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PostPosted: Sat Mar 17, 2018 2:51 pm 
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Bottle Rocket

Joined: Wed Feb 28, 2018 11:14 pm
Posts: 5
I’m curious if some of you technical type guys think these are fairly normal Bias numbers? I know I’ve read MESA typically bias’s DR’s cold.... According to the online Webber Bias site it’s biased REALLY cold.

‘94 DR Solo Rev. G - Amp is retubed with Groove Tubes GT6L6CHP Performance = 6

Outside Pair of Tubes “Silicon Bold” Setting
Vp 487 Ik 26 W12.6
Vp 489 Ik 27 W13.2

Outside Pair of Tubes “Silicon Spongy” Setting
Vp 409 Ik 19 W7.7
Vp 411 Ik 20 W8.2

Outside pair of Tubes “Tube Rectifier Bold” Setting
Vp 458 Ik 17 W7.7
Vp 460 Ik 17 W7.8

Outside pair of Tubes “Tube Rectifier Spongy” Setting
Vp 384 Ik 11 W4.2
Vp 386 Ik 12 W4.6

Middle (Inside) pair of tubes matched very closely with the outside tube pairs....

Thanks for your help!

Luke


Last edited by Luke Gibson on Thu Nov 29, 2018 9:04 am, edited 4 times in total.

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PostPosted: Fri Apr 13, 2018 12:59 am 
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Bottle Rocket

Joined: Tue Jan 03, 2017 10:16 pm
Posts: 20
If your IK number is the milliamp bias reading and vp plate voltage the standard 70% bias calculation yields about 42 milliamps per tube for the silicone bold settings. I'll address that mode as that is the amp basically in it's most powerful state. So going off the ik number you posted it would be considered to be biased fairly cold. I own a 2 channel dual rec and a Soldano SLO. The SLO I bias at 36 milliamps in my experience it sounds best there. I'll Check my DR and report what I find. For reference another amp that is said to be biased cold is the 5150. I've seen those as low as 18ma per tube. Now that is ICE cold. The reason for cold bias settings (tone wise) is to keep the power section clean and rely on the preamp for the distortion.

Regards
George C

_________________
George C

Dual Rectifier 2 Channel rev G magic 8 mod
Mark III SR blue stripe
Trem O Verb bone stock
Soldano SLO
Peavey 5150 the original
Marshall JCM 800


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PostPosted: Wed Apr 18, 2018 8:44 am 
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Bottle Rocket

Joined: Wed Feb 28, 2018 11:14 pm
Posts: 5
goaltender46 wrote:
If your IK number is the milliamp bias reading and vp plate voltage the standard 70% bias calculation yields about 42 milliamps per tube for the silicone bold settings. I'll address that mode as that is the amp basically in it's most powerful state. So going off the ik number you posted it would be considered to be biased fairly cold. I own a 2 channel dual rec and a Soldano SLO. The SLO I bias at 36 milliamps in my experience it sounds best there. I'll Check my DR and report what I find. For reference another amp that is said to be biased cold is the 5150. I've seen those as low as 18ma per tube. Now that is ICE cold. The reason for cold bias settings (tone wise) is to keep the power section clean and rely on the preamp for the distortion.

Regards
George C


Thank you for the reply! You are correct, Ik is the milliamp bias reading. I bought some Mesa Branded STR420 tubes off of eBay to experiment with and the results were unsatisfactory. I found some that were labeled WHT and RED. The WHT were WAY too cold like around 16ma and the RED were at the other end of the spectrum around 56-59ma (silicone bold settings). So I reinstalled the GT's.

I'm interested to see what your reading are as well! Thanks again!


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PostPosted: Sun Apr 29, 2018 9:53 pm 
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Bottle Rocket

Joined: Tue Jan 03, 2017 10:16 pm
Posts: 20
So I checked my amp its sitting at an ice cold 18ma with red Mesa tubes with settings on silicone rectification and bold. Your thread is inspiring me to do the adjustable bias mod on my amp. I've done it on countless 5150s its pretty simple. I think I'll do it to this amp and I'll report with my tone findings!

_________________
George C

Dual Rectifier 2 Channel rev G magic 8 mod
Mark III SR blue stripe
Trem O Verb bone stock
Soldano SLO
Peavey 5150 the original
Marshall JCM 800


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PostPosted: Fri May 04, 2018 5:58 pm 
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Bottle Rocket

Joined: Wed Feb 28, 2018 11:14 pm
Posts: 5
goaltender46 wrote:
So I checked my amp its sitting at an ice cold 18ma with red Mesa tubes with settings on silicone rectification and bold. Your thread is inspiring me to do the adjustable bias mod on my amp. I've done it on countless 5150s its pretty simple. I think I'll do it to this amp and I'll report with my tone findings!


Glad to help! If you can post a link or document the mod I will more than likely do it as well.....

Thanks!


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