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Dirty-South Blues Harp forum: wail on! >
A Tube Fell Out
A Tube Fell Out
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Patrick Barker
460 posts
Sep 17, 2012
11:34 AM
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I don't know anything about repairing tube amps, so I'm hoping to get some advice on how to fix my amp (Fender Princeton) since one of the tubes fell out during a car ride. Here are some pictures of the tube that fell out and what I believe is the socket:
Is it just as simple as plugging it back in? Does anyone know which pins go where? How can I prevent this from happening again?
Any tips would be greatly appreciated! Thanks.
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tmf714
1263 posts
Sep 17, 2012
11:43 AM
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You should be able to plug it right back in-there is a small cut -out in the scket wall-align the small tab on the tube base with the slot in the metal socket.
There are various methods of securing the tube to the socket-spring retainers being the most common.
http://thetubestore.com/retainersetc.html
These mount on the phillips head screws on the socket seen in your last photo.
You may also want to investigate further to see WHY the tube came loose-if the tube is loose in the socket,it may be time to replace the socket itself.
I noticed in the picture if you look closely at what I beleive is pin #6,you can see a small crack in the base of the socket.
Last Edited by on Sep 17, 2012 12:00 PM
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ElkRiverHarmonicas
1293 posts
Sep 17, 2012
2:21 PM
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The tube will only go in one way, the right way. If it's not lined up, it won't go back in. the way you tighten a tube in the socket, is to carefully, with your fingers, not a tool, bend the pins out slightly - you don't want to break the pins. It won't take much bending, but they will go in a little more tightly. I've done it a million times probably on radios.
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David
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
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5F6H
1368 posts
Sep 17, 2012
2:44 PM
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If the socket is damaged, it should really be replaced, the part costs a couple of $, one hour bench time for fitting (I'm being generous - once the chassis is out it's 4/5 wires & 2 screws).
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Greg Heumann
1789 posts
Sep 17, 2012
4:44 PM
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"The tube will only go in one way, the right way." That's only true if the tube has a key "bulge" on the center black plastic. I can't see one in the photo. If it IS at all possible to plug the tube in more than one way DON'T DO IT. That's the rectifier tube and its inputs are typically 400-500 volts AC. At the minimum you could damage the tube; you could potentially do a lot worse.
IF the round center black plastic "guide" has a key on it (a part that sticks out from the circle) - THEN line it up with the keyway in the socket and all should be well.
I had experience with a poorly keyed tube that DID allow insertion in the wrong orientation. It was not pretty.
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/Greg
Last Edited by on Sep 17, 2012 4:44 PM
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ElkRiverHarmonicas
1294 posts
Sep 17, 2012
5:43 PM
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Yeah, Greg, good point. My experience, of course, is with radios, not amps, but tubes are tubes. I didn't look at the socket first time.
I can't get my head wrapped around why a five-pin tube is going into an octal (8-pin) socket. Then, when I look at the bottom of the tube again, I see it's octal, just doesn't have those pins.
I did some research on the tube and see that's the way it's supposed to go. and that there are no 1,5, and 7 pins on the tube. I had just never come across those.
From what I read, pins 2 and 8 go the filament... 4 and 6 to the anodes.
Patrick, can you look at the socket and see which are live?
The worst case scenario Greg is talking about would be that it catches on fire.
Greg, is that the key at 2 o'clock on the socket? Patrick, does that black thing visible at 2 o'clock stick up?
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David
____________________
At the time of his birth, it was widely accepted that no one man could play that much music so well or raise that much hell. He proved them all wrong.
R.I.P. H. Cecil Payne
Last Edited by on Sep 17, 2012 5:47 PM
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Greg Heumann
1790 posts
Sep 17, 2012
5:48 PM
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A rectifier tube is very simple compared to, say, a 12AX7, which has 2 complete amplifier circuits. A Rectifier tube has 2 inputs for high voltage AXC, 1 or 2 more for the low voltage heater, and two outputs for the rectified DC current output that the amp runs on. It was common for these tubes to be made without unused pins.
If you know what you're doing, and know which pins correspond to the AC input and DC output you can figure out how to put the tube in based on an inspection of the circuit. But because Patrick was up front saying "I don't know anything about repairing tube amps" - I think caution is the watchword of the day.
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/Greg
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tmf714
1264 posts
Sep 17, 2012
6:22 PM
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The tube locator is placed at the 11:00 position in the above photo-I check all my 5U/5AR tubes-Fender,Tung-Sol,Sovtek,JJ,RCA,Sylvania-they are all located at the same position as the picture above,and they are all 5 pin.
Last Edited by on Sep 17, 2012 6:24 PM
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