OR80 low output

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rickcruz
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OR80 low output

Post by rickcruz » Mon Jul 13, 2009 10:13 pm

Hello Peoples Of Orange,

This is my first post, and I'm honored to be here. I've never worked on an Orange amp.
I have a used OR80 head that exhibits lower volume output that I would expect. When it was first brought in, the amplifier had an over-twisted gain pot and the customer suspected that as the problem leading to the low volume. I've since reinstalled it with a lock washer in place. The pot tests fine, but the output was still low. I then installed a new set of JJ E34L's and put in new JJ preamp tubes.
I have measured an average of 505 volts on the plates of the power tubes, and have set the tubes to draw around 30ma's.
With the amplifier turned off, I have measured the primary windings of the output transformer (between the center tap and each wire going to pin 3 of each E34L). They are almost balanced....one measuring about 13 ohms and the other side 16 ohms. A "plate to plate" measurement yields 29.4 ohms, which is about right for a 100 watt OT.. Perfectly normal, right?
The secondary of the output transformer measures consistently low resistance....5,4,and 3 ohms respectively between ground and each parallel tap. Again...normal readings.
So what gives? I cannot find a schematic for comparison. Strangely, I disconnected the negative feedback wire from the speaker selector and it made no difference in volume. Something fishy is going on. I would love to get an accurate schematic of this OR80. The serial # is 5*5, if that helps.
Thanks for the time and someone shoot me a link to a schematic!

chrismathewsjr
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Post by chrismathewsjr » Mon Jul 13, 2009 11:50 pm

Here is the schematic for the OR120.
http://users.telenet.be/orangefg/OFG_SC ... post74.jpg

The OR80 is identical, minus two EL34s.

You've more or less gone through everything I would have done at first test, replaced the valves and biased, and checked the OT (which appears normal).

I would leave the feedback pot connected.

Have you tried swapping out preamp valves? Have you checked to see if any of the cathode resistors have drifted? It's possible preamp bypass caps have blown open as well.

Has the amp been recapped? It's possible for low volume and output power to be caused by failing or old power supply filter caps.
'74 Orange OR120 w/Contemporary Avatar 4x12 V30s
'04 Orange AD30 w/Traditional Avatar 2x12 w/G12H30s

http://www.jooniorstudios.com/
http://www.youtube.com/user/chrismathewsjr/

rickcruz
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test points

Post by rickcruz » Tue Jul 14, 2009 3:32 pm

Thanks for the reply, and in answer to your questions, yes, yes, and yes.
I've noticed that there are 5 test points on the circuit board labeled TP1 through TP5. It would be nice if anyone knew what the voltages should read. The readings I get are;
TP1 507 vdc
TP2 399.8 vdc
TP3 348 vdc
TP4 .001 vdc or .076 vac (maybe some leakage?)
TP5 .002 vdc or .080 vac (leakage?)

Anyone know about this?

Thanks.

rickcruz
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Post by rickcruz » Tue Jul 14, 2009 4:47 pm

Also, the schematic you sent me does not match up with what's on this circuit board. So far, there are about 18 (!) resistors that DO NOT match this schematic. I am putting in another call to Orange to see if any of their amp gurus know anything about this.
I'll try and keep you posted.

chrismathewsjr
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Location: Seattle, WA - USA

Post by chrismathewsjr » Tue Jul 14, 2009 5:11 pm

Is this a pics & text model or a pix only model of the amp? If it's pix only, we'll have to get to the pre-'72 schematic, found here:
http://users.telenet.be/orangefg/OFG_SC ... hem_72.gif
'74 Orange OR120 w/Contemporary Avatar 4x12 V30s
'04 Orange AD30 w/Traditional Avatar 2x12 w/G12H30s

http://www.jooniorstudios.com/
http://www.youtube.com/user/chrismathewsjr/

rickcruz
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Joined: Mon Jul 13, 2009 9:30 pm

Post by rickcruz » Mon Jul 20, 2009 3:39 pm

This is a pics and text model, but the schematic you just linked me to is closer to what I'm seeing on this circuit board.
Look at the inside of this amp. Does it look like it was rewired by someone else?

<img>
<img>

Like I mentioned earlier, when I disconnected the negative feedback wire from the "16" ohm lug, there was no change in volume, which would lead me to believe that something went wrong in the neg. fb. loop. Further investigation of the low output problem reveals that the presence control does not work either. I have no information on the history of this amplifier. It was a trade in at a local music store and the salesperson did not check it out before it was bought in as a used item. If the components on the board do not match any of the schematics, I will have to assume that this amp was built or badly modified by someone else. I noticed lots of plastic zip ties around most of the wiring and thin, newer looking wire used. I've looked at some photos online of some Orange amps and the wire they used looks different.
Let me know if anyone out there has any insight on this. In the meantime, when I get back to my shop I'll compare components with the schematics and rebuild everything if necessary!
If my pictures don't post, I'll reply with a link to them.
Thanks for reading this!

rickcruz
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Post by rickcruz » Mon Jul 20, 2009 3:41 pm

Image

Image

Tibor
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Post by Tibor » Mon Jul 20, 2009 4:16 pm

its a 90s reissue...maybe an schematic for an Orange OTR should be closer...
to me it looks like stock....at least my both reissues look quite the same!

Image

bclaire
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Post by bclaire » Mon Jul 20, 2009 6:01 pm

That amp looks pristine to me. I have both original and reissue OR80M's and the reissue is definitely less loud. Also the volume knob was put on oriented wrong so just moving the knob helped me to turn it up louder... :D

rickcruz
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Post by rickcruz » Thu Jul 23, 2009 3:13 pm

Hey Orange Hero,

Thanks for the schematic. I'm sure that the output problem is originating from the negative feedback loop circuit. The presence control does not function and the volume of the amplifier does not change when I disconnect the negative feedback wire from the speaker selector switch's "16" ohm leg. I wish I had more history on this amp so I can find out if anyone has been messing with it!

kevinjose356
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Re: OR80 low output

Post by kevinjose356 » Fri Jan 20, 2012 2:05 am

Still I have original one & Its works perfectly fine for me at least !

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