Should plate voltage fluctuate?

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MetalHeadMike

MetalHeadMike

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I just checked voltage at pin 3 and it fluctuates from 477-500. I was first plugged into power through a Furman AR-15 voltage regulator but then bypassed it and took power direct from the wall outlet and same thing. Voltage slowly, but consistently fluctuates whether I check at pin 3, across a screen grid resistor, or one of the HV caps.
 
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Depends on the voltage in your house. It can fluctuate. Every structure has its own quality of electricity.
 
Check and see if the wall voltage flucuates, if it does, it's not your amp.
 
The voltage in your house will fluctuate on a particular breaker depending on how your house is wired associated with fridges turning on and off, washing machines, dishwashers, regular light load switches turned on and off, etc.

The power company is only required to be within a percentage of 115 or 120V, but to be exact on the frequency of the voltage at 60Hz in the US.

If you’re concerned, voltage regulators are what you’re looking for.
 
Line voltage & current draw will make plate voltage flucuate.
230v HVAC/Stoves/Washer/Dryers can all affect plate voltage/bias.
But it all should be within spec. Don't really trip.
 
RedPlated said:
I'd say it's a bit odd to fluctuate that much in a short period of time. Get a $50 Variac and your voltage will always be consistent. Mine is set at 117v all the time. Doesn't matter what the wall voltage is. For voicing an amp it's a must.
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No, that’s not true.

A variac is not a voltage regulator. It only steps up or steps down voltage, it does not regulate to a particular voltage. It will not solve the problem of variance, only the minimum and maximum for which it will fluctuate.

As far as how much, that’s also expected. It’s stepping up 115V AC to 360-0-360V AC, where the outer taps secondary are used to rectify and filter the DC voltages we normally know of. Lower supply filtering on the secondary will make the change even more noticeable.

OP needs a voltage regulator to resolve the problem and a variac after to change that regulated voltage to something else if desired.
 
All good input folks, thanks!

Like I said, I'm using a Furman AR-15 voltage regulator, so I thought it odd the voltage across the plates was fluctuating. I get the voltage straight out the receptacle will vary...hence my investing in the Furman.
 
MetalHeadMike said:
All good input folks, thanks!

Like I said, I'm using a Furman AR-15 voltage regulator, so I thought it odd the voltage across the plates was fluctuating. I get the voltage straight out the receptacle will vary...hence my investing in the Furman.
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Spec on the unit says it will regulate to +/- 4V on the output which means 8Vpp AC, which is exactly what you’re seeing on the secondaries in DC plate voltage change. You’ll need a tighter regulator to get better accuracy in AC so that your DC regulated plate voltages aren’t walking. Have you verified something isn’t wrong with the regulator?
 
MetalHeadMike said:
All good input folks, thanks!

Like I said, I'm using a Furman AR-15 voltage regulator, so I thought it odd the voltage across the plates was fluctuating. I get the voltage straight out the receptacle will vary...hence my investing in the Furman.
Click to expand...
I was wondering why all the regulator advice when you said it in the op. And I would assume your regulator is probably doing its job. But just to be sure; you have verified the input AC voltage is not fluctuating, right?

That is very strange. Do you have another set of tubes you could try? And this would be a super longshot but pull the PI tube and see if it changes.

Also, measure the bias voltage. Does it vary?
 
I use the regulators as well. Wall voltage can fluctuate within 5- 7 volts on the average, maybe a little more depending. This will affect your tube's current draw. If you bias the amp when voltage is lower, your bias will jump up some when the voltage fluctuates higher, and vice versa.

This will effect the tone hence part of the reason one complains why his amp sounds like shit one day and not the next. Kidding there but there might be something to it. :cool:
 
I think it's the house supply/wiring. Checked this morning and it was solid at 493 at the plates but then after playing checking a back/forth, it was dipping down to 487 and back up. That was power straight from the wall receptacle. I think House voltage is all over which makes sense since it's an older house with shitty wiring. The lights throughout this house often flicker and do weird things.

I'll wait and see where things are at the plates once we move into our new house in January.
 
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