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#26 pre amp
#26 pre amp
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Old 5th December 2017, 12:49 PM   #4541
king4joy is offline king4joy  Hong Kong
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Thankyou....Andy
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Old 5th December 2017, 01:09 PM   #4542
pieter t is offline pieter t  Netherlands
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With 126C you might parallel primary and secondary for use as plate choke.
Nothing would change wrt to inductance, but DC resistance would be halved; that's never bad.
Did you try and measure the series connection of 126C??
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Old 5th December 2017, 01:38 PM   #4543
andyjevans is offline andyjevans  United Kingdom
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Quote:
Originally Posted by pieter t View Post
With 126C you might parallel primary and secondary for use as plate choke.
Nothing would change wrt to inductance, but DC resistance would be halved; that's never bad.
Did you try and measure the series connection of 126C??
Hi Pieter - that's another idea to try. Thanks! I didn't measure anything - just listened. The treble drop in series was quite substantial.
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Old 7th December 2017, 01:57 PM   #4544
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by pieter t View Post
With 126C you might parallel primary and secondary for use as plate choke.
Nothing would change wrt to inductance, but DC resistance would be halved; that's never bad.
Did you try and measure the series connection of 126C??
how come ??
unless this is made by aliens.
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Old 7th December 2017, 03:09 PM   #4545
andyjevans is offline andyjevans  United Kingdom
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I just tried 10Y into both a single 126C and two 126C in series used as plate chokes, just primaries used. FT-2 coupling caps. Conclusion was that two in series is definitely better. This gives 200H and the gains are in clarity, timbre and treble air and presence. Certainly worth the extra modest outlay.

This would no doubt be the same for the 26 so that's an idea for a plate choke. I previously just tested the 26 with a single 126C but I'd expect the same gains with two in series.

However, I just tested out a different plate choke with the 2P29L and that's as good as the 10Y with two 126C, maybe even a tiny touch better. So next is to try it with 10Y and see what that gives. There's no markings on it so I don't know the value, make or anything. I'll see if I can take a photo.
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Old 7th December 2017, 04:31 PM   #4546
andyjevans is offline andyjevans  United Kingdom
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My other plate choke is marked 750R and 50H - sounds great with a 2P29L (Ra 3K) but a little flatter with a 10Y, it doesn't sound quite comfortable with its higher Ra of 5K-ish.

I'd like to know who made this plate choke - looks quite generic but maybe someone knows. I think I got it off Thorsten Loach around 10 years ago. Measures 80x65x55mm
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Old 7th December 2017, 07:06 PM   #4547
kevinkr is offline kevinkr  United States
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#26 pre amp
Quote:
Originally Posted by hpeter View Post
how come ??
unless this is made by aliens.
That's actually correct as the windings are in parallel, the resistance is halved, but the inductance doesn't change. Magnetically it is equivalent to substituting a single larger piece of wire because the number of turns on the core has not changed. Connecting them in series would give you twice the number of turns, twice the DCR and four times the inductance.
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Old 21st December 2017, 06:54 PM   #4548
Vbenonisen is offline Vbenonisen  Norway
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I see that many uses quasi-choke input filters for B+ with a very small capacitor before the first choke. What are the advantages of using this little capacitor?
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Old 21st December 2017, 07:00 PM   #4549
mogliaa is offline mogliaa  United Kingdom
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#26 pre amp
as you say, it creates a hybrid between choke-input and cap-input and you can increase the output voltage with the value of that cap.
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Old 21st December 2017, 07:15 PM   #4550
Rod Coleman is offline Rod Coleman  United Kingdom
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#26 pre amp
Quote:
Originally Posted by Vbenonisen View Post
I see that many uses quasi-choke input filters for B+ with a very small capacitor before the first choke. What are the advantages of using this little capacitor?
With no capacitor, the instant when the rectifier output is at (or near) zero can produce a rough waveform from the effect of leakage inductance and stray capacitance. A carefully chosen value can remove the roughness, without increasing the dc output. If possible, use this value.

Raising the value such that the dc output increase has the drawback that load-regulation is degraded.
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