Anyone ever made the EL84 P-P circuit referenced on the Tubecad Journal site? - Page 3 - diyAudio
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Old 21st December 2010, 01:18 AM   #21
cjkpkg is offline cjkpkg  United States
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Yes, there is an error in the schematic. 200 would get you closer but I ended up with an LM317 CCS biased to ~82mA per pair. Highly recommend this mod... YH's Lazy Man Constant Current Source

My PSU is the Tubecad PS-4. Its a CRC with 47uF at each C. R is 150ohms (2x300 parallel) B+ is spot on 340V. Heater voltage comes by a voltage doubler rectified to 12.6VDC - the 6n1p's are in series and each el84 pair is wired in series.

The Edcor transformers perform flawlessly.

I just started messing around with LED cathode biasing at the front end where you only need 5-10mA of current...I may convert this amp next once the 300b is "done"...
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Old 21st December 2010, 03:50 AM   #22
jeffe is offline jeffe  Canada
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Yeah I guess for one extra component, the CCS is the way to go, I'll read up on that.

The cap I'm wondering about is the one on the B+ at the top of the schematic. I was thinking of a PS4 as well.

Just had a look at Edcor's site, good prices on their stuff...

Thanks,

Jeff
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Old 21st December 2010, 05:20 AM   #23
6L6 is offline 6L6  United States
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Can you get some voltage measurements on the Vin and Vout pins of the 317? I'm curious about the differential...

I have an amp that I want to try this on, but it has individual cathode resistors, so I would need the YHLMCCS set to 40ma (requiring 4 in total and probably 30ohm resistors)

Would the Vin to Vout be higher or lower with the current set lower?

Do you still have the cathode bypass caps in the circuit with the YHLMCCS ? Or are they removed?

Would it be possible for you to draw a schematic of what you have right now? That would be really quite helpful.

Looking forward to your LED bias on the front end. (I think you should do that before your 300B..)

Thanks!!
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Old 21st December 2010, 01:48 PM   #24
cjkpkg is offline cjkpkg  United States
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I will dig in tonight and post my findings...I forget how I last had it set up.

The beauty of adding pots and sharing one CCS for the EL84 pair is it makes tube matching not a major issue as you can tweak so each tube draws the same and reduces complexity and cost.

You can always count on the LM317 to drop 1.25V so a 31.25 ohm will give you your 40mA. I guess dedicated CCS per cathode would also address tube matching...
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Old 21st December 2010, 01:56 PM   #25
6L6 is offline 6L6  United States
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Thanks! It will be very appreciated!

The biggest reason for the individual CCS is to keep the existing wiring as intact as possible...

What about the cathode cap? is it removed with the CCS?
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Old 21st December 2010, 02:58 PM   #26
cjkpkg is offline cjkpkg  United States
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I will doublecheck but I believe I removed the cap when I implemented the CCS...
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Old 22nd December 2010, 04:48 AM   #27
cjkpkg is offline cjkpkg  United States
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Here is how I implemented this...
Click the image to open in full size.
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Old 22nd December 2010, 04:56 AM   #28
6L6 is offline 6L6  United States
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AWESOME! That actually answers most of my questions.

Thanks!
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Old 22nd December 2010, 04:43 PM   #29
jeffe is offline jeffe  Canada
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Thanks for posting the schematic. How's the Edcor power transformer? It's way cheaper than a similar Hammond. Does it run fairly cool?
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Old 22nd December 2010, 06:40 PM   #30
cjkpkg is offline cjkpkg  United States
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Yes the edcor runs very cool. I have three of the xpwr transformers in different projects and they all run cool.

I have two Allied/Hammond transformers for two SE projects and they run VERY hot...
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