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Christmas mod? (Read 2855 times)
Alan H
Senior Member

Posts: 63
Christmas mod?
06/18/09 at 23:00:39
Looking forward to starting the kit shortly - sounds like I should build in the "Christmas" mod straight away. Any problem with that?
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FLAC via Ethernet-over-Mains
Squeezebox 3
Valab 6N Solid Silver Coax
GD-Audio DAC19 DSP
Decware SE84DIY (V-Caps + CCE mod)
Solid silver / teflon cables
Scotmoose Sachiko FE206En Horns
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Seasoned Member

pair of dual 18

Posts: 284
Re: Christmas mod?
Reply #1 - 06/19/09 at 00:09:07
You defiantly need to connect pin 6 to pin 3 of both output tubes (for 6P15P-EV tubes anyway).  Whether the sound is better using a capacitor (Christmas Mod) or a wire I'm not sure.  My ears couldn't tell the difference, but a scope did show a slight difference in the shape of a sine wave.  

There is a HUGE difference between a floating pin 6 and either a wire or a cap from pin 6 to pin 3, but I'm not sure if there is much difference between a wire connection or a cap connection.  Anybody?

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dam*ed if you do,
and dam*ed if you

Posts: 372
Re: Christmas mod?
Reply #2 - 06/20/09 at 02:14:25

Since the cap mod is so very inexpensive, and I bet Steve and crew probably experimented with the straight wire vs the series cap; that out of trust to Decware's findings, I'd personally go with the cap mod.

You could get a pair of two suitable Xicon metallized film caps, .1/600v, for around a buck a pair from Triode Electronics, which are small and would easily fit between the other components in there.

The mod has worked freakin MIRACLES on my SE84CS: no ifs or maybe's. I also have a friend on the forum here that would make similar comments about the mod who has long been accustomed to running his SE84C with boutique EL84's (where the suppressor is internally connected to the cathode which is kind of similar to the straight wire connected mode with the SV83).

Although I've been too lazy to do it (having too much fun just listening), it seems like it would be easiest to compare the straight wire to the cap if you ALREADY had the cap installed.

If one wanted to be really aggressive about comparing to a straight wire, one could get some cheesy Radio Shack alligator clip test leads and short out the cap with a test lead for kicks, to see. Or, before permanently soldering, just try bridging the pins with a shorting test lead, and then bridge the pins with the cap between two test leads for comparison.

It goes without saying you should bleed the power supply caps each time before fussing around in there if you do all the A/B-ing (as you know, the voltages in there can be quite breath taking).

I'm about to try this same mod with some triode strapped EL34's (old refurbished ST70) where the suppressors have in the past always been wired to the cathodes. This will answer the question for me, albeit somewhat obliquely.


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« Last Edit: 06/20/09 at 02:14:52 by veryoldcat »  

SE84CS (vcapped), CSP, zbox, Dec685, ZP 1.0, Sota tt/Well-Tempered Arm/V15XMR, Parker 98's, Parker Audio *Power Chords*, cat 6 wires, OSX; a garage sale of other stuff...
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Ryan H
Verified Member

Posts: 9
Re: Christmas mod?
Reply #3 - 10/01/09 at 00:16:52
Hello All,
As I'm waiting for a set of new tubes, I thought I'd replace my cathode bypass cap and install the CCE mod.  Way back when I was getting the amp up and running, I ended up having to jumper pins 8 and 3 on the output tubes to get them to conduct.

My question is ... will having the CCE mod allow me to disconnect the pins 8 to 3 jumper?  I think I have an older version of the boards, judging by builds of other photos.  Only relevant in that I don't believe I have to break any traces on the board.  If I am mistaken, please let me know.

Any advice before I make one too many snips of wire would be greatly appreciated.

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