5F6A low volume

[Helmholtz]

UK mains voltage is now 230V +10% -6%. It's not fudging if it meets the standard
The fudge was opening the window wide enough for everyone to get in without anyone having to change voltage.

Thanks, I misinterpreted.
Sometimes transition periods last much longer than intended, because no consent can be reached.
As reported, Germany raised mains voltage around 1987. I typically measure 225V to 230V. Nominal voltage doesn't account for voltage drops in the installation wiring.

[vinceg]

Yes, I forget I'm in a forum where the language is English. In Italy we say "primary winding" and "secondary winding" but to shorten we often use to say "the primary" and "the secondary". So, to understand each other better, let's say that first I measured the voltage across the two wire of the secondary winding and I read 694VAC. Then I measured the voltage across each one wires of the secondary winding and tap center, wich is connect to ground, and I read 314 and 223 VAC. This I not understand. I should have read 325 VAC. The 223VAC seems abnormal. Anyway, I found the the bias filter capacitors anod was not to ground. Now it's evening in Italy, tomorrow I'll check better.

[Helmholtz]

Yes, I forget I'm in a forum where the language is English. In Italy we say "primary winding" and "secondary winding" but to shorten we often use to say "the primary" and "the secondary". So, to understand each other better, let's say that first I measured the voltage across the two wire of the secondary winding and I read 694VAC. Then I measured the voltage across each one wires of the secondary winding and tap center, wich is connect to ground, and I read 314 and 223 VAC. This I not understand. I should have read 325 VAC. The 223VAC seems abnormal. Anyway, I found the the bias filter capacitors anod was not to ground. Now it's evening in Italy, tomorrow I'll check better.

As Juan indicated it seems that the center tap is not (well) grounded. You may measure secondary voltage between each "325V" wire and center tap (not chassis ground).
More important: Disconnect from mains, make sure that filter caps are discharged and measure resistance between center tap and chassis.

[vinceg]

As Juan indicated it seems that the center tap is not (well) grounded. You may measure secondary voltage between each "325V" wire and center tap (not chassis ground).
More important: Disconnect from mains, make sure that filter caps are discharged and measure resistance between center tap and chassis.

Sorry, but I do not understand what is happening to me. After I read your post, I unscrew center tap from chassis and measured between each "325V" wire and center tap. One is 323V, the other is 214V. Then, I measured voltage across the two "325V" wires and it is 694V. Then, I measured resistance between center tap (disocnnect from chassis) and chassis, it is 0. After, I measured voltage between "50V" wire and center tap (disconnect from chassis) and it is 18V. Now, or I'm crazy, or tester is faulty or I do not know but surely I will become crazy.

[Chuck H]

You should unplug the amp and not power up again until the problem is known.

Do you have all the power transformer secondary leads disconnected from any circuits?

EDIT: I mean the HV and bias secondary leads, not the filament leads.

[J M Fahey]

measured between each "325V" wire and center tap. One is 323V, the other is 214V.

Which adds up to 537V AC.

Then, I measured voltage across the two "325V" wires and it is 694V.

So somebody stole 157V from you
Clearly we have a measuring or gross miswiring problem here.
Please remove all secondary wires, including filaments, strip ends , tape them to a piece of wood so you can measure without need to hold them and remeasure.
Draw a transformer winding schematic and back it up with a picture, as a double check.

Weīll ask you for specific colour/tap pairs resistance and voltage measurements.

If itīs a "known brand" transformer also upload its winding data plan or schematic, BUT, do not copy it and say "this is what I have", rather draw what you see at the transformer, both drawings may not match at all.

[Chuck H]

Here's a thought...

If the bias supply secondary was not disconnected during the testing then a mistake in the bias supply wiring may be a problem because the bias supply is "tapped" from one side of the HV secondary.

What confuses me is zero resistance between the HV CT and chassis with the CT disconnected.

[vinceg]

Which adds up to 537V AC.

So somebody stole 157V from you
Clearly we have a measuring or gross miswiring problem here.
Please remove all secondary wires, including filaments, strip ends , tape them to a piece of wood so you can measure without need to hold them and remeasure.
Draw a transformer winding schematic and back it up with a picture, as a double check.

Weīll ask you for specific colour/tap pairs resistance and voltage measurements.

If itīs a "known brand" transformer also upload its winding data plan or schematic, BUT, do not copy it and say "this is what I have", rather draw what you see at the transformer, both drawings may not match at all.

I hade removed all secondary wires, exluded filaments, before make measuraments. Anyway, I'll remove also filaments. My transformer is Hammond 290DEX and these is datasheet. All wires colour match. Can you Tell me what to do, step by step, please?

[vinceg]

Here's a thought...

If the bias supply secondary was not disconnected during the testing then a mistake in the bias supply wiring may be a problem because the bias supply is "tapped" from one side of the HV secondary.

What confuses me is zero resistance between the HV CT and chassis with the CT disconnected.

To be honest, I did not understand what you asked me when you said to measure resistance. Probably the language does not allow us to understand well, especially when you use the abbreviations (HV, etc. ..) because in Italian probably the abbreviations are different. For this, I ask you, kindly, to help me to understand well what you ask me to do. I am grateful for your help.

[Pedro Vecino]

The stolen volts (it's funny) could come from having confused the center tap (CT) with the bias tap?

[eschertron]

The stolen volts (it's funny) could come from having confused the center tap (CT) with the bias tap?

I thought that too, but I see that while the two halves would not match, they would still need to add up to the total 694vac.

[Helmholtz]

I hate to say it, but if we can trust the measurements, the most probable explanation is an internal transformer short between part of the HV secondary and the core.
Needs to be verified, though.

[J M Fahey]

I hade removed all secondary wires, exluded filaments, before make measuraments. Anyway, I'll remove also filaments. My transformer is Hammond 290DEX and these is datasheet. All wires colour match. Can you Tell me what to do, step by step, please?

Yes:

Please remove all secondary wires, including filaments, strip ends , tape them to a piece of wood so you can measure without need to hold them and remeasure.
Draw a transformer winding schematic and back it up with a picture, as a double check.

Weīll ask you for specific colour/tap pairs resistance and voltage measurements.

If itīs a "known brand" transformer also upload its winding data plan or schematic, BUT, do not copy it and say "this is what I have", rather draw what you see at the transformer, both drawings may not match at all.

You did less than half of this, so we canīt check for inconsistencies.

And when I ask you to draw or measure something without looking at the transformer datasheet or trusting memory or written notes, please do that.

[Reader]

Also I wish to ask if you have been getting any other strange readings when using your meter? Many other threads ask that the battery in the meter be replaced in such situations. Also, you could try a different meter if you have one. These suggestions are not a guaranteed solution. Just an idea.

[vinceg]

Yes:

You did less than half of this, so we canīt check for inconsistencies.

And when I ask you to draw or measure something without looking at the transformer datasheet or trusting memory or written notes, please do that.

Ok, I hope I've done well until now. I removed all secondary wires and strip ends. I isolated the wires and I left Orange wires connect to chassis.
Voltage at wall of my home is 220 VAC

-I measured resistance between the two Red wires and I get 74 Ohm
Voltage between the two Red wires is 690 VAC

-I measured resistance between the two Yellow wires and I get 0.1 Ohm
Voltage between the two Yellow wires is 5.09 VAC


- I measured resistance between the two Green wires and I get 0.05 Ohm
Voltage between the two Green wires is 6.4 VAC

I have not measured between Bias and center tap because last night while I was measuring the 500mA fusein bias wire is burned, then I'm scared. I suspect the problem is at 50 VAC out winding.

Now I'm waiting for instructions