princejqman
TDPRI Member
Well i just opened the amp. Im checking the filter caps. Dont see any leak though!
Fender Vibroking problems! Tech still fighting!
- Thread starter princejqman
- Start date
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corliss1
Poster Extraordinaire
@princejqman - you removed all the preamp tubes from the amp and there is still crackling, correct?
princejqman
TDPRI Member
Well i took out the chassis, removed the dog house, checked the filter caps, cleaned all tube sockets with contact cleaner, used a duster spay on the central board, and sprayed d5 lube in all the potentiometers. Swapped some 12ax7 tubes. Noise is gone. How much should i ask for this amp? 1500usd?
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princejqman
TDPRI Member
They dont know much about tube amps. In Panama if you have a tube amp you need to learn to do your own bias and fix it yourself. Im not calling any any fender shop!
Congratulations on doing some basic service with success.
What have you done to prepare for tube amp repair? Do you understand the elements of vacuum tubes? There is a Wikipedia article on the history of vacuum tubes that is a good basic primer. With that knowledge and the info at Tube Data Sheet Locator which gives data for individual tubes, one can begin to learn to read schematics.
One has to gather equipment. A multimeter is basic. Can you make a voltage chart for a circuit? Can you do a ‘pop’ test. This is perhaps the oldest test for tube audio….crude but quick and necessary until one has more sophisticated tools other than just a multimeter. An Audio generator, signal tracer, and an oscilloscope make tech work easier and more complete.
There are great sources for free on the internet. I like Aiken Amp’s Tech pages. The Valve Wizard site is a great resource.
There are many books on amplifier repair and service.
As to what that amp is worth? If I were in Panama and knew there were no technical services available, it would not be worth much to me. Harsh observation maybe, but why would I put that kind of money into something that cannot be easily fixed.
And…..That could be a great amp. In your situation, I would keep it and play it.
What would I use for an amp in Panama if I owned this VK and it stopped working properly? A cheap, modern, and disposable tube amp. I would use that while I learned how to maintain the good tube amp that I already own. (;^)
Good luck with it all.
What have you done to prepare for tube amp repair? Do you understand the elements of vacuum tubes? There is a Wikipedia article on the history of vacuum tubes that is a good basic primer. With that knowledge and the info at Tube Data Sheet Locator which gives data for individual tubes, one can begin to learn to read schematics.
One has to gather equipment. A multimeter is basic. Can you make a voltage chart for a circuit? Can you do a ‘pop’ test. This is perhaps the oldest test for tube audio….crude but quick and necessary until one has more sophisticated tools other than just a multimeter. An Audio generator, signal tracer, and an oscilloscope make tech work easier and more complete.
There are great sources for free on the internet. I like Aiken Amp’s Tech pages. The Valve Wizard site is a great resource.
There are many books on amplifier repair and service.
As to what that amp is worth? If I were in Panama and knew there were no technical services available, it would not be worth much to me. Harsh observation maybe, but why would I put that kind of money into something that cannot be easily fixed.
And…..That could be a great amp. In your situation, I would keep it and play it.
What would I use for an amp in Panama if I owned this VK and it stopped working properly? A cheap, modern, and disposable tube amp. I would use that while I learned how to maintain the good tube amp that I already own. (;^)
Good luck with it all.
Ime, Long before an electrolytic exhibits visual signs of leakage of the dielectric material; there are Sonic signals of weakening. Some of these Sonic ‘qualities’ are ignored by most users because they occur gradually, but with experience the ear will recognize them. Weak attack, out of tune subharmonics, lack of sparkle in the high frequencies, and a lack of a three-dimensional soundstage ate indicators of weakened filter caps that are no longer properly doing the job.
I think you have to start somewhere around there and be prepared to take something closer to a thou.
And then play what? I say PLAY that VK while learning to do the tech work….maybe becoming a needed repairman person for decent tube amps???
princejqman
TDPRI Member
Well now i got some whistling if i turn the dwell control of the reverb section over 11 oclock. This amp should be quiet. Any suggestions?
GotA24Fretter
Tele-Holic
Disconnect the tank and see if it still happens.
Simply press on the tank a bit and that feedback will stop, ime. Set the tank outside the cab , and it will not exhibit this feedback.
Is the tank in a bag? You can try some
foam insulation strips between the tank snd the cab?? I have tried duct tape on the top of the tank and as m threatening to paint the next tank either sound deadening material as used in automotive doors. Some tanks have some annoying resonance when you tap them….others don’t.
So
E old accutrimics tanks came with a strip of fairly dense foam rubber glued to the top of the tank??,
princejqman
TDPRI Member
Ill disconnect the tank first and revert.
princejqman
TDPRI Member
The tank is inside the bag and has cardboard underneath it.
Supertwang
Tele-Afflicted
IMHO,…all those “IC” branded electrolytic caps are highly suspect in that age of amp. They can be bad and not show.
princejqman
TDPRI Member
Whistle is still there even with the tank disconnected. Could it be a preamp tube or something else? Now we know its not the reverb tank or anything related to the reverb section. what a hassle.
GotA24Fretter
Tele-Holic
As stated before, almost anything.
That's a bridge too far. You said it happens when dialing up the reverb dwell control. Or is this no longer the case?
Another post above mentioned the IC filter caps. These are replace on-sight in my opinion. Lots of mystery issues vanish when the stages become properly decoupled.
princejqman
TDPRI Member
I disconnected the rca cables from the tank to the reverb tranny and raised the volume. It started whistling after 10 oclock or volume at 4.
GotA24Fretter
Tele-Holic
If I'm understanding you correctly you pulled the send to tank from the reverb transformer. That leaves on open input at the reverb recovery.
Pull the reverb driver tube and repeat.
Ground the grid of the reverb recovery stage and repeat.
These methods reduce variables.
Pull the reverb driver tube and repeat.
Ground the grid of the reverb recovery stage and repeat.
These methods reduce variables.
princejqman
TDPRI Member
You mean pull the 6v6 tube!
