It is currently Mon Mar 16, 2020 9:04 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 84 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Go to page Previous  1, 2, 3, 4, 5, 6  Next
Author Message
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 2:02 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
What I do with Flickr, change picture size
I can do smaller or bigger too

Image


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 11:54 am
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
stratele52 wrote:
BMW2002Ti wrote:
Try tapping the resistors in the power rail, with a wooden chopstick, and see if it effects the noise.

Good luck!


Why a wooden chopstick, this is not a insulate tool and could be not safe :(


Well this is another discussion for another day, as "wood" can be a very broad term as insulator. But I am the type who believes in Belts and Suspenders, so in my tools is a modified chop stick I use for poking around where my hand should not be, it has a couple layers of shrink tube on the stick where my hand goes
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 12:05 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
BMW2002Ti wrote:
Well... guess we can rule-out PSU issues. Cap can is new. Power rail resistors are not damaged. One other thing, you have any compressed air in a can? Try spraying those PSU resistors and see if the noise comes back. Could be an internal conduction issue, within the resistor which are temp sensitive.

One other thing... the rectifier. Try pulling and cleaning the socket and pins. Do you have another 5Y3GT you could try?


I will use the compressed air, as I do have some, I guess it may do the same as "Freeze it", which I do not have right now.
I do have another 5Y3GT, I will give that a try, and check socket pins .
Spent the morning looking for an electronic store that sells parts, did some calling, and did some physical looking, to no avail so I will have to go online for the 716p and spend more on shipping than the actual part cost. Working late so I most likely will not get to it tonight
Thank you for your time
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 1:52 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
mud wrote:
stratele52 wrote:
BMW2002Ti wrote:
Try tapping the resistors in the power rail, with a wooden chopstick, and see if it effects the noise.

Good luck!


Why a wooden chopstick, this is not a insulate tool and could be not safe :(


Well this is another discussion for another day, as "wood" can be a very broad term as insulator. But I am the type who believes in Belts and Suspenders, so in my tools is a modified chop stick I use for poking around where my hand should not be, it has a couple layers of shrink tube on the stick where my hand goes
mud


Many beginner here in high voltage we should be very careful and write ; insulating tool


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 3:44 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Well, better this

Image

than this...

Image


:)


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Tue Nov 07, 2017 4:11 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
I use screw driver.
I use the tip as a handle and tap the circuit with the insulate plastic / rubber handle.
Every body have à screwdriver at home.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Wed Nov 08, 2017 10:04 am
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
Mud, I want to back up for a bit. While most Fender's with mid controls will completely ground out the signal, your Vibrochamp is a bit different.
The 10K in the tone stack to ground prevents the volume from going completely away.
you can test this by clipping a test lead across the 10K. Now all the sound should go bye bye.
This 10K may also be responsible for the tone controls not working very much. The normal value for this resistor in a tone stack is 6.8K. The lower the value, the more effect the tone controls have.
It was probably raised to get more gain out of the amp because the lower the value, the lower the signal coming out of the tone stack. This unit looks like its from the Silverface era, when Fender was trying to squeeze more gain out of all their amps.Some of them used 15K resistors.
If you want to play around with lowering the value there, I have seen 1.8K resistors used in one custom amp. It had 220K plate resistors to get more drive into the stack, but there was an incredible range to the tone controls.

On the power-down crackle, does it do it with the preamp tubes removed?


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 09, 2017 4:26 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
TimsAudio wrote:
Mud, I want to back up for a bit. While most Fender's with mid controls will completely ground out the signal, your Vibrochamp is a bit different.
The 10K in the tone stack to ground prevents the volume from going completely away.
you can test this by clipping a test lead across the 10K. Now all the sound should go bye bye.
This 10K may also be responsible for the tone controls not working very much. The normal value for this resistor in a tone stack is 6.8K. The lower the value, the more effect the tone controls have.
It was probably raised to get more gain out of the amp because the lower the value, the lower the signal coming out of the tone stack. This unit looks like its from the Silverface era, when Fender was trying to squeeze more gain out of all their amps.Some of them used 15K resistors.
If you want to play around with lowering the value there, I have seen 1.8K resistors used in one custom amp. It had 220K plate resistors to get more drive into the stack, but there was an incredible range to the tone controls.

On the power-down crackle, does it do it with the preamp tubes removed?


Thanks for your input. It is a Black face but it was of the last batch made prior to the silver face assembled April 1967 by the stamp QD
Being I am new at this trouble shooting, I am a little nervous about bypassing the 10K by cliping the leads, so I will take your word for it, and who know maybe I will get adventurous, down the road.

"On the power-down crackle, does it do it with the preamp tubes removed?" No I have not removed the tube and shut down I will give that a try, the thing is if I power up and leave all on 0 and power down I do not hear the crackle fad-out, but after I plug in my guitar and play for 1 to 2 minutes set all back to 0 and power down I then hear the noise. This week end I will do this a few more times to see if happens like this

My gut feeling is this .02ceramic disk, coupling cap between the preamp and the power amp, is not right as I see debris that was not there the first time I opened it up. I do wish I took a close up the first time it was opened, but this is what I got notice no derbies Image
New Photos after crackle
ImageImage
I have a 715p coming to me next week I will change it out and see what happens
Let me know if you can't see the photos I am still figuring out how to enlarge them in Flickr
Thank you very much
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 09, 2017 10:16 pm
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
OK, it sounds like the difference is whether something is plugged in or not.
With nothing plugged in, the input is grounded and so the crackle is muted.
As the caps discharge, the ps caps discharge quickly. If you have to wait awhile, only the cathode caps are discharging then.
Again, I would just clip across the cathode cap and see if the problem went away.
There is less than 2 volts there. Some amps use grounded cathodes, so there's no harm done to the circuit to short it to ground for a test.
Same with the 10k in the tone stack. There is no dc there to get anything upset.
The debris around the coupling cap you see is just epoxy flaking off around where the leads have been bent around. It doesn't affect performance.
While these disc caps seldom get leaky, they do get microphonic. If you tap on it with a chopstick, you can hear it in the speaker.
There is a tone secret hidden in these caps. Musicians i talk to tell me of some vintage fenders with a warm fuzzyness to them and others that sound harsh.
I have found that the amount of microphonics this cap generates is responsible for this quality.
The plates come loose over time and impart a kind of bell tone as you tap them. One that is too loose gives a dull thud. Don't just replace it, listen to it.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 10, 2017 3:16 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
TimsAudio wrote:
OK, it sounds like the difference is whether something is plugged in or not.
With nothing plugged in, the input is grounded and so the crackle is muted.
As the caps discharge, the ps caps discharge quickly. If you have to wait awhile, only the cathode caps are discharging then.
Again, I would just clip across the cathode cap and see if the problem went away.
There is less than 2 volts there. Some amps use grounded cathodes, so there's no harm done to the circuit to short it to ground for a test.
Same with the 10k in the tone stack. There is no dc there to get anything upset.
The debris around the coupling cap you see is just epoxy flaking off around where the leads have been bent around. It doesn't affect performance.
While these disc caps seldom get leaky, they do get microphonic. If you tap on it with a chopstick, you can hear it in the speaker.
There is a tone secret hidden in these caps. Musicians i talk to tell me of some vintage fenders with a warm fuzzyness to them and others that sound harsh.
I have found that the amount of microphonics this cap generates is responsible for this quality.
The plates come loose over time and impart a kind of bell tone as you tap them. One that is too loose gives a dull thud. Don't just replace it, listen to it.

"Again, I would just clip across the cathode cap" This is where I get confused are you talking about the Power Amp Cathode resistor and bypass cap, or Preamp1st stage Cathode resistor and bypass cap, or 2nd stage Cathode resistor and bypass cap, I think power am I right.
When you say clip across, I should use a alligator clip cable and clip from the + lead to the - Lead, bypassing the cap ?
"The 10K in the tone stack to ground prevents the volume from going completely away.
you can test this by clipping a test lead across the 10K. Now all the sound should go bye bye"
I think I only see one10K resistors in the whole Schematic and Layout, one on the power rail. I do see a 15K resistor off the bass pot. Are you talking about the one on the Bass pot to ground, or from the PS ?
Thanks for the info on the .02 cap I will leave it alone for now, except to tap on it and listen
Thanks for bearing with me I am still learning
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 10, 2017 7:29 pm
Offline
Professional Musician
Professional Musician

Joined: Thu Aug 07, 2014 3:25 pm
Posts: 1023
Yea, I was looking at your schematic wrong. Old blind eyes. The 15k on the bass pot is the one I'm talking about. When you short it with a clip lead, it will lower the volume, the tone controls have more range and the sound will go away when the controls are zeroood.

The cathode cap I'm referring to is on the input stage. There is only a couple volts there and clipping across from the cathode to ground is safe.


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 11, 2017 3:59 pm
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
TimsAudio wrote:
Yea, I was looking at your schematic wrong. Old blind eyes. The 15k on the bass pot is the one I'm talking about. When you short it with a clip lead, it will lower the volume, the tone controls have more range and the sound will go away when the controls are zeroood.

The cathode cap I'm referring to is on the input stage. There is only a couple volts there and clipping across from the cathode to ground is safe.


I have seen different values on different layouts, for that 15K resistor off the bass pot and some of them are pretty blurry and hard to read, I have the schematic that was born with this amp.

OK so I jumped the 1st stage cathode cap and I get the same scratchy crackle I get without jumping except it seems longer and louder, and it seems that sound, but not as loud happens when I power it up with the jumper connected. Also I noticed that when it was jumped the volume was lower than
not jumped. It got me thinking that being the cap is bypassed, that would mean no extra push of electrons coming to the cathode, which makes sense that the volume is lower from lack of electron to the tube
Would that mean the cap is working
I also observed that when I probed pin 6, plate on the preamp 12ax7 going to .02 coupling cap it makes the same crackle sound as I am getting
I also observed that all bypass caps go to 0 on the negative side except from pin 8,cathode I get a reading of .0062 ( not much )
Tapping the .02 coupling cap, does give a ringing bell tone
Again thanks to all for your help
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 13, 2017 10:33 am
Offline
Professional Musician
Professional Musician

Joined: Wed Dec 15, 2010 7:06 am
Posts: 1662
BMW2002Ti wrote:
Well... guess we can rule-out PSU issues. Cap can is new. Power rail resistors are not damaged. One other thing, you have any compressed air in a can? Try spraying those PSU resistors and see if the noise comes back. Could be an internal conduction issue, within the resistor which are temp sensitive.

One other thing... the rectifier. Try pulling and cleaning the socket and pins. Do you have another 5Y3GT you could try?


I cleaned and tried a a different 5Y3GT and a different 6v6 with same results, I haven't froze resistors yet, with compressed air.
mud


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 13, 2017 12:19 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Check all resistors and solder points. Including that resistor strapped across pins 1 & 6 of V2. Because of the tight area of these sort of connections --- the factory something can't make a completely good solder. I had a couple amps where small cracks develop in these inner-socket connections, over time (sometimes many years).

Good hunting!

http://www.electronicstudio.net/schemat ... layout.pdf


Top
Profile
Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 13, 2017 5:22 pm
Offline
Professional Musician
Professional Musician

Joined: Tue Nov 27, 2012 6:56 am
Posts: 1677
Location: Coastal Bend, Tx.
Haven't been around for a while, a 3k resistor in the first stage of the PSU rail will help drop your voltages from the screens of the output through to the 12ax7's. The only thing it wont do is drop the plate voltage and what your 5y3 is seeing from the power transformer. It might help some to preserve the original characteristics of the amp but many prefer to just keep it original. Again, I like to use the brown box in order to adjust the input voltages. just sayin.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 84 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Go to page Previous  1, 2, 3, 4, 5, 6  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: