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Heater Wiring - the Good the Bad and the Ugly
Heater Wiring - the Good the Bad and the Ugly
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Old 3rd February 2016, 01:44 AM   #101
Wavebourn is online now Wavebourn  United States
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Heater Wiring - the Good the Bad and the Ugly
I use centre-tapped winding, rectify it using Shottky pair, and stabilize for small tubes. Output tubes are powered by AC, with one end grounded, as the result.
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Old 3rd February 2016, 01:47 AM   #102
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Heater Wiring - the Good the Bad and the Ugly
Quote:
Originally Posted by DF96 View Post
However, it would be good to know what caused the buzz. Strange buzz/hum problems are often a symptom of parasitic oscillation.
...or current flowing from the rectifier to the cap through the same ground with signal. Why some people prefer vacuum rectifiers, because they have high resistance and such errors don't cause audible hum.
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Old 3rd February 2016, 08:11 AM   #103
vuohi is offline vuohi  Finland
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Would this be possible even when the rectifier and the smoothing capacitors are grounded at a different point than the rest of the circuit? This seemed to cause the least noise when I was trying different grounding schemes.

Just wondering about the lower picture from the Valvewizard site, if I only have one heater winding and I'm powering two or more heaters, is the artificial center tap referenced to only one of the cathodes or what? So would the best implementation be that I run the twisted pair from the transformer to one of the tube bases, put the center tap resistors between heater pins and the cathode, and then run another twisted pair to the other tube bases in a daisy chain fashion?
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Old 3rd February 2016, 11:59 AM   #104
DF96 is offline DF96  England
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A heater circuit can only have one voltage reference. It doesn't matter too much what it is. If ground gives hum, try the cathode of an output stage.
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Old 3rd February 2016, 04:20 PM   #105
hewo is offline hewo  United States
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Isn't hum induced via cross talk inside the pt?
Were a different pt featuring dedicated windings used, would hum be favorable?
How are secondary windings wound independent of each other to optimize rejecting hum crosstalk?
Or is hum stemming from massive current (four bottles power, five or seven bottles preamp, plenty massive current)
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Old 3rd February 2016, 08:47 PM   #106
DF96 is offline DF96  England
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Hum is 50/60Hz AC. It is there in the secondary - that is what the secondary is there for. Heater wiring can cause hum via capacitive coupling, magnetic coupling or heater-cathode leakage. DC elevation helps reduce the last one (or just buy good quality valves). Good wiring practice reduces the first two.

Buzz can come from crosstalk inside the power transformer. AC grounding the heater wiring can reduce this.
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Old 4th February 2016, 06:52 AM   #107
hewo is offline hewo  United States
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Agree, massive heater draw of current has impact directly on hum noise, the equations revealing the propensity of it by way of a dimensionless representation of magnitude will be a power relational to amperes, and likely copper topology and mass (worse with heavy gauge)
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Old 16th March 2016, 03:52 PM   #108
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Quote:
Originally Posted by hewo View Post
Agree, massive heater draw of current has impact directly on hum noise.......................
Just repaired a friends 2A3 amp which failed prematurely; the output tubes were out. The cause too high mains voltage on the direct heaters. I checked this whilst in the UK and by chance found his 230V AC rated transformer actually running at the correct 230V AC voltage; but a minute later the supply rose to a wopping 248V. The 2A3 requires 2.5V so the ratio at 230V is easily determined, which makes it 8% over the limit at 248V, the heater running at 2.7V.

Anyone else had longevity issues with a 'wildly' high mains voltage ? Some parts in the UK has a shocking variation.

richy
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Old 16th March 2016, 08:29 PM   #109
hewo is offline hewo  United States
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Default utility power company line excursions

you're suppose to incorporate those MOV (metal oxide varistor?) protectors that blow shorts to the circuit breaker in the bldg, but at least surge is arrested before feeding amp vitals
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Old 16th March 2016, 09:29 PM   #110
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It isn't a surge when the 248V sits there for hours and gradually burns the emitters out ! The only solution is a constant volt transformer or go to indirect heating. This must also happen in the US; the line goes way out of operational spec.
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