- Amps [BG]
|wighat ||12-03-2013 09:28 AM |
Tube socket tension question
My newly refurbed and 6550-converted 1973 Ampeg V4B is doing this weird thing that has happened three times now. It works great, sounds great for an entire gig. I leave it on standby during breaks. Turn it off at the end of the night. Next time I turn it on, it hums. So I re-tension the tube socket "springs" or what ever they're called. The amp works fine. For the entire next gig. Until I shut it off, it sits until I turn it on and the hum is back again. So obviously heat from the output tubes is causing the tube socket springs to open up. What can be done?
|P Town ||12-03-2013 09:35 AM |
You may have a defective filter capacitor in the power supply.
|InsanityAmps ||12-03-2013 09:43 AM |
Can you make the hum go away by wiggling the output tubes? Possibly a bad solder connection at one of the tube sockets.
|beans-on-toast ||12-03-2013 09:48 AM |
You pinch the socket terminal in enough so that when the tube is inserted, the terminal opens a little and clings to the pin. It shouldn't be slack. It could be that you are not closing the contact enough but you don't want to close it too much and deform the terminal. That could make the contact worse.
It could be that the tube pin or socket terminal is dirty or oxidized. When you clean it with a product like Deoxit, you need to apply it more than once and scrub the contacts to remove all the gunk. Proper cleaning can make a difference and provide a better contact.
As was mentioned, there are other heat related possibilities. A bad solder joint is another one.
|B-string ||12-03-2013 09:50 AM |
Also very possible the hum is from a tube. Hum can be induced from the tube heater to the cathode or signal (control) grid. A slight misalignment or sag. Disturbing the tube to retension the socket temporarily lessens the defect. After the tube has been fully heated the defect shows up after it cools down. They are supposed to work in just about any position, if they were not hanging upside down it may have not shown up.
|beans-on-toast ||12-03-2013 10:13 AM |
That's true. It is important to remember, whenever you have an issue, the first thing to try is to change the tube. It is the easiest thing to do.
If you can afford it, keep a set of "gold standard tubes", ones that you know that work to use when testing. In the case of a spare pre-amp tube, it doesn't cost that much. Power tubes are a different story.
|wighat ||12-04-2013 06:12 AM |
Thank you all for your responses. It will be at least a couple of weeks before I can really look at that amp.....today I am crating all my gear, putting it on a freighter and heading back to Texas.
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