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Old 16th November 2010, 06:27 AM   #31
Ian444 is offline Ian444  Australia
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Yep, that's right, I changed the four screen resistors from 100R to 820R to clean up the sound when not using global feedback. I found 1K5 too much and 470R not enough. It may be different with your dual-driver speakers compared to my 4 ohm single driver speakers, I don't really know. Definitely worth trying though!
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Old 17th November 2010, 01:26 PM   #32
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It may be different with your dual-driver speakers compared to my 4 ohm single driver speakers, I don't really know. Definitely worth trying though!
Different tubes respond differently too. I find that on my old Sylvanias the measured distortion goes up as I increase the resistor value but the sound improves, up to a point (about 470 ohms). At 390 ohms there is audible loss of punch on transients with loud music. All tests are in pentode mode with GNFB on low efficiency speakers. The good speakers aren't done yet.
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Old 17th November 2010, 06:14 PM   #33
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Originally Posted by tubelab.com View Post
Different tubes respond differently too. I find that on my old Sylvanias the measured distortion goes up as I increase the resistor value but the sound improves, up to a point (about 470 ohms). At 390 ohms there is audible loss of punch on transients with loud music. All tests are in pentode mode with GNFB on low efficiency speakers. The good speakers aren't done yet.

Well, FWIW this puppy will be running 6P14P-EV - and to start in pentode with no feedback and 820R on screens, speakers will be mid efficiency dual Mark Audio EL70s. Hopefully bench tested in the next day or so and making no smoke, just music at home by weekend.

BTW, thanks to y'all for the suggestions - this is almost as much fun as my early days on the Bottlehead and old Decware forum
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Old 17th November 2010, 06:17 PM   #34
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Hopefully bench tested in the next day or so and making no smoke, just music at home by weekend.
You need a variac? I've got one here you can borrow.

jeff
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Old 17th November 2010, 08:19 PM   #35
chrisb is offline chrisb  Canada
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You need a variac? I've got one here you can borrow.

jeff

thanks, but not necessary - I do have my own variac, but bench testing will be at "the mountain" - where there's more thorough gear and know-how
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Old 18th November 2010, 08:24 AM   #36
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Well, FWIW this puppy will be running 6P14P-EV - and to start in pentode with no feedback and 820R on screens, speakers will be mid efficiency dual Mark Audio EL70s. Hopefully bench tested in the next day or so and making no smoke, just music at home by weekend.

BTW, thanks to y'all for the suggestions - this is almost as much fun as my early days on the Bottlehead and old Decware forum
What type of speaker did you build?
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Old 18th November 2010, 03:03 PM   #37
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..... Hopefully bench tested in the next day or so and making no smoke, just music at home by weekend......
I'm sure it will be fine! In my own case, the SP-P was the first DIY amp (out of a half-dozen I've built) that worked 100% perfect at switch-on. Simple is good! Interested in hearing your impressions when it's up and running.
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Old 19th November 2010, 07:50 PM   #38
chrisb is offline chrisb  Canada
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What type of speaker did you build?

rather a few (mostly Fostex and Mark Audio drivers presently)

this particular amp will be used with the ones on the left - dual Mark Audio/CSS EL70 paper cones with polka dots
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Old 22nd November 2010, 03:22 PM   #39
chrisb is offline chrisb  Canada
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okay dokay - y'all was patient over the past couple of weeks or so it's probably time to post my initial impression

system= MacBook Pro Airplay / Airport Express Toslink / Citypulse DAC / Simple PP / Castle Microtower CSS EL70

Sovtek 5AR4 / NOS Sylvania 12AT7 / 6P15P-EV / pentode (with feedback) + a "little" help from Daniel =

input sensitivity is lower than the CCS loaded LTP in the El Cheapo variant, but tons more power, dynamic snap and low end "authority" - those 4" paper cones never sounded so big

too good to take out of the system for tweakage

nah, who'm I trying to kid - but just where to start

George, et al - thanks
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Old 22nd November 2010, 06:50 PM   #40
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too good to take out of the system for tweakage

nah, who'm I trying to kid - but just where to start
Maybe Santa will bring you a NOS Mullard GZ34.

What are the coupling cap values? I have a hand-full of 0.22uf K40's here, they are a little on the large side physically.

Are you really using 6P15P's, or that a typo?

jeff
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