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Old 17th May 2013, 01:04 AM   #1
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Default I am Trying to Design this Darling Amplifier

Hi Everyone,
I have a pair of 5965's and I wanted to use Jeremy Epstein's
DC coupled Paralleled 1626's Darling. OK here is the Issues, I want to
use my old Wards Transformers and they are a little different than what
Jeremy has. Mine are 2K primary 4-ohm OPT'S His are Hammond 3k 8ohm
So, I wanted to get the Maximum power but stay in safe limits. Jeremy
Epstein used a 8532 I will be using the 5965's 1/2 per channel and I will be
running this like mono blocks in stereo, if thats possible. This is for a
Compression driver amp in a tri-amp setup! Notice the 8uF cap in the signal
path to the 1626's... I want that 2500hz Freq. setpoint for the Compression
drivers which by the way are 4-ohms, which match up with the wards OTL.
I am New at this, and I got my values from the RCA tube manuals and plate curves,
BUT; I really don't know If I got this right and If Anyone can advise some changes
I can amend my schematic. We have taps off of the power supply of 275VDC,
200VDC, 190VDC, 125VDC, at different points along the chain of resistors and caps.
I like having the meters, just cool to see what is actually going on when the amplifier is operating,
So I hope I hooked those up right! Again, I have really been working very very Hard on this
and I have finally found the tubes and design I LIKE just need to make this work somehow!
Thanks and bless You All, Please help me finish this out! PianoLydia
Attached Files
File Type: pdf PSE 1626 AMP.PDF (825.2 KB, 146 views)

Last edited by pianolydia; 17th May 2013 at 01:11 AM.
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Old 17th May 2013, 03:13 AM   #2
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ammeter needs to be in series with the cathode resistor. Currently (haha) it is in parallel with the cathode resistor
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Old 17th May 2013, 03:16 AM   #3
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is your crossover external and between source and amp? If so, why are you putting the 8uf cap in the signal circuit?
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Old 17th May 2013, 04:21 AM   #4
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Default Because The crossover is in this case a PLLXO

The crossover will not be between the outputs on the amplifier going to the speaker, This Passive/active situation where the Cap is placed in the Signal Path between the pre-amp and output stage sends only those frequency's to the output transformers will only really see that cutoff frequency and above to be amplified out to the compression drivers.
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Old 17th May 2013, 04:55 AM   #5
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Default I just corrected the Ammeter and put in series!

Here I corrected the Ammeters and put those in series with the Cathode
bias. Done! Any more help would be appreciated! Thanks and bless you all!
P.s. Remember I am new, And my friend and I are trying to get this
right, So Please be courteous and Understand this is my First and Only amp I
will be designing, Thanks! pianolydia
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File Type: pdf PSE 1626 AMP.PDF (906.4 KB, 45 views)
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Old 17th May 2013, 05:17 AM   #6
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Not sure where you got this schematic from...

A few points, the grids need a ground reference, or else they will float up on the ends of those coupling caps.

The value of 8.0ufd is way too large. You're going to want a much much smaller cap to make the xover around the frequency you want it to be.

The bypass cap on the cathode resistor isn't going to be of particular value because you want a high pass filter, you can adjust that value to make a sort of gain shelf to help out ur xover idea.

The meter has an internal resistance, you don't want it in series with the cathode. You want a voltmeter that is calibrated based on your choice of cathode resistor - which in turn is set to provide the bias for your particular tubes. The scale on the voltmeter can say amperes (and show the nominal range required). Or you could put an ammeter in the plate lead or in the ground return of the power supply - in the latter case it would show all current drawn, including the first tube, IF you use a single power supply source and only want a relative indicator.

You should be aware that in a class SE amplifier, the current drawn is more or less constant.

FYI, this is likely to only your first amplfier... you'll see...

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Old 17th May 2013, 06:18 AM   #7
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Epstein's 1626 Darling has nearly twice the B+ voltage than those indicated on your schematic, that will significantly impact your output power and distortion...
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Old 17th May 2013, 06:52 AM   #8
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Think this is what the OP is trying to accomplish.
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Old 17th May 2013, 04:24 PM   #9
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The operating point for the first stage needs to be properly set up. Presently it is 0V on the plate with 8.63mA current: that's impossible.

So I would first look at the B+. 190 V will work but will result in a lot of 2nd harmonic distortion. I didn't draw the plate curves for the 1626, but I expect that there is too little B+ there too.

Here's what I would recommend: use an appropriate power transformer that gives you at least 350V - 400V. Use a B+ of 350V for the 5965 stage and a plate resistor of 50k ohms. Bias the tube at 4mA @ -2.6V; the plate voltage will be 145V.

Attached is some plate curves I drew for my own project. Notice I mislabeled the 130V plate voltages by 5V.
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Old 17th May 2013, 05:11 PM   #10
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I had a look at JE's schematic and it looks like he is using a B+ of about 260V. That being the case, use the load lines above but change the first stage B+ to 250V use the 50K plate resistor; plate voltage will be about 110V with a bias about -2 for a plate current of about 2.6mA. I would use a red LED for bias and delete the cathode cap.
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