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Old 19th December 2011, 01:02 PM   #1
rock12 is offline rock12  United States
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Default SOHA headphone amp

I just completed the soha amp and barely get any sound out. What should be the voltages to the 2 heater connections numbers 4 and 5 on the 12au7 tube? I have a -12.55 on number 4 but in the milli amps on number 5
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Old 19th December 2011, 02:16 PM   #2
GloBug is offline GloBug  Canada
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You either have a 6.3volt or 12.6volt heater transformer.

If 12.6v, then you should have one wire connected to "9" and the other wire connected to "4 AND 5" You should get ~12.6 volts when measured from pin 9 to pins 4+5.

Milliamps is a current measurement of current not voltage.

Set your meter to AC Volts. Some amplifiers may have DC heaters, but most are AC.

Be carefull and have fun.
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Old 19th December 2011, 04:46 PM   #3
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by GloBug View Post
You either have a 6.3volt or 12.6volt heater transformer.

If 12.6v, then you should have one wire connected to "9" and the other wire connected to "4 AND 5" You should get ~12.6 volts when measured from pin 9 to pins 4+5.

<snip>

Be carefull and have fun.
The above advice is for 6.3V filament connection, if you have a 12.6V filament transformer or supply connect one side to 4, and the other side to 5. There should be nothing connected to pin 9.

For 6.3V operation connect pins 4 &5 together and to one side of the filament transformer. Connect pin 9 to the other side.

See: http://www.mif.pg.gda.pl/homepages/f...7/1/12AU7A.pdf

Note that the filament between 4 and 9 is rated for 6.3V, and the filament between 5 and 9 is rated for 6.3V. Place them in series using only pins 4, 5 for 12.6V operation and in parallel by shorting together 4 & 5 and applying 6.3V between the shorted pins and pin 9. Hope this is sufficiently clear.
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Old 19th December 2011, 09:23 PM   #4
rock12 is offline rock12  United States
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thank you for the quick reply's yes this is a 12.6 volts DC to the heaters. the way I measured was to put the negative at my star ground and touch poles 4 and 5. 4 came in at 12.6v but 5 was in milli volt range and is my confusion. this is my first point to point attempt and I found it quite addictive
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Old 19th December 2011, 10:24 PM   #5
GloBug is offline GloBug  Canada
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Oops, sorry that's what I meant thanks.
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Old 20th December 2011, 12:30 AM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by rock12 View Post
thank you for the quick reply's yes this is a 12.6 volts DC to the heaters. the way I measured was to put the negative at my star ground and touch poles 4 and 5. 4 came in at 12.6v but 5 was in milli volt range and is my confusion. this is my first point to point attempt and I found it quite addictive
So you need remove the connection to pin 9 and connect it to pin 5 instead.. If no connection to pin 9 then you need to find the other side of your filament supply - there has to be a loop for the current to return to the supply after all - and it actually should not be through your chassis GND.
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Old 20th December 2011, 09:43 AM   #7
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hey i would like some ideas for the headphone amp. which is used vacuum tube@@
For example what tube should i use and i also wanna use in out door which means it is hand carry@@
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Old 20th December 2011, 10:46 AM   #8
rock12 is offline rock12  United States
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thank you all for your help. I got the amp working this morning and it sounds great now to build a case...One last question I have 2k trim pots to adjust the voltage on the plate to 40 volts one of the pots will only let me raise the voltage to 36.5 volts is it possible that this is a bad pot or can I change the 560 resister that follows this to another size to acheive 40 volts?
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Old 20th December 2011, 10:49 AM   #9
rock12 is offline rock12  United States
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check at headwize. head-fi.org it is a nice site for headphone amps
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