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stratplayer1

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So my friend has this old laney pro tube lead 100 watt head, Im thinking of buying it from him, it sound great but, on the low gain imput it sounds like it should be louder when its turned all they way up and on the high gain imput it sequels and cuts off when the master volume is above half. Is this a bad output transformer? or what usually causes this type of problem? I would love to fix it and buy it because it sounds great but with the current problem its not loud enough for large gigs. Also it cuts off when I boost the low gain channel with a eq volume boost or distortion that raises the volume dont know if thatll help any. Thanks I appreciate any help.
 
The squeal sounds like noise from the transformer, from what you describe.  That would imply a wiring/component problem.  I would wait for CB to chime in on the potential transformer issue, but if it works I would guess that is not the problem.  I could see it heating up and failing, but then it wouldn't work...  If you are looking for a project this might be good, but if you just want an amp, I would be very wary.
Patrick

 
Oh yeah, if you do not know anything about the insides of the amp, don't go poking around.  It will fry you.  Death by electric shock is not nice.  Leave that for the shallow end of the gene pool.
Patrick

 
Yeah I'm not an amp expert by any means this would be my first tube amp, I've head output transformers can cause problems like this but after reading since I've posted this I've heard it can also just be the tubes, It only sequels for a sec after you turn it to the cut off point and then once you go past that it just goes dead, I'm really hoping its something minor cause its a pretty sweet amp, and yeah it has no problem playing I played it at quarter volume for like an hour straight so I don't think its anything to do with heat.
Oh yeah I've head plenty of fun electrocution stories, im taking the ask novice questions approach as opposed to the ooo whats this do approach.
 
If the guy selling it is reasonable, he won't mind you or he taking it to a shop to get an estimate for repair.  If not, then walk away.
 
Its not the output tranny.

Output trannies do not give different results from different channels.  Also... they tend to squeal when the plate leads are reversed, but the squeal is evident at the lowest, and in fact any volume level. 

I'd say... without looking... that you have a real good case of "shit for tubes".  Buy it.  It can be fixed.  Tubes, and maybe other simple fixes... such as... replace leaking (DC leakage) coupling caps, replace a screen grid resistor or two.. and voila... back in business.
 
Good news I'm definitely going to jump on it and start getting it worked on, thanks CB and everyone else for the input.
 
and don't ferget to slam the price wayyy down! :hello2:

Edit- for your troubles :occasion14:
 
hey guys i just put the new tubes in it and it didn't fix it, although it sounds a lot better it still cuts out above about half volume any other suggestions? should i just take it to a tech?
 
Yea, take it to a tech - it's almost impossible to diagnose without it on the bench in front of you.

It's fixable though - might even just be a bad pot on the master for all I know.
 
Before you take it to a tech, try one more quick and easy fix. Get a can of electronics cleaner and take the knobs off the front of the amp.  Get a whole bunch of paper towels, individual ones not on the roll, and clean the pots.  To do this I generally crunch up a towel, put it under the pot, spray the shaft of the pot, twiddle it around, wipe off the cleaner, spray, twiddle, and wipe it all off.  Do this for all of the knobs.  It clears up quite a number of problems.  You can also spray the instrument cord shaft and clean the input jack/s the same way.

I am not guaranteeing that it will work, but it just gets you to a point where you have a better idea of what is wrong.  And a cleaner amp to boot.
Patrick

 
On some heads, the low gain will have less volume, or maybe it's a perception but .....

the squeal is something to be concerned about, simple, tell him you want to buy it but this squeal will need to be fixed.  Ask him if he will give you a discount, say half the price of the repair, and if the repair is more than $100 he eat what ever is over $100.  After all he doesn't want to sell you piece of crap?
 
Tried the electronics cleaner, it didn't work, oh well, I'm gonna drop it off at a tech tomorrow I'll let yall know how it goes, thanks for all the help and ideas. :guitarplayer2:
 
Rats...  The electronics cleaner works wonders on pots that live with smokers, and they tend to have interesting scratchy sounds.  For 10 bucks, cleans those things right up...  Too bad that wasn't the problem, next up is the caps...
Patrick

 
Another "cut out" example is a poor ground on the input, or volume control.

And... another is a leaky coupling cap (or tone stack cap).  When they leak DC voltage, they tend to whack the bias of the next tube in the signal chain.

 
as usual you just went over my head with the coupling cap thing, your knowledge of all things amp never ceases to amaze me, i dropped it off at a tech today, he builds his own line of amps so im pretty confident in him, maybe one day I'll buy a book to learn about amps, they are quite interesting anyone know of any good amp books?
 
The guy already got into the amp today and called me, he said my output transformer is pretty messed up so there goes 150 for a jcm 800 spec output transformer, hopefully it'll be back to me the end of next week, thats the prediction anyway
 
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