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December 07, 2021, 10:25:06 AM

Author Topic: adding a mA meter to the Kaiju  (Read 1095 times)

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Offline Larpy

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adding a mA meter to the Kaiju
« on: December 04, 2020, 12:14:24 PM »
I love the idea of adding a couple of mA meters to my Kaiju, but there's not much room under the chassis.  If I were to remove the input pots, is there a way to install meters in their place, or is that spot too sensitive in terms of picking up noise from the cathode?
Larry

Online Paul Birkeland

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Re: adding a mA meter to the Kaiju
« Reply #1 on: December 04, 2020, 01:22:32 PM »
You can drill holes in the wood base to add meters.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Larpy

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Re: adding a mA meter to the Kaiju
« Reply #2 on: December 04, 2020, 03:40:22 PM »
Better to place them in the middle of the wood base than where the input pots are?
Larry

Online Paul Birkeland

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Re: adding a mA meter to the Kaiju
« Reply #3 on: December 04, 2020, 04:37:13 PM »
If you are comfortable enlarging the holes in the chassis where the pots are, you could probably do that.  You'd have to relocate the pots or eliminate them from the design. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Larpy

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Re: adding a mA meter to the Kaiju
« Reply #4 on: December 11, 2020, 08:28:12 AM »
I added a couple of meters.  Pretty straightforward procedure.  Now for one last question:  both channels of my Kaiju have 72 mA of current going through the cathodes.  I assume that as the tubes age, the mA measurement will go down(?). At what point should I become alarmed and think about getting replacement tubes?
Larry

Offline johnsonad

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Re: adding a mA meter to the Kaiju
« Reply #5 on: December 11, 2020, 09:03:26 AM »
Nice job Larry! That looks great and a really nice looking build!
Aaron Johnson

Offline Paul Joppa

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Re: adding a mA meter to the Kaiju
« Reply #6 on: December 11, 2020, 11:17:38 AM »
I added a couple of meters.  Pretty straightforward procedure.  Now for one last question:  both channels of my Kaiju have 72 mA of current going through the cathodes.  I assume that as the tubes age, the mA measurement will go down(?). At what point should I become alarmed and think about getting replacement tubes?
There are many ways a tube can fail. But if it is simply worn out, the cathode loses emission. An often used criterion is when the transconductance drops to 70% of new. For Kaiju, that amounts to about 4mA reduction in current. This is a small change and hard to see on a meter! Even worse, it's sensitive to power line voltage - a 5% change in the power line has the same effect as a 30% change in transconductance.


The reason it's so small is the self-adjusting nature of cathode resistor bias.
Paul Joppa

Online Paul Birkeland

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Re: adding a mA meter to the Kaiju
« Reply #7 on: December 11, 2020, 12:01:49 PM »
I assume that as the tubes age, the mA measurement will go down(?). At what point should I become alarmed and think about getting replacement tubes?
I have some very dead 300Bs that still draw about 70mA, it can be pretty tough to tell in a Kaiju!
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Larpy

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Re: adding a mA meter to the Kaiju
« Reply #8 on: December 11, 2020, 04:09:51 PM »
So the appeal of adding meters is mostly cosmetic?
Larry

Offline Larpy

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Re: adding a mA meter to the Kaiju
« Reply #9 on: December 11, 2020, 04:14:00 PM »
Nice job Larry! That looks great and a really nice looking build!

Thank you, Aaron.  I still plan on springing for the Takatskis you recommended.  A matter of when, not if.
Larry

Offline 2wo

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Re: adding a mA meter to the Kaiju
« Reply #10 on: December 11, 2020, 04:33:43 PM »
It may be mostly cosmetic but they sure look good...John
John Scanlon

Online Paul Birkeland

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Re: adding a mA meter to the Kaiju
« Reply #11 on: December 11, 2020, 05:24:39 PM »
So the appeal of adding meters is mostly cosmetic?
Yes.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Natural Sound

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Re: adding a mA meter to the Kaiju
« Reply #12 on: February 21, 2021, 01:31:57 PM »
Yes.

Is that true of the MonAmour 2A3 as well or is the meter more useful in the 2A3 topography?

Offline Paul Joppa

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Re: adding a mA meter to the Kaiju
« Reply #13 on: February 21, 2021, 03:20:17 PM »
The MonAmour has a switch which changes the 2A3 plate current, and in the high-current mode it requires a modern 2A3 with higher plate dissipation rating than old-stock 2A3s. So the meter indicates the current to help prevent accidentally risking older tubes.
Paul Joppa

Offline Natural Sound

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Re: adding a mA meter to the Kaiju
« Reply #14 on: February 21, 2021, 03:48:14 PM »
The MonAmour has a switch which changes the 2A3 plate current, and in the high-current mode it requires a modern 2A3 with higher plate dissipation rating than old-stock 2A3s. So the meter indicates the current to help prevent accidentally risking older tubes.
Thanks for the explanation P.J. That is a very useful feature indeed. You guys always think of clever stuff like that.