finalizing paper

[shooter]

I did a BB 2 channel earlier here;
http://el34world.com/Forum/index.php?topic=22161.msg236559#msg236559

I've lightened it up by 1 ch, on the schematic below I left the 220K "mix" R's in.  It sounds fine with the "other" ch dialed to 0.  Looking for "better?" options 

thx
dave

[TIMBO]

Hey shooter, From what I can see the two mix resistors are acting like another volume pot (voltage divider)
Try deleting them.

[kagliostro]

Ciao Shooter

you are posting about your new amp realizations

I would like to know if you have also new paintings done    

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On this single channel version the pair of 220k resistors act as a 50% voltage divider

if you want you can give a try to a Split Load Resistor on V2B instead to use the voltage divider

Franco

[jjasilli]

Hey shooter, From what I can see the two mix resistors are acting like another volume pot (voltage divider)
Try deleting them.

But the bottom resistor must stay; it's the grid leak resistor for the next gain stage -- though it's a low value for that function, in terms of signal loss, with hi's to die first.  Is there really enough signal voltage to properly drive, or overdrive, the KT88? (N.B.: a guitar will typically output only a fraction of your 1V test signal voltage.)

[shooter]

Is there really enough signal voltage to properly drive

Yup, I can get to square wave at the speaker.

I was thinking of 33k/470k, just because

if you have also new paintings done

I'll post the last one I did couple days ago, no pic handy now

[kagliostro]

Is there really enough signal voltage to properly drive, or overdrive, the KT88? (N.B.: a guitar will typically output only a fraction of your 1V test signal voltage.)

Yup, I can get to square wave at the speaker.

Do you mean using guitar or the signal senerator ?

--

I'll post the last one I did couple days ago, no pic handy now

I'm waithing for that 

Franco

[shooter]

guitar or the signal generator ?

I'm mostly a sig/gen guy, but she gets nice n spanky with a guitar
I used 150mVrms and dimed, at the speaker I get this waveform;


(also posted my last piece)

[jjasilli]

Is there really enough signal voltage to properly drive

Yup, I can get to square wave at the speaker.

This is not sufficient info.  E.g., the square wave may originate in the preamp, and then get only a weak, clean boost from the power tube.  So, where does the square wave originate?

I was thinking of 33k/470k, just because
This is not the proper approach to design.  Instead, work backwards, preferably from the speaker.  But let's start working backwards from the power tube.  Use the tube charts, or plot your own loadline, to determine what input signal voltage is needed to drive & overdrive the power tube.  KT-88's need a relatively large input signal voltage compared to other tubes.  Measure the power tube's input signal voltage at various amp (tone & vol) settings .  Then tweak the preceding circuitry to achieve the proper signal voltage range into the power tube.

BTW:  I don't think the CF driver is needed for your KT-88.  I've seen CF's used to drive multiple KT-88's; i,.e., 4 of them.  OTOH the CF's low output impedance may justify the use of the power tube's low value grid leak resistor.  But I doubt the CF is actually accomplishing anything in this circuit; though it's not hurting anything either.

[shooter]

This is not the proper approach to design.

In the linked thread you can see the "design" work
I've done a handful of SE kt88s, most of how I go about it, I get the 88 close to max Plate, this one is at 39W.
I already have "whatever" preamp I'm interested in sketched up, I stitch them together and tweak till satisfied. 

the image below shows 150mVrms in, dimed,  looking at G1 of the 88, so there is some clipping from the pre, and the PA adds the rest.  that 2nd 1/2 the volume pot takes it from nice cleans into happy grit, almost roar.  More gain gets to too much SE distorted where in my world it's less musical.
This will be going into production, I got my lump-sum from 8yrs at GE, so FL, amp, and art!!!

[jjasilli]

Ok, then I'm convinced your amp design is good to go as-is -- based on the objective waveforms and your satisfaction with overall tonal quality.

[shooter]

good to go as-is

Thx JJ, this one was a fun BB build, I had most everything "solved", but taking the 88 from somewhat anemic
to panky happy was fun.  I wasn't as happy with the 2 channel, but liked the kingsnake channel.  my biggest problem now is trying to get an Edor 1628SEA on Dougs stout chassis
it's only 3 tubes but I don't want any coupling issues.   Hopefully by Monday I have the layout complete

[shooter]

I live by a 50/50/90 principle, if you have a 50/50 chance, 90% of the time you're wrong

I updated the 1st post with the correct channel to be used in the build, after of course I drew up the layout for the wrong channel.  layout to follow 

EDIT: put 1st pass layout in 1st post