Origin 50 low output, short circuit

Pete Farrington

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Ok, my guess is that valve isn’t drawing any HT current.
Hence it isn’t working and so not passing any signal.
It would be a good idea to investigate that.
Without a schematic I can’t be more specific unfortunately.
 

Chicungo

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Ok, my guess is that valve isn’t drawing any HT current.
Hence it isn’t working and so not passing any signal.
It would be a good idea to investigate that.
Without a schematic I can’t be more specific unfortunately.
I have a schematic of the origin 20, is almost the same.
Was drawn by Jason Tong from Headfirst amplification. In his website is a more complete drawing.

Not in the drawings I can see in my amp that, Pin 1 of V2 receives HT from a eletrolitic cap (450V. 10uF), through a 4,7k dropping resistor. 400V is the HT through this resistor.


Origin 20  - original 2.jpg
 

Pete Farrington

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That drawing shows the V2 pins1-3 section as a cathode follower, so the pin1 anode voltage will be higher than normal due to the absence of an anode load resistor. What’s the pin3 voltage?
 

Chicungo

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That drawing shows the V2 pins1-3 section as a cathode follower, so the pin1 anode voltage will be higher than normal due to the absence of an anode load resistor. What’s the pin3 voltage?
The voltage at pin 3 is 74V

voltages V2 pins
1- 388V
2- 26,4V
3- 74V
4- ground
5- 14,2V
6- 206V
7- 0
8- 0
9- 7V
 

Pete Farrington

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Pin8 shouldn’t be 0V.
How about a full voltage survey, every pin of every valve.
Be careful, it’s much better to use probe clips on valve sockets and terminals etc, that can help to avoid the probe tip slipping off the terminal and shorting stuff.
 
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Chicungo

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Pin8 shouldn’t be 0V.
How about a full voltage survey, every pin of every valve.
Be careful, it’s much better to use probe clips on valve sockets and terminals etc, that can help to avoid the probe tip slipping off the terminal and shorting stuff.
I have the voltages IMG_20221005_133746.jpg
 

Pete Farrington

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Is R54 shorted?
eg what’s the resistance between V2 pin8 and 0V common?
If not, maybe a bad connection, eg failed solder joint somewhere in that area. Generally need strong lighting and visual magnification to see that kinda stuff.
 

Chicungo

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Is R54 shorted?
eg what’s the resistance between V2 pin8 and 0V common?
If not, maybe a bad connection, eg failed solder joint somewhere in that area. Generally need strong lighting and visual magnification to see that kinda stuff.
R54 is not shorted. And there is no resistance between pin 8 and 0V.

have a good light, but only 3x magnification.

I will try to see with that, but I will buy a macro lens for my Phone
 

Chicungo

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I’m confused, can’t make sense of the above, seems contradictory?
Hi, I am sorry, there was a thick layer of solidified flux on pin 8. is clean now.

The correct values are, Pin 8 voltage is 1,8V and resistance to ground is 2,2Kohm


I tested all resistors in the pre amp with the short circuit bip sound, and R72, R63 and R90, biped in the multimeter. I don't no if this is a valid test.

I learned now that I need to disconnect at least one leg of the resistor to accurtelly mesure it, do I need to do it with all the resistors?

Because the values are all ok and R63 in circuit mesures 0ohm and of circuit mesures the correct value.

Also mesured 1,8Amp around R58, that is a 1w resistor, but is visualy ok and the multimeter says the resistor is ok too.
 
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Chicungo

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I’m confused, can’t make sense of the above, seems contradictory?
I have made a video to show how the amp reacts when touched with probes on the pins with high voltage.

V1 almost no sound V3 very loud sound.

I noticed the gain knob does not work at all, the volume knob rises the volume to conversation lever.

The volume knob does nothing at all, no change in volume or gain.

 
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Pete Farrington

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I learned now that I need to disconnect at least one leg of the resistor to accurtelly mesure it, do I need to do it with all the resistors?
In most places, resistors can be measured fine in circuit. No necessity to lift one leg.
Occasionally there will be parallel resistive paths, and the measured value will be lower than the nominal value of the colour coding. In that case the schematic and some basic circuit analysis will indicate whether the measured value is reasonable / whether further investigation (eg lifting a leg) is called for.
Because the values are all ok and R63 in circuit mesures 0ohm and of circuit mesures the correct value.

Also mesured 1,8Amp around R58, that is a 1w resistor, but is visualy ok and the multimeter says the resistor is ok too.
I can’t make sense of either of the above points.
By 0ohm, do you really mean 0ohm, same as a short piece of wire, or do you mean infinity, an open circuit?
Each clause of the second sentence needs to be explained in detail.
When referring to a component reference number, eg R58, it’s helpful to also describe where it is in the circuit, eg V1 pin1 anode.
Given the fault, a full, readable schematic is pretty much essential to help you any further.
V1 almost no sound V3 very loud sound
Maybe the fx loop switching is bad, have you tried plugging a cable between send and return?

Have you eliminated a bad valve as being the cause of the issue?
 

Chicungo

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In most places, resistors can be measured fine in circuit. No necessity to lift one leg.
Occasionally there will be parallel resistive paths, and the measured value will be lower than the nominal value of the colour coding. In that case the schematic and some basic circuit analysis will indicate whether the measured value is reasonable / whether further investigation (eg lifting a leg) is called for.

I can’t make sense of either of the above points.
By 0ohm, do you really mean 0ohm, same as a short piece of wire, or do you mean infinity, an open circuit?
Each clause of the second sentence needs to be explained in detail.
When referring to a component reference number, eg R58, it’s helpful to also describe where it is in the circuit, eg V1 pin1 anode.
Given the fault, a full, readable schematic is pretty much essential to help you any further.

Maybe the fx loop switching is bad, have you tried plugging a cable between send and return?

Have you eliminated a bad valve as being the cause of the issue?
The resistance at R63=47k ( in series with C37 and pin 8 of V1), read the same resistance the same as a short piece of wire when in circuit.

R58 is a 22k that is in series with R69 and pin3 of V2.
I believe this one is faulty, I think I should not be able to read amperage here with the resistor in circuit.

I have already did the cable in fx loop, cleand it many times. Swap all the valves for new ones.

Tried different speacker, tried a load box.
 

Chicungo

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Ok.
The amp is fixed!

I want to thank all for the help.

The very low output was due to a resistor R65 (470K) by my mistake in it's place was a 470ohm, this made the output really low.

But the real problem of the amp was low and distorted output at 50W(was lower than 5 or 10W)

And the cause were the diodes in the backboard ( 1N4148 ), just before the speaker output jacks.

And new tube sockets, they looked good but were not.

Now I can rock again!

Thanks and hope this can help someone else.
 
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