first post-biasing

[dearlpitts]

hi i/m david from central ca-joined today and first post is about biasing-i/ve never had a amp thats had a fixed bias-so whats simpleist and easyest way to bias a crate v50 1x12 with 2 6l6s,-just got one-herd lots of bad things about it as far as breaking down go-so i/d like to get some good tubes in it to start,great sounding amp,did wonderfull today at first band practice, so any advice would be great and thanx in advance.

[R45VT]

Welcome to the forum.

[Steve Conner]

Well, maybe you don't have to worry about that until it actually breaks down! The tubes in it might have plenty of life left, so if they sound good, why retire them prematurely?

According to this old thread http://music-electronics-forum.com/t14742/ there's a pot inside the thing for adjusting the bias. But I can't find any indication of how you might measure the bias current to make sure it's right. All in all, probably not a job to attempt unless you have some electronics experience.

If you're swapping in the same tube type, there is a reasonable chance that it might just work with no adjustment of the bias. But if the new tubes get a lot hotter than the old ones did, it'll need adjusting.

[pdf64]

Page 3 of that pre-amp schematic http://www.blueguitar.org/new/schem/.../crate_v50.pdf shows R80 and R81 as being 10 ohms; it's likely that those are cathode resistors for the 2 x EL34 power tubes.
If so, the amp could be considered to be suitably biased when the voltage across each was about 400mV (350 - 420mV), adjustment made by CW9. The lower the voltage, the cooler/more long lasting the tubes, and stress on the amp. There may be suitable test points which are externally accessible, that enable the voltage to be safely measured?
Pete.

[dearlpitts]

thanx-it has 6l6s

[Jazz P Bass]

If the amplifier works and you are happy with the tone, why, oh, why would you want to mess with it?
Let It Be.

[dearlpitts]

well mainly because i heard there where 2-3 problems with this amp1-switching system2-cheap tubes-3poor speakers,and one item i read stated that that cheap tubes blowing also provoked the switching system to blow which rendered the amp unfixable-though am on board with if it aint broke leave alone notion,but i will be giging alot with this amp and know i will at least need to change power tubes out once a year.so knowing how and what the cheapest and simplest way to bias would be nice .

[big_teee]

well mainly because i heard there where 2-3 problems with this amp1-switching system2-cheap tubes-3poor speakers,and one item i read stated that that cheap tubes blowing also provoked the switching system to blow which rendered the amp unfixable-though am on board with if it aint broke leave alone notion,but i will be giging alot with this amp and know i will at least need to change power tubes out once a year.so knowing how and what the cheapest and simplest way to bias would be nice .

Here's a pretty extensive Schematic Library Listing for the V50.
Index of ./crate/V50-112/
Here's the Power section.
CrateV50-0024347_revA00-SCH (OUTPUT).pdf
Good Luck,
Terry

[g1]

pdf64 gave the cheapest and simplest way earlier in this thread. All you need is a voltmeter. The only simpler way is to take it to a tech, but that is not the cheapest. You are concerned about reliability of the amp, but in another thread you asked about power chord biasing. That is a recipe for disaster.
Make sure you read up on safety when working with tube amps before you open the amp.

[big_teee]

pdf64 gave the cheapest and simplest way earlier in this thread. All you need is a voltmeter. The only simpler way is to take it to a tech, but that is not the cheapest. You are concerned about reliability of the amp, but in another thread you asked about power chord biasing. That is a recipe for disaster.
Make sure you read up on safety when working with tube amps before you open the amp.

Yes that is the normal way on most amps, this has 10 Ohm resistors instead 1 Ohms.
T

[dearlpitts]

well thats why i asked and i read in that thread that someone was stating it was easy -anyways how this ? what do u guys think the going price i s to have a shop just bias it for me?think since i/ve totaly come to the fact that all i/m going to use from now on are tube amps i should learn how to bias myself-also i always here that one should bring a spare pair of tubes to a gig in case one blows and i need to replace-can those be pre biased?or is it safe to finish the gig without biasing? how safe is to just not bias? i/m a guitar player not a electrician thoo i am a rv tech and do do some electronics.

[pdf64]

Re spare tubes / biasing, see posts #9 & #10 in http://music-electronics-forum.com/t28019/
Re 6L6GC vs EL34, the 6L6GC can take a little higher dissipation, so a suitable test point voltage (across 10 ohm cathode resistor) might be in the range 400-500mV.
From the schematic in post #8, CW9 is the bias adjust control; probably a trimmer on the PCB.
Note that the VB+ is 'only' 420V with a 5k5 OT primary, so the output tubes are under less stress than Twin Reverbs or Super Reverbs etc that run at >450V at 4k; so if the bias is adjusted to keep the static dissipation reasonable, the tubes have a fair chance of having a good service life.
Pete.

[dearlpitts]

so any idea what i should expect to pay a tech to do it?

[big_teee]

so any idea what i should expect to pay a tech to do it?

It will depend on his shop hourly rate, and how long it takes to bias.
Are you replacing tubes or just getting it biased?
Ask up front what the fee will be.
I have an adjustment knob, and test points, on the back of my amp.
I can re-bias the amp in a minute or so.
If the amp requires some disassembly, then it will cost more.
Good Luck,
B_T