Orange or120 glow screen grid

[g1]

Dropping 65v across the 1.5k screen resistor at volume is a screen current draw of 4.3mA, or 2.8W dissipation - well within limits and not enough in itself to cause the screen to glow.

He mentioned DC, regardless, I wouldn't trust many meters to give a good reading of the AC voltage across the screen resistors.
But he did mention the PI being imbalanced, and I think it is probably the "hot" side giving the screen problem.

Still waiting for the wall voltage and heater voltage readings in case there is a more appropriate primary tap available.
And having triple capacitance for the screen filtering may also be a contributor.

[binito]

He mentioned DC, regardless, I wouldn't trust many meters to give a good reading of the AC voltage across the screen resistors.
But he did mention the PI being imbalanced, and I think it is probably the "hot" side giving the screen problem.

Still waiting for the wall voltage and heater voltage readings in case there is a more appropriate primary tap available.
And having triple capacitance for the screen filtering may also be a contributor.

238 V AC Wall voltage
6,75 V AC heaters
5,1 V DC across the screen resistor without signal

Tomorrow I should like to inject a signal 1Vpp 1khz to see the outputs of the PI

https://dl.dropboxusercontent.com/u/...0/IMG_2495.JPG

https://dl.dropboxusercontent.com/u/...0/IMG_2497.MOV

https://dl.dropboxusercontent.com/u/...0/IMG_2487.JPG

[g1]

Make sure the PT primary is using the 240V tap, not 220.
Check that you have at least a couple volts drop across the choke.
From the video it looks like all the screens are doing it, just one side is happening sooner.
If you have caps closer to original value of C5 & C6, it would be worth a try to see if it helps. Perhaps who ever added the extra "stiffening" of the screen supply went overboard. More sag at the screen supply could make a difference.

Edit: supply stiffening of C25 & C26 could also have similar effect, what value are they?

[binito]

Make sure the PT primary is using the 240V tap, not 220.
Check that you have at least a couple volts drop across the choke.
From the video it looks like all the screens are doing it, just one side is happening sooner.
If you have caps closer to original value of C5 & C6, it would be worth a try to see if it helps. Perhaps who ever added the extra "stiffening" of the screen supply went overboard. More sag at the screen supply could make a difference.

Edit: supply stiffening of C25 & C26 could also have similar effect, what value are they?

It is rare that the primary of the transformer only has 2 wires and ground. No more wires in primary and and it seems the original transformer
C25 and c26 are 50 + 50uF
I think that screen voltage = 530v is too much for the current manufacturing valves.

[Mick Bailey]

Does the amp have an unused rotary voltage selector on the back?

[binito]

Does the amp have an unused rotary voltage selector on the back?

Yes. This rotary voltage selector is unused. No wires there . The wires of primary transformer go to on-off selector.

[g1]

The filter capacitors are somewhat larger C5-C6 are 100uF (33uF schematic) and c3-c4 are 22uF (16uF schematic).

C25 and c26 are 50 + 50uF

C25&26 should be the 100uf's, C5&6 should be 33uf (50uf close enough). Either they are installed in the wrong positions or you are confusing them. Try to get that sorted out.

Also, using a power resistor instead of the choke would drop more voltage to the screens.

[binito]

C25&26 should be the 100uf's, C5&6 should be 33uf (50uf close enough). Either they are installed in the wrong positions or you are confusing them. Try to get that sorted out.

Also, using a power resistor instead of the choke would drop more voltage to the screens.

C25- 50+50uf = 100uF
C26- 50+50uf = 100uG
C5- 100uF with 100k resistor
C6- 100uF with 100k resistor

What size of resistor after of choke?
Thanks

[binito]

Make sure the PT primary is using the 240V tap, not 220.
Check that you have at least a couple volts drop across the choke.
From the video it looks like all the screens are doing it, just one side is happening sooner.
If you have caps closer to original value of C5 & C6, it would be worth a try to see if it helps. Perhaps who ever added the extra "stiffening" of the screen supply went overboard. More sag at the screen supply could make a difference.

Edit: supply stiffening of C25 & C26 could also have similar effect, what value are they?

before of choke 528Vdc . After of choke 526Vdc. Pin4 power tuve 522Vdc.

[nickb]

before of choke 528Vdc . After of choke 526Vdc. Pin4 power tuve 522Vdc.

Just butting in here. Also measure the AC heater voltage. If it's much more than 6.3V it might be another indicator that the line voltage is too high (or not) for the power transformer primary.

[Mick Bailey]

Seems odd that there's an unused voltage selector. Does it look like it's had previous solder connections to it? Thinking about this from a manufacturing/liability perspective; fitting a non-operation voltage selector that suggests it may do something (but doesn't) would be insanity.

[Leo_Gnardo]

Seems odd that there's an unused voltage selector. Does it look like it's had previous solder connections to it? Thinking about this from a manufacturing/liability perspective; fitting a non-operation voltage selector that suggests it may do something (but doesn't) would be insanity.

Possible explanation - maybe something like this going on with the Orange. A customer recently brought in a '79 Hiwatt DR103. He said he thought it's a "Canada import" model. There was an AC line voltage selector, but no knob or plug on the back of the amp, just a cover plate. The appropriate 120V tap had been pre-selected and jumper wire soldered into place on the business end of the selector. Back of amp had an "Ontario Hydropower Approved" sticker on it.

OR the voltage selector was pre-fitted to the chassis on the Orange, then an "export" 120V mains transformer installed.

[g1]

C25- 50+50uf = 100uF
C26- 50+50uf = 100uG
C5- 100uF with 100k resistor
C6- 100uF with 100k resistor

What size of resistor after of choke?
Thanks

Change those caps up so that C5 & C6 are 50uf each, use the 100uf's for C25&26, you will end up with two 50uf's left over.
If that doesn't help, maybe someone will suggest a value to replace the choke with a voltage dropping resistor.

[binito]

Seems odd that there's an unused voltage selector. Does it look like it's had previous solder connections to it? Thinking about this from a manufacturing/liability perspective; fitting a non-operation voltage selector that suggests it may do something (but doesn't) would be insanity.

The voltaje selector has a previous solder connections . But now it hasn't wires conected.
I saw that the transformer had to be changed, although the side shields are the originals. Smell of burned inside, possibly from a previous transformer burned.
I saw that the secundary voltages are too high. 208-208 Vac( 180-180 in schematic) and 6,7Vac heaters. Therefore it has a B+ too high . 545Vdc and 535Vdc in screens.
I think that the primary of the transformer is 220Vac and i am introducing 238Vac
I think that the new tubes doesn´t support 535vdc in the screens and i need increase the value of screen resistors.
Another option would be to change the power transformer with one that has less voltage.

Can I put a resistor between the choke and the screen resistors ? Attached schematic with a example.
https://dl.dropboxusercontent.com/u/...OR120_BENI.jpg
Now the screen resistors are 1k5 7W
if i can, what value can i put between the choke and the screen resistors? 470ohm 5w for example?

Thanks in advance.

Change those caps up so that C5 & C6 are 50uf each, use the 100uf's for C25&26, you will end up with two 50uf's left over.
If that doesn't help, maybe someone will suggest a value to replace the choke with a voltage dropping resistor.

Now the C25&26 has a dual radial cap 50+50uF in parallel . (Equals to 100uF 500V?)
But the c5&c6 (100uF now) Yes, I'm going to change by a 33uF
By be 100uf c5 &c6 could be the problem, although the voltage is so high ?

Thanks

[TimmyP1955]

After I have tried to reverse the outputs of c23 and C24 (output inverter tube to input grid power tubes) and the glow screens moved to the other side of power tubes.

Sounds like a leaky coupling cap to me. Replace C23 and C24.