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Old 14th August 2012, 04:19 AM   #1
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Default New 6L6GC Project. DC -> LTP

It's been a while since my last project. Now that I'm done with college I have a little more time for tinkering. I had to do this one by hand, the old school way. (Except the PSU which I designed with PSUDII). Any glaring errors before I start ordering parts?

Signal
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LTP Curves
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Input Curves
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PSU to follow but it's nothing special. 282X -> 2xUF4007 -> 193M choke input, then another 10H 500 ohm choke for the B+2. The -80V supply will probably come from a tiny 56V Hammond from Mouser, then 187B56.
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Old 14th August 2012, 04:23 AM   #2
AJT is offline AJT  Philippines
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you have direct coupling from your 6ag5 plate to the grid of the 6n1p, voltages do not add up, did you mean to do cap coupling instead?
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Old 14th August 2012, 04:54 AM   #3
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Sorry, 230V on the top of the 6N1P is misleading. The supply is 430V, and it only loses 50V to the plate resistor, so that should say 380V instead. It's "230V effective" when using the curves to determine a load line, yes?

Last edited by sorenj07; 14th August 2012 at 04:59 AM.
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Old 14th August 2012, 04:58 AM   #4
AJT is offline AJT  Philippines
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ok...i just saw the one nearest the upper cathode.... 6n1p is a nice tube.... plentiful and cheap...
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Old 14th August 2012, 05:00 AM   #5
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It is That and the 6AG5 should be pretty easily obtainable in NOS condition.

I could have gotten ~20V more swing from the LTP by giving it 8mA instead of 10 and increasing the plate resistors to 15K (iirc). However, I think they like a little more current, and the lower output impedance might help if I decide to triode-strap. The 10M45 is also probably happier at 10mA..

Last edited by sorenj07; 14th August 2012 at 05:03 AM.
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Old 14th August 2012, 05:11 AM   #6
AJT is offline AJT  Philippines
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i used the Russian 6J9 as input, it is equivalent to 6688 and has mu of 60 in triode.....if you use the Russian 6p3s in place of the 6l6gc,(they are interchangeable) then you can have an all Russian tube amp...good luck on your build...
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Old 14th August 2012, 01:41 PM   #7
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by sorenj07 View Post
Sorry, 230V on the top of the 6N1P is misleading. The supply is 430V, and it only loses 50V to the plate resistor, so that should say 380V instead. It's "230V effective" when using the curves to determine a load line, yes?
Your diagram has obvious mistakes.
The 6AG5 is triode connected to a 'current source' that is bypassed to ground through a 1uF capacitor - the way it is drawn, the plate load for this section is the 545ohm resistor. This will provide a lot of attenuation and distortion, not gain.
The bottom half 6N1P grid must not be connected to ground, since the top half is DC coupled to ~143V if you want this to work at all. This way the bottom half of the 6N1P is WAAAAY into cut-off (-140 something volts at G1) so no phase splitting.
The output tube bias network has a common flaw, namely if the wiper of the adjustment pots go open (which may happen during adjustment as they turn even on pots that normally seem to work OK), the tubes will be left with no negative bias, i.e. maximum current will flow.

Last edited by ilimzn; 14th August 2012 at 01:48 PM.
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Old 14th August 2012, 02:08 PM   #8
DF96 is offline DF96  England
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In addition to the major points mentioned by ilimzn, you are using an 8ohm speaker on the 16ohm output secondary. This will work, but not as well as using the right ratio.
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Old 14th August 2012, 02:48 PM   #9
TheGimp is offline TheGimp  United States
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Since you have a -80V supply for bias, why not use it for the LTP tail as well.
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Old 14th August 2012, 03:51 PM   #10
20to20 is offline 20to20  United States
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The 1M grid leak R at the input is redundant since you have a 100K volume control.
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