing the bias filter caps (C-4, C-5) since this is a negative (with respect to ground) output voltage and the positive side of these filter caps must be connected to ground.

Rodger WQ9E

The B+ is the one going to the input of the filter - a choke, followed by a cap, iirc.

It's a full wave, with a center tap - refer to your ARRL or Bill Orr handbook for the standard wiring configurations for choke input power supplies, and tube rectification for full wave.

You'll see it there!!  ;D

                   _-_-bear

Well, the parts are on their way.  Hopefully this will solve the power supply problems.  Here's the list, just in case someone else (newbie) out there wants to tackle a TX-1 project.

1  140-LS121M2W-2240    2 @ 450V 120uF 

2  75-TE1301-E3    1 @ 50V 2.0uF

3  140-XAL50V100-RC  1 @ 50V 100uF 20% 
 
4  140-XAL160V22    2 @ 160V 22uF 20% 
 
5  140-XAL450V22-RC    3 @ 450V 22uF 20% 

6  140-XAL25V10-RC    1 @ 25V 10uF 20% 

7  598-DME6P1-1K-F    2 @ .1UF 630V 10%

8  512-1N5408    8 @ 3.0a Rectifier  (diodes)

Mouser didn't have the .1uf @ 400 volt paper capacitor, so I ordered polyester film caps.  Will those work?

Thanks Rodger and Bear for your recent postings; every bit of info helps.  We've covered a lot of ground in the past 3 days.

I will be careful with HV.  Back in the late 60's, I built a homebrew SSB grounded grid amp using a pair of 813s with a voltage doubler circuit.  Did get zapped a couple of times; I thought I was a goner.  So thanks for the safety reminders throughout our discussions.

I'll report back when the parts get here/installed.  In the meantime, maybe I should check resistor values and study the wiring in relation to the schematic.

Thanks again everyone.

Russ

Diodes don't wear out it takes a short so find the short before you turn the power on unless you like to replace diodes. If it is a choke change it to the negative lead filter floating transformers can kill you.
Film caps are fine for audio.

Hi Russ,

The polyester cap will be fine, I don't think paper caps have been available new for a long time.

I have a feeling that those original rectifiers were probably the problem (given the measurements you made) so hopefully your HV failure will be gone.

I agree with GFZ that floating the choke case above ground is generally a bad idea; if for no other reason you or a future owner will forget about this and touch something that is normally safe to touch.  A potential problem of negative lead filtering was pointed out by Bill Orr in his handbooks in that some transformers do not like having their center tap above ground (lack of insulation) and putting the filter choke in the negative lead will cause this issue.  It probably isn't a problem with most transformers (for example the low voltage units used in receivers often have the CT lifted for standby) but when in doubt I would leave the choke connected as it was originally and replace it if it is defective.

By the way, keep an eye on Mouser quantity discounts when ordering as often times it is worthwhile to order a few extras to hit quantity 10 and receive the discount; particularly for items you will likely need more of in the future.  I remember when I first started collecting and restoring boat anchors I ordered 10 replacement 3 wire power cords and thought I had plenty for a long time; recently I have been going through 30 or more each year.

73, Rodger WQ9E

At the antique radio store I used to work at, we would order 200~300 caps of each value commonly found in old radios at a time. Typical invoice was $1500+ but he got the deep quantity discounts. We went through some caps at that place.

use the old positive leads of the twist-loc caps to solder mount a 90 degree angled term strip of 3 leads, and use the leads to hang your new caps off of. Solder the ring term to the old positive lead of the old cap and disconnect all wires from it. Reconnect to your new terminal leads right above where they used to hook up and reconnect as required, making sure you remember that HV caps in many transmitters of that era are floating above ground,  with the minus side of one cap going to a B- point above ground or chassis
potential. if he can is insulated from ground thats whut ya got. Believe both TX-1 and DX-100 are this way.

A couple of things...

Modern caps tend to be substantially smaller for the same values than older ones.
You can generally increase any cap that is doing filtering (usually an electrolytic cap) in both voltage rating and value at least 100% and gain benefit and margin.
For small caps, non-polarized type (not an electrolytic) it is a good idea to put in film type caps today. Again, higher voltage rating is often a very good idea.

In an old rig, it's often a good idea to replace all of the filter caps - and all of the signal path caps as well. To keep the freq response the same in the signal path, use the same or very similar value capacitance (ufd), higher voltage rating is ok fine. You can substitute a 0.2 ufd for a 0.22 or even use a 0.3 in 99% of all situations. There are a few circuits where the actual value is critical, but not that many.

It is fine to substitute a film cap for an electrolytic, IF you can find the film cap and it doesn't cost an arm and a leg. For example there may be a 5 ufd. cap used as a bypass on a cathode - a film cap in that slot will actually perform better, and probably last longer (if that matters).

I'll go along with the don't float ur choke - but floating it temporarilly might be a way to make certain that you do have a possible short to ground inside the choke... KEEP UR HANDS OFF FLOATING CHOKES!!  :o

Btw, those twist-loc caps with the cardboard sleeves on them? Those are the ones that are floating above ground, they have a phenolic mounting base... do not remove the cardboard, and if it is missing, replace it with heat shrink, or tape or something insulated!!

                      _-_-WBear2GCR

PS. one does not have to buy new twistloc caps - you can generally just install regular single caps under the chassis to substitute for the two or three (maybe 4) caps that were internal to the twistloc unit. I've even substituted for just one section that went bad...

I found one of the 6CA7 sockets had significant carbon tracks as well as pin 3 (plate to modulation xfmr)) had a cold solder joint.  Pin 4 measures infinity.  Socket on topside of chassis looks healthy; no cracks.

In regards to floating the choke above ground, is there a way to rewire so the case is not hot?  Or should I just wait until I get the rectifier circuit repaired with new parts when those arrive?

Russ

Just change it to negative lead filtering and the voltage will be only a couple hundred volts of ripple across it and you won't have to float it.

GFZ, there are two wires from the choke: a red and a black.  The black wire is soldered to an insulated post bolted to the chassis.  This point is the middle of the diode string.  The red lead is connected to the large double section resistor (bleeder?)  Are you saying to reverse these two wires?

Russ

Russ,

As far as I have heard the HV choke shorting to the core or case is not a common failure point in the TX-1 and unless you have good reason to believe that it is shorted or "leaking" to ground I would leave the power supply as designed by Heathkit.  Realistically, this choke is not at that high a voltage above ground since this is a transmitter and not a 4-1000 amplifier and the choke was designed/specified for this type of service.   Again, I would caution you that you may run into an issue if the plate transformer in the TX-1 was designed to have the center tap at or very near ground or else you may run into an internal arc; this is the same reason that some center tap transformers are not usable in a full wave bridge as the center tap was expected to be at near zero volts.  Furthermore, if the choke ever opens up then the center tap is going to be at a very high potential to ground and this may well lead to the demise of the transformer if it was not designed for this voltage level on the center tap.

At the very least I would want to get the rig to the point where identified problems (such as the rectifier problem you found) have been fixed and then troubleshoot from there.  If you start making a lot of changes now it will be difficult for you to determine whether the original problem has been fixed or if additional problems were created during modifications.

If you do want to go ahead with negative lead filtering then you will need to lift the center tap of the plate transformer (T-2) from ground, disconnect choke L-30 from its connections to V-16 pin 2 (or where it connects to the current rectifier string) and where it connects to R-52, C-1, and the "bottom" of the modulation transformer, and then re-connect L-30 between the center tap of T-2 and ground.  You will then have to place a jumper between V-16 pin 2 (or where the choke was originally connected) and the junction point for R-52, C-1, etc.

Rodger

Time for an update.  Been busy studying the manual and relating the rig's wiring to the schematic.  It's fun but has been a sharper learning curve that previously thought.  Been identifying parts, numbering conventions and component color codes, and comparing physical layout to the schematic. 

The electrolytics and diodes have been replaced in the Apache.  I used the convention of  calling the marked ends of these components as the cathode or negative.  Attention was given to polarity shown on the schematic as well as when the old part was unsoldered.

Found one of the two 15K/5 Watt resistors to be 200K ohms+.  I replaced both with what I remember as being a 25K/20 watt wirewound milatary surplus type.  Diameter is .5" with a hollow core.  Is this OK to use?

The plate switch was replaced with a 3 amp Radio Shack.  The original specs call for 6 amps or so.  Is 3 amps suitable?

Upon firing up the AC to test my work (removed all tubes), the lights came on a little hum and a minute puff of smoke came from the modulator compartment.  I hope it isn't the audio choke or worse, the LV filter choke.  I double checked wiring from that point and tired again.

When I click on the plate switch to operate, the relay does not click in.  There is 120VAC on both lugs measured from chassis ground to each lug.  The lugs traced back to strip JM are as shown in the pictorial.  The relay tested fine when removing the relay and connecting to a 120 power cord.

No HV at all.  There is a 5 VAC and a -200 volts reading in the left and right power supply compartments.

What should I do next?  May I have your help?

Russ

That would depend on where it is in the schematic and what its function is/was.
The type of resistor is fine. IF the value is correct or reasonable depends on what the resistor is supposed to be doing.


Probably not for long.
But if it is a DPDT you can just parallel two contacts!  ;D


Well, if there was a puff of smoke something fried.
I'd look for shorts to ground with an ohmeter. Also, look for any signs of bulging caps, or cracked or burnt resistors. Your nose can help the search. Sniff it out - UNPLUGGED FROM THE AC. Something burnt. Find it.

Next step is to go back to the basic troubleshooting method I described before.
There are three main power supplies. B+, LV & bias.
You need to fire them up one at a time. That will require desoldering the AC going in to the transformer you are not testing. I'd start by testing the LV only.

IF you had all the tubes out, and the PS is using tube rectifiers, there was no connection to the filters, and no DC. Sounds like you had the rectifiers in place. That's a no-no in an unknown rig, unless you don't mind smoke.

Test one section at a time.

So you have to check the AC out of the transformers, THEN put a rectifier in place, preferably without there being any of a connection OUT of the PS filter... a series'd 100 watt incandescant lightbulb with the AC mains, OR better still a "Variac" (tm General Radio) to bring up the mains slowly is the best idea. That limits the current and voltage available, for testing. A dead short and the bulb will show full brightness, otherwise it will share current with the transformer, which is not drawing much current without a load... so probably not full brightness...




Again, the idea is to break down the testing to specific supplies and go from the AC input out through the filter to determine that the power supplies will make the requisite voltages.

Without any other circuitry connected to the supplies the voltages will be higher than shown in the "book" - but it will work. After you have power supply voltages working, you can then connect each supply to the rest of the circuitry, ONE at a time - testing the related circuitry for function. Start with the LV DC supply and you can test the things that it supplies. Then check the bias supply & HV power supply. THEN try it connected to the circuitry in the rest of the rig. WITHOUT THE 6146 or 6CA7 tubes! That way you get to not draw any real current and see if any of the passive components want to smoke. Again, a series bulb or variac is a good idea to both keep the voltages down where they want to run and to limit current in case of a dead short.

Next, you can check to see that the relay works, and that there is B+ being supplied to the 6146 plate caps in CW, and then you can try AM and see if B+ flows through the mod iron to the plates of the 6CA7s...

You can test the VFO's operation with only the LV supply, for example...

I'd guess that you may have put a cap in backwards, although that's just a guess.

Appreciate your response, Bear.  A structured approach is much needed!

Do you recommend I plug back in all tubes except modulator and RF tubes ?

The series light bulb...  If I follow you correctly, I can use an incandescent bulb to prevent higher voltage and current load capacity, and as a visual indicator?

You say, lift all of the AC input leads except for the LV transformer...  I can do that.

By the way, I replaced the Heath AC line power cord with a 3- wire 16 gauge cord with the green wire going to chassis ground.  Added a chassis mounted fuse holder and wired to the input line caps on rear apron.  Is this the proper method?  There was no double fuse AC plug when I got the TX-1.

Can I use 3 amp fuses for testing purposes?  I've got a couple of 7 amp.

I'll replace the plate switch with a higher amperage rating.

The HV filter cap(s) has a series of "O's" within a color band down the length of the cap.  The numerous other caps replaced have a series of dashes to indicate the negative terminal.  Is there and significance to the O vs. dash, such as plus and minus?  Or is the marking convention for Xicon caps universal in that a banded terminal is always negative?

Thanks.


Russ

Not exactly, please review what I wrote before... first get the power supplies operational and certain. Then sequentially fire up the LV supply with the smaller tubes and make sure that they are working, such as the VFO. Then fire up the HV supply WITHOUT the larger tubes that use the B+ voltage. Make certain that screen voltage(s) and B+ and bias is being applied to the proper pins and locations. Only then try to put in either the outputs or the modulator tubes to test them.


Yes, but an ammeter and Variac are preferable, as is an ammeter with the bulb.


Well not all of the wires! Just one leg of the input to a given transformer is needed, or if there is no voltage applied until you flip a switch (and the switch works) then you don't need to do anything on that one.  ;D


In theory this is fine. Wired what to the input line caps? you mean the feed-throughs for the AC mains? Fine. Some ops may not prefer the AC grounded chassis because of RF issues, but that is for another day...

Sure, if that is less than the thing draws when you turn it on or flip a switch...


Dunno. Look at the caps carefully, most caps have either a + or a " - " indication and in the case of those that have the indication all along the length, an arrow points.

Fwiw, most caps are built with the "can" being negative, the " + " terminal is usually in the middle of a plastic or rubber circle and the connection is usually a nub with a wire coming out - in the case of an Axial lead cap. The radial lead type with the terminals on one end are usually labeled or indicated by a symbol or color via a legend on the side of the cap.

You can check the Xicon website for that specific cap's labeling I would expect.

Or post a jpeg of it here and someone will figure it out...



        _-_-WBear2GCR

Bear, yes, the caps are the feed-throughs on the back of the rig.

The VOM has an amp meter function: small milliamp ranges up to 20 amps.  I'll need some instruction on testing current (AC and DC), such as lead polarity in a DC circuit.  I'm assuming the meter will be in series with the circuit and completing the path if the leads are attached to give a forward meter reading.  Wheras, AC current the leads are interchangeable with the test points.

Appreciate all the help on this forum.  And the patience!

Back to the Apache.

Russ

Hey Russ,

Would ya mind sharing your callsign with us?
That would be nice, if you would...

And yes, you seem to have the right idea on the Ammeter...

         _-_-WBear2GCR

Call sign is WA1JFX, located in Maine, Bear.

I just replaced the plate switch with a 10 amp DPDT toggle.  Also wired a light bulb in series on one side of the AC line.

Powered up the rig, moved plate switch to transmit to hear the relay click in and see dim light from the incandescent lamp.  I must have made a mistake with wiring the first replacement switch.

I'll get some readings on low voltage and let you know what I find.


Russ
WA1JFX

Hi Mack.

Yes, I'm enjoying the challenge and realize I've got a lot of learning in store.  Thank my lucky stars for this forum!

It's something in the modulator section or close by.  That's where the smoke signal and sound came from I believe.

I plugged in all the tubes except finals and powered up the rig.  The series light bulb glowed dimly.   Then switch on plate switch to hear no relay click.  And the light bulb became quite bright, so I shut off the AC.

When pulling all of the tubes in the modulator compartment sockets and flipping the plate switch on, the relay clicked and the bulb had a dim glow.  I know, Bear, this is not what you said to do.  So, I better begin following orders or I'm going to pooch something else.


Russ
WA1JFX.

I guess the lightbulb might glow brightly if sufficient current is being drawn by the rig. May not be a fault...

If the rig is supposed to draw 3 amps when keyed, that would be ~300 watts. So it might be reasonable for the 100 watt bulb to be pretty darn bright. Of course, it is tough to pull 300 watts through a 100 watt light bulb!  ::) ::)

Hmmm... so that might be how the bulb limits the current... I'm not sure.

You might want to test the modulator or else test the VFO and then key it for CW only, for a first smoke test.

Resistors tend to make smoke, fyi... especially carbon resistors. The show the heat by having the colors change. I just proved that point in the VFO in my Valiant Duece earlier today.  ;D

How close are you to Timtron up thar in Maine??

              _-_-bear

Tim HLR is about 80 miles away from me, Bear.

Russ
WA1JFX

Hey Russ,

If ur really having too much trouble with it, and depending on what sort of horse and buggy roads you folks have up in Maine, it might be worth the trip to Timtronia and have the expoit have an "up close and personal" meeting with ur 'Pache?? That is, if he is willing...

You own a 'scope Russ?

That would help you a bunch.

                 _-_-bear

Nope, don't own a scope, Bear.

You're right on the word trouble and I surely would be better off to have Timtron's expertise, so that's what I will work on.

Thank you.

Russ
WA1JFX

Negative lead filter choke. Remove Choke leads and and connect the two points with an insulated wire. Now find the HV center tap coming out of the HV transformer.
Disconnect the lead from the transformer. Connect the CT lead from the HV transformer to one lead of the Choke. Connect the other lead of the choke to the place you just removed the HV transformer CT from.  This puts the choke in the negative lead of the supply.

Russ,

Don't give up hope yet!

I supposedly know something about what I am doing... yet on an Apache that is still boots up on my bench I spent at least 2-3 days in the rear corner (underside of the chassis) near where the AC line comes in trying to find a good reason that the voltages that were going to the modulator section were just plain wrong when everything looked absolutely correctly wired and perfect!!

Well, it turned out that the problem was very high on the list of all things that can go wrong - actually the number one thing that goes wrong with kits: a solder connection!

Fyi, the list is: (skipping outright miswiring)
1- solder connections
2- capacitors
3- resistors
4- active devices: tubes or transistors
5- everything else

What was wrong with the supply was that the cluster of wires that went back to ground via that solder type terminal strip that hangs on the inside of the rear chassis side has multiple wires on it. At least one of them was held in place and looked perfectly fine under close inspection (magnifying glass!). BUT, you could only see it from the top, and the wire(s) that counted most (center tap return) was actually held in place by onlyrosin!! Looked good, held well, but wasn't exactly electrically connected, there was a lot of leakage, so it sort of worked!  ::) 

I got seriously PO'd at it after that, and haven't gone back to it yet... I will though.

I figure the alignment of the planets needs to shift a bit first...  ;)

So, don't bail on it yet!
Remember it did work, and it can work!

You can find the problem(s) - and when ur done, you'll really know your rig well, and if something ever goes south again, you'll really know what it is and how to fix it!  ;D ;D

                    _-_-bear

Everything Bear said with one addition:

the ability for you to solder and solder well, using the correct tool for the job, from 3 wire grounded 30 watt iron with static mat for IC's and hollow state to 300 watt gun for soldering/bonding heavy rf strap direct to chassis is 50% of the game. After that comes inspection ability, to be able to see or smell or hear what's wrong, followed by everything else. You'll get there.

Russ, if you cant get Tim to help you out, bring it up to the Bangor area. I will be glad to help you out on a weekend.
Regards,
Gary...WZ1M

Thanks Bear, Derb, and Gary for your offer to help.

Lifted one leg of each transformer secondary LV abd HV.  Got a variety of low voltages" 5 volts; 6 volts; 125; 320; 600.  The HV windings intially read in excess of 1000 volts on my VOM highest range of 1000 volts.  But after several tests the HV AC disappeared.  When I turn on the plate switch the relay clicks and the series light bulb emits a dim glow but no HV.

Resistance between both HV xfmr red leads is 65 ohms; 30 ohms either side of center tap.

Suppose the HV transformer is bad?

I've gone over the Apache head to tail and corrected several errors I made,  The process of removing one leg and then testing for a short and presence of voltage has been a good exercise.  The schematic is not as foreign to me as it was several weeks ago.

Russ
WA1JFX

Russ...!

Please pull out a handbook and read the section on types of rectification, filters and power supplies!!

Then identify the types of set ups used in your Apache.

You'll be wanting to check the AC on the secondaries - according to both what the handbook says the voltage relationships will be AND (if you have the manual) according to what the test voltages page says by Heath!

There are going to be 5vac, 6.3vac, and maybe 12vac filament windings.
A bias voltage is going to have a winding too.

But ur looking for the secondaries that provide "juice" to the rectifiers first - IF ur "lifting" transformer legs.

But - You don't need to do that - just pull the rectifier tubes and check the voltages on the bottom side or from the top side, once you ID the pins on the rectifier sockets.

That will tell you if the AC is present properly.

With the rectifiers in place, and the wires going AWAY from the filter components (caps and  if used, chokes) removed you can check the DC voltages.

Again this is where I suggested a bulb in series to knock down the unloaded DC voltages enough so that you don't over voltage the capacitors...

Doing this ought to take about an hour maximum, including identifying the various supplies and where you want to go to test the voltages.

IF THERE ARE NO BIG TUBES IN THE RIG THERE IS NOTHING TO DRAW CURRENT.

You can also just test the B+ voltage by merely throwing the plate/transmit switch in the CW position, and looking for B+ on the plate caps, or off the RF Choke or underneath the chassis. You'll need the rectifier tubes for the B+ in place to see DC from that supply.

There are TWO supplies: a high voltage (~700vdc or so) and a low voltage (max voltage is (~300vdc, iirc). Separate transformers, separate rectifiers.

Test separately.
Refer to schematic for typical voltages.

The low voltage first.
The HV second.
Rectifiers removed in the same order for AC voltages, then with the rectifiers installed, respectively for DC. That means you test the LV AC and then the LV DC. Then the HV AC, then the HV DC.

Once those voltages are found to be ok - then you can go forward and test the functionality of the RF section, then the Modulator section.

HANDS OUT OF THE RIG AT ALL TIMES!

Read the handbook section on how power supply rectification and filtering is set up before doing anything more. My 2 cents worth...

           _-_-bear

Hey All! Here's my 2 cents in this pot. I tried to load up the Apache today to run with the SB-10 on the vintage SSB nets. I'll I got was low B+ and a blown fuse. So I yarded it out of the cabinet and on to the bench. Someone had already replaced the HV tube sockets with ceramic ones. No short apparent when the rectifiers were pulled. I lifted the plate caps on the finals, and still had the short. Then God must have smiled on me today, as the very next item checked proved to be the problem. C49, the bypass cap at the base of the PA plate choke, is shorted. I removed the screw from where the choke attaches to the side of the final cage, and with the cap's grounded lug floating, NO SHORT! The rig loads up as good as ever! Maybe this will help someone else along the HV way of the ol' Apache. I sure am lucky that it was this simple, and I stumbled on the problem with a minimum of diassembly. I don't know if you checked the HV  circuits at this end, but it may be worth a try. I will definitely use a better rated cap for the replacement. Good luck!
Norm K7NCR

Good deal, Norm, thank you!  I'm glad to hear of the victory.  I'll check the bypass cap on my TX-1 here.

I've got the rig so it doesn't pop fuses anymore.  Just discovered by disconnecting one of the AC primary leads to the plate power supply that I'm able to tune the driver and grid.  But if I connect the HV I'm not able to tune the driver and there is excessive voltage and current readings on the rig's meter without throwing the plate switch.

This new revelation is encouraging.  Hopefully, I can soon get the rig fixed and on the air with the help of one of the Maine ham.  I'm a workin on that, and will let you all know of the outcome.

**********

I picked up a 1994 ARRL handbook.  Wow, this is serious business.  The technical aspects are a science for sure.  Congratulations to all of you who have learned and thanks for sharing your time so far.

Russ  WA!JFX.

Russ,

For working on units that use tubes a pre ~1969 handbook is best. Late 50s and early 60's are pretty good that way.

As far as your HV supply... obviously there is some issue relating the HV supply.

Looking at the schematic, comments refer to the HV supply:

If you remove V16 and V15, there will be no DC.
So, if the unit does not blow fuses then the HV tranny is probably ok.
You should be finding the filament voltage (AC) on pins 2 & 8 for each rectifier tube.
Next, with the unit OFF and unplugged from the AC mains, and checking the voltages using a DC voltmeter at the junction of C1 and L30 to ground, and then between C1 and C2 to ground, IF it is zero, then: change to ohms and look for ~15kohms (may rise to about that after a few seconds or so) across C1 and also across C2. IF the ohms reading seems to be significantly below 15kohms (the shunting bleeder resistor value) then you have likely a shorted filter cap.

You can REMOVE the wires that goes from the junction of C1,R51,L30  and measure the B+ voltage there with the rectifiers put back in. The plate switch turns on the primary of the HV transformer. Switch off, no HV.

Looks to me that the plate meter is actually a CATHODE meter, so if you remove the 6146 tubes (again, make 100% certain there is no B+ on the plate caps before you touch them - UNIT UNPLUGGED!) there should be NO meter movement.

R20 looks like the shunt that the plate meter measures.

So, if the thing draws HV with the 6146 removed, but works ok with that wire going to the C1 junction removed it has to be some sort of short elsewhere.

Looking at the schematic, it appears that the B+ is fed from the C1/L30 junction to the bottom of the Mod iron (T5), and to the mode switch M7 - which is in the CW position in the schematic - meaning that that switch essentially is shorting the mod iron by applying the B+ to both sides of the winding. In AM it will apply the B+ to only the lower side in the schematic. See?

So, no matter what, IF you remove the wire that comes off T5's secondary (the side that we're feeding in the B+) and which then goes to the junction of L16 and R29, then nothing is going to the RF section.

That wire is pretty easy to find, because it goes to the bottom of the RF choke in the RF final tank compartment and is DC connected to the plate caps of the 6146. So you can take the ohmeter and look for it on the bottom of the chassis (again assuming no DC present, and checked for first). Then desolder the wire either on the bottom of the RF choke or at the terminal strip that is likely near the mod iron. Then if you fire up the B+ with the mod tubes removed, the only things in the circuit are the mod iron and what comes from the rectifier tubes.

This is how to isolate the location of the fault.

Although it may just be that pesky RF bypass cap - C49.

So you do this stepwise... either from the V15/16 side forward or back from the 6146s, then to the V12/11 combo, then back to the filter caps, then to the V15/V16...

Ok? Make sense now??

             _-_-bear

Good news!  Today I got the Apache to produce 100+ watts output into a light bulb and wattmeter.

For the past two weeks, I've gone through the rig checking component values and tracing the wiring.  There were a couple of bad resistors, a bad 12BY7 and some of my own cold solder joints.

Last night I blew a cap.  I had plugged in the 5V4 wrong - the octal key pin was broken off.  Today the filament let go in the 5V4, so I pulled the tube and soldered a 1N5408 on each 340 volt HV lead of the low-voltage B+ at the pins on the socket and soldered them togeter for a B+ feed to the filter choke and caps.  The voltage measured 466 volts DC; the schematic calls for 370.  Can someone tell me how to properly solid state the LV B+ (5V4)?

After tuning up the rig for full output, smoke came out of the LV filter choke.  This prompted me to think I had used the wrong rated diodes and too much voltage was getting into the circuit, so I cut the diodes tie-point so only one side of the transformer and one diode in series was feeding the filter choke.

I let the filter choke cool down for an hour and fired the rig up again.  I now measure 444 VDC at the filter choke and caps; still too high, but the rig still puts out 100 watts on CW and AM.

The rig has been powered up for testing while the chassis is in a vertical plane vs horizontal.  I don't know if this is hard on the internal tube parts, such as sagging filaments, etc.

Russ
WA1JFX