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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 09 Nov 2017, 09:49 
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I presume you mean 10R resistor from cathode to cathode. Just out of interest why do the cathodes have to be connected by the resistor? Surely if each CCS is correctly set then each tube will draw the correct current all the time?

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PostPosted: 09 Nov 2017, 10:01 
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poty wrote:
From my experience - no, usually there are only advantages in using MOSFETs.


Do you mind sharing the schematics of you implemented solutions? Thanks.


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PostPosted: 09 Nov 2017, 10:08 
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I'm afraid my English is not so well to explain it correctly. In short: the cathodes must be connected together to "transfer" the signal from the "active" tube (which receives the signal directly to its grid) and "passive" tube (which is controlled by cathode-ground potential). It is from balanced circuits world. The value of the resistor defines the amount of negative feedback.
Your second point of view could be interpreted (at least from my non-native English side) in several ways. If we have the inter-cathode resistor then without signal your thoughts are mostly right. The word "mostly" relates to the case of using tubes with very different parameters: the balance of currents through the halves is limited to the voltage which could be dropped across the resistor.
If we do not have the resistor the circuit won't work at all. Both CCSs will stabilize the current and the output transformer will not receive any signal.


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PostPosted: 09 Nov 2017, 10:12 
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Greg2109 wrote:
I presume you mean 10R resistor from cathode to cathode. Just out of interest why do the cathodes have to be connected by the resistor? Surely if each CCS is correctly set then each tube will draw the correct current all the time?


Only the top tube is driven by the signal. Without the 10R resistor connecting the cathodes, the lower tube would only idle at the current set by the CCS.


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PostPosted: 09 Nov 2017, 10:14 
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Thanks Poty. I completely forgot the signal is only fed to one grid. That's why you need the resistor!

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PostPosted: 09 Nov 2017, 10:24 
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victorzwk, no problem sharing the schematics. I do not want to occupy the thread though. I believe there is a private messenger and I can send you the schematics there. I know at least three SIPP versions which work very good and listened to the original Oddblock to compare with.


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PostPosted: 09 Nov 2017, 10:46 
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poty wrote:
victorzwk, no problem sharing the schematics. I do not want to occupy the thread though. I believe there is a private messenger and I can send you the schematics there. I know at least three SIPP versions which work very good and listened to the original Oddblock to compare with.


Great! Please PM me with the schematics. I am eager to try them!


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PostPosted: 09 Nov 2017, 10:50 
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poty wrote:
Regarding low frequencies distortion: in my case the problem has not occured. Most probably it is the output transformer problem, not LM317.


You are probably right. I am using toroids as outputs. They are very sensitive to current imbalance and could be saturating because if that for frequencies Bellow 25Hz.


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PostPosted: 24 Nov 2017, 01:16 
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I am thinking of building this amp for my old Energy 22 bass reflex loudspeakers. I think it will have enough power for the types of music I listen to (jazz, big band, chamber music) but I am concerned about the output impedance. My speakers sound very boomy using my low powered SET amp. It seems to me that the CCS used in the power tube circuit would result in a high output impedance which would not work well with my speakers. Am I right or am I missing something?


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PostPosted: 24 Nov 2017, 03:22 
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Well, actually there are "yes" and "no" answers possible for your message. According to my experience the output impedance is not an issue with this amp. It is not as low as based on transistors (chips), but in the low values area of tube based amps.
CCS here works as an element of a differential (balanced) design and is not reflected into the output. Most problems are from tetrodes with their high anode impedance, but the problems are mitigated partly by push-pull layout, partly by optimally choosing the output transformer ratio.


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