What causes my 0D3 to extinguish?

arnoldc · 23rd December 2007, 02:05 PM

I brought my latest 300B amp to a friend who has an ARC SP-8 preamp. We hooked up my amp, but every time he switches on the MUTE lever, the 0D3 on my amp extinguishes its purple glow.

Tonight, it happened that I turned off my preamp before the amp, and I saw the 0D3 extinguish its glow again.

What's going on?

(There was a thread on my 300B amp, but can't find it now. Current schematic attached. The series resistor to the 0D3 is 5k6.)

Zen Mod · 23rd December 2007, 02:12 PM

what's current through WE396B and through OD3?

arnoldc · 23rd December 2007, 02:14 PM

Almost 40mA... 16mA for each of the 396A

tubelab.com · 23rd December 2007, 02:16 PM

The direct coupling to your input tube's grid can turn your input tube into a shunt regulator if there is any DC on the input. I would add a resistor from the grid to ground. Your input impedance is very high and any leakage in the tube, or the preamp will affect the bias on the input tube, possibly causing it to draw far more current than you intend.

arnoldc · 23rd December 2007, 02:22 PM

Geez, wrong schema...

Hi George, there's a 100K from the 396A grid to ground...

Here's the correct one...

Zen Mod · 23rd December 2007, 02:31 PM

Quote:

Originally posted by arnoldc
Geez, wrong schema...

Hi George, there's a 100K from the 396A grid to ground...

Here's the correct one...

hairy guy gives you right answer ....... but - in your boots I'll use one 0D3 per one WE396 ........... taking care that each 0D3 draws no less than 20mA

arnoldc · 23rd December 2007, 02:34 PM

Ok, fair enough.

But what's exactly happening? If I'm playing music, how loud or dynamic it is, the 0D3 is fine.

astouffer · 23rd December 2007, 04:20 PM

An 0A2 was giving me similar results, connecting a small cap across the tube like .01uf cured the problem.

Tony · 23rd December 2007, 08:49 PM

Quote:

Originally posted by arnoldc
Ok, fair enough.

But what's exactly happening? If I'm playing music, how loud or dynamic it is, the 0D3 is fine.

hmmm.....only way i could think of is the mute circuit on your friend's preamp forces 0 volts on your input tube grid making it conduct heavily and starving your OD3 to cause it to eaxtinguish....try a coupling cap on your amp input.

arnoldc · 24th December 2007, 01:40 AM

guys, thanks to you all for your thoughts. I will try the recommendations.

Merry Christmas!

23rd December 2007, 02:12 PM	#2
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	what's current through WE396B and through OD3? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

23rd December 2007, 02:16 PM	#4
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	The direct coupling to your input tube's grid can turn your input tube into a shunt regulator if there is any DC on the input. I would add a resistor from the grid to ground. Your input impedance is very high and any leakage in the tube, or the preamp will affect the bias on the input tube, possibly causing it to draw far more current than you intend. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

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23rd December 2007, 02:14 PM	#3
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Almost 40mA... 16mA for each of the 396A

23rd December 2007, 02:34 PM	#7
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Ok, fair enough. But what's exactly happening? If I'm playing music, how loud or dynamic it is, the 0D3 is fine.

23rd December 2007, 04:20 PM	#8
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	An 0A2 was giving me similar results, connecting a small cap across the tube like .01uf cured the problem.

24th December 2007, 01:40 AM	#10
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	guys, thanks to you all for your thoughts. I will try the recommendations. Merry Christmas!

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