Marshall Bluesbreaker Self-Biasing?

Simon · Post by **Simon** » Wed May 25, 2011 12:32 pm

The singer from our band is borrowing one of these. He needs to know whether he can just do a straight swap of the Valves or will he need to bias it too?

Wasn't sure whether this should go in the 'Marshall FAQ' thread but it probably has more chance of being seen here.

Cheers!

johnnyseven · Post by **johnnyseven** » Wed May 25, 2011 12:35 pm

I would suggest looking in the instruction booklet, look up the instructions online or contact Marshall directly just to be sure you're getting the right info.

Simon · Post by **Simon** » Wed May 25, 2011 12:38 pm

johnnyseven wrote:I would suggest looking in the instruction booklet, look up the instructions online or contact Marshall directly to be sure.

Hmmm... not sure how easy it'll be to track down the instruction booklet, think the amp is about 11 years old

I'll have a look on the Marshall site though.

Cheers!

Post by **Doog** » Wed May 25, 2011 1:06 pm

I don't think any Marshalls are self-biasing, to be honest.

Simon · Post by **Simon** » Wed May 25, 2011 1:23 pm

Doog wrote:I don't think any Marshalls are self-biasing, to be honest.

Nah, I've tried searching for details on them and had no joy. I don't really know how you determine whether an amp is self biasing or not. I'm thankful that my Rocker 30 is and don't have to mess on with it too much.

johnnyseven · Post by **johnnyseven** » Wed May 25, 2011 1:34 pm

What valves ar eyou looking to change? I was under the impression that pre-amp tubes don't need biasing anyway, only power amp tubes.

George · Post by **George** » Wed May 25, 2011 1:48 pm

Doesn't look self-biasing (I googled "Marshall Bluesbreaker internal bias pot"), but you can bias power tubes yourself very easily. I bought a kit from Torres Amps (only place in the UK that sells them as far as I know). You'll have to call them up though as it isn't listed.

Product Name: BCMA
Product ID: 0339
Amount(each): Â£17.05 GBP

I had to work out the plate voltage myself but for a Marshall you can probably just google it. Then all you have to do is use a calculator like this http://www.ax84.com/contrib/biascalc.php , get a multimeter and find that internal bias pot.

Simon · Post by **Simon** » Wed May 25, 2011 2:04 pm

johnnyseven wrote:What valves ar eyou looking to change? I was under the impression that pre-amp tubes don't need biasing anyway, only power amp tubes.

I think he was after swapping the whole lot. To be honest I think he'll just end up taking it in to get serviced. It hasn't had any maintenance/TLC in the whole time the other guy has had it!