Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
TR4CW tune cap arc
|
I had left the rig powered on overnight after working a number of guys.? Came back the next morning and the rig was showing no life.? Fuse was popped.
With the rig on the bench, I could turn on the power and after maybe 20-30 seconds, I could see an arc starting on the tune cap. On close examination of the tune cap, 4 of the plates in one section had arced enough to have slightly melted away a bit of the plates on the fixed half. Repaired the damage and checked the cap out with the HV leakage tester - looked good to about 1500V or so. Put it all back together and almost put it back on the shack shelf when it occurred to me.? With the rig sitting at idle, there should be NO voltage across the tune cap.? That assumes the coupling cap was working properly in it's DC-block role.? I replaced the 2700pf/2KV with a 4700pf 3KV ceramic I had in the junk box and then put it back on the shack shelf for check out. Tested the old coupling cap and the leakage even at 1KV was only slightly higher than the new Vishay ceramic part I had put in as the replacement.? Even warmed it up with the heat gun - no change.? This is pretty weird as I almost never see ceramics leak but maybe they do. The rig is working fine now although power is about 1/3 to 1/2 what I would expect.? The unloaded HV was OK when it was on the bench and I'm thinking there may be another problem.? I can't imagine that a leaking coupling cap, arcing through the tune cap, would damage the finals though. Wanted to toss that scenario out and see if anyone on the reflector may have run into a similar case in the past. HNY! -- 73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com |
|
That is a good point Jerry.? I should look at the coax switch that this rig feeds into to see if it's open or shorted when not selected.? Did not think of that but it certainly makes sense as a possibility.? Especially since I have a T4C as well as the TR4C and the note on the switch is not very clear.
toggle quoted message
Show quoted text
I've found myself selecting the wrong rig among these two a couple of times.? Maybe I won the lottery the last time and had the pleasure of the arc event as my reward for not paying attention to details.? And not taking time to properly label the switch positions.? Just the sort of thing Murphy loves to do here as well. 73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com On 1/9/2025 12:16 PM, jerry wrote:
I once had a tube transmitter arc across the tune cap when the output SO-239 was shorted to ground. |
|
On the other hand, this happened while the rig was just sitting overnight.
toggle quoted message
Show quoted text
And assumably not transmitting. - Jerry, KF6VB On 2025-01-09 10:25, Jeff AC0C wrote:
That is a good point Jerry.? I should look at the coax switch that |
|
Which reinforces the bromide that one should never leave vintage equipment powered up and unattended.? I try to avoid this situation, even with rigs that I have reconditioned.? Steve Wedge, W1ES Time flies like an arrow. Fruit flies like a banana. Sent from for iOS On Thu, Jan 9, 2025 at 13:46, jerry-KF6VB <jerry@...> wrote:
On the other hand, this happened while the rig was just sitting |
|
I wonder if something in the VOX circuit malfunctioned, allowing the transmit relay to pull in? I too never leave old stuff powered up.? Glad that seems to be the worst of it. John K5MO On Thu, Jan 9, 2025 at 1:46?PM jerry-KF6VB via <jerry=[email protected]> wrote: On the other hand, this happened while the rig was just sitting |
¿ªÔÆÌåÓýThat's really why I posted the scenario here.? I was hoping that
with the history here on the board, there was some known sort of
"this does not happen often but I've seen a couple of similar
cases over the decades" with a root cause that is unlikely.? The logical and most obvious explanation (failed coupling cap)
tests fine even with 1KV applied and tests with vertically no
leakage compared to the new one.? Of course that does not mean
there is some physical mechanism where the cap could be low
resistive and then fully functional, I would guess.? Just never
encountered a ceramic failing like that.?? Got to say, the VOX
failure is a good out-of-the-box thinking idea.? I do appreciate
the comments on all of these...? Going to run that rig another few
days and see if it continues to behave properly going forward.?
It's really a lovely TRX.? And has a very sweet CW note. I hear what you guys are saying about not leaving gear powered
up.? But I'm not sure there is much benefit to something failing
while you are sitting in front of it as opposed to while you are
in the shack but not actually looking at the rig, or in another
room.? Most rigs that I've had which failed while I was using them
just stopped.? On a couple of occasions I would hear something or
see something but that's been the exception.? My objective to leaving this rig run a few days is to get some hours on it.? Get those infrequently used caps reformed nicely.? Get the moisture baked out.? Get everything up to and held at operating temp.? And in my case apparently, if it's going to blow up, then do that also.? With the gear that's in the lineup and used in rotation here, I would prefer it to work when I want to use it.? Not be an adventure in "well, it worked the last time I tried it - hope it's going to work now!"? For that drama queen role, I have an otherwise very fine TS-820S which fills this "reliability question mark rig" function completely.? ha ha. Uggg.? More snow falling now. 73/jeff/ac0c alpha-charlie-zero-charlie On 1/9/2025 5:19 PM, John K5MO via
groups.io wrote:
|
|
The thought is that you can remove power immediately and prevent further damage to unobtanium parts. Transmitters for example have been known to go into TX with maximum possible plate current when the bias supply fails.
On Thu, 9 Jan 2025 18:11:06 -0600 "Jeff AC0C via groups.io" <keepwalking188@...> wrote: I hear what you guys are saying about not leaving gear powered up.? But -- 73 -Jim NU0C |
|
Lyndon VE7TFX
Jeff AC0C writes:
I hear what you guys are saying about not leaving gear powered up.? ButIt does if it fails in a way that burns your house down. |
|
That's a good point Jim!
toggle quoted message
Show quoted text
73/jeff/ac0c alpha-charlie-zero-charlie www.ac0c.com On 1/9/2025 7:41 PM, Jim Shorney via groups.io wrote:
The thought is that you can remove power immediately and prevent further damage to unobtanium parts. Transmitters for example have been known to go into TX with maximum possible plate current when the bias supply fails. |
Jim Shorney
to navigate to use esc to dismiss