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Old 16th March 2003, 06:17 PM   #41
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Passfan,

Actually, I hadn't thought about that at all. But then you would need two solid state rectifier bridges and two 10,000µF capacitors, but that would sure reduce any doubts about crosstalk. Perhaps too instead of 2 10,000µF, one could use two 4700µF caps, which are more easily obtainable at your local Radio Shack.

OTOH, that would also allow one to simply use the AC. But... there would be that annoying hum. Of course, the whole point of DIY is experimenting and trying new different things. I wouldn't know how to apply hum reduction in that instance yet.

However, the reason I didn't think about it is because not every power transformer has a center tap on the rectifier 5 volt winding.

Otherwise, excellent point! I will modify my schematic and add it to the page as an alternative.

As for others' stubbornness, there is nothing wrong or stubborn about sticking to certain tried and true design practices. I myself believe as they do. I am merely offering simpler and cheaper alternatives that are effective, sound good and easy on the wallet.

I actually enjoy the volley of knowledge and experience. The Bible says "Iron sharpens iron", and I am sure that we all benefit from bringing up exceptions and arguments against and/or for a certain design practice. I certainly admit I don't know or remember everything I learned about electronics (after college I got into computers, so didn't profesionally practice), while those who have learned things strictly from their reading books don't understand that sometimes things don't always work as the book says.

I have read that most writers of texts write based on what they have read from others... right or wrong. Books that go against the standard don't sell well. I know... I am a... not very successful... writer. But I have done the research, and this is a true statement. I think it was Nils Bohr that said that no new theory is accepted until after the current generation dies away... or something like that. This is because those in authority don't want to look bad being that someone else thought of the new idea. Human nature, I guess.

Thanks!
Gabe
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Old 16th March 2003, 06:24 PM   #42
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Default AHUM.

Hi,

Quote:
OTOH, that would also allow one to simply use the AC. But... there would be that annoying hum.
Actually the 2A3 has an advantage here over other DHTs.
Due to the lower voltage, hum is much less of a problem.
Just use some humbucking method on the heaters and it should become inaudible.

You may want to give it a try and it's definitely cheaper than DC.

Cheers,
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Old 16th March 2003, 07:06 PM   #43
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Hey Passfan,

Sorry, I forgot to answer your question re the 6L6 amp. If you tie the two channels to one cathode resistor, you just need to half the resistor value. So for all four output tubes you need 175 ohms.

I have been toying with making a fully differential amp like that one to see how it sounds. I suspect it may be more like a solid state amp.

fdegrove.

Thanks for the input. It may very well be that the hum is much lower. I have tried the hum bucking techniques (applying inverted hum to the grid, etc.) with no success. But that is my failing.


Gabe
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Old 7th April 2003, 03:20 AM   #44
PassFan is offline PassFan  United States
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Gabe:
What kind of diodes do you use in your power supply? I plugged in 1N4007's into the PSU Designer II program and exceeded the piv ratings. Can diodes be paralleled to double their rating? The program has a diode it calls 1N4007X2. Just wondering if they mean doubling it up. Thanks
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Old 7th April 2003, 03:30 AM   #45
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No, Radio Shack sells a 1000 PIV diode. That's the one I use. Don't know the part # off hand.

I have recently ordered a bunch of 1500 PIV ones from Arcade Electronics (they are a reseller of NTE products).

http://www.arcade-electronics.com

Gabe
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Old 7th April 2003, 03:43 AM   #46
PassFan is offline PassFan  United States
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Quote:
Originally posted by Gabevee
No, Radio Shack sells a 1000 PIV diode. That's the one I use. Don't know the part # off hand.

I have recently ordered a bunch of 1500 PIV ones from Arcade Electronics (they are a reseller of NTE products).

http://www.arcade-electronics.com

Gabe
Wow, that was great service Gabe. Yes, I bought a few of those from radio shack and then had second thoughts. So you use those with the 272JX without a problem, good. Do you put snubbers on them (I think thats the term)? Thanks
Did you see my new project yet?


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Old 7th April 2003, 01:36 PM   #47
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Hey Passfan,

No.. I don't use snubbers. (Go ahead everyone... yell at me! Flame me! Tell me how bad an engineer I am! No need for snubbers! Don't see a lick of spikes.)

The more important thing to do... which I don't because have you seen the price of 1500 volt ceramic caps????... is use ceramic caps across the diodes to ease the reverse voltage transition. But... haven't had any trouble yet... after three years of constant use.

The old saying, the proof is in the pudding.

No I haven't seen your latest project.

Gabe
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Old 7th April 2003, 02:00 PM   #48
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The new one is under "Running Tube Amp Construction" Thanks for the info Gabe.
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Old 7th April 2003, 02:43 PM   #49
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Hi PassFan

>>>...I plugged in 1N4007's into the PSU Designer II program and exceeded the piv ratings. Can diodes be paralleled to double their rating? The program has a diode it calls 1N4007X2. Just wondering if they mean doubling it up....<<<

You can get more voltage rating by putting a pair of 1N4007's in series - each sees 'half' the potential difference (this is what PSUD II means by 2x1N4007 if I'm not mistaken). If you need more current carrying, you can put a pair in parallel instead (and I suppose you could use 4 of 'em with 2 parallelled series pairs in each leg of the rectifier, though I've not tried that).

Another option that's not covered by PSUD is the use of hybrid rectification - you build a bridge, with 1N4007's on the 'ground' side and say a 5AR4 on the 'B+' side. That way you'd have the slow start with a bridge and a single valve rectifier. Lots of ways to skin a cat.....

All the best,
Morse
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Old 7th April 2003, 02:55 PM   #50
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Passfan... What's the URL? Or is that a thread here?

Densely yours,
Gabe
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