60hz filament hum from high wall voltage?

[lightfoot]

Has anyone on the forum experienced excessive filament home due to higher than normal wall voltage? At first I thought it was a shielding problem and that may still be something I have to address but I noticed that when I took my amp to my friends house the hum was much quieter and his wall voltage was 5 Volts less than at my house. For some reason the power company has my wall voltage at 125 V AC. Currently my filament voltage is hovering around 7 1/2 V. I took the amp to work which also had a lower wall voltage and it was right around 7 V. As far as I’m aware this power transformer is rated for 120 V AC. That being said I suspect that I may be down around 117-118VAC before it goes down to 6.3 volts. I’m beginning to think that the need for a variable voltage supply is becoming unavoidable at this point.Any thoughts would be appreciated

[xtian]

My service is commonly at 125v, no issues. This has never caused increased hum in an amp here. But if your heater voltage is that high, I'd definitely try to address it, to preserve tube life if nothing else. You can install one or two 1R/5W resistors in series with the heather circuit.

[lightfoot]

My service is commonly at 125v, no issues. This has never caused increased hum in an amp here. But if your heater voltage is that high, I'd definitely try to address it, to preserve tube life if nothing else. You can install one or two 1R/5W resistors in series with the heather circuit.

One resistor on each filament lead?

[sluckey]

Sounds like you could use one of these...

[lightfoot]

Sounds like you could use one of these...

Yes either something like this or a Variac of some sort. I suspect that some good coaxial cable will really help as well but I’m trying to address the issue right at the source. It’s a single-ended 5-watt amplifier so you don’t have the benefit of the phase cancellation of a push/pull set up but it seems like it should still be a bit more quiet. In a perfect world I could take a variable power supply and start around 115 V with test lead hooked up to the filaments and just increase the voltage until I get 6.3 V on the money from the filament supply. I think I would be in a better position to assess than 60 cycle noise level once the voltage is correct.

I have tried moving the output transformer all over the chassis and it makes absolutely no difference so it doesn’t seem like it’s related to inductive coupling between the two transformers.

[R.G.]

Yes either something like this or a Variac of some sort.

A variac that will run your amp is much heavier and more expensive. You could also read up on the Vintage Voltage Adapter from 1999 at geofex.com. The "Buckaroo" looks remarkably like the schematic of the deluxe version. I packaged one of these into a single Bud Converta-Box for a friend with a vintage Fender and manged to get the transformer and electrical fittings all inside the box. Tight fit, though, to do safely.

[sluckey]

The "Buckaroo" looks remarkably like the schematic of the deluxe version.

The idea came from your website. Not many ways to disguise that simple circuit. Thanks... Steve

[xtian]

My service is commonly at 125v, no issues. This has never caused increased hum in an amp here. But if your heater voltage is that high, I'd definitely try to address it, to preserve tube life if nothing else. You can install one or two 1R/5W resistors in series with the heather circuit.

One resistor on each filament lead?

Start with one resistor on one leg of the heater winding. Use a second resistor if more voltage drop is needed.

[WhopperPlate]

Has anyone on the forum experienced excessive filament home due to higher than normal wall voltage? At first I thought it was a shielding problem and that may still be something I have to address but I noticed that when I took my amp to my friends house the hum was much quieter and his wall voltage was 5 Volts less than at my house. For some reason the power company has my wall voltage at 125 V AC. Currently my filament voltage is hovering around 7 1/2 V. I took the amp to work which also had a lower wall voltage and it was right around 7 V. As far as I’m aware this power transformer is rated for 120 V AC. That being said I suspect that I may be down around 117-118VAC before it goes down to 6.3 volts. I’m beginning to think that the need for a variable voltage supply is becoming unavoidable at this point.Any thoughts would be appreciated

About a year ago I posted a thread dealing with similar issues at my home. Environmental buzzing and amp hum were severe at my home compared to anywhere else the amps were played . It was determined to be related to poor house grounding and compounded by nearby construction sites and radio towers . A new 8ft ground rod installed solved the majority of issues. Can’t help what gets picked up by a single coil pickup , but amps are happier now and silent .

While lowering 125vac to 120vac is a good call, electrical hum and buzz from poor power quality , grounding issues, and environmental interference won’t be remedied by bucking transformers , variacs and resistors.

[lightfoot]

Is it possible that an output transformer that’s out of phase based on the wire color code could cause a little hum even without negative feedback?

[WhopperPlate]

Is it possible that an output transformer that’s out of phase based on the wire color code could cause a little hum even without negative feedback?

I just spent a few days testing playing around listening to the sonic differences when reversing transformer input and output polarity on a twin style single tap 4 ohm output transformer. Hum was never an issue .

You already said it boss, your friends house was quieter. probably less environmental interference over there or better electrical grounding . Maybe you can optimize your amp further , but for me that says it all . Play a bunch of small clubs and venues and this won’t be a surprise.

[R.G.]

Good points Whopperplate. A high impedance ground is a subtle but possibly dangerous variant of a bad building. In the USA, buildings are actually fed center-tapped 240-250VAC. If the distribution panel has a high impedance to actual solid earth ground, a heavy load on one "120V" side will pull down that side, and anything on the opposite side will see voltages above the nominal 120-125Vac. Like - a lot more. A high impedance ground can get you 150Vac or more on the less-heavily loaded side. That will saturate your transformer's primary, all right.

[lightfoot]

Is it possible that an output transformer that’s out of phase based on the wire color code could cause a little hum even without negative feedback?

I just spent a few days testing playing around listening to the sonic differences when reversing transformer input and output polarity on a twin style single tap 4 ohm output transformer. Hum was never an issue .

You already said it boss, your friends house was quieter. probably less environmental interference over there or better electrical grounding . Maybe you can optimize your amp further , but for me that says it all . Play a bunch of small clubs and venues and this won’t be a surprise.

I think the reason I’ve been uncertain about this is because of the fact that the OPT is single-ended rather than push/pull. But if that’s a moot factor then it is what it is. I will add that a lot of new residential construction is going on immediately behind my house as we speak so there’s that. Interesting point about the fact that U.S. line voltage is center tapped 240 and the importance of grounding…

[WhopperPlate]

I will add that a lot of new residential construction is going on immediately behind my house as we speak so there’s that.

I had two houses in my neighborhood remodeling at the time . Before the grounding rod was installed I could hear all kinds of oddball noises whenever the workers plugged in their tools. Power drills were the best.

I had also used an AM radio turned down to “listen” to the induced noise from different circuits in the house; they would all squeal and tweak through the air . In this condition things like LED lights would be horrendously noisy

God bless the ground rod , that mostly went away, but I will still get occasional interactions from neighbors power tools

[LOUDthud]

In the USA there is supposed to be a ground wire at the power pole connected to that center tap of the 240V. Each "customer" is supposed to also ground the center tap at the incoming breaker panel. In my city, they caught a guy that was going around to power poles cutting off the safety ground (it's only #10 or #8 AWG) with a hatchet to steal the ground wire and sell it for scrap.