Ampeg svt pro2.HELP!!!

[estiy]

I have a recurring problem.I can do a months gigs or more and the amp performs perfectly and then on the occasional gig the protection circuit cuts in and shuts the amp down.This can take place in any venue,club or festival.I have had it looked at by a tech who could find no problem.Just in case,I got him to change the 6550 output valves,and,the circuit readings are as given on the schematic.Last night I was using the amp in a club and after an hour the amp shut down,I switched it back on,and it was allright for another 15 minutes,then it shut down again,after that each time I turned it on,it only functioned for 30 secs or so,sometimes shutting down before I could even get it out of standby.After 30 mins of trial and error I left it for 10 mins,I started it up again and it stayed on until the end of the show(30 mins).This fault never occurs when I'm with the tech.As I live and work in Spain it is not easy to find experienced Ampeg repair techs,however,the guy I use is highly rated by my associates who use Fender,etc.Has anyone had a similar problem that could maybe shed some light on possible causes.Then I can get the tech to check these out.Thanks in hope!!!.

[black_labb]

I have a recurring problem.I can do a months gigs or more and the amp performs perfectly and then on the occasional gig the protection circuit cuts in and shuts the amp down.This can take place in any venue,club or festival.I have had it looked at by a tech who could find no problem.Just in case,I got him to change the 6550 output valves,and,the circuit readings are as given on the schematic.Last night I was using the amp in a club and after an hour the amp shut down,I switched it back on,and it was allright for another 15 minutes,then it shut down again,after that each time I turned it on,it only functioned for 30 secs or so,sometimes shutting down before I could even get it out of standby.After 30 mins of trial and error I left it for 10 mins,I started it up again and it stayed on until the end of the show(30 mins).This fault never occurs when I'm with the tech.As I live and work in Spain it is not easy to find experienced Ampeg repair techs,however,the guy I use is highly rated by my associates who use Fender,etc.Has anyone had a similar problem that could maybe shed some light on possible causes.Then I can get the tech to check these out.Thanks in hope!!!.

i have little experience but it seems heat may be the culprit. the heat must be setting something off.

[Amp Kat]

Tubes. Have them checked by a tech who has a tube tester. The light won't come on unless it detects a fault and bad tubes create shorts. If you change all the tubes and it still does it then a tube caused a resistor to either fry or open up.

[Enzo]

How about your speaker cord? Is it a real speaker cord, NOT just a guitar cord? And is it in 100% condition? The amp might be shutting down for load problems.

[oc disorder]

I've seen a couple of them the faults all relate to dry joints that I have encountered.
The main board has to be removed and flipped and all solder joints touched up.
Its a major pain to get it out but thats what I would do.
The last one I saw the graphic led was flickering on and off.
I thought it was just a dirty remote switch jack but there was a dry joint
on one of the pins in one of the multipin connectors causing it .

The other one just had the usual dry joints around the power amp section
and didn't show up on the bench but only when it was getting hammered
in a real life situation...

To speed up dissassembly take a photo of all the transformer spade connections and even do a little song and dance number sorry a little sketch
of where they all go (colours to pin numbers) this will save time on the bench.

Thats my 2c worth....

[oc disorder]

Whoops I was referring to the SVT 111 pro the transistorised o/p one in the above post.
Sorry .. got my 2's and 3's mixed up.

[Amp Kat]

The II is similar to the Original Classic but has a graphic EQ board in the front. I can take it apart with my eyes closed almost. The main thing to remember is to take the preamp tubes out before pulling the main board out. Mark your connectors and spade connectors and it's not that bad. Check the 10 ohm resistors and the traces going to the TLO-72's & 74.Not very much to them they are just flat ass heavy and hard to menuever. The Fault light is a power issue and could be a bad connection as Enzo was stating or tubes or a connection.

[estiy]

Thanks guys for all your input(especially Amp Kat,I will get the 10 ohm resistors and the traces to TLO-72's and 74,s checked).I have one more question.As I often play the night following a problem gig and the amp performs perfectly,could it be the power supply in certain areas(are these amps that sensitive?)does anyone know the lower and higher tolerances of power supply.As I live in Spain the voltage is supposedly 220/240 A.C(but not to be guaranteed).If I had an idea of the drop-off points e.g 200/250,then I could arm myself with a test-meter and measure mains voltage whenever the problem occurs.If I get a reading outside the limits,then,the responsibility switches from myself to the promotor.I have already spent a load with two different techs,neither could find anything wrong on the bench,I have had the valves replaced,and,the valve bias was set with a meter while the amp was on bench-test.It is such a great sounding amp it would be a crime if I had to substitute it.