Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chocopower on September 19, 2011, 09:24:36 am

Title: Low power Orange OD120
Post by: chocopower on September 19, 2011, 09:24:36 am

Hi there!

I´m working with an Orange OD120  (4xEL34) that with volumen and master volumen on 10 has less power than my 2 6V6 amp.

Voltages on power tubes are pretty high and seems ok.

After play it for ten minutes, two of the power tubes get redplating (left side ones).
i have to check the bias and install a new set, just for eliminate posibilities, but i dont think the redplating can produce the low power problem.

my next step is check the coupling caps after the P.I.

any other idea?

thanks in advance.

Title: Re: Low power Orange OD120
Post by: chocopower on September 20, 2011, 06:59:23 pm

schematic:

http://users.telenet.be/orangefg/OFG_SCHEM/ODschem_A.gif (http://users.telenet.be/orangefg/OFG_SCHEM/ODschem_A.gif)

Title: Re: Low power Orange OD120
Post by: PRR on September 21, 2011, 07:46:08 pm

Low output AND redplating means you really have to go through EVERYthing.

If your car was slow and overheating, it could be spark-plugs, spark timing, soot in the pistons, fuel injectors, dragging brakes, bad wheel bearings, trash on the radiator.......

Title: Re: Low power Orange OD120
Post by: chocopower on September 21, 2011, 08:13:17 pm

thanks,
that was i affraid...

Title: Re: Low power Orange OD120
Post by: scarlett amps on September 23, 2011, 08:38:51 am

Sounds like it could be the ot. Do this and check it out.Marshall trafo de saída (http://www.youtube.com/watch?v=QQNVyYEzcJ8#)

Title: Re: Low power Orange OD120
Post by: chocopower on October 31, 2011, 10:50:06 am

i think is the OT too..... :BangHead:

I open the amp and found damages in bias circuit and diode rectifier bridge. Several diodes burned and some resistors out of range.
After make a complete rebuild of those areas and check the hole amp, the problem still is there...

I´ll check the OT next week and come back with the results...

Title: Re: Low power Orange OD120
Post by: chocopower on November 18, 2011, 12:23:48 pm

One question?

I have a trafo with 34v secondaries. Is safe put those 34v into the secondary to measure it in the primaries or should i use a lower voltage?