Quicksilver 8417 Power Supply Question - diyAudio
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Old 3rd May 2012, 03:02 AM   #1
john65b is offline john65b  United States
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Default Quicksilver 8417 Power Supply Question

Hey all,

Looking into building a Quicksilver 8417 amp - but don't know what the Choke inductance / DCR is - Is it a 15H, 200ma??

Thanks in advance!!
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Old 6th May 2012, 12:07 PM   #2
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Having owned a number of the mono block Quicksilvers I can tell you that they sound good. I will also tell you that you can purchase them off ebay cheaper than you can build a pair. Also, there are amplifiers that sound better than they do. So, why bother? The 8417 uses a 12aX7 as the VA and a 12au7/12bh7 as the phase splitter and the circuit is a copy of what Bogan first used in their commercial 70 volt PA amp. Downfalls of the 8417 is the bias circuit. It requires that you either re-design and build a different bias circuit like I did to give the capability of individual tube bias or use the circuit as designed and have to purchase matched output tubes.

Last edited by Original Burnedfingers; 6th May 2012 at 12:14 PM.
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Old 6th May 2012, 01:34 PM   #3
john65b is offline john65b  United States
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Hey - Thanks Burned - I had a real 8417 and really liked it, but reluctantly sold it - it came to me with 6550's and no real mods that I could remember.

I have a nice pair of monoblock chassis, KT88's, 12AX7, 12BH7, a pair of 4300 60W Edcor OPT, and a pair of 350-0-350 250ma with 60v bias tap power trannies.

I got everything in order, except the Choke. I like the simplicity of the 8417 circuit. I also plan to drop the tube rectifiers in favor of the Diodes -similar to what you did years ago...not even the soft start tubes...

You have a schematic of something better with more or less same parts? I have not torn into the chassis, and have pairs of 6DJ8, 6H30, 6SL7, 6SN7, 6NP1, 12AT7, 12AU7, 5693, 5687, oh hell...don't want to get into Williamson types...something simple, great sounding..thought the 8417 would be a perfect build.

Besides, the ebay 8417 amps are a rarelty and commanding upwards of $750...
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Old 6th May 2012, 02:50 PM   #4
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"350-0-350 250ma with 60v bias tap power trannies"

Well, with Edcor you have a choice of at least two suitable chokes based upon your power requirements:

CXC150-10H-300mA @ 72 ohms dcr

XC75-1.5H-250mA @ 17 ohms dcr

Your choice depends on what your budget is and if you want an ultra low dcr choke or not. You might even try two XC75-1.5H-250mA in series as CLCLC.
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Old 6th May 2012, 11:57 PM   #5
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I have a pair of bastard child 8417's that I converted to use 6550's. Some idiot replaced the original Quicksilver output transformers with Hammond. I re-did the bias circuit also and it sounds really good especially for what it is.
If it were me I think I would try the XC75 choke. I would use diodes and 5Ar4's on it. To me it just doesn't sound as good with straight diodes in the power supply.

Take a look at the mapletree driver board circuit. I has used that a number of times and in my opinion its a lot better than the original circuit. This winter I will gut the mono blocks again and change it over to a 6SJ7 VA with a 6SL7 long tail or a 6SJ7 VA with a 6SN7 long tail phase splitter.
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Old 7th May 2012, 11:13 AM   #6
john65b is offline john65b  United States
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I have looked at that circuit, while not as simple as the Quickie, it is a Mullard type design, which I have wanted to build for a long time...you feel its performance / Sound best the quickie 8417 w /KT88's? Pretty much same tranny (4300 ohm) and power supply requirements. I think I even have the 6SJ7's too.
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Old 7th May 2012, 02:07 PM   #7
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"change it over to a 6SJ7 VA with a 6SL7 long tail or a 6SJ7 VA with a 6SN7 long tail phase splitter."

That looks like a great circuit to me. The Dynamutt circuit from Classic Valve also looks interesting with a 6SL7 VA direct coupled to a 6SN7 LTP with a CCS in the tail.
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Old 7th May 2012, 03:02 PM   #8
Mr. dB is offline Mr. dB  United States
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Quote:
Originally Posted by Original Burnedfingers View Post
Having owned a number of the mono block Quicksilvers I can tell you that they sound good. I will also tell you that you can purchase them off ebay cheaper than you can build a pair. Also, there are amplifiers that sound better than they do. So, why bother? The 8417 uses a 12aX7 as the VA and a 12au7/12bh7 as the phase splitter and the circuit is a copy of what Bogan first used in their commercial 70 volt PA amp. Downfalls of the 8417 is the bias circuit. It requires that you either re-design and build a different bias circuit like I did to give the capability of individual tube bias or use the circuit as designed and have to purchase matched output tubes.
Front end for the 8417 is essentially the same as a Dyna ST35 isn't it? Didn't the early ones even use 12DW7s?
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Old 7th May 2012, 10:10 PM   #9
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Hi,

I know the 35 uses a 7247 front end and I don't know if they used something prior to that.

http://www.triodeel.com/8417.htm

Quote:
************************************************** ************************************************** *************
The general circuit looks like it was borrowed piecemeal out of a Bogen MO-100 PA amp (not a bad place to start, actually). These amps have problems with output tube instability due to unnecessarily high grid circuit resistors on the 8417 tubes, and occasional arcing over of the 5AR4 rectifier tubes due to the input capacitor being 3 times the maximum size allowed according to the tube specifications. The manufacturer uses 1 each of 12AX7 and 12AU7 (or 12BH7) tubes, but only uses half of each tube, the other half just sits there and does nothing.
************************************************** ************************************************** **************
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Old 8th May 2012, 12:11 AM   #10
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Click the image to open in full size.

I don't know who first used that front end but Altec used it for their A333A.

Edit: sorry I forgot the ST35 used a triode front end.

Last edited by Palustris; 8th May 2012 at 12:14 AM.
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