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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 Mar 2016, 01:21 
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I was given a bag of NOS and not so NOS 6V6s and metal can 6L6s. I would like to make a 6L6 SE UL power amp. I would like the driver tubes to be 12AT7s. 12AT7s because I bought some top of the range expensive Psvanes which I could not use what I thought they could be used for. Regardless a very interesting combo.

Suncalc informs me that the combo will work all I need now is a schematic using both tubes. Two 1944 JAN RCA metal can 6L6s were in a bad state and a little rusty. I have sanded them down and sprayed them in high temp. black gloss paint. My engraver (who is about to retire from his post) will do some engraving down the front of these tubes.

Images to follow but for now the sanded tubes. Look good as they are I nearly left them this way.
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PostPosted: 13 Mar 2016, 13:44 
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Here's what I would recommend. Push the B+ a little. Run the plate at about 315v with about a 30v cathode bias. Using a 3.5kUL GXSE this will give a little over 7W peak power with a Ds≈1%/w. Here is the load line:
Attachment:
Screen Shot 2016-03-13 at 1.35.42 PM.png
The 12AT7 in a 4S configuration is low distortion and gives about Av=33 with a bypassed cathode. Run it at 300v B+. This is simple and should sound really nice. Add some L/R channel chokes to the power supply for good channel separation and you should be good to go.


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PostPosted: 13 Mar 2016, 16:10 
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Hi, Remember that pin one on the metal tubes is connected to the metal case. I have seen folks use it as a tie point. Doing that can get rather exciting depending on what it was used for :hot:

Good listening
Bruce

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PostPosted: 13 Mar 2016, 18:46 
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Let me through a small spanner in the works. Firstly I have a stack of Edcor 5K OPTs amd would like to use one and just one small detail - a schematic?

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PostPosted: 13 Mar 2016, 20:22 
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mwhouston wrote:
Firstly I have a stack of Edcor 5K OPTs amd would like to use one and just one small detail - a schematic?
Geez. Some guys are just never satisfied. :D

Because you asked... I modified the power stage design to use a 5kΩ output transformer and drew a schematic. First the schematic...
Attachment:
img158.jpg
One thing to note. The schematic says use a GXSE10 but I think you need a GXSE15 for this current level. Sure enough, Edcor specs the GXSE10-8-5K at 80mA max. The GXSE15-8-5K is specified at 100mA max. So you'll need to go with the 15W versions. I don't know which you have. Here is the power stage load line design...
Attachment:
Screen Shot 2016-03-13 at 8.08.13 PM.png

Overall it looks reasonable. Peak power out should be over 6W. Ds is less than 0.5%/W so the amp should be very clean. Low end will be output transformer limited. High end should go well above 50kHz.


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PostPosted: 13 Mar 2016, 21:40 
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Matt mate, your a gem. Thanks a bunch. I have most parts including a really nice Australian Spotted Gum base made by my amp building mate Don. Top plate colour against the black tubes, I'll to think about that one? In the meantime I have sprayed the tubes with a high temp. black paint. Soon to be engraved. These are 1944 RCA JAN 6L6 Tubes. I may just have all this info. engraved on them. I think the date is interesting.

Attachment:
image.jpeg


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PostPosted: 13 Mar 2016, 21:55 
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Now I know expected total current draw (or near enough) I can choose PS parts and as mentioned above OPT. I like to use 10H chokes. I know I will need one which will handle about 200mA. These tubes can handle more current than the 6V6 by a long shot.

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PostPosted: 14 Mar 2016, 15:23 
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Oops. :blush: Looks like I made one little mistake. The design is fine... if using a 6L6GC with it's 30 watt allowed plate dissipation. But if you use an older 6L6 or 6L6G in this design, with it's rated 19W plate dissipation, you'll likely melt your tubes.

Stand by for a modified design which is NOT a fire starter. Sorry about that. :censored:

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PostPosted: 14 Mar 2016, 16:38 
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Ok, lets try this again. FOR THE OLDER 6L6 or 6L6G WITH 19W PEAK PLATE DISSIPATION.

First, here is he modified schematic...
Attachment:
6L6 UL Schematic (low power).jpg
And here is the load line design...
Attachment:
Screen Shot 2016-03-14 at 4.32.23 PM.png

Happily, with this design the plate current is lower, so you can use the GXSE10-8-5K as opposed to the 15W version. This should work out well and not melt your nice old tubes.


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PostPosted: 14 Mar 2016, 16:46 
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I would imagine being metal can tubes the max watts dissipation would be lower. They are marked just 6L6. But all this was worked in my favour, my Edcor OPTs are only 10W and I really don't want to purchase anyone. I think the DIY God was smiling down on me.

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