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Old 2nd November 2004, 03:17 PM   #1
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Default Tube vicinity heat problems(maybe?)

Hello Forum!

I'm building a tube amp, a 2A3 PSE. I think i've made a huge mistake in laying out the chassis top plate.

I'm using Valve Art 2A3's. The mistake i made was:

Between the CENTER of the holes for the 2A3 sockets, there is only 70 mm(~2.7"), and the space between the tubes at the knee is only 18 mm(~0.7")!

I do intend to run my 2A3's at less than max ratings, as well as possibly slightly starved filaments. But still, i worry about this close vicinity of the tubes.

In your esteemed opinions, should i scrap this plate and redo from start?

Sincerely,
Kristian Kjeldsen
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Old 2nd November 2004, 03:32 PM   #2
mcs is offline mcs  Denmark
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That is a bit close, but if there's some airflow around the tubes it may be OK - any experiences, anyone?

But why would you want to starve the filaments? Are you shure that won't actually reduce the tube life rather than improve it?

Best regards,

Mikkel C. Simonsen
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Old 2nd November 2004, 03:48 PM   #3
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Quote:
Originally posted by mcs
That is a bit close, but if there's some airflow around the tubes it may be OK - any experiences, anyone?

But why would you want to starve the filaments? Are you shure that won't actually reduce the tube life rather than improve it?

Davs!

I will try to provide ample airflow around the tubes, and monitor the situation. What are the electrical signs that a tube is running too hot?

The only source i have for info on starved filaments is this:
Steve Bench Tube Pages on DHT starved fil.

I do not intend to lower them that much however, but rather 5-15% below rated voltage.

Regards,
Kristian
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Old 2nd November 2004, 04:22 PM   #4
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2A3's are not a very high power tube so I think 0.7" spacing at closest point between envelopes will be fine between a pair of them if they aren't boxed in with large transformers on all sides.

Do not ever starve the filaments of power tubes or you will drastically shorten their life!
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Old 3rd November 2004, 08:06 AM   #5
SHiFTY is offline SHiFTY  New Zealand
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I have about 20mm between my 6B4G tubes. They are fine, no probs at 15W dissipation. I wouldn't be too worried, or if you are just punch slightly bigger holes further apart and mount the sockets well down in the chassis.

They don't run too hot anyways, not like EL34s or similar.
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