Orange AD50 Bias

[Perkinsman]

I'm unable to find a schematic on this Orange amp. I'd like to calculate the plate dissapation for the EL34's in the AB mode. Can someone assist on the location of the power transformer center tap is in this picture?

[vintagekiki]

1)
For schematic as a first aid can serve schematic for Orange Retro 50
https://forum.orangeamps.com/viewtopic.php?t=53587

https://ampgarage.com/forum/viewtopic.php?f=6&t=14754
^{You must log in or sign up}
http://ampgarage.com/forum/download/file.php?id=55164
^schematics
http://www.mediafire.com/file/m3unb3gklb4zdwb/Cattura_2.JPG/file
^lay

[Mick Bailey]

It looks like a bridge rectified HT supply without a centre tap. Check the resistance between the grey and black leads to see if that's the heater CT.

If you meant to say the output transformer centre tap, this is usually taken off the first filter cap, which looks to be the orange lead coming off the can cap top right. With the amp discharged check the resistance between this and pin 3 of each output tube and you should see the primary resistance each side if this is correct.

EDIT; the black leads look like they only feed the indicator lamp in this amp. If the grey lead isn't a CT it could be connected to an internal screen.

[J M Fahey]

I´m guessing diffeent.

I see NO bridge rectifier but a "full wave" one, "2 rectifiers", on ly that each of them is made out of 2 x 1N4007? in series.
Violet wires to their anodes are the ends of a CT HV winding expect some 300VAC at each of them relative to grpund, and some 600VAC violet to violet.
If so, probable HV CT is the grey wire soldered the star shaped star ground multi-terminal bolted to chassis.

Rectified HV appears at joined HV diodes.

Using white wire **everywhere** (was it on sale?) definitely does not helpfollowing connections.

&.3V filament winding does not need a copper center tap, for ages it has been simulated by a pair of 100 ohm resistors.

In any case, why do you wnt to calculate dissipation for?

I bet Factory knows what they are doing when they release an amp to the public.

Do you want to bias it to mythical 60% orn 70%?
That´s only Forum nonsense, with no base on reality.

Proper bias is no less, no more, than what´s necessary to erase the low level crossover notch, anything higher is a waste of energy and useful amp power.

[Jazz P Bass]

"Proper bias is no less, no more, than what´s necessary to erase the low level crossover notch, anything higher is a waste of energy and useful amp power."

Eloquent & beautiful statement, Juan.

It brought tears to my eyes.

Thank you.

[vintagekiki]

http://www.orangefieldguide.com/orange_mods.htm#_bias
Bias Orange Amps

http://www.orangefieldguide.com/orange_mods.htm
Tech info and Modifications for Orange Amps

https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/51116-help-please-1973-marshall-super-lead-el34-to-6550s-bias-question/page2#post783007
About biasing tube guitar amplifiers

http://web.archive.org/web/20120623045707/http://www.diyguitarist.com/GuitarAmps/PowerTubeBias.htm
Common Power Tube Bias Charts

[Mick Bailey]

I see NO bridge rectifier but a "full wave" one, "2 rectifiers", only that each of them is made out of 2 x 1N4007? in series.

Taking another look and I realize my lack of observation!

[Perkinsman]

""probable HV CT is the grey wire soldered the star shaped star ground multi-terminal bolted to chassis....Do you want to bias it to mythical 60% orn 70%?
That´s only Forum nonsense, with no base on reality....."

Oh boy, every time I think I'm getting the hang of some of these electronic concepts, I read something different...Yes, I was aiming for about 70% of max plate dissapation for tube longevity. According to Uncle Doug on youtube, in order to achieve that, several resistance and voltage measurements & calculations need to be made from each plate to the B+, which is off the rectified side of the rectifier OR (correct me if I'm wrong), the center tap of the OT. I know that pin 8 is where the B+ lives on a typical guitar amp rectifier but I'm just learning where it comes off solid state rectifiers.

So, I'm a little confused. Which is the B+ here, the white wire coming off the rectified violet wires? the grey wire from the PT to the ground wheel? or the first cap orange wire?

[Perkinsman]

Ok, maybe I didn't explain that right. The B+ can always be measured at the plate but I also need to the resistance between the plate and the OT center tap and I'm not sure how to locate that on a solid state rectifier.

[The Dude]

There will be 3 wires on the OT primary. One to each tube and the center tap. Just find the CT wire.

[Helmholtz]

See post #3.

[vintagekiki]

Ok, maybe I didn't explain that right. The B+ can always be measured at the plate but I also need to the resistance between the plate and the OT center tap and I'm not sure how to locate that on a solid state rectifier.

Orange AD50 Bias

Set the switch on the back to position Class AB 50W.
Connect a DVM (200mV range) to the Bias test point.
With VR47k set the quiescent current for one tube to a value of 25 - 30 mV.
The setting of the quiescent current has no effect when the amp works in Class A 30W.

[Jon Snell]

Orange AD50 Bias

Set the switch on the back to position Class AB 50W.
Connect a DVM (200mV range) to the Bias test point.
With VR47k set the quiescent current for one tube to a value of 25 - 30 mV.
The setting of the quiescent current has no effect when the amp works in Class A 30W.

You have drawn the 1R resistor in the wrong line!
Move the resistor to the switched ground line. Your calculations and method are correct.

[vintagekiki]

You have drawn the 1R resistor in the wrong line!
Move the resistor to the switched ground line ...

The 1R resistor is drawn where needed.
See better schematic.


When the switch is in position Class AB 50W, the right section switch shorts Rk and connects the cathode power tubes to the 1R bias test point resistor.
If you still think the 1R resistor is in the wrong line, please draw it properly.

[Jon Snell]

The 1R resistor is drawn where needed.
See better schematic.


When the switch is in position Class AB 50W, the right section switch shorts Rk and connects the cathode power tubes to the 1R bias test point resistor.
If you still think the 1R resistor is in the wrong line, please draw it properly.

Your schematic is now identical to my drawing and correct.

[vintagekiki]

You're right. You have the Eagle's Eye. Thanks.