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Post subject: 1970s Twin with an electrical buzz...???? HELP
Posted: Wed Oct 31, 2012 8:06 pm
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I have a 1970 SF Twin that was working perfect last Saturday night when I bought it and now it has an electrical buzzing noise that comes and goes when its tilted back and forth. I actually found it when I tilted it forward to move it. When tilted it has the buzz and when I put it back level it stops. Now it’s starting to do it while its level?? It I tilt it forward then back it goes away then after a few minutes it starts a little sputter hum/buzz and comes back…. Now if I tilt in back it goes away, then forward and it comes back????? Almost like a wire or maybe a tube or something is moving or shifting around….it’s really weird and I hate to haul it in for service when it might be something simple. I will take it apart again this weekend and have a visual… he are the pix I took when I got it Saturday. If anyone has any thoughts let me know…
Thanks.

http://www.flickr.com/photos/digitalcan ... 868531035/

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Last edited by mackaygtrs on Thu Nov 01, 2012 3:12 am, edited 1 time in total.

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Post subject: Re: 1970s Twin with a buzz...???? HELP
Posted: Wed Oct 31, 2012 11:15 pm
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I see nothing amiss on the chassis.

Could be a tube heading south -- have you tried the "chopstick test" by gently tapping on each of the glass envelopes to see if the symptom is replicated?

Arjay

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Post subject: Re: 1970s Twin with a buzz...???? HELP
Posted: Thu Nov 01, 2012 3:08 am
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Retroverbial wrote:
I see nothing amiss on the chassis.

Could be a tube heading south -- have you tried the "chopstick test" by gently tapping on each of the glass envelopes to see if the symptom is replicated?

Arjay

Thanks,
I'll give that a try tonight when i get home, i hope its not a tube!! But i hope it's also something simple...

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Post subject: Re: 1970s Twin with a buzz...???? HELP
Posted: Thu Nov 01, 2012 3:15 am
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Retroverbial wrote:
I see nothing amiss on the chassis.

Could be a tube heading south -- have you tried the "chopstick test" by gently tapping on each of the glass envelopes to see if the symptom is replicated?

Arjay


I revised my symptoms, it’s an electrical buzz.....another friend thought i was talking about a vibrating buzz!!!!

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 3:16 am
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You may also wanna try some contact cleaner on the tube pins and sockets. Sometimes, amps that have been sitting for awhile develop oxidation on contact points. Just like Humans that have been out of action for awhile. :lol:

I like CAIG De-Oxit D5 or GN5


Good luck!


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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 6:01 am
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Thanks guy’s, OK I have a question??? Can the power tubes (not pe-amp) be taken out and put back in (while the amp is off) without being re-biased. I thought about doing the contact cleaning thing and just removing ALL the tubes (power and pre) and re installing them and see what happens. Again, it just seems like something is touching or not touching as the amp tilts forward. The sound is like when you touch the end of a live guitar cord… maybe not as loud..
Thanks

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 7:52 am
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mackaygtrs wrote:
Can the power tubes (not pe-amp) be taken out and put back in (while the amp is off) without being re-biased?


Yes (assuming the idle bias has been correctly set to begin with).

Whenever I pull power tubes for any reason, I mark each bottle and its corresponding socket "A", "B", "C", and "D" so when I'm finished with whatever ongoing work I'm performing each of the the tubes is positioned back into the socket from whence it came. Small bits of masking tape marked via black Sharpie are ideal for this purpose (put the tape on the tube's bakelite base rather than on its glass envelope).

HTH

Arjay

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 8:12 am
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Did you have an instrument cable plugged in when you where experiencing the problem or was it unplugged? It could very well be a bad instrument cable. Just something else to check as I've experienced what you've described and in my case it was a bad guitar cable. But it could also be a bad input jack as well.
HTH,
socal323

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 8:15 am
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Retroverbial wrote:
mackaygtrs wrote:
Can the power tubes (not pe-amp) be taken out and put back in (while the amp is off) without being re-biased?


Yes (assuming the idle bias has been correctly set to begin with).

Whenever I pull power tubes for any reason, I mark each bottle and its corresponding socket "A", "B", "C", and "D" so when I'm finished with whatever ongoing work I'm performing each of the the tubes is positioned back into the socket from whence it came. Small bits of masking tape marked via black Sharpie are ideal for this purpose (put the tape on the tube's bakelite base rather than on its glass envelope).

HTH

Arjay


Thanks ...going to pull m....clean m, the re-install m.... :D

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 8:20 am
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socal323 wrote:
Did you have an instrument cable plugged in when you where experiencing the problem or was it unplugged? It could very well be a bad instrument cable. Just something else to check as I've experienced what you've described and in my case it was a bad guitar cable. But it could also be a bad input jack as well.
HTH,
socal323


Makes the noise wheather a cable is pluged in or not, volume up or down.... but like i said, if I tilt it back it goes away.... almost like something is moving insdie and touching another part or wire.... i tried the reverb and made sure they were good and tight, moved them around, messed with the speaker jack, unpluged it, checked the wires....everything seem to be OK on the outside. I just started doing this when I got it home, I did not hear it at the guys house where I bought it... its not a heat problem, does it cold and hot.

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 10:45 am
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Could be a loose element within one of the tubes.

Arjay

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Thu Nov 01, 2012 11:05 am
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Retroverbial wrote:
Could be a loose element within one of the tubes.

Arjay


Thants what i've been thinking... and they are such nice tubes... :(

They have no play time on them, said he had it retubed and then put away a week or so later. That was around early '90... he traveled alot and the amp went with him and his wife, he just never used it.... maybe a tube has a little breakage inside and is shorting out , i guess there like a heavy duty lighbulb in there....lol, little things could go wrong behind the glass...........wwwooooo, it like another little world in there...lol, ok now i'm being silly.....

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Post subject: Re: 1970s Twin with an electrical buzz...???? HELP
Posted: Fri Nov 02, 2012 4:36 am
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First off , Thank you everyone for all their help!!! I got home last night and gentle (like a surgeon) took each tube out starting with the power tubes and cleaned the female receptacle sockets with a little tiny brush and male prongs of each tube very carefully and had a really good inspection of each tube (I had no idea what I was looking at or looking for but I did give then a certified clean bill of health …. lol) They sure are pretty when the glass is all shinny!!!!, WELL, I checked everything else including the reverb in and out, speaker cables, foot switch, unplugged everything and cleaned all the plug terminals and after all that…… well it is so quite now that I have to keep checking to make sure it’s still on. Hell this bad boy makes no noise at all. (Unless I start my horrible gtr playing) Now I realize my “73 has a hum… always has but now I notice it a lot more.
Anyway, unless it starts back up again I think it’s good to go…. Man I love this thing (all 2 of them)…..lol…
I was too tired to post the outcome last night so until next time,
Talk to ya’ll soon…..woowho :D :D :D

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