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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: 23 May 2018, 18:34 
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Joined: 07 Mar 2012, 09:23
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Hi ... to get more gain I'd like to try to use a 6N6P instead of ECC802S.
Anybody tried to do it before? Any suggestion about changes?
Thanks


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PostPosted: 24 May 2018, 03:13 
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Joined: 24 Oct 2010, 07:05
Posts: 267
Why do you think you'll have more gain? You'll have to rise current through a 6N6P to be linear and it'll work better to interconnect's capacitance, that is all.
I used the tube in SRPP version as a driver for 300B, but connect it with a CCS in the top cathode resistor position to increase gain.


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PostPosted: 25 May 2018, 15:09 
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Joined: 06 Mar 2015, 16:31
Posts: 4
I have been studying this circuit and am wondering what function the 3k9 resistor on the grid of the upper valve performs. I apologize if this has been answered, I may have missed it, but I have gone through the entire thread without success thus far.
Thanks for any insight regarding this.
Jazzzman


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PostPosted: 25 May 2018, 18:15 
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Joined: 04 Jun 2008, 20:59
Posts: 3745
Location: Arizona, USA
Hi, All grid stoppers have much the same function....preventing oscillation. Or to some extent in gain stages ringing and overshoot. The mechanism is the same. The resistor and internal capacitance of the tube form a filter. It is possible to leave them out (many folks do), but my scope shows better high performance with them in there. Without them the top end goes up into the lower RF ranges and sensitivity there is not wanted. By essentially reducing the high frequency response of both sections it may also make them track together closer. I don't know if I could prove that though.

The other question regarding more gain....not usually needed in a line stage preamp. Actually the gain is on the high side for one. However there is no reason the circuit can not be used with other tubes. With changes in the cathode resistors you can use 12AT7, 12AX7, 5751, 6/12SL7 and being careful with the B+ 6DJ8s all work. For 12AX7 at 200V 910R at 300V 1200R, 5751 at 200 820R at 300V 1200R, 6/12SL7 the same as 5751. I don't recall what values I used on the others. I would not use the 6DJ8 as an SRPP much above 200V as it is moderately easy to harm on or the other triode on start up. You naturally can use other values, and many will work, just these seem to be the sweet spots IMO. Remember that the Z out will be higher for most of them. You can use any of the ECC/EC clones of the tubes as well.

Good listening
Bruce

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PostPosted: 09 Aug 2018, 06:10 
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Joined: 09 Aug 2018, 03:15
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Attachment:
bygge1.jpg
Hi all! This is my version of this project with rectifier tube and also choke. I powered it up yesterday and it works. No listening yet. Just checking voltage. I havent got my ECC802S tubes yet so I used a spare 12AU7 from another project.


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PostPosted: 13 Aug 2018, 18:09 
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Joined: 07 Jan 2018, 07:13
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Hi, what should the 5k trim pot be rated for on the LR8’s? I had a 1/2 watt there and it failed in about a month of listening. Not sure if it was under rated.

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PostPosted: 13 Aug 2018, 20:04 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Clearly something wrong with it. I use 1/4 watt ones. You can of course, measure it when you get the voltage right and then replace it with a fixed resistor.

Good listening
Bruce

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PostPosted: 14 Aug 2018, 17:48 
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Joined: 07 Jan 2018, 07:13
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That’s what I ended up doing. Both channels came in between 213-214V.

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