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Old 15th March 2013, 03:23 PM   #11
rknize is offline rknize  United States
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Quote:
Originally Posted by Cold Macaroni View Post
Apologies to the OP as this is a bit off-topic.

I've been meaning to ask you about your TSEs Boywonder. My next project is a TSE of one flavor another. I have the board already and will be bringing some James transformers back to the US with me when I leave Korea this summer. The plan was originally to build a 300B, but as I'm also planning a large house-shaking PP octal amp after that (how's that Universal Driver board coming George ), I've been toying with the idea of a 45 TSE and some smaller efficient speakers. Anything you can share on the merits of the two? (If I remember you have a 300B and a 45?)
You can just start your own thread...

I have one TSE that can drive both. It's still on the breadboard and has been neglected for a while now, but it is setup to drive a variety of output tubes including the 45 and 300B. I like the 45 setup the best so far. It can drive by 98dB speakers quite well and it gives detail unlike any other amplifier I have used to date.
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Old 15th March 2013, 03:28 PM   #12
rknize is offline rknize  United States
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Quote:
Originally Posted by myfi View Post
Do we need the 80 - 100v PP after the input stage (Va) or after the ďcompleteĒ power drive stage i.e. at the source of the MOSFET and the grid of the Output tube?

Anybody know what a typical signal voltage peek to peek that is riding on Vg is?

Thanks Steve
Steve,

The answer is: both. The FET stage is a source follower. That means it has a voltage gain of about 1. Its purpose is to provide current gain to feed the grid of the output tube when it strays out of pure class A.
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Old 15th March 2013, 03:53 PM   #13
myfi is offline myfi  United States
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Thank you Russ.

My CD player lists itís output at 1 KHz at 2.0 Ī0.3v so Iíll use that.

Input Stage Amplification (Av) = ∆Va/∆Vgk = 100/2 = 50

Steve
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Old 15th March 2013, 04:12 PM   #14
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Here is my take on the source followers from what I've learned so far, which may or may not be totally correct:

As Russ mentioned, they are a unity gain buffer stage between the 5842's and the output tubes. This greatly reduces the need for the driver tube to source current to the output tubes.

Typically high voltage gain drivers have high plate R (so high output impedance) have a limited ability to provide the current that the output tubes require to drive their Miller capacitance. Triodes typically have relatively higher Miller C than tetrodes and pentodes since they lack the additional elements (grids/screens) used to reduce Miller C. Low mu drivers can source some current but have limited voltage swing. You can't have both since voltage x current =power and the small tubes max power spec will be exceeded (no free lunch...)

The mosfet follower provides a high input impedance for the driver tube so very little current is required from the driver tube. The mosfet follower has low output impedance to easily drive the output tube's Miller C.

The power supply for the mosfets needs to have low output impedance since this current is what drives the Milller C of the output tubes.

The negative voltage for the follower has to be at least as negative as the bias voltage plus some headroom. I'm not exactly clear on the positive voltage for the follower but if you are running A2 (or AB2 in PP designs) you need it to drive the output tube's grid positive.

So, in summary, the driver tube provides the voltage swing and the mosfet follower provides the current.
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Old 15th March 2013, 04:40 PM   #15
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Quote:
Originally Posted by Cold Macaroni View Post
Apologies to the OP as this is a bit off-topic.

I've been meaning to ask you about your TSEs Boywonder. My next project is a TSE of one flavor another. I have the board already and will be bringing some James transformers back to the US with me when I leave Korea this summer. The plan was originally to build a 300B, but as I'm also planning a large house-shaking PP octal amp after that (how's that Universal Driver board coming George ), I've been toying with the idea of a 45 TSE and some smaller efficient speakers. Anything you can share on the merits of the two? (If I remember you have a 300B and a 45?)
I like them both. If you've got the James 6123's (90ma IIRC) they are plenty big enough for 300B's, although you could also run 45's. James also has a smaller output transformer that could be interesting with 45's, especially if bi amping.

My speakers are TB-1772's in half Chang cabinets (95db) with a separate home brew isobaric woofer/plate amp. My listening room is somewhat large (vaulted ceilings, connected to other rooms) and the 45 amp may be a bit marginal at louder volumes, then again, maybe not........I mostly listen to acoustic stuff. The imaging with either of these amps is great in my setup.

The 300B TSE has been my main amp although recently I've been using the 45 amp since I just got it finished and dialed in. The 300B amp has vintage tube sockets that work fine, the 45 amp has new Chinese sockets that needed their contacts massaged with a small screwdriver to be happy.
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Old 18th March 2013, 04:56 PM   #16
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Quote:
Originally Posted by boywonder View Post
Well, it looks like I'll be hoisting both of my TSE's back on the bench, and firing up Rightmark and the sound card........I'll use my attenuator box thingy and proceed carefully to preserve the remaining functional sound card channel.

Should be interesting......
Slightly off-topic, but here goes.....

I put my 300B TSE on the bench yesterday and connected up my sound card and attenuator box thingy in an effort to tweak the 5842 anode voltage and look at the distortion spectra.

Two observations: My two soundcards (both 24/96) differ greatly in their performance (duh!). My Azuntech Xplosion card has a least a 1 db rolloff between 10K and 20K on loopback testing. My M-audio firewire card is flat past 20K when looped back, and appears to have slightly better noise performance.

Anyway, I adjusted the 5842 anode voltage by twisting the pot and looking at the voltage with a DC voltmeter and observed the distortion using Rightmark Audio Analyzer software. I adjusted the anode voltage between about 180VDC and 115VDC. The higher harmonics (4th and higher) began to climb at voltages below around 130-135V. Going lower than 135V, the second and third also started to rise a little. Raising the voltage above 150-155V or so, nothing moved much. I had similar results on both channels.

I then set the anode voltages back to 175VDC and buttoned everything up.
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Old 19th March 2013, 12:10 AM   #17
myfi is offline myfi  United States
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Interesting.

Quote:
Raising the voltage above 150-155V or so, nothing moved much.
Are you saying the distortion was about the same from 150vdc to 175vdc?
I wish my electronics re education was a little further along, so that I might be able to understand this some what better.

I have tried to model this stage in LTSice but Iíve not been able to find a model for the CCS IXYS 10M45S. I did find one for a 10M90s but I canít get it to run. I have substituted in a DN2540 but itís not the same.


Thanks


Steve
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Old 19th March 2013, 02:44 AM   #18
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Quote:
Originally Posted by myfi View Post
Interesting.

Are you saying the distortion was about the same from 150vdc to 175vdc?
Yes, pretty much the same.......at least with my setup......
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Old 19th March 2013, 03:23 PM   #19
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Just curious, any images?
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Old 19th March 2013, 04:59 PM   #20
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Quote:
Originally Posted by Evenharmonics View Post
Just curious, any images?

Sorry, no. I suppose I could have captured some screen shots......

If I get motivated, I'll do the same test with my 45 TSE.
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