Login / Register
 
Ampeg svt classic head tube problem
New Reply
Subscribe
Naindurth
Thread Starter
#1
5th December 2012
Old 5th December 2012
  #1
Gear addict
 
Joined: Apr 2011
Location: Buenos Aires, Argentina
Posts: 313

Thread Starter
Naindurth is offline
Ampeg svt classic head tube problem

Hi there!

The bass player in my band is having issues with his ampeg head.
After a proper warm up, one 6550 tube starts glowing orange, and the head automatically cuts off sound, I'm guessing to protect the circuitry.
We have already tried biasing but the first section is always off.
We're bringing it to a tech on friday, but he already said that it will need at least a complete retube of the 6550 power section.
Now a complete retube is a lot of money over here... I'm asking for a second opinion, because this tech guy is the only one we know of.
Any thoughts? Is his early diagnose accurate enough?
#2
6th December 2012
Old 6th December 2012
  #2
Gear maniac
 
Joined: May 2008
Posts: 282

Vitalis is offline
More than likely a faulty plate load resistor. Either it's open or, one of the socket contacts, where it's strapped across, isn't making contact with the tube pin. So, you either have to replace that resistor, or repair / replace the tube socket. When I say repair, I mean that a good tech could just squeeze the contacts together, but it will loosen up again eventually and have to be replaced anyway. If you just need to get through a gig than you can just remove that particular tube from it's socket and the amp should still have power enough to get you through.

As far as a complete re-tubing, I really can't say. If it's just the one tube red plating than I wouldn't re-tube it. There's really no failure - that I know of at least - that could cause all the tubes to go bad at one time, so first check all the plate load resistors and replace that tube that was in that socket.
#3
6th December 2012
Old 6th December 2012
  #3
Gear maniac
 
jlaugh87's Avatar
 
Joined: May 2008
Posts: 234

jlaugh87 is offline
I have an SVT-2Pro. At one point, I had a the same tube keep failing. Everytime I'd replace it, I'd re-bias and bam! the signal would cut off. This model SVT had a nice protection mechanism for when a failure occurs.

My SVT, and most (correct me if I'm wrong)have the power section in two sets of 3 6550's. There are two bias adjustments for each set, which is why matching the tubes is important (but can also be expensive). My problem was that my replacement tubes were some junky ones that I was trying to throw in with nicely matched JJ's.

This affected the bias current, causing problems.

My problem was resolved by buying a new matched set. Like I said though (and you probably know) matched tubes are more pricey, but the SVT is a hell of a machine that needs proper components.
Naindurth
Thread Starter
#4
10th December 2012
Old 10th December 2012
  #4
Gear addict
 
Joined: Apr 2011
Location: Buenos Aires, Argentina
Posts: 313

Thread Starter
Naindurth is offline
All right! Thanks for answering. It's good to know this info.
At least we'll know if the tech is trying to rip us off =P

I'll post back when we finally fix the ampeg head, to set the matter straight and close the thread.
Naindurth
Thread Starter
#5
29th March 2013
Old 29th March 2013
  #5
Gear addict
 
Joined: Apr 2011
Location: Buenos Aires, Argentina
Posts: 313

Thread Starter
Naindurth is offline
Well, a few months later we were finally able to bring the ampeg head to a trusted tech guy, and strangely it was only a bias problem.
I guess he adjusted it properly (or maybe the bias adjuster was faulty)... we feel a little ashamed of not being able to bias our head, but there you go.
Bias problem. Solved!
New Reply Submit Thread to Facebook Facebook  Submit Thread to Twitter Twitter  Submit Thread to LinkedIn LinkedIn  Submit Thread to Google+ Google+ 
 
Topic:
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Similar Threads
Thread
Thread Starter / Forum
Replies
Ronnie Dixon / Remote Possibilities in Acoustic Music & Location Recording
29
jebjerome / Geekslutz forum
8
SurfingMusicMan / So much gear, so little time!
6
jamesosullivan1 / So many guitars, so little time!
25
klaukholm / Remote Possibilities in Acoustic Music & Location Recording
4

Forum Jump

SEO by vBSEO ©2011, Crawlability, Inc.