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Post subject: Blues Deluxe RI: Blue or White Groove Tubes? And BIAS...
Posted: Wed Sep 22, 2010 10:44 am
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Dear Friends!

First, I have seen some stock BDRI with WHITE label tubes. My amp comes with the BLUE tube... what is default?
Second, what JJ/Tesla tube is the best suit for an upgrade?
Third, I checked the BIAS settings from factory, measured 68,5 mV at test point... So, I moved down to aprox. 61,8mV. Manual describes 60mV as default, what's right?

Thx bros!


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Posted: Wed Sep 22, 2010 11:10 am
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After buying a bias probe to measure cathode current and plate voltage, I have found the Fender bias test point to measure high compared to the actual current readings.

For tubes I recommend:

https://ssl.eurotubes.com/cart/index.ph ... ory_id=122

You can pick your poison. I am using the 6L6GC Blues option in my BDRI.

For bias measurements I use this:

http://www.amp-head.com/product_info.ph ... ucts_id=70

I have my bias set to 38 mA per tube at a plate voltage of about 408 volts. At the Fender test point that translates to 83 mV! Don't try this with Groove Tubes. They won't last long.

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Posted: Wed Sep 22, 2010 1:36 pm
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They are a lot of good valves, SED Winged C can also be considered and Fender bias 60mV on BDRI is usually considered as cold.

(grille current is in the range of mA, the error seems to big to me between resistor and probe ??? what is the 1 Ohm presision ?)

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Posted: Wed Sep 22, 2010 2:05 pm
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Tissan wrote:
(grille current is in the range of mA, the error seems to big to me between resistor and probe ??? what is the 1 Ohm presision ?)


See the Amp-Head link in my post above. They say they use a 1 ohm, 1% resistor. The Fender 1 ohm resistor is listed as 5% in the parts list. The difference between the two readings works out to be about 8%. Also need to consider that I used my "good" DVM for the current measurements and my "cheap" DVM to measure the Fender test point. As I recall, the cheap DVM read slightly higher than my good one at the Fender test point when I did it that way before. So the difference seems about right. I trust the Amp-Head bias probe more than I do the Fender test point.

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Posted: Wed Sep 22, 2010 3:00 pm
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I agree, it 's also my calculation ! (I'm sure you made the measurement after temperature stabilzation). Rougly 10% of error seems acceptable for a biasing of a tube at 50% of max power that could partially explain that some sound hot and some sound cold. I've also seen differents GT origins (the brand is still on the glass ! Sovtek, JJ ...).
By the way Sovtek is only a brand and made by Reflector compagny in Saratov.

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Last edited by Tissan on Wed Sep 22, 2010 3:10 pm, edited 1 time in total.

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Posted: Wed Sep 22, 2010 3:09 pm
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+1 on JJ's from Eurotubes. Bob has bias videos on the Eurotube site.

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Posted: Wed Sep 22, 2010 3:11 pm
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Typically in 2 output tube Fender amps, 68 mV at the test point = 68mA total cathode current for both tubes (68 mV / 1 ohm = 68 mA). Each output tube gets approx half of the total current, that is 34 mA per tube, cathode current. Cathode current is {plate current + grid current(s)}. The grid currents are around 5 mA each tube for 6L6s , so the plate current will be about 5 mA lower than the cathode current. That is about 29 mA plate current for each tube, although they may be out of balance somewhat.

The test points, and nearly all bias probes measure cathode current, NOT plate current. The plate current and plate voltage are what is important, as far as bias is concerned. At 408 plate volts, the recommended plate current would be about 29.2 mA each tube for 6L6s (my Groove tubes at 29 mA, at 440 plate volts, just a little hot). Two tubes, 58 mA total plate current, add grid currents, 5 mA each tube = 68 mA. We already know that the mV reading at the test point can be directly read as mA. 68 mV at test point = 29 mA plate current on each tube.

Of course there is always error/tolerances so these reading can vary a little and still be good. As bluesky636 pointed out, the test point reading can be different than a bias probe, due to tighter tolerance on the bias probe. You can change the 5% resistor to a 1% for more accuracy, but usually +/- 10 % is fine. :)

My HRDlx came with red label, and I think that the BDlx comes with blue label. Just check/set the bias if you put in new tubes. I actually prefer Groove Tubes.

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Posted: Wed Sep 22, 2010 3:52 pm
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Tissan wrote:
I agree, it 's also my calculation ! (I'm sure you made the measurement after temperature stabilzation). Rougly 10% of error seems acceptable for a biasing of a tube at 50% of max power that could partially explain that some sound hot and some sound cold. I've also seen differents GT origins (the brand is still on the glass ! Sovtek, JJ ...).
By the way Sovtek is only a brand and made by Reflector compagny in Saratov.


I let the amp cook for about an hour before the first measurement and about 30 minutes between each adjustment! :lol:

My blue label "6L6-R" GTs say "5881WXT Sovtek Made In Russia 07 11" on the side opposite the GT paper label.

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Posted: Wed Sep 22, 2010 4:21 pm
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May be you know Sovtek is a USA company located in NY (New Sensor), usually using Reflector plant in russia and also other plants. Reflector produces also EH ! New sensor owned Svetlana"S" (do confuse with Svetlana SED "C" logo), tung-sol and Mullard.

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Last edited by Tissan on Wed Sep 22, 2010 4:38 pm, edited 1 time in total.

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Posted: Wed Sep 22, 2010 4:23 pm
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bluesky636 wrote:
My blue label "6L6-R" GTs say "5881WXT Sovtek Made In Russia 07 11" on the side opposite the GT paper label.


The 5881 WXT Sovteks seem to be the ones that primarily come with the amps. The GT6L6-R are the Sovteks, and the GT6L6 S are the JJs. :idea:

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Posted: Wed Sep 22, 2010 4:38 pm
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shimmilou wrote:
bluesky636 wrote:
My blue label "6L6-R" GTs say "5881WXT Sovtek Made In Russia 07 11" on the side opposite the GT paper label.


The 5881 WXT Sovteks seem to be the ones that primarily come with the amps. The GT6L6-R are the Sovteks, and the GT6L6 S are the JJs. :idea:


Obviously! :lol:

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Posted: Thu Sep 23, 2010 4:06 pm
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sorry to highjack the thread....bluesky did you ever get to try the compressor withthe bdri?


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Posted: Thu Sep 23, 2010 5:07 pm
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blackstrat71 wrote:
sorry to highjack the thread....bluesky did you ever get to try the compressor withthe bdri?


Yes. Boss CS-3. Did the Monte Allums Ultra Plus Mod to it. I use it in front of the preamp before my BD-2. Works and sounds great.

Now back to our normally scheduled program. :D

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