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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

View Poll Results: a kit amplifier or home-brew amplifier
A kit amplifier 3 10.71%
Home-brew amplifier 18 64.29%
Both are equally good 6 21.43%
No opinion… 1 3.57%
Voters: 28. You may not vote on this poll

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Old 26th Jan 2012, 11:23 pm   #101
Don_Zalmrol
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Default Re: I want to build a stereo headset valve amplifier

Project is done, the feet and chassis are mounted together and it sounds great!

Thank you all for your help. If someone wants to take a close look, here is the link to my website (sorry, it's in Dutch)

12AU7/ 6CG7 amplifier
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Old 27th Jan 2012, 1:28 am   #102
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Default Re: I want to build a stereo headset valve amplifier

Well done Laurens, I'm really pleased you finished it, and so quickly too.
I'm glad you found all the help you needed here.
So what is the next project going to be...?
Rob.
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Old 27th Jan 2012, 10:45 am   #103
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Default Re: I want to build a stereo headset valve amplifier

Thx, maybe fiddling around with some nixie valves
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Old 31st Jan 2012, 9:45 pm   #104
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Default Re: I want to build a stereo headset valve amplifier

Problems
Hi all, I'm playing my OTL headphones amp now for almost a week.
And without any problems, hums or anything out of the ordinary until today…

Suddenly the right channel was nearly completely silent. So I've opened the amp and everything checks out from the connections.

I've plugged it back in and everything plays as it should.
I've tested it on another source (my laptop) and will change it back to my TV as it was.

Since I've opened the amp I've made a small change in the power distribution from the HT caps (1 and 3) by soldering a bleeder resistor (22K/ 2W) to dissipate the power from the caps when the amp is turned off and is much safer to work with if I ever needed to change anything…

What also gotten my attention is that the pin 9 on both 6CG7's valve sockets aren't connected. Should I ground these pins or let them stay as they are?
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Old 31st Jan 2012, 9:50 pm   #105
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Default Re: I want to build a stereo headset valve amplifier

The datasheet here shows pin 9 connected to an internal shield, so best connected to chassis but may not make any difference at AF.
Rob.
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Old 31st Jan 2012, 9:58 pm   #106
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Default Re: I want to build a stereo headset valve amplifier

Ok, soldering them to the chassis.
I'm noticing that the bleeder resistors I've put between caps 1 & 3 are starting to have a faint brownish colour from overheating.

Can I leave them there or should I replace them with stronger ones?
The circuit for the bleeder I've gotten from the website Fun with tubes: 8 PSU designs

UPDATE:
I've disconnected the bleeder resistors
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Old 31st Jan 2012, 10:57 pm   #107
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Default Re: I want to build a stereo headset valve amplifier

Ok, found the problem…
There was a bad connection between the RCA plug and the TV…
Idiot that I am… ><

But I soldered the 6CG7's pin 9 to the GND of the chassis.
I can't notice anything different. But it's probably for the better that it's grounded.

However the bleeder resistor isn't installed.
Should I install one or not?

I am not going to fiddle with that amp, except when there is something wrong with it…
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Old 1st Feb 2012, 12:17 am   #108
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Default Re: I want to build a stereo headset valve amplifier

Laurens, without a doubt you should fit a bleeder.
It will;
a) discharge the capacitor, making the amp safer to work on
b) improve the regulation of the power supply
c) reduce (slightly) the voltage on the smoother caps whilst the valve heaters are warming up and the anodes are not drawing current.
Somewhere around 47 - 100k should be about right for a 250v supply, 2 or 3 Watt minimum rating.
Rob.
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Old 1st Feb 2012, 4:21 pm   #109
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Default Re: I want to build a stereo headset valve amplifier

Thx Rob!

I will order the parts from Distrilec.
Is there anything else I should change on my amp, or is this the only fault still in the design.
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Old 6th Feb 2012, 8:14 pm   #110
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Default Re: I want to build a stereo headset valve amplifier

I've installed two 100K 3W resistors parallel on the first (L-channel) and third (R-channel) HT capacitors.

Voltage is around 302VDC stable and bleeds the caps quickly.

Now only to redraw the schematics and save them for another time.

Thank you!
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