Orange Rockerverb Mk1

[totoxraymond]

Hi everyone,

My dear friend brought me this beauty, he bought it about a year ago, but we don't get any sound anymore.
I found a schematic attached to this post.

First, i spotted that the HT fuses for the output tubes we 500mA instead of specified 250mA... Looks like a "put a bigger fuse and it will stop blowing away" kind of thing, doesn't look right to me...

Then i started measuring voltage for the power PCB, everything looked normal. So i then looked at the preamp and there i found i got no C, D, E or F voltage.
This obviously pointed me toward R1 which effectively measures open.

My plan is to change this resistor obviously, but i'm wondering what could cause this resistor to burn? maybe there's a bad tube in the preamp somewhere.
I'm not very experienced with tube amps so i thought i might ask you guys what do you think about this?

Unfortunately i don't have a tube tester so i might buy a few preamp tubes just in case i have to change one.

Another thing that puzzled me is that D1 (flywheel diode for RL2) has been paralleled with a 330R resistor and it looks a lot like a "repair job". Why would someone do that? D2 has been left untouched.

Thanks in advance for your help.

Thomas

 

[Alva Goldbook]

This is a puzzle. It's interesting that Orange made R1 a 4w resistor. Why it would blow, I'm not sure. There's a few higher current preamp tubes in this amp, so maybe it demanded it. I think I would use a panel mount 5 watt resistor for R1 if the circuit board looks like it sustained any heat damage. The 330r in parallel with the relay flyback diode makes no sense to me either. I would replace the ECC81s just to be on the safe side. Double check the plate resistors too. Beyond that, things are a mystery. I have seen bad preamp tubes do some weird things before. Especially JJ's.

 

[totoxraymond]

Hi!

Thanks for you answer!

Since then, i replaced R1 with a 5W resistor (mostly because i didn't find a 4W). R1 Was really dead but didn't seem to have suffer any heat damage. Maybe it's been damaged during transport... (The resistor was installed a few cm from the pcb, probably to allow more heat dissipation).

I also changed all preamp tubes, mostly because they were no-brand chinesium tubes (somme were marked e83cc others ecc83...)

As for the resistor in parallel with the flyback diode, i left it there for now, since it's not looking to cause any harm. I'll have to revisit the amp to change a fuse holder when i receive the part, i might remove it then.

For now, the amp is working again though i have yet to test it for more than a few minutes.

Thanks again,

Thomas

 

[CJ]

47k 4 watt , probably just in case a tube goes south and you get plate voltage into the bias circuit.

250 ma fuses, best to jumper those silly things and get some RCA or Amperex power tubes.