How are the MK VI+ meters measuring plate current?

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ViperGeek
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How are the MK VI+ meters measuring plate current?

Post by ViperGeek »

I realize the topic of MK VI+ and MK 8 meters has been covered before, but I'm trying to get a better understanding about the magic of tube amplification (yes, I know, 70 years late).

Based on previous posts here and on Head-Fi.org, I understand that the meters on the MK VI+ show the positive (+ve) plate current for one of each pair of power tubes resulting from grid voltage auto-bias. Typically, my OTL/OCL amp shows both meters at 70mA using vintage RCA 6AS7G power tubes. However, when I research the product sheet for the 6AS7G:

http://tdsl.duncanamps.com/show.php?des=6AS7G

it shows an "average characteristic" plate current of 125mA.

I'm assuming the specs show a maximum plate current and not an optimal plate current? If so, does the MK VI+ auto-bias the grid to achieve approximately 50% of the maximum plate current for a given power tube, or does it always try to maintain a ~70mA plate current for all power tubes?

Obviously, I'm very close to clueless and unaware of vacuum tube (valve) technology. Any details or background on how the Little Dot MK VI+ manages bias voltage/current, making such beautiful music using a variety of power and driver tubes would be greatly appreciated.

Thanks!

- Dave

DavidZheZhe
Posts: 1718
Joined: Mar 14th, '06, 01:25

Re: How are the MK VI+ meters measuring plate current?

Post by DavidZheZhe »

The meters actually show working plate current rather than maximum plate current. Due to the Class-A design, the amplification plate current is fixed.

djj65
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Joined: Mar 23rd, '17, 09:41

Re: How are the MK VI+ meters measuring plate current?

Post by djj65 »

Do the meters have to show the same values? When running my HD800S with a balanced XLR cable, they show the same current for left and right. I purchased an XLR to 1/4-cable to allow me to connect a different set of headphones, Denon AH-D7200. The left meter shows 30, the right shows 80, yet the sound seems very balance (equal sound left and right). Is that normal? or is it a concern?

DavidZheZhe
Posts: 1718
Joined: Mar 14th, '06, 01:25

Re: How are the MK VI+ meters measuring plate current?

Post by DavidZheZhe »

djj65 wrote:Do the meters have to show the same values? When running my HD800S with a balanced XLR cable, they show the same current for left and right. I purchased an XLR to 1/4-cable to allow me to connect a different set of headphones, Denon AH-D7200. The left meter shows 30, the right shows 80, yet the sound seems very balance (equal sound left and right). Is that normal? or is it a concern?
That's perfectly normal and nothing to be worried about.

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