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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: 13 Dec 2013, 18:08 
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After much consideration I have cold feet with regard to a tranniless amp. I will now use a power tranni. I want to do the best by Matts design even of I use carbon film resistors etc. I was lamenting over not using valve rectification to comply more with the old school build. Now I can.

I will be planing the layout today. Now to find an appropriate tranni in my mess of a lab.

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PostPosted: 14 Dec 2013, 12:50 
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Mark;

Please allow me to make two small recommendations.

First, if you decide not to include the volume control between the driver and power stages, then insert a 5kΩ grid-stopper resistor in the grid lines of the power tubes. This will control blocking and bias excursions.

The second item is that I would include 2kΩ grid-stoppers on the 6SN7 and bypass the cathodes on the driver with 50µf capacitors. This will make the amp considerably more sensitive and easier to drive.

Anxious to see your build.

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PostPosted: 14 Dec 2013, 17:56 
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I will make changes on my hard copy. Thanks any other suggestion let me know early. I'm still in the layout stage so good time to make changes.

Matt if you still have the drawing on file would you make those changes and put in on this thread.

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PostPosted: 14 Dec 2013, 19:45 
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What about a grid resistor into the 6V6 to take the place of the 100K pot. Just make it 100k to ground after the 0.1uf interstage cap and prior to the grid stopper?

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PostPosted: 14 Dec 2013, 21:25 
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mwhouston wrote:
What about a grid resistor into the 6V6 to take the place of the 100K pot. Just make it 100k to ground after the 0.1uf interstage cap and prior to the grid stopper?
This is exactly what I meant above. If you want to forego the volume control, then the 100kΩ potentiometer becomes a simple grid resistor and the 5kΩ grid stopper goes from the upper end of the grid resistor (where the connection is to the coupling cap) to the grid of the power tube. It looks like this...
Attachment:
pic243.jpg
Simple.


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PostPosted: 14 Dec 2013, 21:34 
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Great, that is how I understood it I just wanted to make sure I had the values right. Sometimes a much large grid resistors is used, 470K or so. I have all the extra parts but may change my low ESR 47uf Ck for a NP type. I prefer to use NPs as bipass caps.

Now I'm using a tube rec. I'll have to find a nice old 5U4 to compliment my over forty year old 6V6s. Just thinking about it have some real nice 80s 4pin. That should look good.

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PostPosted: 17 Dec 2013, 18:38 
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While waiting for the power tranni to come from my local supplier I thought about including two rec sockets on the amp. A four pin and octal socket both hot wired. As long as there is only one tube inserted at any time there should be no problems. This will allow me to use the vintage 80 rec. tube (4pin) but any octal socket based rec. tube also. Such flexibility is so easy to do and I have not seen it done before. I must see if there is sufficient room to do this.

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PostPosted: 07 Mar 2014, 22:00 
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About to start "Black Lace", my version of Matt's 6V6 and wanted to use an "80" rec tube of which a I have a few. This will keep the tubes old school as I hope to do with components and build. I see the tube can handle 125mA total. As the amp should only pull about 100mA this tube should be OK. Am I right? First cap will be a 4uf PIO so no huge current surges at turn on.

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PostPosted: 08 Mar 2014, 12:36 
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mwhouston wrote:
I see the tube can handle 125mA total. As the amp should only pull about 100mA this tube should be OK. Am I right? First cap will be a 4uf PIO so no huge current surges at turn on.
The type 80 is electrically identical to the 5Y3. As such it should work fine. You may however want a higher voltage transformer because the 80 will have about 35v more drop than the 5U4GB. I'd go with a 300-0-300 secondary rather than the 275-0-275 transformer which I used.

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PostPosted: 08 Mar 2014, 17:55 
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Suncalc wrote:
mwhouston wrote:
I see the tube can handle 125mA total. As the amp should only pull about 100mA this tube should be OK. Am I right? First cap will be a 4uf PIO so no huge current surges at turn on.
The type 80 is electrically identical to the 5Y3. As such it should work fine. You may however want a higher voltage transformer because the 80 will have about 35v more drop than the 5U4GB. I'd go with a 300-0-300 secondary rather than the 275-0-275 transformer which I used.

The power tranni I put aside for this is a 275-0-275. I'll have to see what else I have or order again.

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