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Need help with Low Voltage - Foreplay III
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Laudanum
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Posts: 575
Need help with Low Voltage - Foreplay III
«
on:
September 23, 2011, 03:50:50 PM »
Just finished my FPIII build with octals for 6SN7's instead of 12AU7. Need some help please, the Voltage is low on two terminals ... I think.
This is not the extended version.
All the resistance checks were fine.
Voltage checks were fine except for two terminals. T15 and T31 are supposed to be 75 volts according to the manual. I have 12.6 volts at both terminals. Again, this is with 6SN7's instead of 12AU7s.
All other voltages were well within 5% or better per the manual.
I also tried a different pair of 6SN7 tubes.
And yes, I installed a .22 ohm resistor instead of the stock .62 ohm as per Docs thread.
I generally am not sure where to start troubleshooting anyway, but building with a different tube, I have even less idea where to start.
I thought/think it was strange that all other measurements, both resistance and voltage are fine ... maybe I zigged instead of zagged at one point.
I double and triple checked the pin-out changes between the two tubes which Grainger sent me (Thanks again Grainger). Everything seems ok there.
So either I missed something ... Or, Do 6SN7's just change the voltage at this terminal pair ? (but 12.6vdc compared to 75vdc? ... thats a big difference).
Thanks in advance for the help.
«
Last Edit: September 24, 2011, 04:47:39 AM by Laudanum
»
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Desmond G.
Grainger49
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Posts: 3078
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Re: Need help with Low Voltage - Foreplay III
«
Reply #1 on:
September 24, 2011, 07:16:26 AM »
Desmond is not the Klutz that you all might think. I gave him the wrong tube connections to swap out. I just went through the manual and got the connections that are needed for the 6SN7 changeout.
These are the
6SN7
tube pin connections that I came up with.
PLEASE
someone check them for me:
1 (grid 1) - a 220 ohm CC resistor to the volume control T17 (T37)
2 - (plate 1) a 22.1k ohm resistor to tube pin 5 (plate 2)
3 - (cathode 1) HLMP 6000 LED to ground, the center isn't a terminal for an octal
4 - (grid 2) 220 ohm CC resistor to tube pin 2
5 - (plate 2) see plate 1 and a red wire to T 12 (T 32)
6 - (cathode 2) a 22.1k ohm resistor to T 19 (T 39)
7 & 8 (heaters, they are interchangeable)
«
Last Edit: September 25, 2011, 02:32:10 PM by Grainger49
»
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Grainger Morrison,
Mozzie quote: Sacred cows make the best hamburgers!
Remember, YOU are the only one who needs to be happy with the sound of your system.
Eros (Mods Have Begun!)/FP-2/Paramour 1/upgrades to all - PS Audio Regenerator, Triangle Zerius Speakers, BA Sub
Laudanum
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Posts: 575
Re: Need help with Low Voltage - Foreplay III
«
Reply #2 on:
September 24, 2011, 11:36:13 AM »
Yep ... lets just say that this one wasnt completely on me :-)
I followed directions to the letter. Bad directions yes, but nonetheless I followed them perfectly :-D J/K
Grainger redeemed himself. It was an easy fix, just 2 tube pins were swapped and that voltage is fine now.
Graingers listed connections are correct.
Thanks again, Grainger.
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Desmond G.
Paul Joppa
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Re: Need help with Low Voltage - Foreplay III
«
Reply #3 on:
September 25, 2011, 11:53:58 AM »
pin 2 to pin 5 is 22.1K, not 221k. Just sayin' :^)
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Paul Joppa
Grainger49
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Posts: 3078
Audio Cheapskate
Re: Need help with Low Voltage - Foreplay III
«
Reply #4 on:
September 25, 2011, 02:31:35 PM »
Yup! Slipped the decimal. I'll edit this so the information is correct.
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Grainger Morrison,
Mozzie quote: Sacred cows make the best hamburgers!
Remember, YOU are the only one who needs to be happy with the sound of your system.
Eros (Mods Have Begun!)/FP-2/Paramour 1/upgrades to all - PS Audio Regenerator, Triangle Zerius Speakers, BA Sub
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