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Old 8th October 2012, 04:51 PM   #31
SandyG is offline SandyG  United States
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Awesome information, need to digest, but looks straight forward.

I will have to get the voltages re-checked. I might have to get a couple of different 6SL7's to try. I had a box of 5 JAN6SL7GT that I got off of EPay and I did swap one out for another and it had the same results. I will re-verify the voltages to make sure.

One thing that I can do to move the power supply voltage up a bit is remove the beloved 5U4GB and pop in a GZ34. I think that will push up the B+ another 20v or so, right to the edge of the 6v6. For grins, I'll get voltages for both.

Just need to have 1 day where I am not working 18 hours

Sandy

Last edited by SandyG; 8th October 2012 at 05:14 PM.
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Old 9th October 2012, 12:42 PM   #32
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what 6v6 are those? are they sylvanias? guessing because of green lettering? lol im hunting for some damn better qauality 6v6 for my stealth current production sux well at least the jj imo I have 1955 CBS clear glass black-plates but they sound just ok really thinking i need some brimars or rcas or sylvanias not sure GE heard good and bad things about them. something is just missing/lacking with CBS
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Old 9th October 2012, 09:18 PM   #33
SandyG is offline SandyG  United States
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The 6V6's are Tungsol re-issues. I also have a set of JJ's that are supposed to be very good and can take a lot more plate voltage. Don't yet know how they sound or how they would sound in a Gutiar amp. I did not see a lot of 6v6's that were affordable on EPay, but you might find them if you poke around

Sandy
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Old 10th October 2012, 06:16 AM   #34
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So many suggestions and tangents in this thread, I'm betting the op is more confused than helped. So just a simple graphical explanation of what your early clipping issue is. Based on your original posted schematic, the first pic is what your operating point and load line look like on the 6sl7 plate curves. I must say it is horrible, very little room for voltage swing in the negative direction. Simplest way to get it more in line, although not the best, is to change r16 47k to 1k, r8 270k to 220k, and r7 1k to 1.3k - 1.5k to get approx. 110 volts on the plate.
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Last edited by jerluwoo; 10th October 2012 at 06:26 AM.
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Old 10th October 2012, 09:06 AM   #35
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Sandy you are right about the about JJ handling High B+ on plates in my stealth I had 420v on plates and they laughed at that had em biased around 22ma so cranked bias pot all the way had em to like 30-32ma and they still laughed not hint of red-plating they are a super monster tube They sound great for clean stuff but distorted tones I don't care for huge bass response but highs were all ice pick and sterile. I was thinking about trying the Tungsol or the EH, heard the Tungsol is smooth and sounds close to RCA glass and EH is more crunchy also heard EH is bad about the screen grid failures and the stealth has screens around 400V so I might be taking a chance.
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Old 10th October 2012, 04:25 PM   #36
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actually I gassed real hard lol I just bought some Raytheon 6v6 black glass black plate gts from fleabay should be here next week can't wait man lol
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Old 10th October 2012, 04:30 PM   #37
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just hoping the raytheons can handle the wild screen volts, the plates should be fine who knows I might pop em in and be greeted by a crazy light show lol
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Old 10th October 2012, 04:46 PM   #38
rongon is offline rongon  United States
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Quote:
Originally Posted by jerluwoo View Post
So many suggestions and tangents in this thread, I'm betting the op is more confused than helped. So just a simple graphical explanation of what your early clipping issue is. Based on your original posted schematic, the first pic is what your operating point and load line look like on the 6sl7 plate curves. I must say it is horrible, very little room for voltage swing in the negative direction. Simplest way to get it more in line, although not the best, is to change r16 47k to 1k, r8 270k to 220k, and r7 1k to 1.3k - 1.5k to get approx. 110 volts on the plate.
I totally agree. Thank you for putting that so simply.

How did I miss that R16 is 47k? Why such a large value? The input stage would benefit greatly from a higher B+. Reducing that 47k to 1k means its associated decoupling cap will need to 100uF, but that's not a difficult value to find.

--

Also, the phase splitter is biased way down near zero volts, and that could be a problem too.
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Old 17th October 2012, 05:49 AM   #39
SandyG is offline SandyG  United States
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Sorry I have not had a chance to jump into the garage and do some testing. It has been crunch time for a project and have not had a chance to get into the garage for some testing. This work thing...

Sandy
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Old 17th October 2012, 03:12 PM   #40
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For the input stage. What is the p-p signal you are sending into the input of the amp? Your supply is 286VDC. You are dropping 40V from HV2 to HVinput across a 47k resistor so you are drawing approximately 0.85mA current. Looking at the 6SL7 loadline, you are biased at about 0.7V - ish. What is the reading on the first input cathode (pin3)? Is it close to 0.7v? If you are sending in a signal greater than 1.5V p-p you are probably clipping here. If your CD player or whatnot send smaller signals, this is fine. Looks to be set up to get max gain up to input signals of 1Vpp

On the phase inverter, you have a similar problem with "headroom" as the others already stated. I would reduce r9/r14 and see what happens first. I think this is your bigger problem unless you are just nailing the input with a huge signal, which would cause an input AND PI problem.
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