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Topic: Fender Vibrosonic problem. |
Austin Tripp
From:
Nashville TN
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Posted 17 Oct 2010 8:05 pm |
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I just got a 1974 Fender Vrbrosonic Thursday from a guy in Tx. I played through it that night and it sounded perfect, very quiet with no noises. Friday morning I played through it and it has this noise (almost like wind blowing into a microphone) and it happens when you turn the volume up and down. I changed some tubes thinking that might be a problem but it still does it. I can't afford to ship the amp or drive it to Ken Fox or I would. Does anyone a tube amp repair guy in South Carolina, near Greenville or anywhere? Or can someone here tell me what kind of problem I might have? Thanks!
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"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 17 Oct 2010 9:11 pm
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If it only makes that noise when you are moving the volume knob it will just need a new pot installed, which is not a big deal as you can easily get a replacement part of the same value and if your soldering skills are decent you can fix it yourself. What IS a big deal is that you can get a hellatious shock from the plate capacitors even when the amp is unplugged until you discharge them.
To do this briefly connect the plate pins of the output tubes to the chassis with an INSULATED wire or screwdriver, being VERY careful to only handle the insulated surface and not touch any metal directly during this process. It will throw sparks (yum!) but only briefly, the important thing being that you not be part of the circuit at the time.... |
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Ken Fox
From:
Nashville GA USA
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Posted 18 Oct 2010 3:33 am
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That sounds more like a leaking tone capacitor putting DC voltage on the pot. That is easy enough to check out with a DC voltmeter. The amp needs to be on the bench, connected to a speaker load (this is a must!!) and then the pots legs can be tested for DC to chassis. A very small DC voltage can make for a noisy pot.
I just finished a N112 with the same noise on the main volume pot and it was a bad cap in that circuit. |
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Tim Heidner
From:
Groves, TX
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Posted 18 Oct 2010 11:38 am
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might just be a dirty pot, buy you some contact cleaner type stuff to spray in there while you turn it
don't use WD-40, and be extra careful where you put your fingers, you might want to google up how to drain the caps beforehand |
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Austin Tripp
From:
Nashville TN
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Posted 18 Oct 2010 3:25 pm
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Thanks everyone. Just a thought,,, what would happen if the tubes were mixed up when they were installed?
_________________
"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Tim Heidner
From:
Groves, TX
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Posted 18 Oct 2010 6:38 pm
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you cant hurt anything mixing preamp tubes around, if they fit they will work, they just might not sound so great.
Is this whooshing sound only happening when you turn the knob? Try cleaning the pot and see if that fixes it. |
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Austin Tripp
From:
Nashville TN
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Posted 18 Oct 2010 7:32 pm
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Hey Tim. The noise is constant, it just gets louder as the "Master Volume" knob is turned up. I called a local guy that does some tube repair and he said a tube may be going microphonic? I don't know what that means but it sounds expensive hehe. If the power tubes were mixed up on accident (unbiased) what would happen to the amp? I'm very new to a tube amp so please excuse the dumb questions. The guy also mentioned that when I turn the amp off, turn the standby off then the power and then wait a few seconds and turn the standby switch back on? He said the power needs to drain or something like that, I'm getting old and can't remember! 
Thanks everyone!!
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"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Tim Heidner
From:
Groves, TX
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Posted 18 Oct 2010 9:18 pm
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well...I'm really no expert, but that doesn't sound like a tube to me. In my experience tubes'll crackle and pop when they go bad, or a power tube will blow a fuse or just start sounding weak, IDK
maybe you should listen to Ken Fox on this one, but it shouldn't cost much to change out a cap in that amp, you could pop one in and out in 10 minutes if you knew which one to go after...
It could be a preamp tube, you can pop them out one at a time and see if that changes anything, that could give you an idea where to look... |
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David Ball
From:
North Carolina High Country
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Posted 19 Oct 2010 2:01 am
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I went through a similar problem with my Vibrosonic earlier this year--http://bb.steelguitarforum.com/viewtopic.php?t=185848&highlight=
Mine didn't get appreciably louder with the master volume, but the noise sounded similar to what you describe. It still isn't perfectly silent, but I haven't heard one that is. It's a great sounding amp!
Dave |
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Ken Metcalf
From:
San Antonio Texas USA
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Posted 19 Oct 2010 6:07 am
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Thump the tubes with your finger and if it's microphonic it will be just like thumping a microphone and you will notice the difference between the tubes.
It shouldn't do that..... AND!!
<b>Always remember</b> there is some juice in there even when it is unplugged.... you can get bit.
Take it to a shop..
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MSA 12 String E9th/B6th Universal.
Little Walter PF-89.
Bunch of stomp boxes |
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Ken Fox
From:
Nashville GA USA
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Posted 19 Oct 2010 9:30 am
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If the power tubes were mixed up on accident (unbiased) what would happen to the amp? NO!!
If it is a constant noise I would suspect a bad plate load resistor, a bad tube or a bad cap.
I do not use a "shotgun" approach of replacing parts until it works. I have two work benches with O-scopes, load testers, cap tester, sine wave generators, tune testers, etc to do the job right.
You would not believe the number of amps I get in here that have been worked on by so called techs that do not have the proper test equipment or knowledge to fix amps. |
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Austin Tripp
From:
Nashville TN
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Posted 19 Oct 2010 3:45 pm
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Is it ok to play through the amp or should I have it serviced asap?
_________________
"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Bill Hatcher
From:
Atlanta Ga. USA
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Posted 20 Oct 2010 5:26 am
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| Ken Fox wrote: |
I do not use a "shotgun" approach of replacing parts until it works. |
Sometimes I do.
These amps are 30 40 years old. The components are thatold too.
I replace ALL the electrolytics. ALL of them. then all of the 100k resistors on the right hand side of the board with precision resistors. that gets rid of the majority of the "eggs frying" sounds when the amp heats up. the 470 ohm resistors on the power tubes with flameproof precision and the 1500ohm resistors on the power tubes. then i replace the phase inverter section, the 2 caps and four resistors all with new precision resistors and orange drop caps. sometimes i will just do new orange drops all through the amp.
good matched power tubes and a new phase inverter tube and set the bias. then turn the amp on and try some different pre amp tubes until you find a good one.
i personally would not go to the expense of having a tech spend time testing individual 30 or 40 year old components. the money charged could almost pay for the "shotgun" approach of replacing every thing critical that needs it most of the time anyway.
These amps will work with bad components in them. You have to think of the amp as it was when it was new. It had good new components not old stuff. I never ceased to be amazed at the sound of a Fender amp that has been "blueprinted". All components as close to spec as possible. They sound amazing. If you look at the schematics...says specs are within +/- 15% !!!! Get them with in say less than 5%! Amazing difference.
Now to the geek factor. Some geeks want amps with all the original tubes and stuff in them. Fine...most of it is worn out and sounds like crap, but that is fine if they want that. Leave those amps as they are for the geeks to gawk over, but the ones i take out to the gig...they are going to be like they were when they came out of Leos factory. He never sent out an amp with 30 year old components. Everything was new in them, and the components today are in most cases better than back then.
Last edited by Bill Hatcher on 20 Oct 2010 5:29 am; edited 1 time in total |
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Bill Hatcher
From:
Atlanta Ga. USA
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Posted 20 Oct 2010 5:27 am
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| Austin Tripp wrote: |
| Is it ok to play through the amp or should I have it serviced asap? |
You can play that amp all you want. As long as sound comes out of it.
You have a noisy pot...so what...you dont turn it while you play anyway. |
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Austin Tripp
From:
Nashville TN
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Posted 20 Oct 2010 1:45 pm
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Hey Bill, the noise is constant, I don't believe its a pot.
_________________
"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Bill Plemmons
From:
Simpsonville, SC
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Posted 20 Oct 2010 2:27 pm
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Austin, it was good to see, hear and pick with you last weekend in Belvedere. "YOU DONE GOOD"! My advice is to take a day off and take the amp down to Ken Fox and let him do his magic. These are great sounding amps when they are working right.
Bill |
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Austin Tripp
From:
Nashville TN
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Posted 21 Oct 2010 3:27 pm
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Hey Bill. You sounded great as usual! I believe the problem with my amp is a bad plate resistor. I did some research on the net and found a great site for dummies like me that dont understand tubes. Ill be taking the amp to Ken Fox as soon as we can set a date. Thanks everyone for helping this young'un out!
Austin Tripp
_________________
"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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Ken Fox
From:
Nashville GA USA
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Posted 21 Oct 2010 4:26 pm
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Most generally I replace all the electroytic caps in the older Fender amps.
I can test them in about 1 minute with my ESR tester, in circuit. Again, having the right tools makes a difference.
I also replace the resistor under the cap can, as long as you are there you might as well get new ones. We clean all jacks, re-tension power tube sockets. clean pots, test all audio coupling caps for DC leakage, etc. |
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Austin Tripp
From:
Nashville TN
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Posted 21 Oct 2010 4:55 pm
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You da' man Ken!! I sent you an email about setting a date. Thanks again to all the wonderful forum members who helped me in this time of crisis 
Austin Tripp
_________________
"Hotrod"
Steel guitarist for Cody Jinks
Member CMA |
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