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Old 21st May 2012, 03:54 PM   #1881
hihopes is offline hihopes  South Africa
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Thanks Thomas for the help and the encouragement. Gotta go give guitar lessons now. Will look into it further tomorrow afternoon.
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Old 22nd May 2012, 02:17 AM   #1882
mach1 is offline mach1  Australia
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Andy,

The main reason I asked about your choke orientation was to find out whether you had tried twystd's recommendation (see below). I have mine orientated in the same manner as you and have never got round to trying it myself.

Quote:
I wrote the recent post you were looking for. I bread boarded a parafeed preamp, first I tried a single choke and got some hum. Then I mounting 2 of them in series base to base on standoffs like Gary suggested, and the hum went away. Then I started thinking that with the 2 cores in direct contact, that I may be losing some inductance due to cancelling.

I next mounted them in pairs, but wired out of phase, and placed the individual series wired chokes in close proximity, and parallel to each other. The parallel pairs (left and right channels) were mounted at right angles to each other. I could hear a definate improvement in bass response, and no hum after this, which would indicate that I was getting more inductance, and still having some hum cancellation. The results were so obvious, that I didn't really feel the need to measure it. Here's the original post that started the discussion: Tube DIY Asylum: Cheap iron parafeed preamp by twystd
and the link below gives the explanation of why it works.

twystd
I believe Magnequest recommend that their parafeed chokes be mounted on insulating standoffs.
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Old 24th May 2012, 04:19 AM   #1883
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Has anyone tried a grid choke instead of a grid leak resistor on the input of a 26 based pre?

Works and sound very nicely on the 437a feeding a 300B in my direct couple amps.

JD
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Old 2nd June 2012, 08:14 PM   #1884
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Quote:
Originally Posted by andyjevans View Post
OK -
I've had numerous suggestions to use Mills 12W resistors in parallel. Three of the 30, four of the 39 or five of the 47. Not cheap!! Also not available at good prices in the UK - they are 4 here.

Andy
Hi, Andy
Did you ever manage to listen to Mills MRA12's in the 26 preamp? If yes, what was your impression of them? Many thanks.
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Old 23rd June 2012, 11:01 AM   #1885
mogliaa is offline mogliaa  United Kingdom
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If you enjoy the sound of a 26 (like me), you may be interested in looking at how this valve performs from a purely linearity perspective (not how it sounds between various brand types, etc.). I have a stock of about 40 valves of 12 brands and mainly used and ST, albeit some NOS and globe as well. So statistical results here must be taken with a pinch of salt:

26 THD analysis | Bartola Valves

Cheers,
Ale
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Old 23rd June 2012, 02:31 PM   #1886
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Have you tried Raytheon yet ??
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Old 23rd June 2012, 03:10 PM   #1887
mogliaa is offline mogliaa  United Kingdom
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Yes and do measure well. Problem is that I had just one pair and didn't want to skew statistics with the single or pair of valves of same brand
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Old 23rd June 2012, 03:15 PM   #1888
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How do you like the sound of Raytheon? I prefer RCA globe.
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Old 23rd June 2012, 07:25 PM   #1889
mogliaa is offline mogliaa  United Kingdom
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Can't remember any significant difference. I do like RCA and Sylvania. Globe provide a warmer tone as they have more H2 presence. Difficult to find good CX326/226 that are in good shape at a reasonable price these days. I found an audible difference between OT and gyrator loaded. Want to do a proper listening test but that would imply building another 26 pre to do a quick switch between the two
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Old 23rd June 2012, 10:06 PM   #1890
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As I remember you did lots of gyrator loaded amps lately. I thought you like gyrator more. I have some DN2540 would love to try. Do you make them with PCB or ??
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