5F6A low volume

[Chuck H]

Sorry to distract, but what is the source of this info?

There was a long thread here about it some time ago. Some trusted documentation was enlisted. I looked for it, but unfortunately "filament voltage" is such a vague term that I couldn't find it easily. I will look some more later and link it if I find it.

[g1]

There was a long thread here about it some time ago. Some trusted documentation was enlisted. I looked for it, but unfortunately "filament voltage" is such a vague term that I couldn't find it easily. I will look some more later and link it if I find it.

http://www.tubecad.com/july2000/page10.html
https://music-electronics-forum.com/...ad.php?t=35157
https://music-electronics-forum.com/...ad.php?t=18776

[Chuck H]

Thank you! It was the drop DC heater voltage thread. I didn't check that one because it's DC and I remembered the discussion being predominantly AC. Where that thread sort of ended up because I straight up hijacked it

[Dave H]

Nominal mains voltage in the whole EU (including Italy and GB) is 230V (+/-23V) since 1987 (IEC standard 60038).

It was a classic EU compromise (fudge). We (UK) were 240V and Europe was 220V so they set the harmonised (fudged) EU voltage limits to be 230V +10% -6% but no country actually changed its voltage. The 250V I measure here and the 220V measured in Italy are both legal! (But I still want to stay in the EU )

[Helmholtz]

It was a classic EU compromise (fudge). We (UK) were 240V and Europe was 220V so they set the harmonised (fudged) EU voltage limits to be 230V +10% -6% but no country changed its voltage. The 250V I measure here and the 220V measured in Italy are both legal! (But I still want to stay in the EU )

I was member of a mains related IEC standardization group for 10 years and know that the UK utilitiy representatives signed IEC 600038. You may call it 240V +5%/-10%, but it is still within the harmonized European voltage range. I wonder who is fudging. BTW, Germany did change from 220V to 230V.

[Dave H]

the UK utilitiy representatives signed IEC 600038. You may call it 240V +5%/-10%, but it is still within the harmonized European voltage range. I wonder who is fudging.

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.

[J M Fahey]

When I was young (mid/late 60Žs) Italian PA equipment designers knew their excellent amplifiers would be used anywhere from modern Technical Milan and guaranteed 220V to very little towns fed from long and too thin lines or small inadequate local "cooperatives" , where a brownout would be the normal situation, not the exception.

So every mixer/tape_echo/power_amps wheeled rack included at the bottom a "Power conditioner" , with an unusually large range of adjustment.

This particular Semprini unit has both coarse (40V steps) switcher, plus a fine 1 or 2V per step rotary control:





I used these 50 years ago and to this day am impressed by their quality, these do not look like Audio power amps but rather commercial TV or FM transmitters, repeaters, etc.

Excellent idea which should have been carried to this day, at least for popular touring bands.

Semprini always offered the highest quality "military/radio_amateur" style construction:

[vinceg]

Nominal mains voltage in the whole EU (including Italy and GB) is 230V (+/-23V) since 1987 (IEC standard 60038).

Yes, according to European standards. But we actually have the 220V

It was a classic EU compromise (fudge). We (UK) were 240V and Europe was 220V so they set the harmonised (fudged) EU voltage limits to be 230V +10% -6% but no country actually changed its voltage. The 250V I measure here and the 220V measured in Italy are both legal! (But I still want to stay in the EU )

I agree

[vinceg]

I replaced the rectifier valve with a solid state rectifier by 4 1n4007 diode soldered on rectifier socket. Can I solder a ceramic cap to suppress 50Hz hum across point 4 and 6, right?

[J M Fahey]

No, main filter caps deal with hum, a ceramic there tries to minimize line carried buzz or transients, but we are talking quite high frequencies.

[vinceg]

I think I've made a big mess even if I do not know how it happened. While I was touching with a chopstick the base board looking for the cause of the hum the amp is died. I read the anodic voltage at standby switch and there was strange. Then I read at secondary power trasformer output (325+325 VAC) and I think the power trasformer is died. These are the readings between ground and each of the two output. It should be 325VAC

These between the two output. It should be 650VAC. Between ground and Bias output I read 18VAC. It should be 50VAC. Also I read resistance between the power output and it is 74 Ohm, then it is right.

[Chuck H]

Swap the power tubes in their sockets and test the anodes again. Does the low voltage reading follow the tube or stay with the socket?

[vinceg]

Swap the power tubes in their sockets and test the anodes again. Does the low voltage reading follow the tube or stay with the socket?

I read the voltage without tubes and disconnect the circuit from trasformer

[J M Fahey]

I think I've made a big mess even if I do not know how it happened. While I was touching with a chopstick the base board looking for the cause of the hum the amp is died.

So some questionable/cold/flaky soldered union opened while chopsticking.
Find and resolder it.

I read the anodic voltage at standby switch and there was strange.

"Strange" ? ... can you please say some number instead?

Then I read at secondary power trasformer output (325+325 VAC) and I think the power trasformer is died.

Luckily for you, I donŽt think so
Transformers are expensive and hard to ship.

These are the readings between ground and each of the two output. It should be 325VAC (picture shows 314 and 223 VAC)

Please do not upload 3000 x 5000 pixel pictures.
Slow to load, waste of bandwidth and server space and in any case NO screen can display them.
Either set camera to no more than 1000 or 1500 pixel maximum or reduce size using any Graphics software before uploading.
Back to your tests: I do not suspect transformer (which if dead would be either open or smoking and burning fuses) but losing ground or some wiring.
Which is confirmed by:

These between the two output. It should be 650VAC.

And you have very normal 694VAC ... remember unloaded transformers usually show higher than nominal (loaded) voltages.

Between ground and Bias output I read 18VAC. It should be 50VAC.

Another stong hint at miswiring.
Reread between bias tap and center tap and I bet youŽll find your "lost" 50 VAC.

In an nutshell, your "ground" or wiring to it is highly suspect.

Also I read resistance between the power output and it is 74 Ohm, then it is right.

Not sure you are talking plate to plate OT DC resistance or 325+325 VAC winding end to end, but in any case that sounds normal.

Again please send smaller pictures, not larger than , say, 1200 x 166 pixel or thereabouts, and even smaller if possible.

Only place where we want high resolution ones is when you show full chassis and we want to be able to zoom in to read parts values.

Swap the power tubes in their sockets and test the anodes again. Does the low voltage reading follow the tube or stay with the socket?

We are talking winding AC voltages here.

"Secondary" in Latin language Countries refers to "winding" in Anglo ones.

[Chuck H]

Yes, I skim read and only caught "anodic". Then saw the two readings and thought he was measuring plate voltages. I'm on board now.