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Author Topic: Ranger problem, 6AX5GT arcs  (Read 4286 times)
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WU1T
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« on: December 24, 2020, 09:15:59 AM »

Hello, I am a long time listener to AM on 75m going back to about 1990, but I have never operated the mode. Recently I came across a Ranger on Craigslist that was being sold by the original owner's son. The ham had just passed away. The Ranger is in practically mint condition inside and out. I was told that the original owner had used it little since he bought it, then put it on a shelf where it sat for decades. The amount of dust inside reflected that. Once I cleaned up the dust it looked new/mint, as I mentioned. There are no mods that I can tell. It even came with the original manual in archival condition, where the owner noted in the back of it that he had purchased it at a Radio Shack in Framingham in 1960. Anyways..

The power cord was completely rotted. It was a 2-conductor non-polarized job with two fuses in the plug. I replaced this with a 3 prong cord, and one of the original 5A fuses on the hot lead. I connected the ground wire to a locking solder lug that I added to the chassis.

I brought the radio up in standby mode on a variac. Meter and band scale light up, and at around 100 volts AC or so I saw a blue flash. The 5A fuse blew. Replaced it. Brought it up again just to see if I could isolate where the arc came from. Indeed again at around 100vac or so, a blue flash from the 6AX5GT and again the fuse blew. I also noticed that this tube gets SUPER hot to the touch, even in the 20-30 seconds or so that it is powered on before I hit 100vac. None of the other tubes seem to get warm or light up although it's a little hard to tell. So that's where I am at.

I'll be the first to admit that I am pretty new to troubleshooting and repairing vintage equipment and do not have a strong electronics background, but I would like to get this radio operational. Any suggestions for a noob on next steps would be appreciated.

73,
WU1T
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KD6VXI
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« Reply #1 on: December 24, 2020, 10:06:51 AM »

Blue flash means gas.

Replace the tube.

However, that radio will most likely need a complete capacitor replacement.

--Shane
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WD4DMZ
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« Reply #2 on: December 24, 2020, 10:12:27 AM »

Looking at the schematic I would suspect the filter cap is shorted. Cut it out and replace it. Hopefully you did not damage the power transformer.

About 3 years ago I acquired a really clean Ranger 2 from an estate. I brought it up slowly with a variac over the course of a day but had a 60 watt light bulb in series with the line cord. If the transformer or anything in the circuit is damaged the full current will flow thru the light bulb and prevent further damage. This must be an old style incandescent bulb. The R2 slowly came to life and I removed the light bulb.  It is a nice transmitter and I use it regularly.

Today I will start the process with a Globe scout 680 using the series light bulb to check the condition of the xformer windings. The filter caps will be replaced before I go to full power.

Rich
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W3SLK
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« Reply #3 on: December 24, 2020, 10:28:33 AM »

Let me add my nickel's worth of free advice here. When I bought my Ranger from my buddy and elmer Eric, WB4VVI(SK), he said it was blowing fuses and he didn't have the time to investigate it. So me and my good friend Duane, KK4AM, (sans KN0R), spent a day working on it. We found that the insulation that covered the solder lugs on the accessory socket had deteriorated, (like your power cord), and the lug had cut through it and was shorting to ground. We actually disconnected each power supply to finally track it down to the line that was causing issues, which so happened to be from the same 6AX5! As Emil Faber so elequently put it, "Knowledge is good!"
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
WU1T
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« Reply #4 on: December 24, 2020, 10:52:08 AM »

Gentlemen, thank you for your suggestions. I have a new tube on order via eBay. I will spend some time checking out that accessory socket, as well as poking around for any other hiding shorts. Also, I ordered the filter caps and bleeder resistors that are described at this site:

https://www.frostburg.edu/personal/latta/ee/ranger/interior/rangerinterior.html#powerinout

If you don't care to click the link, this person used two 33uF 450v in series to replace the stock 10uF 700v. As well as two 270k 3W bleeder resistors. If anyone can explain why this arrangement may not be desirable, I'd appreciate your thoughts.

Fingers crossed I didn't damage anything but, the radio was not on for very long at all so I am hopeful.
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WU2D
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« Reply #5 on: December 24, 2020, 11:05:51 AM »

There is Ancient and Old. The radio is ancient enough that it already needed cap replacement at some time...the repair is old. If you didn't have a 10 uF cap at a high enough rating, back in the day where electrolytics were BIG, the repair artist would find two capacitors of at least double the value and and at least half the voltage required, series them up and carefully use a the 270K resistors to make sure that the voltage divided evenly between the series capacitors. They are not really bleeders, but they do that too - lightly. So those caps likely must come out and be replaced, because they too may have dried up. You can do the same with two 33 uF caps or get a couple of 100 UF 450V caps and do the same thing and you end up with an 50 uF cap at 800V.
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WU1T
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« Reply #6 on: December 24, 2020, 11:11:21 AM »

WU2D, just to clarify, the radio has the original factory 10uF 700v cap. My proposed replacement is the series connected 33uF @ 450v pair described at the link I provided, along with the resistors. I've already ordered them from Mouser. I'll also get replacements for the other paper caps.
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W3SLK
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« Reply #7 on: December 24, 2020, 02:03:07 PM »

That one 'rf' choke looks like it has seen a little too much current at one time in its life!
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Mike(y)/W3SLK
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« Reply #8 on: December 24, 2020, 03:47:40 PM »


Follow the previous suggestions. The Dr. Greg does a nice job splanin the ckts.


My advise..

Pull the Rectifiers and try the dim bulb test. Change out, at the beginning, your 10 uF cap and then the LV filter cap. Then the bias supply cap(s). I learned the hard way to not change out multiple things at one time. Change out the first two caps, and see what happens.

Replace the Chernobyl resistor.

There are a few xperts here, and they will have the goods fer you.

Replace the Chernobyl resistor.

klc
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DMOD
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« Reply #9 on: December 24, 2020, 04:02:52 PM »

WU2D, just to clarify, the radio has the original factory 10uF 700v cap. My proposed replacement is the series connected 33uF @ 450v pair described at the link I provided, along with the resistors. I've already ordered them from Mouser. I'll also get replacements for the other paper caps.

Yes it would be ok to do that but I think what UD was saying is there are better ways of approaching Ranger PS upgrades.

I would also recommend checking the actual circuit you presently have with the schematic to see if changes have been made.

FWIW, here are upgrades I make on Rangers:


* Ranger PS Upgrades.pdf (98.17 KB - downloaded 136 times.)
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WD4DMZ
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« Reply #10 on: December 27, 2020, 08:21:58 PM »

Today I finished up the Globe Scout I bought myself for Christmas. It had the two original 12mfd 700 VDC filter caps in it. I cut one open and it was in fact two caps in series with no resistors. So, I replaced each one with two 33mfd 350 VDC caps in series with no resistors. One filter cap did have a 50k ohm 10 watt bleeder around it though.

Put it on the air this morning and had a nice chat with Russ in Erie, PA. The output is less than 25 watts but had solid copy for about 20 minutes. Audio is acceptable for now.

So, are the balancing resistors necessary? For this radio is seems not.

Rich
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WQ9E
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« Reply #11 on: December 29, 2020, 12:09:48 PM »

The original "HV" filter caps were produced with two closely matched caps in series and as long as they aged equally no equalizing resistors were needed.  But whenever I replace these, then I always use equalizing resistors.  The proper equalizing resistors for modern caps are going to be of high enough value that they aren't going to have a material impact upon existing bleeder/voltage divider resistors.

Whether you can get away with no equalizing resistors depends upon how close the caps are operated to the series voltage rating and how well they remain matched over time and temperature.  If I was using a pair of 450 volt caps in a 500 volt circuit, then I wouldn't worry about it but if the actual applied voltage is anywhere close to rated then equalizing resistors should be used to ensure the caps have their expected lifespan.

And when replacing filter caps, I always go for 105C or better rated parts since the price differential is very small.  When replacing filter caps in later gear (like SSB linear amps without choke input filtering) make sure that the caps are designed for high ripple service because this ripple is what causes capacitor heating.  In a typical 70s era SSB linear amp, the filter caps are seeing a repetitive high current charge/discharge cycle under load.  At one time, "energy storage caps" (intended for service in large studio strobe units and similar applications) were popular with builders because they put a lot of capacitance into a small container at low cost.  But these units were designed for intermittent charge/discharge service and had to be severely de-rated to live in an amateur radio transmitter supply.

Rodger WQ9E
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Rodger WQ9E
WU1T
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« Reply #12 on: December 30, 2020, 09:10:45 AM »

Hello, I thought I would update on where I am with this.

I replaced C77 with two 33uF 450vdc in series and 3W 270k balancing resistors. I replaced C78 with a 33uF 450vdc. I pulled all the tubes but the LV rectifier, and slowly brought it up on the variac. No problems getting to 117vac on the variac and hanging out there. Measured 300vdc+ across C78. Slowly added the tubes back, retesting each time. Finally, tested 600vdc+ across C77 with all of the tubes back in. So things are looking promising. No blown fuses, no smoke, no fire.

Unfortunately the caps I used are 85c rated, had I read the post above I would have tried to find 105c rated. What is the worst case scenario? Just shorter cap life?

I might try to put some RF out of it today into a dummy load and maybe also test modulation with the D104 that came with the radio. I will tackle the Chernobyl resistor soon as well. I really appreciate everyone's suggestions.
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W3SLK
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« Reply #13 on: December 30, 2020, 10:37:27 AM »

W1UT said:
Quote
I will tackle the Chernobyl resistor soon as well. I really appreciate everyone's suggestions.
Set yourself aside for a day undisturbed! My old elmer and friend Eric, WB4VVI(SK), had another Ranger that the VFO stopped working one day. We dismantled the VFO and found a completely unsoldered wire on a terminal strip, (it was clean! Never had any solder!). We resoldered it and put it back together. Everything worked FB but the whole process from beginning to end was about 5~6 hours. Take your time!
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Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
WU1T
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« Reply #14 on: December 30, 2020, 12:02:01 PM »

Yes I have read getting into the VFO to do the resistor can be amusing. I take it a wirewound resistor should be OK for this application? I have found numerous mentions by other hams of using a wirewound. I'd also like to know what the appropriate type of capacitor is to replace the "bumblebee" cap on the top side of the chassis.
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WQ9E
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« Reply #15 on: December 30, 2020, 06:35:48 PM »


Unfortunately the caps I used are 85c rated, had I read the post above I would have tried to find 105c rated. What is the worst case scenario? Just shorter cap life?

The 85C will be fine, the difference is in life expectancy and reliability.  Most vintage gear runs pretty warm and a lot of filter caps see a lot of ripple so you get heating from both inside and outside the cap.  Most original caps were 85C but better caps are available today and the price differential is small. 

I buy most passive components from Mouser and for common parts like filter caps it makes sense to order them in quantity if you anticipate doing a lot of restoration because the quantity discounts, generally starting at quantity 10, are often significant.

The Ranger is a little more difficult to replace the resistor inside than the Valiant (same VFO box but outside access is even tighter in the Ranger) but it can be done.  The resistor should go back in the box in order for the VFO to stabilize more quickly.  A 6AH6 can be used to replace the 6AU6 in the VFO and this provides a little better VFO stability, the same applies to the Heathkit VFO (VF-1, DX-100, etc.) which is largely a copy of the Johnson circuit much like the DX-100 was inspired to be a Viking and VFO-122 in the same box.

Every Johnson rig of this era that has crossed my bench needed the ball reduction mechanism in the VFO drive to be cleaned and lubricated.  It should provide very smooth tuning but over time the grease dries out and picks up grit which will cause wear to the ball bearings and even worse the shaft.  It is pretty simple to remove and worth doing for better tuning feel and to prevent damage to the mechanism.  I repack with the same synthetic grease I use for my tractor and pickup zerk fittings.

Rodger WQ9E
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