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Old 23rd December 2012, 10:28 PM   #1271
Salas is offline Salas  Greece
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Get a 50K log pot. Cheapish carbon ones, those with the tin body are surprisingly good tone for short term. Just load the output cap with 1Meg or 470K to ground before RCA for bleeding any small charge to avoid pop sounds when connecting up.
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Old 23rd December 2012, 10:33 PM   #1272
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OK, will test with higher-ohms-output pot. And send photos when ready
And now sleepy-time.
Steven
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Old 23rd December 2012, 10:37 PM   #1273
Salas is offline Salas  Greece
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Just walk in a guitar spares or electronics shop in your city and there will be cheap log pots galore. Nighty nighty.
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Old 25th December 2012, 07:48 AM   #1274
stajo is offline stajo  Sweden
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Quote:
-Wich secondary value for output tx 600 ohms or other value for a SS amp? wich power in mA have to be rated? wich kind of material? suggested brands? or better order a special tx with the necessary specs?
I have a pair of http://www.lundahl.se/pdf/1660.pdf 18 mA laying around, I'm inclined to test them 4.5:1 in this application because preamps with to much gain is not fitting anywhere around my other stuff. And I'm not to fond of CFs in general. Its gonna take som fiddle around with B+ I think.

/Staffan
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Old 25th December 2012, 02:30 PM   #1275
Salas is offline Salas  Greece
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This pre runs near 30mA bias originally though.
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Old 25th December 2012, 03:04 PM   #1276
stajo is offline stajo  Sweden
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Quote:
Originally Posted by Salas View Post
This pre runs near 30mA bias originally though.
Oh, I thought it was around 22 or something for the tube. I have it on a breadboard somewhere and either I can try some different B+ and bias settings or try with another tube. I have a box of 6G6-G somewhere. A bit weaker but nice tubes running around 11 mA in triode. Rp 4750 and under 10 in amplification.

Merry Christmas
Staffan
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Old 25th December 2012, 03:33 PM   #1277
Salas is offline Salas  Greece
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Yes it is designed for 22mA. But it has been seen hitting higher, depends on tube brand and vintage a bit also. Merry Xmas!
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File Type: png Snap 2012-12-25 at 18.27.43.png (28.6 KB, 226 views)
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Old 25th December 2012, 03:55 PM   #1278
stajo is offline stajo  Sweden
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Yes it is designed for 22mA. But it has been seen hitting higher, depends on tube brand and vintage a bit also. Merry Xmas!
1660 takes up to 50 easy, it just starts to saturate at a certain signal level so I think its safe to experiment. Can also try Alt T 2:4.5

Staffan
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Old 26th December 2012, 09:32 AM   #1279
DimZ is offline DimZ  Greece
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report after some "technical" problems ...

tubes - tungsol reissue
Vin - 363V, Vout - 340
R4 set to 63mA
plate voltage 231
14.62V / 14.73V on cathode reistors

dc offset under 12mV at both channels - but still varies ,
output caps at the moment are jantzen mkp 3.6uf bypassed by teflon 0.056uf K72p6

I'll upload pics later ....
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Old 26th December 2012, 04:40 PM   #1280
Salas is offline Salas  Greece
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There can't be DC offset in AC capacitive coupling, only leakage, but modern capacitors have minimal. Is the DMM zeroing at DCmV when you touch its probes together? If yes, maybe those K72 are a bit dodgy? If you lift one side of those, does the DCmV change?
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