The AM Forum

My questions: (1) Could arcing caused by movement of the unsoldered wire connection to a pin on the tube socket for a 600 volt rectifier destroy the tube?; (2) Have you heard noise from a tube when it fails?

Background: Upon powering up my Apache yesterday, I heard arcing so I immediately shut down the transmitter. Inspection didn't reveal any thing amiss that I could see or smell so I fired up again and again heard the arcing, then I heard what I would describe as a fluttering noise immediately followed by an orange flash from the area of the 5V4 socket (presently a 5Y3 is subbed for the stock 5V4), transmitter went dead before I could switch power off.  One of two fuses in the stock Apache line-cord opened.  Visual inspection of the 5Y3 revealed no clouding of the glass envelope or apparent damage of the elements, but tube tester shows it is dead so I will assume for now that the orange flash was from the 5Y3. From where I was when the event happened, I could not see the rectifier tube.

Inspection of the rectifier tube socket reveals that the wire from the T1 secondary was wrapped around pin #6, but it appears that no solder was ever applied to it, so the builder must have missed it.  I moved the transmitter around quite a bit yesterday while working on a misaligned VFO capacitor shaft sprocket, and that movement for sure would have vibrated the chassis, so maybe the once-secure unsoldered wire that is merely wrapped through the pin holes got jiggled loose.  Photo attached.

Thanks for any thoughts you may have on this.

73,
Brad

I looks reasonably secure even without solder. The Apache has obviously had a  lot of physical movement over the last 50 years, so if it was "the problem" it probably would have surfaced earlier. Personally I would have used a 5U4 in place of the 5V4 rather then a 5Y3. I seem to remember the specs of the 5U4 were closer to the 5V4.

Maybe. How old are the filter capacitors?

Don't know. I bought the rig last May - have not changed the filter capacitors.

A leaky cap will overload the rectifier tube. Probably a good idea to check into the cap's age and replace if over 10 years old unless it is a quality part.

Pete - I don't have any information about the maintenance history of this Apache.  Considering higher line voltages would it be better to use a 5U4 (or other tube) for the rectifier permanently?

W2VW - Thanks. I don't know the age fo the capacitors, but the cap enclosures appear to be an older style.  I'll try to find replacements.

The last time I looked, it appeared that the 5Y3 didn't have the current handling capacity required that the 5V4 or 5U4 provided. You should check the tube charts. That supply pretty much supplies all low voltage B+ for the entire transmitter. And, as Dave points out, it the filter caps haven't been changed out ever, they're probably working on their hairy edge. I got rid of my tube rectifiers years ago and solid-stated both supplies (perf board, gaggle of diodes, board epoxied to 8 pin octal plug).

A 5R4 is a much better replacement plus the bit more voltage drop is good at high line voltages.

Carl

Carl - I was wondering about using a 5R4 after reviewing a 2010 amfone thread about a rectifier problem in a Ranger in which WQ9E mentions  higher line voltages. And I saw your note in my other Apache thread - thanks.

I soldered the unsoldered wire to pin #6 of V14 for the rectifier, plugged in a 5V4 I pulled from my DX-100B, replaced the open fuse and powered up, this time watching the rectifier tube. Within seconds it was glowing orange and there was that popping or snapping noise again, so I shut it off. It must be the cap as W2VW suspected. The rectifier tube appears to have survived. I'm guessing all filter caps are original so I'll replace all.  So far I have found sources on the web for all but the 125 mfd 450 V electrolytics.

Pete's suggestion of SS the rectifier interests me so I will search for that info in the database. I may do that at some point.

Thanks all for your thoughts.

73,
Brad