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Old 23rd December 2012, 07:52 PM   #311
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How are you going to cancel 3H?
And 2H cancellation by 2 stages is not so straight: curves are multiplied, not summed!
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Old 23rd December 2012, 08:07 PM   #312
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Just going back to the VR150 tube - it's an 0D3 octal base and I put 22.5v through it. So add the 18mA and you get 40mA. I have a 100R resistor followed by a 10uF polypropylene cap before the DN2540, so I adjust the sense resistor on the DN2540 so as to measure 4 volts across the 100 ohm resistor.

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Old 23rd December 2012, 09:53 PM   #313
regal is offline regal  United States
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Originally Posted by Wavebourn View Post
How are you going to cancel 3H?
And 2H cancellation by 2 stages is not so straight: curves are multiplied, not summed!
Anode followers are inverting, there is cancellation in a 2 stage SET, maybe we are talking about different topologies ?



I didn't say it would be easy, going all DHT means thinking out of the box and this 4P1L with its high gain and drive allows that. It reminds me have a poor man's EML 20B



If you are interested just run a quick simulation 6n6p vs 6c4Pi driving a 6C4C, no matter what the 6N6P always gives less 2H distortion on the output because its curve shapes are similar to the 6C4C. I know its a just a sim but there has to be some truth to it. I don't find the high gain high mu space age tubes to match well with the older DHTs in the shape of thier curves. I can upload my asc files if anyone is interested.

As far as 3H, cancel isn't the technical term but cancelling 2H leads to less 3H on the output, I would need a chalkboard to show you.

Again this is just a hobby for me, it is supposed to be fun. To me building a canned 5842-2A3 is more like work than fun.

Waveborn if I am wrong let me know, I'm a constant learner
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Old 24th December 2012, 12:59 AM   #314
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Originally Posted by regal View Post
Waveborn if I am wrong let me know, I'm a constant learner
In this particular question high school Algebra and trigonometry are needed. As my daughter said, it is part of Advance Math Class. Particularly, what is the difference between summing of functions (P-P stage) and multiplying them (2 stages). How it is reflected on an order of the resulting function.
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Old 24th December 2012, 05:14 AM   #315
regal is offline regal  United States
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Originally Posted by Wavebourn View Post
In this particular question high school Algebra and trigonometry are needed. As my daughter said, it is part of Advance Math Class. Particularly, what is the difference between summing of functions (P-P stage) and multiplying them (2 stages). How it is reflected on an order of the resulting function.
You are assuming the mismatch between the two tube's characteristics is greater than the topology's inversion. Basic math as you said, I think your assumption could be wrong, at least it is according to the simulations, but we both know that the sim tube models aren't perfect. One thing for certain at the same output level if we compare a simple two stage amp:

4p1l-6C4C vs 6c45pi-6C4C the 4P1l has 10dB less distortion according to the math. The 6n6p still beats them both because it has more inverted 2H to cancel the 6C4C's 2H.

My goals with the 4P1L are a little different than most (1-2W into 40 ohms) but it is an interesting discussion.
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Old 24th December 2012, 07:39 AM   #316
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No, I am assuming that if to multiply 2 functions the result will be quite different from when you sum them.

It is easier to understand once for yourself than to guess which opinions you read on forums are better.
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Old 24th December 2012, 08:34 AM   #317
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This is what I am coming up with for a 2W all DHT 4P1L headamp, I think it is worth the cost to try and build (FYI there is more 2H going in the output tube than coming out.)
I am not showing the input transformer. Any feedback appreciated. My design decision is coming down to either this SET or a 4P1L + SS Buffer hybrid.

Click the image to open in full size.

Last edited by regal; 24th December 2012 at 08:38 AM.
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Old 24th December 2012, 09:45 AM   #318
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Quote:
Originally Posted by Rod Coleman View Post
Hi Andy,

If you don't like fixed bias, it's more than likely the lack of noise rejection (passive solutions), or real noise injection (any regulator with a bandgap reference - i.e. 99% of them).

If you like the bias performance that the Filament Regulators provide, but don't want to deal with the huge power dissipation, you could try separate regulators for each.

The diagram shows the idea. The Filament is heated normally, and a second regulator provides an adjustable current that is fed into the 50K bias resistor.
0.5mA gives 25V at very low noise - probably 100x lower than typical gas tubes. In fact the noise should be lower than with filament bias, since excess-noise in resistors in often proportional to current.

Recent regulators are temperature-compensated, allowing a stable supply to be developed. Why not give it a try!
Hi Rod,
Building on your idea, here is my first sketch of a 4P1L into 6C4C (or 4P1L PSE). 4P1L driver is using LL1671 IT in filament bias. The fixed grid bias is using your regulator as suggested above. 6C4C/4P1L PSE with output transformer LL1623/60mA. Looks like a good approach. Couldn't simulate it as the ideal current source used in the IT secondary prevents the AC signal to develop in the grid. Any idea of how to overcome this in LTspice?
Thanks
Ale
Attached Images
File Type: png 6C4C:4P1L PSE version 01.png (24.3 KB, 356 views)
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Old 24th December 2012, 09:53 AM   #319
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Quote:
Originally Posted by regal View Post
If you are interested just run a quick simulation 6n6p vs 6c4Pi driving a 6C4C, no matter what the 6N6P always gives less 2H distortion on the output because its curve shapes are similar to the 6C4C. I know its a just a sim but there has to be some truth to it.
Hi Regal,
From my multiple THD tests I found that the 4P1L is unbeatable in terms of linearity (and followed closely by 6C45P and 6e5P. Even 4P1L PSE is slightly more linear than the 6C4C.
I also was puzzled to find out that the 6N6P is not that linear when swinging large signals ( I tested a batch of 10 valves and hopefully I'm not the owner of a poor one!). Please don't take this as the 6N6P doesn't sound good when driving a SE stage, I personally haven't tried it so can't comment on this. Either way, Spice simulation may be tricky sometimes as model may not be that accurate...

Cheers,
Ale
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Old 24th December 2012, 10:35 AM   #320
regal is offline regal  United States
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Originally Posted by mogliaa View Post
Hi Regal,
From my multiple THD tests I found that the 4P1L is unbeatable in terms of linearity (and followed closely by 6C45P and 6e5P. Even 4P1L PSE is slightly more linear than the 6C4C.
I also was puzzled to find out that the 6N6P is not that linear when swinging large signals ( I tested a batch of 10 valves and hopefully I'm not the owner of a poor one!). Please don't take this as the 6N6P doesn't sound good when driving a SE stage, I personally haven't tried it so can't comment on this. Either way, Spice simulation may be tricky sometimes as model may not be that accurate...

Cheers,
Ale
Still missing the concept, the 6n6p distorts more 2H in the model above which results in less 2H on the output. The sim shows it. Basic stuff.
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