single ended 6l6 help

[Zephedone]

I have a new build that I am trying to figure out the value of the cathode resistor of the 6l6 tube . This is based on a champ circuit , no negative feedback , with the pre-amp section from Doug Hoffmans stout circuit . I have a hand drawn schematic with voltages I measured while clipping in three different value resistors . I need a lesson please . I have built a pile of amps and it's always hit or miss . Monkey following a schematic , that's me . I guess I need to figure out how to bias this thing by choosing the right resistor .

[Zephedone]

Here is the schematic and voltages measured with each resistor . The voltages notated in the schematic were taken a day ago with the 200 ohm resistor in place . You can see the difference from one day to the next in the first line of the voltage chart at bottom left . I guess this is due to line voltage fluctuation .

[billc]

Is this a modern 6L6GC or an old one? They are biased differently...but at any rate you can definitely find the answer by searching the AX84.com site and forum, LOTS of SE amps including many w/ 6L6's were built by the regulars...it is pretty slow there these days but was busy a few years back.
Some relevant info is at http://www.ax84.com/static/p1x/AX84_P1x ... 101004.pdf

[LeftyStrat]

I think 200 is too low, I calculate that your exceeding the max dissipation of 19. I get 21. The plate value, is that measured between pins 3 and 8?

You can use the calculator here scroll down for cathode bias. 220 or 250 should be about right.


http://www.webervst.com/tubes1/calcbias.htm

[matt h]

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[passfan]

Keep in mind SE outputs can run at hotter dissipitation values than push pull. 50% of the time they will be pushing well below their quiescent value

[Zephedone]

Thanks for the help guys . The 6l6 in fact is a vintage RCA 6l6GC . It looks like a 1K at 5 watt resistor is what the ax84 P-1 calls for . I may have one of those if not I will have to order . Should I be using a 6v6 ? I have a few to choose from , GT , GTA etc ...

[matt h]

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[Paultergeist]

The following is of the "give a man a fish, he eats for a day; teach a man to fish, he eats for a lifetime." school of thought. This will give you the background necessary to figure this stuff out on your own in the future............

WOW! That was a great post! Even I -- with my "dropped-on-his-head-as-a-child" brain -- understood all of that explanation. (Admittedly, I have been over this terrain before, but it was still a fantastic refresher for me!). *Cut-and-paste-and-save* in the "Amp-Building" folder.

Thanks for taking the time to write all that out Matt!

[Paultergeist]

After looking at the schematic, I am going to confess a wee bit of ignorance and say that I cannot quite see where V1A is getting its (B+) plate voltage from?

[matt h]

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[billc]

Thanks for the help guys . The 6l6 in fact is a vintage RCA 6l6GC . It looks like a 1K at 5 watt resistor is what the ax84 P-1 calls for . I may have one of those if not I will have to order . Should I be using a 6v6 ? I have a few to choose from , GT , GTA etc ...

How about maybe using two of your 6V6's in parallel SE for about 9W output? I recently built a Gibson GA-9 and like its tone the best of the several amps I've owned and/or built...the GA-9 uses a 6SJ7 for the preamp but the Angela Super SE uses a 12AX7 like your schematic (The double tube rectifier is superfluous IMHO though and FWIW I used a SS rectifier on mine)

[img:771:543]https://lh4.googleusercontent.com/-KSOp ... 71/ga9.gif[/img]

[img:489:437]http://angela.com/images/Super_SE_6V6_Amp.gif[/img]

[Zephedone]

Sorry guys I forgot to note on the schematic that V1-A gets plate voltage from the last node of the power supply . matt h I meant that 1K resistor as the screen grid resistor . Sorry about that . Also thanks for the explanation as well . Easy to follow and to the point . I will also be cutting and pasting this one . I have a question . How would I determine DC resistance of my OT ? would this require cutting the OT loose from the circuit ? billc I have in fact built a version of the Angela Super Single . Here is the thing . It was one of my first builds and it sounded and still sounds fantastic . It is also pretty much exactly like the schematic I have up in this post but with two 6v6gta tubes and a 250 ohm cathode resistor . I tacked the stout pre onto the Angela output section . I also used SS rectification for that amp and the one in this post . I should be able to find a little time to get out to the shop and do some work/math on this project tomorrow . I will post my results when that happens . Much appreciated for all the help guys .

[tubeswell]

I built a 2||6V6 or 1 x 6L6 SE amp a couple of years back. (This amp also had variable HT selection and could take a range of octal rectifier tubes).

It could run the 6L6 with 250R or 470R cathode resistor with either a 5U4G or 5AR4 rectifier.

Schematic below (silly Flickr has changed their settings and I can no longer post hi-res original size images from their website sorry - even though I put them there. How fucked-up is that?)

[img:240:170]https://c1.staticflickr.com/9/8029/8031 ... bd9c_m.jpg[/img]

Voltage notes attached

[M Fowler]

Pete is this the one?