Bias Meters for the Bee Pre for that Retro Look

[vinayarora]

I have just joined this forum and currently in the waiting for the Bee Pre kit. I ordered it few days ago.

I want to install the analogue bias meters to give my amp a Retro look.
Appreciate if anyone can tell me if I need the 100mA / 200mA / 300mA

Since I would be doing a custom chassis and should not have any problem mounting it easily on the front panel.

-Vinay Arora

 

[Grainger49]

You will need one per channel, or one that reads the sum of the current.  Summing it really gives no information.

 

[vinayarora]

You will need one per channel, or one that reads the sum of the current.  Summing it really gives no information.

I will be using two (one for each channel)
How much mA meter will I need?

 

[Paul Joppa]

The bias is unconventional. It is fixed, and so is the plate current - both use regulators.

The best thing to monitor would be the plate voltage (not current) which should be about 100 volts -  a 150vDC or 200vDC meter would be suitable.

 

[Paul Birkeland]

The bias is unconventional. It is fixed, and so is the plate current - both use regulators.

The best thing to monitor would be the plate voltage (not current) which should be about 100 volts -  a 150vDC or 200vDC meter would be suitable.

Could the meter go between the output of the voltage regulator and the input of the C4S?  It would be a touch high because of the LED bias, and there'd be ~145V coursing through the meter, but assuming the meter is plastic, this might work?

 

[Paul Joppa]

Well, it could, but it would always read 145 volts. The 300B plate voltage will drift up as the tube ages, alerting you to replacement needs before things fail. The filament voltage, bias voltage, regulated voltage, and plate current are all regulated and won't change unless something catastrophic happens - and you'll know that anyhow! So I figured the useful thing to do with a meter is monitor the health of the tube.

 

[Grainger49]

Is there any concern about the meter resistance affecting the  sound?

 

[vinayarora]

The bias is unconventional. It is fixed, and so is the plate current - both use regulators.

The best thing to monitor would be the plate voltage (not current) which should be about 100 volts -  a 150vDC or 200vDC meter would be suitable.

Thanks PJ for the insight. I will then go with the DC voltmeter as suggested.
I guess the input of 220 Volt which I am getting as I am in India will not affect this DC voltage and I will still be good with a dc meter with 150V DC range. Can you please confirm this.

--Vinay Arora

 

[Paul Joppa]

that is correct.

Sorry, I forgot the start-up transient. The voltage will go high, possibly 250v, initially, then pull down to 100v as the 300B warms up. The regulator will kick in later, but it's isolated by the current source plate load so the plate voltage won't change then.

So, I would go for a 250v meter. Most meters can take a short-term excess if it's not too large, but unless you can find manufacturer's specifications on that it's unwise to rely on it.

 

[Grainger49]

Paul,

Will the plate voltage float high before everything turns on, or will the regulator keep that from happening?

 

[Paul Joppa]

Ooohhh good point, it will go very high at first!  Maybe 250v.