Biasing a Blackstar Soloist 60

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DrGit
Posts: 12
Joined: Wed Oct 15, 2014 7:02 pm

Mon Oct 20, 2014 7:41 pm

Ok, so i bought a set of tubes and figure i give this a go. I have my amp powered up for 20 minutes now, so its at operating temperature. I was told to put the red lead on TP7 and the black lead on TP1, so i figured i'd see what Blackstar had the bias set at. Only thing is my multimeter isn't giving me a reading. Do i have it on the wrong MM Setting, i have it set to mV and had it on the 200 setting. I touched the tp7 and tp1 silver microscopic looking solder marks. Here's my view but way blown up
Image

DrGit
Posts: 12
Joined: Wed Oct 15, 2014 7:02 pm

Mon Oct 20, 2014 9:31 pm

OK, the dummy i am, i had it on standby. When i turned it on and left it on for 40 minutes, i get a reading of 26.4 mV....is it really possible that they run it that cold, or what...I thought this reading was supposed to be for both tubes...26.4 sounds like 1 tube....it says right near the test points it should read 50....so, i'm going to let it cool down, and install the Mullard's. I'm probably going to set it at like 30-40

DrGit
Posts: 12
Joined: Wed Oct 15, 2014 7:02 pm

Mon Oct 20, 2014 9:42 pm

ok, testing the old tubes, i'm getting a reading of 26.4 mV ....Blackstar can't be running this cold, can they...its supposed to read 50....says it right on the board, check out the prior pic i uploaded

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thephantum
Posts: 1160
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Location: Virginia, United States

Mon Oct 20, 2014 11:14 pm

Without knowing the plate voltage, it's hard to call...it does sound like it's biased very cold. The odd thing is that it clearly says 50mV between those test points on your amp...but you are right...26.4mV sounds like an individual tube measurement.

The only way to really know is going to be to put bias probes in and take actual readings from the tubes......or a install 1ohm/1w resistors between the cathode and ground on each tube, then take measurements from there.

3827715
Posts: 2
Joined: Tue Oct 21, 2014 10:07 pm

Tue Oct 21, 2014 10:16 pm

Hi, just to help here, you should measure 50mv at the test point, firstly, make sure you have a speaker load connected and a jack in the guitar input, there is a protection system that protects the output valves if either is removed while the amp is on,
turn the bias pot until you read 50 mv, if for any reason you cant read 50 then its possible you either have a valve that's not conducting or a poor connection on the valve base where the valve plugs in, if still no joy then its a good idea to contact your local amp tec or contact Blackstar's service department for help,

hope this helps you a little :)

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thephantum
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Location: Virginia, United States

Tue Oct 21, 2014 11:47 pm

That's a good point....was there a load (speaker) connected when you checked it? If not, that would explain the low reading....

DrGit
Posts: 12
Joined: Wed Oct 15, 2014 7:02 pm

Wed Oct 29, 2014 1:42 am

yes, a speaker load is essential unless you want transformer damage, and was connected at the time of reading....The amp def sounds much better with the new tubes (though it should even if the bias is wrong- the old tubes were 3 years old)

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thephantum
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Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Wed Oct 29, 2014 2:15 pm

Just curious: Did you set the new bottles at 30-40 or did you dial them up to 50?

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