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January 26, 2020, 07:57:24 AM

Recent Posts

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1
Crack-a-two-a / Re: Possible Channel Imbalance
« Last post by XforceVesa2 on Today at 07:24:40 AM »
Are these measurements on the Crack-a-two-a without headphones plugged in?  If not, do be sure to give that a try too.

The Headphone wasn't plugged in during the measurements(Only the cable as the Headphone is detachable from the Headphone cable)
2
Crack-a-two-a / Re: Possible Channel Imbalance
« Last post by Paul Birkeland on Today at 06:41:14 AM »
Are these measurements on the Crack-a-two-a without headphones plugged in?  If not, do be sure to give that a try too.
3
Crack / Re: No sound in either channel
« Last post by Paul Birkeland on Today at 06:40:07 AM »
What DC resistance do you get between OA and OB and ground on the big board?  As always build photos can help too.
4
Crack-a-two-a / Re: Possible Channel Imbalance
« Last post by XforceVesa2 on Today at 01:43:17 AM »
I've mad new measurments on the Crackatwoa and it seems like that the Channel Imbalance is at every Volume setting at about 0,5dB.

I've also made new measurements on the Crack with different Volume settings and it seems like that the Channel Imbalance on the Crack is a lot lower than on the Crackatwoa(only about 0,2dB).

I don't know what causes this Imbalance on the Crackatwoa as all solder joints seems to be ok :/


Edit: The strange thing is if I plug the Input Tube from the Crack in the Crackatwoa the Channel Imbalance seems to be going worse(about 0,6dB)
5
Technical topics / Re: Preventing "Mullard flash"
« Last post by Deke609 on Yesterday at 07:18:28 PM »
Many thanks Tom and PB - this is good information and news.  So I'll chalk it up as "not a real world issue".  I do like, though, his simple auto-delay schematic using a fet. I'm sure it's quire common, but it was new to me.  Looks like a handy circuit.

cheers and thanks, Derek
6
Crack / Re: No sound in either channel
« Last post by Jimb0 on Yesterday at 06:08:20 PM »
Yes both tubes are glowing and OA and OB on the big board

LED's light up on the small board and the two at the bottom but not on the big board
7
Technical topics / Re: Preventing "Mullard flash"
« Last post by Paul Birkeland on Yesterday at 03:31:25 PM »
I have some issues with what's presented in the video.  Most importantly, the tube he's messing with has a manufacturing issue (as he mentions).  One side flashes very brightly (not the Mullard flash that I'm used to seeing) and the other side doesn't.  The other immediate issue is that he speaks in the beginning of "large tubes" having filament failure.  I would presume these were something closer to a thoriated tungsten transmitting triode perhaps, which is a lot different than a 12AU7. He then moves to the 5751, but it doesn't have a heater flash...


Next on the solution, so you put a 27 ohm resistor in series with the heaters that you can short with a switch.  If you forget to throw that switch, you're either putting only 2V into the filament half (just using his numbers for half a 12AU7).  If you leave a Crack like that with the power on, the 12AU7 won't draw the plate voltage down and you will risk damaging the rest of the amp.  You could also destroy the cathodes in the 12AU7 in the process because they are not adequately heated. 

My last issue is that I have piles of used Mullards that flash, but I can't ever remember throwing one away that had an open heater.  This is just anecdotal of course. 

8
Crack / Re: Low voltage on finished Crack (repost)
« Last post by Paul Birkeland on Yesterday at 03:06:53 PM »
You have to get the 6080 glowing before you do anything else.  If pin 7 to 8 on the tube measures 1 ohm, the tube should glow.  Perhaps the green wires running to the octal socket aren't well connected?
9
Crack / Re: No sound in either channel
« Last post by Paul Birkeland on Yesterday at 03:06:01 PM »
At which OA/OB, the big board or the small board?  Are both tubes glowing?
10
Eros Phono / Re: optimum output cap value
« Last post by kip.duff on Yesterday at 02:24:18 PM »
So since I'm feeding signal to 56k Ohms impedance (BeePre), 1.0uF is where I'm supposed to be.

Thanks so much.....
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