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Peavey VTX Classic 212 65w Need Help???

Started by Bquick, December 21, 2017, 11:20:10 AM

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Probing around on the tube sockets I can't locate a negative -15 volts DC.  Pin #5 has +15.35v on both tube sockets.  Should the tube sockets have a negative voltage?


I cleaned out the tube sockets with contact cleaner.  sprayed a little deoxit in each socket and pulled tubes in and out several times. 

Now when I turn the amp on I hear a Humm that goes up in volume then back down after a couple seconds when I turn the amp on.  The amp is quiet after that.  When I strum the strings on the guitar I can hear the guitar but it also has a crackling kind of distortion along with it. 

The LED's are working fine the red one comes on with power switch and the green status LED comes on when I switch the stand by. 

To be honest when I look at and study the Schematic I have a hard time comprehending it???  I have been able to locate both negative and positive DC voltage on the pre amp side.  I did notice that the positive is around 15.60 vDC  and the negative is a little higher -16.36 vDC. 

Maybe information will help someone with more experience than me???   


Look at the schematic.  DO you see -15v there on the power tubes anywhere?   Pin 5 of each is wired to the +15v supply through a couple resistors.  it is normal to find +15 there.

Read the schematic notes for what Vk should be, the cathode voltage on those tubes.  Ther is no negative voltage anywhere on the power tubes.

Start with the power amp, is your Vk in range?  Also the associated Vi reading, is yours in range?

Plug your guitar into the POWER AMP IN jack, next to the PREAMP OUT jack. How does that sound?

A quick check, see the pairs of diodes to +/-15v near the input jack, and also by the power amp in and preamp out jacks?   Make sure none are shorted, easiest way is to check for 15v on the jacks or IC pins they are wired to.


Just wanted to let everyone know that after watching countless hours of youtube videos like D-Lab I was able to figure out how to test capacitors for leakage.  I thought that was what this site was about???  Experts trying to help folks with less knowledge.  I guess I was wrong about that..  Because the only thing that anyone said to me was read the schematic.  Just letting you know if you don't have any experience doing that it is a lot easier said then done.  I originally suspected the caps being bad and ordered new ones and someone on this site said that's like replacing you radiator when it only needs a new cap.  Well that might be true but for about $6.00 It sure is nice to have the piece of mind knowing that I replaced parts that can and usually do go bad after forty years..  Even if it's not bad.  Big deal I spent $6.00.

Maybe some of you experts will realize that not everyone has as much experience as you do and if you really read the post you could take just a little more time to help someone out.  Don't take it personal but if your going to respond to someone's post it only takes a little more effort to really try and help them instead of ridiculing them and/or trying to make yourself sound so smart...  Think about it???  Thank you to everyone that tried to help me.   

Oh yea, after replacing the one capacitor that I originally suspected the amp worked.  I went ahead and replaced all of them and it has been working fine all day.  I hope that was the only problem.  Because getting any real help is next to impossible...   


I am sorry you approach this with such bitterness.  I can talk to you from the other side of this discussion.  I have been training technicians for over 40 years.

When I tell someone to look at the schematic, it is in hopes they learn more about reading schematics, because all that information is there, even if you don;t see it now.  it may not speak to you now, but as we go through it, you might pick up something about relating the diagram to the circuit in the amp.

For example you were expecting a negative voltage on the grid.  I pointed out that the schematic shows only positive voltages there.  Hopefully if it comes up again you might remember that.  We all build our experience by accumulating information.

I don't believe any ridicule was involved.  I mentioned the notes in the corner.  I very often do that in any schematic.  You did not seem to know what voltages to expect in the circuit.  The schematic shows Vk at the cathode of the power tube, pin 8, and the note tells you what range of voltage is normal there.  Likewise nearby the schematic notes Vi, and abbreviation for the voltage indicating current through the tubes.  it is across a resistor for each tube.  The notes tell you the normal range of voltages to find there.

I could have taken the time to make up a chart from that same information, but I chose to tell YOU to read that information, as it will better make you understand what you are working with than me just rattling off some voltages, voltages you would then have no idea where I came up with them.

Troubleshooting and repair is a systematic approach to circuits with problems.  If I can impart that approach to you, you are then better armed in the future when problems arise.   When I/we tell you not to just wholesale replace a bunch of parts it is because that assumes a part is always the problem.  I am glad replacing your caps solved your problem.   That series of amps tends to have trouble with the connectors between the power supply board and the tube board.  What if you replaced every cap in the thing and still had the problem because the ribbon cable had a bad contact in the connector?  That is why we try to lead you through a systematic approach.

I am sorry you see no value in any of that.  if you thought we could just say "replace this and replace that" and all your problems would be solved, well it just doesn;t work that way.   There are people here like myself who are industry professionals, and we have given countless hours - hours I could be doing repairs and charging for - in free assistance.  SO it rings a bit hollow to be told I should take the time...

In any case, I wish you well.


Like I said don't take it personal. 

What I expected was some help.  If you really were concerned with helping someone you could take just a little bit more time and explain things.  Believe me I looked over the schematic for hours after you said "Read the Schematic"  I even posted the voltage readings that I found...  Yes you called me out because I asked if I should have found a negative voltage on the tube socket...   

Look I'm not here to argue or point fingers.  The point I was making is: You have a tremendous amount of knowledge and I don't!!!  Why are you so aggressive and angry?  If you really wanted to help me you know you could have???  But you choose to take a different approach...  Maybe you had a bad day? Maybe your sick of dumb questions? I'm not sure what it is but I am sure that you could have made this experience a better one.

If your going to take the time to respond to a post, try and help someone not make them feel like a dummy.

We all live here on this place called earth.  We should be kind and compassionate.  Not rude and condescending.

I could sit here all day and give you examples of the point I'm trying to make.  Maybe you can think about what I'm saying and leave it at that.  I said Thank you for the help that I did get.  Out of all the people I really didn't want to argue with you because your probably the most knowledgeable person on this site and a couple others that I looked at and read over the last couple of weeks Enzo.  It's not the first time I've seen your name.  Believe me I read a lot of your post and sometimes you try and help and sometimes your a DICK. LOL

I learned a lot about reading a schematic, Capacitors, Circuits, the components that make up an amp.  I don't understand all of it.  I probably got Lucky with my fix.  But like I stated in the earlier post the amp sounded great a couple weeks ago.  Then in a matter of seconds it sounded like crap.  In my mind that probably means something failed.  That's why I assumed it was a component.... 

Have a Good day and maybe, just maybe when you make your next post you will  think about what I'm trying to say.  I'm not saying because it makes me feel better I'm saying it because maybe the next kid that ask a question, could possibly get a little help instead of being made fun of or feeling like a dumb *s!!t* for asking...         


No one here has been angry or aggressive toward you.
That you misunderstood and took it that way does not make it so.
This is a technical discussion and may seem short and to the point, but that is often how technical discussions go.
I'd suggest you re-read what was said without taking the attitude that anyone was talking down to you, rather just presenting stripped down facts.


Sorry I had to post something to just laugh at this thread... Good thing Juan didn't chime in yet...  :dbtu:
"A person who never made a mistake never tried anything new." -Albert Einstein


@ Bquick,
Yes you got lucky and I'm happy for you but when the amp does have a really hard problem to solve you won't get much help if you take offense. This is not face book where everyone slags off at anything that has the slightest whiff of insult.
I was not trying to de-mean you in anyway,, just imparting the fact that you could go round in circles replacing parts shotgun style. More often than not it just complicates the problem.

As we say in my world,, shut up and play your guitar and don't take life so seriously.
So get over it as there are far bigger things in life to worry about.

And Don't forget to have fun. :tu:

Now that you understand (hopefully?) lets get back to the amp.
As you have the amp working again did you happen to note which cap was dud?
I'd be interested to know so we have record of the suss component for future reference.
That way you can help for the common good.
Thanks, Phil.