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Post by TooManyWires on Jun 11, 2005 10:01:40 GMT -5
So I bought this old guitar amp at a yard sale and it runs on tubes. The preamp tubes are 6at6's, and then theres a 6v6gt or somethign in there for power, and something else as a rectifier, a 5y3 maybe. I have it all written down somewhere, but off the top of my head I forget exactly. Anyways, it makes a godawful crackling noise every time you play or touch it when it's on. I had some tubes replaced when I got it, and I'm pretty sure they were the preamp tubes, and that fixed the problem for a little while, but then it got worse again. So then I was at another yard sale recently and I picked up a tube powered hi-fi FM tuner that has 6au6's for preamp tubes. I had that plugged in and it ran fine, no noise or anything. Does anyone know if I could put the 6au6's from the stereo amp in as replacements for the 6at6's in the guitar amp? They have the same base, and would fit in the same holes with no problem physically, but it's electrically that I have no idea about. Any help would be greatly appreciated. Thanks,
Alex
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Post by Trey on Jun 11, 2005 10:31:17 GMT -5
It's a VERY VERY bad idea to use diffrent tube types if you are unsure if they are compatable(usually they aren't) The power ratings of tubes vary greatly between diffrent types, even if they do fit in the sockets they maybe getting too little or to much power, both of which are very bad. I suggest you buy the proper tubes for those amp instead. Those tubes are kinda hard to find but there are several good online retailors who have good suppliers of tubes for old radios, I particularly like www.tubesandmore.com Great service and good prices. Good luck with your amps. The problem with your other amp could be anything, probably not the tubes either. If you really like it I would take it to a good amp tech and see if maybe they could figure it out. Changing the power tubes is a good idea too, they're probably shot as well... |
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Post by TooManyWires on Jun 11, 2005 21:11:56 GMT -5
Well, I was having a look at the guitar amp today, and as it turns out the tubes might just be a tad loose. Putting a set of those spring loaded tube shields on it might do a great deal to help it. So that might work. And I had figured that it probably wasn't a great idea to just start swapping tubes in and out, but I know that it's sometimes ok to use a 12at7 or a 12au7 where a 12ax7 goes, so since this would seem to be a similar situation, I thought maybe it was something that might be ok to try. Anyways, thanks for the help,
Alex
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Post by UnklMickey on Jul 13, 2005 13:47:53 GMT -5
Alex:
DON"T DO IT!!!!!!!!!!!!!!!!!!!!!!!!
I just looked at Bill Beech's site (nj7p) the tubes are completely different types and the pins are connected to differing elements in each. The only way it is reasonable safe to interchange tubes is to compare the data sheets to make sure they have the same pin-outs and similar characteristics. For instance if you replace a 12ax7 with a 12au7 it will not hurt the tube or the amp, but you will get LOTS less gain. Sometimes this is quick fix for an amp that has way too much gain. (e.g. pignose g40v). If you put a 12ax7 in an amp that was designed for a 12au7 you need to check the operating parameters. The 12au7 can handle much more plate current and power. If the amp is running with high plate current on this tube, a 12ax7 will fry in that environment and may ruin other components.
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Post by TooManyWires on Jul 13, 2005 17:48:43 GMT -5
Yeah, I didn't try. Since I was unsure I decided that I'd be better safe than sorry. However, I also had a noise in it that a friend identified as a loose tube, so I poked at all the tubes very carefully while it was on, and it turned out that all of my preamp tubes were noisy. So I got the idea to replace the sockets with some other ones that had tube shields to go with them. It has 3 of them, and I did the sockets one at a time testing to make sure I put it all back together right after each change. As far as I can tell it did go back together right. But I think I blew up a tube in the process. When I had it all back together and turned it on to test it started to make this godawful distortion but worse crackly fuzzy farting noise that fades out far faster than the signal from the guitar does. It is a lot worse when the amp is warm. It made this noise before and I took it to a friend who is studying electronics and he took it to his shop and had a look and brought it back with a new tube and said that that was the problem. So I'm going to try putting a new set of preamp tubes in it and hope that fixes it again. Anyone have any other ideas of what that kind of noise could be? It has 3 6at6's two preamps, and one driving the tremolo circuit. A 5y3gt for a rectifier, and then some other tube for a power tube, I'm not sure what it is and I don't know how to identify it, but it is the same size, shape and socket as the 5y3. I think it might be a 6v6 or 6l6...I forget which, I have it written down. Anyone know how to identify tubes? It also only has 3 knobs, volume, tone and tremolo. I'd like to add a standby switch, can anyone help with that, or direct me to a site where I can do some reading on that? Thanks,
Alex
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