5E3 voltages

[shagual]

Hi,

I've built a 5E3 some time ago and all seemed to be perfect, but today I bought myself a new multimeter (Fluke True RMS 175) and went through the amp to measure the voltages. It seems that I get different voltages on both DMMs especially on the filaments. Is this due to the new true rms multimeter?

I'll write below the voltages first the ones with the new Fluke.

AC wall voltage: 235AC, the amp is wired to 240ac on the PT primary.

-B+ voltage: 373 vs 374 (seems to be ok)
-b+1 voltage (5k 5watt): 325dc vs 326dc (ok)
-b+2 voltage (22k 5 watt): 240dc vs 238dc (ok)

I guess these voltages are fine on both multimeters for B+, B+1 and B+2.

Plates of V1 (12ay7):
- PIN 1: 119dc vs 115dc (already 3% difference)
- PIN 6: 123dc vs 119dc (3% difference)


filaments:
- with the old multimeter for ground: 2.8ac and 2.9ac, when connecting the meter between the 2 filaments I get: 6.1AC

- With the new one: 3.34AC and 3.19 measured from ground and between the 2 filaments: 6.52.


I guess I'm measuring the filaments the right way but 6.52AC is quite high to my opinion, especially when the power transfo is wired to 240AC with 235 from the wall.
Is there anything about a True RMS reading I'm forgetting?

Thanks,
Wim

[cminor9]

I cannot answer your question about true RMS being any different, but my first thought was when did you take the readings?

The voltage differences you are seeing are pretty small. Did you measure them at the same time using each DMM, or were the measurements from the old DMM taken at a different time? It might very well be that your wall voltages were different when you took the readings.

You probably know this, but I'll say it anyway: I don't think the voltage differences are anything to be worried about.

[Tom Phillips]

I agree that there's nothing to worry about for any of the voltage readings you took.
True RMS should not make any difference since the heater voltage will be a pretty clean sine wave.
You don't say what your first meter is, how old it is etc but I suspect that you are just seeing differences in accuracy for each meter. In reality, there is no way to know which is correct from the information you supplied. However, my gut feeling is that the new Fluke is probably more accurate.

[shagual]

Thanks,

well the old meter is a pretty cheap instrument but it gave me a perfect 6.3 on the heathers when I wired my PTs on 230AC with around 235 from the wall. All voltages above were taken at the same moment

That was my only concern, wiring my amps to 240 or 230 in function of the filaments I was getting.

We are getting on an average around 235 from the wall, so I guess wiring them up to 240 on the primary won't be any problem.

thanks

[tubeswell]

Lots of meters give slightly different readings, and even the same meter can 'give' slightly different subsequent readings. (makes it sound like one of those gypsy psychic women aye? - Hey - I have a new nickname for my meters ) And what's more the AC voltage at your wall supply will be varying any how. The battery could be flatter on one of the meters. The older one might be more worn out. But pinpoint accuracy is not important. As long as its within a few volts of 'true', it gives an indication that the amp is functioning as it should. If you like the readings that the old meter gives you, why not use that one .

[Alby]

The meter is only as good as the factory calibration, and over time it will only get worse from there. Unless you can have your meter calibrated to factory specifications or better, this tolerance is the best you can hope for.

As stated above, with respect to guitar amps it's nothing to worry about.

Alby.

[d95err]

Within 10% should be considered more or less spot on.

[shagual]

Thank you all.

I made a summary of all the voltages I'm getting compared to the current Custom Shop and from there on the voltages with a NOS rectifier and a 12ay7.
Might be intresting for new builders.

http://users.telenet.be/pierssens/5E3/