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Old 6th December 2004, 07:57 PM   #1
newears is offline newears  United States
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Smile Quicksilver zener diode mod

I have a pair of original 8417 Quicksilvers (1985) and am going to upgrade the caps and resisters and apply some of Ned Carlson's mods.

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

I noticed that his last mod is to put a 5watt 80v zener diode into the 2nd screen line from the output transformer to reduce IM distortion. Has anyone tried this? Any theories or ideas on this mod?
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Old 6th December 2004, 09:40 PM   #2
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Other than modifying the bias circuit I run mine without any other mods without any problems.
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Old 7th December 2004, 06:49 AM   #3
newears is offline newears  United States
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Default Feedback circuit mods

That reminds me of another question. I noticed that the feedback circuit in the original 8417 Quicksilver schematic has a 562 ohm resister from the 8 ohm output connecting back to the cathode of the 12AX7 through an 820 ohm resister and with a 120 pf capacitor to the plate of one of the 8417s. In other circuits posted here this has been changed to a 5K resister connected to the 16 ohm output and a 100pf capacitor to the 8417 plate. Is this a change that should be made? What is the effect of leaving this like the original?
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Old 7th December 2004, 10:48 AM   #4
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There are two different versions of the 8417 amp depending on the year made.

My suggestion is to leave as is. Your amps don't have 16 ohm out would be my guess. A quick check of the terminal strip will answer the question. Your feedback is taken off the 8 ohm leg and this is the reason for the different values from what is in the schematic.
The 8 ohm leg has the 562 ohm resistor and different values on the 12AX7.

If you wanted to try something you could purchase 2) caddock resistors of say 300 ohms and replace the 562 ohm with these. One for each mono block amp. In addition, place a 500 ohm pot in series to allow the adjustment range from 300 ohms to 800 ohms.

Personally, the only modification I like and have kept is the bias mod to allow the usage of either 6550's or KT88's.
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Old 7th December 2004, 06:01 PM   #5
newears is offline newears  United States
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Default Feedback loop

Ahhh.. thanks for the explanation. You are right, my amp does not have a 16 ohm output. I think I will stick to just the bias changes. I am however, planning on changing the power supply by doing the following:

1. Remove the 2 Mallory 320uF cans (mine are bulging at the seams anyway). Add a ASC 50uF 600v PIO cap as the first cap in the CLC network. Add a Unlytic 650uF 500v cap as the last cap in the CLC network. Bypass the caps with Film and Foil .22uF Rel Caps. Frank indicated using .1 uF ... not sure which I should use since .22uF is in the schematic.

2. Add the 8 1N4007 diodes rectifier in front of the 5AR4s per your Quicksilver mod and schematic on this forum some time back.


While I am making the bias mods, I am planning on using Auricaps for the coupling caps and Multicap polypropylene film and foil RelCaps for the other caps.
Do you think upgrading resisters is worthwhile too?
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Old 7th December 2004, 09:36 PM   #6
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I consider Frank to be "Mr Tube". If Frank suggests to do something you can bet he is correct. Frank has done hundreds of Quicksilver modifications and knows all the tricks to make them really shine.
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Old 7th December 2004, 10:00 PM   #7
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Hi,

Quote:
Bypass the caps with Film and Foil .22uF Rel Caps. Frank indicated using .1 uF ... not sure which I should use since .22uF is in the schematic.
If you replace the electrolytics with ASC (polypropylene in oil) and Unlytic (polypropylene?), bypassing with filmcaps isn't really necessary.
In fact I doubt it would bring any advantage at all.

Quote:
Do you think upgrading resisters is worthwhile too?
Can't quite remember what's in there as standard but the Caddocks and Vishays are both fine sounding resistors.
Start with the gridstoppers first if you like, later you can tackle the plate and cathode Rs.

Personally, I'd rather spash out on solid core high purity (4N+) silver wire to redo the P2P internal wiring rather than spending dollars on the resistor upgrade but YMMV.

Joe,

Thanks for the thumbs up. Glad to see you like the QSs as much as I do.

Cheers,
__________________
Frank
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Old 7th December 2004, 10:11 PM   #8
newears is offline newears  United States
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Default Quicksilver mods

Sounds good. Any comments on the rest of what I proposed? Are you happy with the PS mods in your Quicksilvers? Would you upgrade resisters too?
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Old 8th December 2004, 05:01 AM   #9
newears is offline newears  United States
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Default Quicksilver mods

Frank,

The previous post was prior to my seeing your reply. Thanks that is exactly what I was getting at. With a somewhat limited budget I think I agree that rewiring the signal path with silver core wire and replacing the connectors (speaker terminal strip and RCA inputs will have more impact than the resistor upgrades.

Joe,

Thanks for all the help too.

Cheers,
Doug
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Old 10th December 2004, 11:16 AM   #10
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Doug

I am happy with the power supply cap size and have had NO problems since the diode add. It sounds good and the bass is killer. I liked the diode add and the cost was ok at less than .04 each.
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