Where should I start: Troubleshooting hum in my CW signal on a Thunderbolt

[K1JJ]

Oh, and another technique that has helped in troubleshooting....

Many times a big plate modulated rig (or even a solid state class E drain modulated rig)  will have "talk back." This is audio acoustic feedback in the rig that finds its way back into the microphone creating a tone that then modulates the rig.

The question becomes, what part or parts is vibrating  during power up conditions?   Believe me, when it is happening and you are looking into the rig to try to determine where it is coming from it is nearly impossible to locate. This is because our hearing cannot differentiate well enough to pin the sound down to a single part.

What works really well for me is to focus the audio like a beam. Use a 1" diameter HV insulated 5' long  rubber hose (HV tested)  that you put up to your ear and point at the various parts. It may be a choke, mod xmfr, HV plate coupling cap, a pi-network connection, a relay or many other causes.  Plate tuning or plate coupling caps are notorious.  This technique will get you to zero in quickly.  After the suspected part is selected, pushing it with the plastic rod (under feedback operation)  will make it louder or change frequency. Then you know you nailed it.

Again, I need to say that these techniques are dangerous (deadly) unless you are very careful and know what you are doing. I realize that the safest troubleshooting is to use an interlock and never open the door of the cabinet, but sometimes we run out of options and closer examination is the only way to find a problem.

T

[WD5JKO]

Great news...

It would be nice to see a partial schematic to see what the connection to C19 and L7 does. This might help others in the future that find this thread.

As to troubleshooting things hot, for the 100 watt class rigs with B+ at 800 volts or less, I use a brand new wooden chop stick. I'd be leery to do that on the big rigs. Something plastic, and longer for the big rigs. Plexiglass, or Lexan are two options.

Quick story about a "Hot Troubleshooting" event that went very wrong. The guy was working for me back in the mid 1980's, and he was troubleshooting a vacuum leak in an ion implant machine that ran the ion source (similar to a tube with a gas fed plasma inside). The source had up to 120,000 volts on it. The guy told me about the leak, and that it was not leaking when everything was shut down and cold. I suggested he leak check with the source hot, but failed to tell him to only light the filament, without the high voltage on. As it went, He used a metal 1/8" OD tube to flow helium at the source...The helium ionized, and conducted like a wire into the man. The guy back pedaled about 10' into a storage rack, and the impact caused items on the upper shelves to fall on his head! He was pretty sore, and scratched up, but OK....

Back to topic....any heating or cooling with the HV B+ on should be viewed as dangerous. A freeze mist stream might become conductive to that metal can.

Good Job!
Jim
Wd5JKO

[W1TTL]

Thanks, guys.  And thanks for the stories. Glad he survived!

As requested, here's L7 and C19 per the schematic.  As well as the photo from the manual so you can see their proximity.

73,
Tony W1TTL

[K1JJ]

Great news...


Back to topic....any heating or cooling with the HV B+ on should be viewed as dangerous. A freeze mist stream might become conductive to that metal can.

Good Job!
Jim
Wd5JKO

Very good point, Jim.

I instinctively know this in practice but it should be emphasized.

I added this comment to my first post:

"Also, a hair dryer gun to warm parts and then freeze them with cold spray works like a champ to expose marginal connections.  (and bad solid state parts too)   ALWAYS spray cold freeze with the HV power OFF and caps discharged.  The actual spray stream may conduct current and fry you thru the metal can, and even more so if it's a HV RF point ...    Same precaution goes for heating with a hair dryer gun.  Keep the HV off as much as possible as a standard practice."

BTW, speaking of HV, ALL of my HV supplies in the shack are keyed. They come on only during PTT key up.  They are all cat-proof. And drunk-proof. You should not be able to touch a HV point anywhere in the shack without using tools or making a deliberate effort...  

[W1TTL]

I should also add that I followed the responsible vacuum tube ham's code:

1. Never work on a rig when tired.
2. Never work on a rig when drinking.
3. Never work on a rig when you're gettin' upset.

And yes, as soon as that Thunderbolt was back in its cage and singing the Ranger's CW note on the air, I mixed me an Old Fashioned.

73,
Tony W1TTL

[K1JJ]

I should also add that I followed the responsible vacuum tube ham's code:

1. Never work on a rig when tired.
2. Never work on a rig when drinking.
3. Never work on a rig when you're gettin' upset.

73,
Tony W1TTL

Yep, so true, Tony.

I think #3 is possibly the most common cause of fatal and not-so-fatal mistakes.  Getting POed is a primordial response from the cave days when we HAD to get things done fast or be eaten by a sabertooth.. :-)  It's only natural to get worked up when ANYTHING breaks and we now have to fix it. Fortunately MOST things aren't dangerous if we get emotional and go wrong.  

Too much familiarity and becoming too relaxed when working on HV is a problem too. I like to have a balance between being scared and respectful to HV.   It pays to make decisions and then review the ideas a few times before turning on the juice and doing tests.    And when parts blow up one after another, we MUST get away from the project to calm down - or suffer the high risk that is not necessary.

I need a good reminder of this stuff every so often. It can be especially dangerous when we've been away from radio for a while and kinda forget some of the rig layout and make a few errors here and there. Blowing up rig parts is one thing...  blowing off body parts is another....      

"And I said to myself, this is the business we've chosen; I didn't ask who gave the order, because it had nothing to do with [ham radio]!"    - The Godfather


T

[W1TTL]

Haha!  Good point about the sabertooth!  

Too much familiarity and becoming too relaxed when working on HV is a problem too. I like to have a balance between being scared and respectful to HV.   It pays to make decisions and then review the ideas a few times before turning on the juice and doing tests.    And when parts blow up one after another, we MUST get away from the project or suffer high risk that is not necessary.

Agreed.   I was probably overly cautious (is that a bad thing?) when working on the Thunderbolt and thought of Ross Hull the whole time, which kept me scared out of my wits and on my toes.  I would make sure there was no HV anywhere before touching anything, not to mention shutting things off at the breaker.  Ross Hull 3JU had his unfortunate day back in 1938 with his "television apparatus" transformer about a mile from my house.  I was told he accidentally touched the 6kV transformer under his bench while showing a doctor friend his kinescope.  I'm not taking any chances!

73,
Tony W1TTL

[KD6VXI]

Might be a good time to bring this up again.....

http://amfone.net/Amforum/index.php?topic=44457.0

--Shane
WP2ASS / ex KD6VXI

[W1TTL]

WOW Shane -- Ross Hull didn't fare so well with 6kV.  So happy you're here!!!

73,
Tony W1TTL

[W1TTL]

I just want to add something about the Thunderbolt's performance on CW:

It's nuts!  I am currently getting 900W out with my Ranger driving it into a G5RV on 80m.  Super happy.

73,
Tony W1TTL

[KD6VXI]

WOW Shane -- Ross Hull didn't fare so well with 6kV.  So happy you're here!!!

73,
Tony W1TTL

It was a life changing experience, to be sure.

Glad to still be here.  For 18 months it was somewhat touch and go.

But, my kids are happy to report (yeah, RIGHT), I'm still here alive and kicking!


--Shane
WP2ASS / ex KD6VXI

[N0YXO]

I have been following this thread just built the hi voltage board in my t-bolt was very careful the hi voltage safety switch was taken out before it came to me and after the first flash over was very gun shy turning the hi  voltage  switch on. Wound up building my own board I was lucky to have two good friends help me with it

[KA2PTE]

I just fired up my Tbolt after some time sitting around to knock the dust off it.

Curious if anyone else sees some small plate current reading
when idling in TUNE mode with the plate volts on?

I think this is normal from what I hear, but in TUNE you have something
like 230V on the screen, not the full 500.

[W1TTL]

Curious if anyone else sees some small plate current reading
when idling in TUNE mode with the plate volts on?

I see 50mA on the plates with the plates on, in TUNE, and idling.

I've been using the Thunderbolt on AM during the AM Rally... getting 300W carrier out on 80m.  Doing good on AM and GREAT on CW!

73,
Tony W1TTL

[N0YXO]

Tony at 300 wt are you able to see 100% modulation when I go over 250 wt my modulation starts dropping off I am using a rea to monitor my modulation

Charles N0YXO

[W1TTL]

Charles,

I finally had a chance to look at the modulation coming from the Thunderbolt.  The quickest way was for me to drag out my Heathkit SB-614 station monitor.  The scope is a bit tiny but I can at least see things.  Increasing the Ranger's coupling to increase output from 100W out to 300W out into a dummy load, the modulation increased.  I did not see a decrease.  I've attached a photo for what it's worth at 300W output (700W input), even though the picture is not that great (the trace is a bit out of focus).

Hope that helps.  

73,
Tony W1TTL