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Old 18th June 2012, 06:18 PM   #11
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Internals

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Old 18th June 2012, 07:13 PM   #12
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gonna have to cite you in the analog forum for Lenco abuse now...
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Old 18th June 2012, 07:37 PM   #13
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Well spotted

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Old 19th June 2012, 12:45 AM   #14
Junm is offline Junm  Philippines
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Hi shoog,,,

How much inductance are you getting from those 40w lamp ballast? I have several of those and you give me idea how put them in use again....
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Old 19th June 2012, 06:12 AM   #15
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I have no induction meter so cannot say exactly. However the amount of capacitance following them would normally fry the UY85 and they are fine. I have ran a similar power supply on my FVP5 clone for well over two years and have encountered no issues with arcing rectifiers. The caps are doing most of the heavy lifting here - but the use of any type of choke brings considerable benefits in terms of line hash suppression.

I have heard of them been used as plate chokes, and I have equally heard people say that they will have next to no inductance with DC present.

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Old 19th June 2012, 06:42 AM   #16
Junm is offline Junm  Philippines
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okay thanks...anyway i will try them..in my tube preamps supply
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Old 19th June 2012, 08:58 AM   #17
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I have just read someone actually measuring 3.5H on a 14W choke, though this would be without DC. However these are swinging chokes so DC maybe less of an issue. This makes it a useful amount of inductance.

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Old 19th June 2012, 09:11 AM   #18
piano3 is offline piano3  United Kingdom
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Hi Shoog,

If you measured the ripple on the power supply under load this should give an indirect answer; I am sure many are wondering about the inductance of these ballasts
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Old 19th June 2012, 09:31 AM   #19
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Hey Shoog,
Could you explain the purpose of the 10u cathode-cathode cap? Is it to help up lowend response as it shorts out the local feedback from the 100ohm resistors above a certain frequency? Why not use a single common 110ohm resistor?
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Old 19th June 2012, 09:47 AM   #20
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The intention is to eventually replace the 60R resistor (common) with a current mirror and two 100R resistors. This will raise the cathode resistance considerably (I believe). This is essential as even though current balance excellent at the moment - it will drift over time and start saturating the OT. The 10uf is a full bypass from cathode to cathode making it an effective LTP output stage. I may raise this to 20uf - but the calculated increase in bass extension appears to be marginal until you reach many 100's of uf.

So the intention is to allow for different bias arrangements whilst maintaining full differential LTP behaviour.

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