6.8k cap resistor blowing

for Dynaco Mark II/III/IV and DIY PP monoblocks

Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 2:21 pm

Geek wrote:Shorted cap?
I've had 'em right from the box that way as a manufacturing boo-boo :$

Not unless is shorted itself out over time....
Worked flawlessly for I'm thinking, hundreds of hrs.
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Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 2:27 pm

20to20 wrote:
wungun wrote:If I pull the tubes from om the Poseidon board, is there anything on it that would cause the issue that would still be functioning?
Pulling the K line is easy enough I guess....desoldering the can cap is something else altogether! Lol
1 step at a time I guess...


Desoldering the can cap (Q- cap) may not be necessary. Since I don't know which lug you have added the JJ caps to I'm assuming you could use them by disconnecting them from where they are now and tie them to the "K" pad on the board. Since you've replaced the 6.8K resistor you can just lift the output end off the Q-cap to make the new connection and disable that one Q-cap lug.

The board itself has a resonably high resistance path so a lower than expected resistance at the "K" pad would be a good clue as to the source of current draw. Could be just an errant solder splash...

One end of the JJ's is soldered to the star ground at the can, the other on the input leg of the can, marked "D" where a lead from the choke and a lead from the transformer attach.
Seeing as the K joint is powered just from that one cap section, and that one cap section is powered from the D point of the cap thru the 6.8K resistor, can I just lift those 2 points off the can and power it, or will something fry from the power to K not being smoothed?
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Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 2:59 pm

Removing the JJ's completely from the D section (80microF) and using them for powering the K point on the Poseidon would work and tell me if its a bad q-cap...but how would this alter performance?
Power to the Poseidon would be very well stiffened, but losing the extra capacity from the main power section...?
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Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 4:05 pm

Well, this is what I did, and the amp is running again! So I have a shorted/bad quad cap.
So I've basically removed the extra capacity from the 80mF section and replaced the 30mF section with 110mF
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Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 5:26 pm

Some anomalous voltages though...the 12V+ where I should be seeing 6.3VAC.
However, these voltages are identical on both amps! So I have to think its not from faulty components....?
I'm assuming those are for the tube heaters, as I'm seeing that at all tubes...
Image
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Re: 6.8k cap resistor blowing

Postby wungun » Sun Jun 28, 2015 8:21 pm

My mistake...should of measure pin to pin not pin to ground....
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Re: 6.8k cap resistor blowing

Postby Geek » Mon Jun 29, 2015 12:05 am

Was that a NOS can cap that had a shorted section or one from AES?
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Re: 6.8k cap resistor blowing

Postby wungun » Mon Jun 29, 2015 9:40 am

It's a Dynakitparts.com unit....the one with slightly more capacity than the originals. So, a remanufactured, new one.
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Re: 6.8k cap resistor blowing

Postby Geek » Mon Jun 29, 2015 2:07 pm

Which I believe they get through CE Distributing (the wholesale arm of AES)? I've had the odd bum one through them. Was replaced quickly with courtesy, though.
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Re: 6.8k cap resistor blowing

Postby wungun » Mon Jun 29, 2015 3:00 pm

Meh....I've run these ones for a couple of years now :(
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Re: 6.8k cap resistor blowing

Postby wungun » Mon Jun 29, 2015 3:47 pm

When I go to order a new one, I'll go for the MUCH less expensive, slightly lower rated one. The extra V overhead is just marketing hype I think.
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Re: 6.8k cap resistor blowing

Postby Geek » Mon Jun 29, 2015 8:19 pm

wungun wrote:The extra V overhead is just marketing hype I think.


Ummmm..... as you get experience with tube circuits, you'll probably reconsider. "Surge voltage" isn't hype... it keeps boiling electrolyte out of your eyes =:o

I personally avoid can caps like the plague. I'd rather use Nichicon GU series or Panasonic ED/EE.
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Re: 6.8k cap resistor blowing

Postby wungun » Tue Jun 30, 2015 5:57 am

My theory being, they are probably the same shitty can...
And I added CL80 thermistor's to each amp to help take the inrush.
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Re: 6.8k cap resistor blowing

Postby 20to20 » Tue Jun 30, 2015 8:15 am

wungun wrote:My theory being, they are probably the same shitty can...
And I added CL80 thermistor's to each amp to help take the inrush.


The CL-80's are not doing what you think they're doing.
Headed for Tishomingo to sing in a can...
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Re: 6.8k cap resistor blowing

Postby wungun » Tue Jun 30, 2015 10:41 am

The NTC CL80 thermistor is doing exactly what I want it to do, which is limit inrush current.
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