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Old 25th February 2011, 05:38 PM   #41
kevinkr is offline kevinkr  United States
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Originally Posted by Wavebourn View Post
I made output transformers for it using Edcor XCPP60-MS-4K -- reassembled laminates with an air gap about 0.2 mm using Capton film. No load inductance is about 18 Henry. Sounds gorgeous!

Click the image to open in full size.

Love the picture!!!
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Old 25th February 2011, 05:56 PM   #42
hihopes is offline hihopes  South Africa
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Sorry Wavebourn, that was meant to be a joke. Guess I should have attached a smiley. I would far rather hear your amp looking like that than one of mine! Are those light blue caps I see underneath there? They are huge!

Do you put all of your trafos and chokes underneath in your pyramid design?

316A, my speakers are only 87dB sensitivity. 3W will be enough, as I will only power midrange and tweeter with it. I have heard that these tubes are microphonic. How do you experience the microphonic problems? Does it pick up vibrations from the output of your speakers?

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Old 25th February 2011, 06:10 PM   #43
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I don't hear any microphonics from 4P1L when I use them as output tubes. No oscillation with no other stoppers except 62 ohm grid stopper.
Right now I turned down volume knob and tapped both of them by screwdriver. Nothing.

May be my rat nest is built more accurate topology-wise, so no oscillations and no microphonics associated with them?
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Old 25th February 2011, 06:21 PM   #44
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Originally Posted by kevinkr View Post
Love the picture!!!
Thanks!

That Magnavox boombox is a bit boomy, but sounds darn loud driven by 2x2.5W amp!
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Old 25th February 2011, 06:22 PM   #45
hihopes is offline hihopes  South Africa
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Thanks, that is excellent news. Have you ever tried them in pentode mode or in push-pull topology?

Last edited by hihopes; 25th February 2011 at 06:25 PM.
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Old 25th February 2011, 07:05 PM   #46
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Originally Posted by hihopes View Post
Thanks, that is excellent news. Have you ever tried them in pentode mode or in push-pull topology?
I did not, but I know they were used in push-pull amps with 10W output, 3 per channel: one driver for phase splitting transformer, and one pair in push-pull output. When I was a kid I disassembled such an amp for parts. Actually, it was a radio receiver with such an output stage, for a military campus. Also, could power up to 200 speakers connected by wires. It was usually working on a horn speaker on top of a pole, pretty loud! It had also turntable and microphone inputs. Was powered from batteries.

Edit: schematic is on page 21 http://www.radioman-portal.ru/magazin/radio/1952/9.djvu

Click the image to open in full size.

Click the image to open in full size.
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Old 25th February 2011, 07:36 PM   #47
hihopes is offline hihopes  South Africa
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Where did you get the pics? Not from when you were a kid? I guess they would have been used in pentode mode in that application?
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Old 25th February 2011, 07:50 PM   #48
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Where did you get the pics? Not from when you were a kid? I guess they would have been used in pentode mode in that application?
Yep, I made a time machine back in 1999 when used to live in Randburg (Joburg suburb)

On the link in my previous post you will find a magazine, and schematic there on page 21. It is self-explanatory.
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Old 25th February 2011, 09:26 PM   #49
hihopes is offline hihopes  South Africa
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You lived in Randburg!? You are full of surprises. Is that you on the front cover of the magazine?

Thanks for the link. Triode strapped output I see.

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Old 25th February 2011, 10:41 PM   #50
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Never heard of that tube, or direct heated penthodes altogether. Seems an interesting little bugger, thanks for bringing it to my attention
There are lots of DH pentodes out there: 813, 814, 1624, being some of the more notable ones (power RF amp types) There are also the low voltage, small signal pentodes like the 1T4 that are DH.
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