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Old 30th April 2011, 03:34 PM   #11
john65b is offline john65b  United States
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OK...that explains that...but why no gain is weird...
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Old 30th April 2011, 05:00 PM   #12
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I don't understand why you went to the expense of some halfway decent caps and then threw a junk 6SN7 in there. By the way I built the same line stage only without the high priced caps and its noise free. I did however use tube VR regulators in it.
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Old 30th April 2011, 05:32 PM   #13
john65b is offline john65b  United States
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6BG6GA - what is your B+? What tube regulator? I have a ton of them just waiting for an opportunity...

Is it crazy to have SS rectifier with Tube rectification? I ask only because I have a single octal socket available if I go SS...would look cool with purple glow of a tube regulator...
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Old 30th April 2011, 08:04 PM   #14
DF96 is offline DF96  England
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Can we clarify something? When you say "remove the output cap" I assume you meant 'simply disconnect it', which would leave you with no noise and no signal. Others assume you meant 'replace it with a piece of wire', which would leave things virtually unchanged apart from the huge DC on the output. Which is right?
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Old 30th April 2011, 09:42 PM   #15
john65b is offline john65b  United States
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He has the dc blocking caps on the input of his amp.

All I can say is be careful of the ampside interconnect cable nipple, as it will have a nice dc voltage on it that can kill.
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Old 1st May 2011, 12:58 AM   #16
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Quote:
Originally Posted by DF96 View Post
Can we clarify something? When you say "remove the output cap" I assume you meant 'simply disconnect it', which would leave you with no noise and no signal. Others assume you meant 'replace it with a piece of wire', which would leave things virtually unchanged apart from the huge DC on the output. Which is right?
Correct - replaced it with a piece of wire.
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Old 1st May 2011, 02:09 AM   #17
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6BG6GA - what is your B+? What tube regulator? I have a ton of them just waiting for an opportunity...

Is it crazy to have SS rectifier with Tube rectification? I ask only because I have a single octal socket available if I go SS...would look cool with purple glow of a tube regulator...


I used 2) OD3's per channel. Dual power supply.
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Old 1st May 2011, 03:17 AM   #18
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lordearl: what you are doing is really quite crazy. You are removing a cap that is virtually guaranteed NOT to be the source of your problem, and as a consequence have ~ 250VDC on your interconnects. Now what happens if you handle the end of those interconnects while the preamp is turned on?

You have modified the design of an amp that worked pretty much correctly without understanding what you are doing, and in the process have made something that is pretty dangerous.

Look, I know its DIY here, and that we all probably take risks we shouldn't... but this is stupid.

Put the cap back in. Adapt some other known circuit using 1 tube that works with lower gain if thats what you want. Pay big attention to grounding, and use a ground breaker (back to back diodes, paralleled with a 10-30r >5W resistor and ~0.01uF cap, all with voltage ratings higher than your B+) to separate circuit ground from chassis (safety) earth.


(ps, you can always draw the circuit and take a photo using a phone/camera whatever).


I'm not trying to discourage you, but feel compelled to tell you what you have there is dangerous.

Fran
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Old 1st May 2011, 11:38 AM   #19
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quote:
lordearl: what you are doing is really quite crazy. You are removing a cap that is virtually guaranteed NOT to be the source of your problem, and as a consequence have ~ 250VDC on your interconnects. Now what happens if you handle the end of those interconnects while the preamp is turned on?


He is absolutely correct. What your doing is dangerous. It can and will bite you in the ***. Installing a coupling cap/s in the amplifier isn't technically correct either. Set up the line stage the correct way. Doing so will eliminate the possibility of electric shock for you or someone else that happens to stumble across what you have done. Your not re-inventing the wheel here but you are creating a very dangerous and life threatening condition that could take your life or someone elses.

Change it now!!!
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Old 1st May 2011, 11:59 AM   #20
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Thanks - I only tested it without the caps once, I know the issue of the DC - but I knew the power amp has caps at the input, but appreciate the concern all the same. I'll try another grounding structure and report back.
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