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Old 3rd February 2014, 04:47 PM   #1
Cassiel is offline Cassiel  Libya
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Default Am I pushing the envelope too far? Layout concerns.

Hi, maybe people can share some experiences on tight packages. Is it OK for the preamp tubes to be that close to the output transformers? Is that power tube too close to the power station? I know that I'm taking risks here but I would like to know how many. 50% chance of success? 20%? None? Am I doomed? Could I get away with this? I'm about to punch holes, some sensible advice needed.
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Last edited by Cassiel; 3rd February 2014 at 04:53 PM.
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Old 3rd February 2014, 05:02 PM   #2
kevinkr is offline kevinkr  United States
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Far too crowded imho.. Would be exceedingly difficult to wire, thermal concerns with the tubes so close together, and potential for magnetic coupling between the two output transformers and between the power transformer and one output transformer.
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Old 3rd February 2014, 05:14 PM   #3
Cassiel is offline Cassiel  Libya
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No problems about the wiring, yes, it would be more difficult but it can be made. Thermal stress? Oh well, I think the tubes can take it. Shorter lifespan? Oh well, that's OK. But there's one thing you said that concerns me - the possible magnetic coupling between output transformers. I didn't know about that. Is there a way I can check that out before wiring?
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Old 3rd February 2014, 05:15 PM   #4
BZed is offline BZed  United States
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Way too close. Get a bigger chassis.
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Old 3rd February 2014, 05:27 PM   #5
Cassiel is offline Cassiel  Libya
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Yeah I KNOW it's too small. Irrationality can make you stubborn. I don't want to buy a crappy Hammond chassis. This is a commercial amp:
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Old 3rd February 2014, 05:33 PM   #6
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by Cassiel View Post
...I don't want to buy a crappy Hammond chassis. This is a commercial amp:
Then why take a shortcut and cram components far closer than the recommended distances?

There are shops that make chassis to order and they are not crappy.
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Old 3rd February 2014, 05:46 PM   #7
kevinkr is offline kevinkr  United States
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And there a lot of very nice and roomy Chinese made chassis on eBay for comparatively little money as well. (The quality of the boxes I have bought was quite good and not matched by anything from around here at anything like a reasonable price.)
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Old 3rd February 2014, 05:51 PM   #8
Cassiel is offline Cassiel  Libya
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Quote:
Then why take a shortcut and cram components far closer than the recommended distances?
Because it can be done. Hum is the only problem I'm really concerned about.

Quote:
And there a lot of very nice and roomy Chinese made chassis on eBay for comparatively little money as well.
I don't want my amp to look Chinese. No disrespect to Chinese people. Oh well, it was some kind of challenge, I'm not too sure about it now. Getting cold feet.
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Old 3rd February 2014, 05:55 PM   #9
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Morgan Jones recommends in his "Building Valve Amplifiers" that you allow at least 1.5 envelope diameters between the tubes. But he also points out that the amount of IR radiation received by a target is dependent on how big of a radiating surface the target "sees". As some tubes have anode plates that are essentially a long skinny rectangular box, you can place the tubes closer if you rotate them such that the individual tubes "see" the skinny side of the anode sleeve. This is from one of the first couple of pages in Building Valve Amps (perhaps page 10ish).

That said, many console amps placed the tubes almost shoulder to shoulder. The placement also depends on how much power you're dissipating in the tubes. The important thing is that the envelope and anode temperatures don't get too high...

~Tom
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Old 3rd February 2014, 05:56 PM   #10
tomchr is online now tomchr  United States
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Don't get cold feet. Either get a bigger chassis or a different layout. How about putting some tubes between the PT and the left OPT?

~Tom
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