It is currently Tue Mar 17, 2020 4:48 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 6 posts ] 
Author Message
Post subject: whats your fav bias setting on a blues deluxe
Posted: Mon Dec 06, 2010 4:59 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sun Dec 05, 2010 12:38 am
Posts: 392
im running gt tubes and have my bias at about 66mv... gives me a nice smoothe tone which is what i like as i play a lot of blues...


Top
Profile
Fender Play Winter Sale 2020
Post subject:
Posted: Mon Dec 06, 2010 5:54 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sat May 08, 2010 4:31 am
Posts: 411
Location: France
The bias can be choosen between cold to warm, too cold will create discontinuity in push-pull 0 crossing and bad sound, too hot will shorten the valve lifetime. It is the idle current from kathode to plate, and other current can be considered to refine power calculation.
For BDRI, a current kathode * plate voltage will give a 1st order estimation, on the drawing 60mV on 1 ohm relates to 60mA, based on hypothesis of perfect valve idle current matching, 30mA by cathode. Measuring rougly 400V on the plate it gives rougly 12W for a 30W max. lower than 50% power, it is considered cold but not bad. On the opposite side, 60% max power is not bad for life time, the you can choose bias beween those values according to the sound you like; This is just an example, you can measure plate voltage and bias current on your own amp, but take care of high voltage that can be fatal.
There are lot of calculation freeware on the web that you can use.
8)

http://www.youtube.com/watch?v=19IUadZJ ... playnext=1

_________________
Tissan '52 Tele RI & Washburn Hawk 1980, Epiphone Casino MIK, Blues Deluxe RI & VOX ...


Top
Profile
Post subject:
Posted: Mon Dec 06, 2010 6:02 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sun Dec 05, 2010 12:38 am
Posts: 392
ya i know the dangers of high voltage... i want to get best sound for the longest life of the tubes so i dont want to run them too hot im happy with my current setting... i read somewhere that a standard setting is 68mv... or 34 per tube...


Top
Profile
Post subject:
Posted: Mon Dec 06, 2010 6:05 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sun Dec 05, 2010 12:38 am
Posts: 392
ill do some accurate measurements when im feeling brave, but for now im going on the way it sounds... thanks for the info


Top
Profile
Post subject:
Posted: Mon Dec 06, 2010 1:23 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sat May 08, 2010 4:31 am
Posts: 411
Location: France
68mA is 8)

_________________
Tissan '52 Tele RI & Washburn Hawk 1980, Epiphone Casino MIK, Blues Deluxe RI & VOX ...


Top
Profile
Post subject:
Posted: Tue Dec 07, 2010 10:49 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
I agree with Tissan, you want at least just over 50% idle on the output tubes, so that the zero crossing point of the two tubes overlap, preventing harsh sound. I have my HRDlx (very similar to BDRI) set at around 70 mV at the test point, which is about 30 mA Plate current each tube. My Plate voltage is about 440 volts, so I have my tubes running at just over 13 watts idle. My tubes are the 5881s 25 watt, so mine is a little over 50% idle wattage.

Pay careful attention to your tubes rated wattage of Plate dissipation, a 30 watt tube will need a higher bias setting than the stock 25 watt tubes will. And keep in mind that the test point reading is Cathode current, which will typically be about 10 mA higher that the plate current for both tubes (5 mA each tube). So a 68 mV reading at the test point, will be 68 mA both tubes, 34 mA one tube, subtract 5 mA for grid currents, leaves 29 mA Plate current. At 400 Plate volts that is just under 50% of the 5881s rated wattage (not sure what your actual Plate volts are). :idea:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: