Crate BV120H bias?

[warlok]

Hi. I've looked around this site many times and got useful info as you guys really know your stuff. This is my first post as I can't find anything on the net about biasing my Crate BV120H. It's a 2003 model with the original GT tubes (4-6l6, 4-12ax7) and I'm planning to get a high gain JJ full retube set from eurotubes. I've been inside the amp, seen the bias pot, but don't know where to hook up leads, voltage, anything else I need to know.... This will be my first time biasing but I have seen videos of biasing on other amps and have an idea of what it's for, etc. But I'm hoping someone can give me actual instructions on the procedure. A video would be great, albeit unlikely, but any help will be much appreciated.
Thanks

[Enzo]

All amps are biased the same. You note the plate voltage and calculate from the tube specs how much current you need to flow for the dissipation you want. The rule of thumb many go by is setting the idle dissipation at about 70% of the tubes rated power.

For example 400v and 20ma (.020 amp) makes 8 watts.

The tubes will affect the B+ voltage, so when you adjust the bias, recheck the B+ voltage - they interact.

That is the first part, deciding your goal.

Then you have to be able to read the tube current while you adjust. MAny guys use a "bias probe" or similar. You pull a power tube, stick the adaptor in the socket, then reinstall the tube in the adaptor. You read current on the meter.

There is also the "shunt method" which requires you to take current readings right off the very high voltage plate leads. I don;t recommend that for the novice. These voltages can KILL YOU.

And then ther is monitoring current through the cathode. Close enough to plate current for us. In many amps a 1 ohm resistor is between cathodes and ground for that purpose. Some guys install those.

You have cathode fuses. You can remove one of those fuses, adn connect a DC ammeter in its place, and read current directly.

[skot10]

biasing a crate bv120h

Its true that the ideas given are good but i just biased my bv120 the easy way. Get a clip-on ammeter that measures ac current and measure the amps draw through power cord set to .8 amps and your done. Simple and it works everytime if you have the ac current draw spec on our bv120 it should be 0.8 amps ac.
Good luck!

[Gtr_tech]

That seems like a rather course adjustment. I don't trust it. I read plate current and plate voltage simultaneously (via adaptor socket) and calculate static wattage that way. Heaters can draw different currents and throw the whole thing off when monitoring I via the AC line.

[Jazz P Bass]

That .8 amp designation is right off of the schematic.
It's not that critical folks.

[Amp Kat]

Never really thought about doing it that way but seems simple as dirt and close enough for rock and roll.

[Jazz P Bass]

I have a Kill-A-Watt hooked up on my test bench.
I would not leave home without it

[skot10]

bias the crate bv120h

Actually, it works great! I had a tube blow due to improper ohms setting on head. I had to buy a matched duo gt6l6-b with same hardness. To broke to by new quad at time. When I put these tubes in I could tell right away it wasnt right. I called loudtech even though I have the schematic, and the guy named Scott gave me the ammeter through ac cord instruction. I waited about 10min for amp to warm up, no signal, standby on and followed his instructions. It worked perfect my amp is actually better sounding then before which leads me to believe the biad was off when I got it. As for the crate haters! I have had VHT, Bogner, marshall, ampeg and others but when I sold my Ampeg v-4 I tried all these amps again and was shocked on how well my bv.120h sounds. Forget the fact it cost me $300 for the crate as opposed to the thousands Ive paid for the many others Ive had over the years.

[rolue]

Actually, it works great! I had a tube blow due to improper ohms setting on head. I had to buy a matched duo gt6l6-b with same hardness. To broke to by new quad at time. When I put these tubes in I could tell right away it wasnt right. I called loudtech even though I have the schematic, and the guy named Scott gave me the ammeter through ac cord instruction. I waited about 10min for amp to warm up, no signal, standby on and followed his instructions. It worked perfect my amp is actually better sounding then before which leads me to believe the biad was off when I got it. As for the crate haters! I have had VHT, Bogner, marshall, ampeg and others but when I sold my Ampeg v-4 I tried all these amps again and was shocked on how well my bv.120h sounds. Forget the fact it cost me $300 for the crate as opposed to the thousands Ive paid for the many others Ive had over the years.

Tubes won't blow due to mis matched ohms

[skot10]

Never really thought about doing it that way but seems simple as dirt and close enough for rock and roll.

Late update! After further inspection I noticed that the biasing schematics actually say .8a@85watts then it says 1.3a@120watts which is what these amps are supposed to be. Running them at .8 wont damage the amp, it will just run the tubes way cooler. they will last longer but wont sound as good or loud. I have since replaced All my power tubes and rebiased at 1.3amps from the wall and have played a bunch of shows and lots of hours of practice and alls great.

p.s. one thing I noticed was that on my crappy ammeter, I could move it around and get dramatically different readings, between .1a and .9a difference. I bought a new ammeter, a nice fluke and all was well. I noticed that the high reading on my crappy ammeter was really really close to the final reading on my Fluke.

[skot10]

That .8 amp designation is right off of the schematic.
It's not that critical folks.

Late update! After further inspection I noticed that the biasing schematics actually say .8a@85watts then it says 1.3a@120watts which is what these amps are supposed to be. Running them at .8 wont damage the amp, it will just run the tubes way cooler. they will last longer but wont sound as good or loud. I have since replaced All my power tubes and rebiased at 1.3amps from the wall and have played a bunch of shows and lots of hours of practice and alls great.

p.s. one thing I noticed was that on my crappy ammeter, I could move it around and get dramatically different readings, between .1a and .9a difference. I bought a new ammeter, a nice fluke and all was well. I noticed that the high reading on my crappy ammeter was really really close to the final reading on my Fluke.

[skot10]

Theres a few schematics for this amp, the full schematic set is like 7 pages. do you have this complete schematic? I have them on my phone which broke and need them to help me with a tone shaping mod I did. I Bought it from triodeamplification and whille I like some of the differences, a few I dont and I need the schematics to see which ones I want to change back based on their part in the tone circut.
Thanks

[g1]

Crate Bluevoodoo 120W Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

[skot10]

g-one,
I actually have that schematic, I meant to say that I needed a parts list which I found.
Thanks for trying to help.

[skot10]

I know this is old but I wanted to say that when my amp was played for 4 hours with the ohms set to 16 but the cab was 4 and it DID blow one of the power tubes. It actually got so hot that the glue holding the glass to the plastic pin base actually boiled. Once I replaced the tubes, I bought a matched set from gt with the same hardness,6, and the problem is gone. It may not be common but to say that tubes WONT blow due to mismatched ohms is incorrect. not starting trouble, just sayin