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Old 24th May 2009, 09:52 PM   #11
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So let me get this straight: Since the sum total current of the two output tubes should stay constant (class A), the cathode bypass caps don't need to be connected to ground except by a 1M resistor, as long as they're connected to each other? It's beginning to make sense.

Also, is there any problem with using another 10M45S with a 300-330 ohm current set resistor to feed 9-10mA into a LTP of 12AV7's? I'm opting for simplicity here.
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Old 24th May 2009, 10:03 PM   #12
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It should work fine in the frontend, but you will probably need to generate a small negative rail. If you have a spare heater winding this would do.
However in this application I have successfully used LM317's and other basic voltage regulators. Because the impedance of the bypass is proportionally so low the relatively poor frequency response is no really to much of an issue on the outputs (people claim they are more important on the LTP. My only point is, you may want to save the IXY chips for an application where their voltage rating will be more useful.

i just noticed - how were you setting the bias on the LTP in the original schematic.

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Old 10th June 2009, 07:52 PM   #13
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Default Layout Pictures!

Almost all set on the layout. There will be a stiff bar of aluminum clamping the 10M45S' up to the chassis, insulated with mica of course

The one thing that's missing is the wood for the sides. I'm about to cut, sand and varnish that now.

Click the image to open in full size.

Click the image to open in full size.

That 5V4GA sure looks a little shrimpy doesn't it? I have several 5Y3GT's that have a much bigger plate structure. I hope it doesn't explode while I try and grab a decent 5AR4 from somewhere to plunk in.
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Old 10th June 2009, 08:07 PM   #14
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I would consider moving the IXy's to the side of the case and running flying leads to the tubes. My experience is that the area between the valves can get hot. Remember to use use gate stoppers on the IXY chips as they are high gain mosfets and tend to oscillate.

Looks good.

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Old 10th June 2009, 08:11 PM   #15
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Quote:
Originally posted by Shoog
I would consider moving the IXy's to the side of the case and running flying leads to the tubes.
Thanks! Yep, I have some 1K carbon comp resistors exactly for that purpose. Two questions: How much power are these suckers dissipating if I set them for around 40mA each (via 75 ohms to ground)? Bias for the tubes is right around 20V, if that helps. And should I worry about potential oscillation/feedback if I do run long leads? Would a ferrite bead help?
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Old 11th June 2009, 07:12 AM   #16
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They will generate one watt of heat each(20x0.040=0.8W). Just so long as the gate is stopped with the 1K resistor, then they should stay stable regardless of lead length. Watch out for hum pickup.

My experience, and Tubelabs, is that they are quite variable. Build them and test them using a 30-40V power supply with a 375R resistor in series. Check the drop across the resistor and calculate the current (voltage/375=current). Design them such that you can adjust the current set resistor by adding or taking away an ohm or two resistance. Aim for matching for a push pull pair of about 1mA.

Shoog
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Old 11th June 2009, 05:55 PM   #17
athos56 is offline athos56  United States
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I like the way thats looking. Two questions, who made those transformers? And what did the final schematic end up looking like?
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Old 11th June 2009, 10:49 PM   #18
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Quote:
Originally posted by Shoog
They will generate one watt of heat each(20x0.040=0.8W). Just so long as the gate is stopped with the 1K resistor, then they should stay stable regardless of lead length. Watch out for hum pickup.
OK, thanks. Sounds like I'll want to chassis-mount them to make super sure they never die.

Quote:
Originally posted by Shoog
Build them and test them using a 30-40V power supply with a 375R resistor in series. Check the drop across the resistor and calculate the current (voltage/375=current). Design them such that you can adjust the current set resistor by adding or taking away an ohm or two resistance. Aim for matching for a push pull pair of about 1mA.
Yeah, I've got a 68 ohm resistor followed by a 20 ohm, 20-turn pot. I ought to be able to match these suckers really close. No 10 ohm resistor but I'll just look for 2.652V across them for 39mA, 2.72V for 40mA, etc.

Quote:
Originally posted by athos56
I like the way thats looking. Two questions, who made those transformers? And what did the final schematic end up looking like?
Thanks! Just wait till she's done. I'm going to spray the perf metal black to match the transformers. That's an Allied 6K7VG for power, a Hammond 193J for choke input, and two original Dynaco Z565's on the output. I took apart the Hammond and Allied transformers and used a razor/sandpaper to strip off all the varnish, and resprayed 2 coats of matte finish metal enamel. An hour or so in the toaster oven at 150 degrees and they were ready to be bolted back together.

I need to redraw and scan the final schematic, that'll be up soon.
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Old 12th June 2009, 12:23 AM   #19
athos56 is offline athos56  United States
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Quote:
Originally posted by sorenj07

Thanks! Just wait till she's done. I'm going to spray the perf metal black to match the transformers. That's an Allied 6K7VG for power, a Hammond 193J for choke input, and two original Dynaco Z565's on the output. I took apart the Hammond and Allied transformers and used a razor/sandpaper to strip off all the varnish, and resprayed 2 coats of matte finish metal enamel. An hour or so in the toaster oven at 150 degrees and they were ready to be bolted back together.

I need to redraw and scan the final schematic, that'll be up soon.
Ahh, that's it, a few coats of matte enamel makes anything look better
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Old 4th August 2009, 04:47 AM   #20
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Here we go at last. Shots of the wiring as soon as I get bored of listening to music.

Click the image to open in full size. Click the image to open in full size.

Slight hum in the left channel but you have to have your head right in front of the speaker to it.. Might have to do with issues outlined below.

I didn't have enough bypass capacitors so I used two 150uF capacitors in the left channel, and two 220uF caps in the right channel. These two caps go right to the 10M45 pins, meet at a floating point, and get connected to ground from there.

The amp has a weird phasey noise that starts up when I flip it on, swings from channel to channel, and quickly disappears. It squeals when I turn it off. Oh well, maybe the 5V4 rectifier doesn't like all its "new-school" solid-state neighbors
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