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Old 2nd February 2012, 01:28 AM   #1
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Default Altec 353A oddity

The attached drawing is from an Altec 6L6GC puch pull amp. Notice the .0015uf 1600V capacitor between the OT primary leads; between pin 3 of each power tube? I can't recall seeing that in another design. What is the reason for or benefit from that cap?

Well that is a pretty small drawing. Here is a LINK to the full scale drawing.
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File Type: jpg Altec 353A screen shot.jpg (177.6 KB, 79 views)

Last edited by Captn Dave; 2nd February 2012 at 01:39 AM.
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Old 2nd February 2012, 02:26 AM   #2
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Quote:
Originally Posted by Captn Dave View Post
What is the reason for or benefit from that cap?
This capacitor reminds me of the old buffer capacitor that was used across the secondary of the old car radio vibrator HV supplies. It's purpose was to reduce sparking in the vibrator points and to reduce noise from same. Extreme potiental voltage spikes were buffered out which reduced wear and tear on the rectifier (0Z4) and transformer insulation. I suspect something similar is being done here. (Excluding the vibrator of course)
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Old 2nd February 2012, 03:53 AM   #3
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The cap could just be a crude brute force killing off of the top HF end to preserve global neg. feedback stability. Ie, dominant pole roll-off before the OT's nasty double pole roll-off.
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