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Old 16th February 2013, 04:47 PM   #1
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Default Eimac 100TL Output Transformers and Bias Point ?

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Last edited by HP8903B; 11th January 2014 at 01:05 AM.
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Old 17th February 2013, 10:30 AM   #2
euro21 is offline euro21  Hungary
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Looking for circuit of SE amp. for Eimac 100TH


Last edited by euro21; 17th February 2013 at 10:43 AM.
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Old 17th February 2013, 10:55 AM   #3
hpeter is offline hpeter  Slovakia
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Location: Electrostats or bust
are this type tubes made even today, like 4-250 , 833 etc..?
14 nice sweetspot, Ra 4k6
old rule of thumb -primary should be 2-3x of plate resistance(?)
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Old 17th February 2013, 02:03 PM   #4
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I have no hands-on experience of 100TL or TH , but a friend of mine built one a year or two ago, so I'll pass on what I know .
Bear in mind the Ra drops if you are going into A2 . He used a 10K output transformer I believe , and reported very nice results, better overall than VT4C he reckoned. You will need an A2 driver for either 100TL or 100TH .
On that basis 100TH is actually no more difficult than 100TL , in fact the voltage swing for the driver is less , which helps. The 100TH are apparently cheaper than 100TL , I'm told .

I think the start point is deciding on available B+ . My friend used at least 1000, perhaps 1200 V . From that he got about 30wpc with the A2 driver. If you can decide B+ then you should be able to narrow down an operating point with some help .

The driver my friend used was the J.Ross McDonald ACM ( augmented cathode follower ) No.2 variant, using some hefty triode-wired pentodes for the driver (CF) part .
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Old 17th February 2013, 05:55 PM   #5
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The B+ will be 1000V - 1200V.

I will not need more than 20W, likely less.
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Old 20th February 2013, 06:05 PM   #6
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Try contacting Dave Slagle on his 'Intact Audio' forum .
Either he or the Colorado boys ( C4 group ) know quite a bit about Eimac operating points.
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