• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

What causes my 0D3 to extinguish?

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#21
arnoldc said:
I was able to finally replace the LED with 120R bypassed with 100uF.

When I measured the voltage at the 396A cathode, it now reads 1.6V.

I plugged it in to my system, but seconds after it played music, the right channel emitted a popping noise, and the 03D is blinking in symphony. I immediately turned it off.

Any thoughts?
Click to expand...


so:

1v6/120R=13mA per input tube

(400V-150V)/5600 = 44,6mA

44,6-2 x 13 =~ 18mA through OD tube

0D3 have range of 5 to 40mA , so middle is 22,5mA , and that must be minimum current through it;

to be safer - choose 25mA through.......

so - overall current is 25+2x13 = 51mA

(400-150)/51mA = 4K9 ........ instead 5K6 ........... use 4K7 !!

in your boots -I'll still use one 0D3 per one input tube
 
#25
When I see two non staggered LC resonators in a row, I worry. I'm not currently on a computer with PSUD2, but if you haven't already, you might want to run a sim, looking at behavior after a current step.

Without regard to hum, it might be interesting to replace one of the chokes with a resistor and see if the problem changes.
 
#26
Zen Mod said:
(400-150)/51mA = 4K9 ........ instead 5K6 ........... use 4K7 !!

in your boots -I'll still use one 0D3 per one input tube
Click to expand...
I heard you but I THOUGHT I will be drawing the same current with the change from LED to resistor. Will change it.

Because of the layout of the chassis I can only have one 0D3. Or I can dump the 5AR4 and use SS on the rectifier and put two 0D3.

poobah said:
Divide and conquer...

Move the OD3 and the 396 from the left channel to the right.
🙂
Click to expand...

I only have one 0D3. In fact I changed to 2C51 (both input tubes) and it still happens.

Tony said:
well, like all tube equipment, first thing you do is to replace the regulator tube and or input tube to see if things improve....

.
Click to expand...
Ok, I failed to change the 0D3 :smash:
SY said:
When I see two non staggered LC resonators in a row, I worry. I'm not currently on a computer with PSUD2, but if you haven't already, you might want to run a sim, looking at behavior after a current step.

Without regard to hum, it might be interesting to replace one of the chokes with a resistor and see if the problem changes.
Click to expand...
Hi SY, my rectifier is hybrid, i.e., 5AR4 + FR107. When I simulated with PSUD, I used 5AR4 bridge...

Will check it out again.
 
#27
arnoldc said:
I plugged it in to my system, but seconds after it played music, the right channel emitted a popping noise, and the 03D is blinking in symphony. I immediately turned it off.

Any thoughts?
Click to expand...

VR tube + parallel capacitor= OSCILLATOR! These puppies aren't like Zeners where you can just wire in a huge capacitor to kill the noise. Any sort of spark, arc, glow discharge has a negative resistance characteristic. That's just fine and dandy if you want an oscillator, but here you don't.

Either use the VR tube as part of an active regulator, or add the noise filter after the VR tube, but don't wire a capacitor across the VR.
 
#28
Miles Prower said:


VR tube + parallel capacitor= OSCILLATOR! These puppies aren't like Zeners where you can just wire in a huge capacitor to kill the noise. Any sort of spark, arc, glow discharge has a negative resistance characteristic. That's just fine and dandy if you want an oscillator, but here you don't.

Either use the VR tube as part of an active regulator, or add the noise filter after the VR tube, but don't wire a capacitor across the VR.
Click to expand...

Ok, ok. 😀 A previous recommendation suggested one, so I had a 0.05uF film across. Will remove it.
 
#37
Tony, I'm on the verge of doing that. While I really love the purple glow of the 0D3, I'm not that good with them.

I plan to rip this thing apart and put it in a better chassis I have or probably get one from Singapore as I'm headed that way two week from now.

In so doing, I will be able to finally make this amp fixed bias. So, in relation to that, what would you recommend for the fixed bias test points? What are they called anyway? I know it's not called RCA :smash:
 
#38
wish i had the time to do those, incidentally, you have done IT, why not try one of tubelab's power drive on your 300B...wonder how it will sound like?.....😀

SY's favorite, IRF820 can be had for 35 pesos or about 90cents...😀

good luck on your singapore trip, don't forget to check out Sim Lim Square, and Burlington Square in Bugis.....hope to be there late this year or early next year for my next job...😀
 
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