I had considered the Bassman combo I built this summer to be finished, but every once in a while it would make a crackling noise on certain chords or notes, or when thumped. I'd take it out of the cab, put it on the bench and could not recreate it, so I'd put it back together and it would be fine for a while. Then, I'd pull it out for some perspective customer, and it would do it again. Quite frustrating and embarrassing. I left it apart for a couple of months until today. This time I was able to find that if I rotated the power tubes just a certain way, I could get the noise. This was on both tubes and both sockets. I figured it had to be a bad connection, (even though I am very meticulous) so I reflowed all the socket connections, but no change. Then I tried another set of tubes, same type NOS GT6L6B (really Sovtek 5881WXT), and now I couldn't get the noise while moving the tubes.
So now I figure it must somehow be the tubes, but I can see nothing obvious. I put them in my pan-vise and reflowed all the pins, and now the problem is gone. So it would appear, as long as the noise never returns, that there were dodgy connections at the pin(s) of both tubes. What are the odds on that I wonder? They are a matched set, so they must have been made on the same machine on the same day I suppose? Anyhow, I feel better that the problem wasn't because of something I did poorly, knock on wood.
It's weird, because it WAS working fine.....
Enjoy. Every. Sandwich.
Had an Orange tiny terror type amp come in where customer had changed the el84's and they just weren't passing signal very well. Inspected the tubes and that red enamel was all over the grid pins. Scraped it off and that was it.
Yeah, that was a good catch and dodgy pins is not something that would have been on my radar.
Yup....good find. I've managed to restore a problem power tube every so often, that was victimized by solder joints inside the tube base pins, after de-soldering then re-soldering the pins/tube wires.
Logic is an organized way of going wrong with confidence
The two half parts of the anode (plate) are joined into a one compact whole in two ways spot welding and mechanical.
The mechanical coupling of the anode (plate) tube into a compact unit is more susceptible to sound sensations when the tube is aged due, long work, weakens the getter, and micro-displacement inside the tube structure probably occurs.
Sound sensations can also occur when lead wire (from socket to tube electrode) loses elasticity due to age and heat, and then micronal displacement of insulating spacer and glass envelope occurs
It is noticed by a fine knock on the glass tube.
Last edited by vintagekiki; 10-07-2019 at 09:03 PM. Reason: spot welding
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