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Old 20th February 2013, 07:02 PM   #1
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Default 6P45S PP, simulation frustration.

Hey All

I have spent a couple of days trying to wrap my head around why my simulation is acting up weird, I have come to the conclusion that I have made some small rookie mistake that I am blind to see.

It is two ECC83 tubes and 6P45S output tubes. OPT is a Generic14K model.

I have cut the circuit up in all kind of smaller parts to make it behave like I expected, no luck. Even just the input stage by itself gives the same result, without NFB.

Blue trace is input -500mv to 500mv. Green trace is from anodes of U1a/b.

I expected a amplified signal, not a amplified signal with a huge DC offset.

Help a blind man see

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Old 20th February 2013, 07:08 PM   #2
45 is offline 45  Italy
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The bias V4 looks wrong. Shouldn't it be the other way around?
The offest on the plate is normal as you are at plate potential, there is no DC decoupling there.

Last edited by 45; 20th February 2013 at 07:11 PM.
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Old 20th February 2013, 07:21 PM   #3
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Quote:
Originally Posted by 45 View Post
The bias V4 looks wrong. Shouldn't it be the other way around?
The offest on the plate is normal as you are at plate potential, there is no DC decoupling there.
It does give out -50V.

This is by the way my first time simulating a tube amplifier, seems like you are right about the plate potential, just got my mind wrapped around that I would get a signal out crossing zero. I feel rookie again
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Old 20th February 2013, 08:14 PM   #4
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I am not sure what you have tried to simulate.
I attached one simple 6P45S PP output stage.
It should work.
Attached Files
File Type: asc 6P45S PP.asc (5.6 KB, 22 views)
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Old 20th February 2013, 08:18 PM   #5
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Concerning your schematic, there are no grid leak resistors at tube U1.
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Old 20th February 2013, 08:24 PM   #6
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Quote:
Originally Posted by artosalo View Post
Concerning your schematic, there are no grid leak resistors at tube U1.
Likewise U2 has a very high cathode resistance.

Last edited by JonSnell Electronic; 20th February 2013 at 08:26 PM. Reason: Error
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Old 20th February 2013, 08:51 PM   #7
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Thanks Artosalo, I can see that I am miles from simulating correctly I have only plotted the schematic and thereby not taken reality into account.

The phase splitter a reuse from my current working amp, schematic at page 19: http://www.lundahl.se/pdf/ovrigt/amplifier_30wpp.pdf

What I tried out here was to improve the APX-100 amplifier with the similar improvements Claus Byrinth made to the Mullard design in his paper.
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Old 21st February 2013, 01:45 AM   #8
heavil is offline heavil  Russian Federation
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I can say without a simulation, but a large number of experiments: 6P45S - this lamp is not for music. It gives the power and sound but not the music.
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Old 21st February 2013, 02:02 AM   #9
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The DC offset you are seeing is simply the B+ of the first stage. Looks to be about 105V with your amplified signal going +-25V from that baseline.

to see it ground referenced you can either subtract the B+ from the waveform with an equation or cap couple off the node to a 10 meg resistor to ground.

dave
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Old 21st February 2013, 06:39 AM   #10
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Quote:
Originally Posted by MadsKaizer View Post
Thanks Artosalo, I can see that I am miles from simulating correctly I have only plotted the schematic and thereby not taken reality into account.

The phase splitter a reuse from my current working amp, schematic at page 19: http://www.lundahl.se/pdf/ovrigt/amplifier_30wpp.pdf

What I tried out here was to improve the APX-100 amplifier with the similar improvements Claus Byrinth made to the Mullard design in his paper.
Did you get my ciruit to work ?
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