Orange Bass Terror 500W Low output signal problem

[stelios]

Hello everyone
I am a newcomer to this awesome forum & i would like to share a problem that i have with my bass amp head.
About a month ago while i was playing with my band at the studio & my amp suddenly stopped.
When my bandmates stopped playing & it was silence in the playroom I raised more the master & gain control knobs to see if i could get any output signal.
The only thing that I got to my ears was a very weak signal & an annoying electrical pulse from the cabinet speakers.
At first i thought it was the preamp tubes causing this so I replace them with newones but I didn't use the same 5751 tubes.
Instead of the 5751 i used a pair of 12AT7.I was planning to do that replacement before this problem with the low output signal occurs for a less high gained signal.
Anyway after replacing the tubes the problem persisted & nothing changed to better.So I decided to get the amp to qualified amp technician to solve the problem.
After a couple of days we spoked at the phone & he told me that he replaced the IC that controls the output circuit but the problem remains.
He also told me that the transistors of the output causing this & it is a very difficult repair for him & he would preffer not to deal with it.
At the end he told me that if I decided to let him to do the repair the cost of the repair would be 150 euros.
So i decided to repair it myself I have some electronics repair experience due to my work but i need some help
Is this a common problem on this amp head?
Should I replace all the output TRs & where i can find TR replacements in Europe?

Thank you in advance!

[The Dude]

Do you or the previous technician have a schematic you could upload?

[stelios]

The only schematic I have is the theroritical of the official manual that is given with along the amp.
I have no circuit schematic.

[Jazz P Bass]

Have you tried contacting Orange?
This is the BT500, correct?

As to troubleshooting this amp:
First & foremost the power supplies must be up to spec.
The correct Vdc & minimum Vac ripple.

If all is well there, then you can go gunning for the root cause.
I would not replace anything without knowing what parts have actually failed.

[Jazz P Bass]

Features & Specs:


Features


Single channel, hybrid – Class D power amp with valve preamp , variable input sensitivity for active or passive basses, balanced DI out, FX loop and built in isobaric speaker system

Controls: Volume, Treble, Middle, Bass, Gain

Output Power (Heads and Combos): 500 Watts

Valves (Heads and Combos): Preamp: 2 x Ecc83/12ax7

[ArdeliaAhrens]

i used to write an email to Orange and maybe you should try to do so...or maybe you can go to some store that sell Orange amps and see if they have the solution there...maybe they know what went wrong...