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Old 18th June 2011, 12:28 PM   #1001
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Thanks for the reply. I figured out the resistace value should be arounf 56 ohm (voltage divided by desired current) according to the graphs in the datasheet. I am actually thinking of using a 100ohm pot and go from there.

I did find this site

K & K Audio - Lundahl Transformers, audio DIY kits and more

but would rather go for a single mosfet per channel with the appropriate resistance. I really did not find any hard evidence that would should a cascode design to offer discernible improvement over a single element in builds similar to this one

As soon as I start soldering I will post the results. I believe the use of a current regulator from a differente manufacturer is welcome by those builders who cannot buy IXYS products due to the limitiations curretly in effect (mouse and digikey cannot selle the 10m45 to countries outside the US)
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Old 27th June 2011, 08:18 PM   #1002
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I finally got around to powering up my red board using 2 Antek 230V transformers in series for the 600V B+ to 6HJ5s. I used an Antek 40V for the bias supply. I used dummy loads instead of speakers for the first power-up.

I measured 640V for the 6HJ5s, 325V for the main board B+, -55V bias supply, and 145V for the screen. I was able to adjust the bias fairly close as an initial adjustment. Tomorrow I suppose I'll hook up the speakers and run a signal through it.

I used a CL90 after the bridge and before the 500uF filter cap on the upper power supply. How hot do these run normally? I left everything powered up for about 30 minutes and the CL90 is a little hot. I can hold it between my thumb and index finger for about 2 - 3 seconds before I'm tempted to let go.
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Old 27th June 2011, 08:21 PM   #1003
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I left everything powered up for about 30 minutes and the CL90 is a little hot. I can hold it between my thumb and index finger for about 2 - 3 seconds before I'm tempted to let go.
That's about right. Those devices rely on heat to work. Their resistance goes down as they heat up. Remove the heat and the resistance goes back up. You can see this with an ohmmeter and a heat gun.
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Old 28th June 2011, 01:34 AM   #1004
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Ya my CL's run HOT. Alot of people put a piece of shrink wrap on them so they dont dance with the load. I also keep them as far away from anything to give them some air flow. I put mine on the mains though. It would be a breaker popper if you put the CL after a 500va torroid.

On another note, can i just put a piece of shrink wrap on the ul taps and tuck them back into the end bells? I really dont want to cut them off, but they are a tight fit in my grommets.
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Old 28th June 2011, 03:50 AM   #1005
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Same here. They are supposed to run hot. Give them some space. The don't seem to run so hot that they melt shrink wrap, but they are toasty.
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Old 28th June 2011, 10:49 AM   #1006
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On the CL90, if you aren't running full current through them, you can insulate them so they get hot enough to drop their resistance further...has to be able to stand some heat though. IME, hotter is better.
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Old 28th June 2011, 12:04 PM   #1007
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I just finished hooking the amp up to speakers and a source.

WOW! This thing is LOUD and CLEAR! Sounds very good. No noise that I can tell. I measure about 18VAC music program across the speaker terminals with it cranked up pretty darn loud. I don't want to really crank it up until I get the distortion levels set properly.

So far all voltages look good and no smoke. The CL90 doesn't really seem much hotter even under load. The 6HJ5s get pretty hot though!

Now I just need to figure out how to cram all this into a chassis. It's going to be a pretty big amp.
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Old 7th July 2011, 09:43 PM   #1008
Perseo is offline Perseo  United States
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I powered up my point-to-point build of the DCPP amp, and it has not been smoothe sailing. My power supply is a nice old 340 - 0 -340 Philco transformer with several 6.3v heater windings.

On a dummy load for the speakers, I am getting 18 to 23 volts AC. Yikes. Both speakers. The next clue is that I was floating the various heater windings at some positive DC voltages. When I checked on my voltage divider for this purpose, one of the windings was floating (for my 6CE3 rectifier tubes), but the separate heaters for the 3cb6 drivers and the 6GV5 output tubes are at 0v DC. The heaters are heating but there is 0 ohms DC resistance to ground through the windings. That seems pretty wrong to me.

So, have a fried something in my power transformer, and if so would that be my source of massive noise? Or is my massive noise likely some other problem. I would not think screwy heaters would inject all that much noise. I could try to determine the frequency of the signal on the speakers, and separately could try to supply my heaters from something other than the suspect windings, but thought I would ask for advice in case anyone has encountered my immediate problem before.

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Old 7th July 2011, 11:24 PM   #1009
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"I powered up my point-to-point build of the DCPP amp, and it has not been smoothe sailing."

If you are using terminal strips attached to a metal chassis, check to see if you have wired inadvertantly to a lug which is grounded by the mounting bolt.
Otherwise, check the heater winding on the xfmr (disconnected from the circuitry), to see if the problem is internal to it.
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Old 11th July 2011, 03:15 AM   #1010
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Looks like I found another driver tube/pinout that should? work in the red board..

Anyone try the 6EV5?
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