Biasing a Blackstar HT Venue amp

[nocaster]

Following on from my Fender Blues Deluxe/Hot Rod thread here I thought I'd do a wee post on the HT Venue. Again.........

You can die when you play with valve amps. Even if they're switched off. If you aren't confident, stop reading. Don't come crying to me when you're dead.

I only have the HT100 so I can't comment on the other amps, but I believe it's the same across the board.

So, start by taking the screws of the back and bottom. Note that there's 6 on teh bottom unlike other amps that only have 4. Yet another example of Blackstars "belt and braces" approach.




Anyway, once you're done, lift out the chassis by reaching in and holding the 2 transformers on either side. Lay it down BUT DO NOT lean it on the valves. I prop it on a bench edge so the tubes are hanging free. Up to you how you do it - but watch the valves.

Then you need to ensure there's a resistive load on the amp. In other words, plug in your speaker cab.



The way Blackstar have designed the amp means that you have to have a cable plugged in to bias/operate the amp. I use a spare George L patch plug. Nice and neat and doesn't leave a cable on teh floor.



TBC

[nocaster]

So - after you've done that.....power up to stand by and let it sit for a minute.

Now, there's 2 ways to bias the HT and both measure mV between the smae 2 points. Basically you need to know the mV reading between R207 and D27....that then gives you your bias value.

To do this you can literally measure the mV with your multimeter between these components and tweak with the wee white pot labeled PR2. These points are :



And more specifically :



and.....




TBC

[nocaster]

Now, you could just do that and set your amp at 100mV.....then you're done. However, Blackstar have built a wee socket for measuring the biass. This is a LOT safer and a lot quicker. The socket is located on the PCB with the power valves.



And more specifically :



You need a wee plug to go on here. That looks like this :





TBC

[nocaster]

Now take the 2 signals from that wee socket and feed them into your multimeter as per above and bias to 100mV using PR2.



Lovely jubbley.

All done.

Power down and put the amp back together.

K

[jdbwales]

Hi Kev, thanks for this mate, most helpful - however, a few questions - what specifically is the plug you're putting onto the bias prongs and would two crocodile clips into a multimeter do the same thing? Also, is 100mv the optimum bias for these things, ie if I was to change the power tubes would a bias too 100mv sort it?
Cheers!

[longtallronnie]

Nice work Kev.

Now let's see you do one for an AC30!