what not to do when biasing ?

[docben]

Hello,

I've never changed tubes and bias by myself but I'd like to give it a try.
There are a lot of posts and some vids about how to adjust bias but …. …I haven't found "tube changing and biasing for the dummies".

I'd like to know where the danger lay (those deadly volts) and how to avoid it.
What should I be careful of ?

Thanks for your advices.

Ben

 

[webrthomson]

What Diezel amp are you talking about biasing? I do my Herbert and it's a walk in the park, even thought I don't have the external bias points.

Also there are guides on the Diezel site in the UK for some of the amps, if you email James there he can normally help (sales@diezel.co.uk).

Let us know what amp you're working on we can chip in some more help

 

[docben]

Thanks for your answer

My Herbert has external bias point so it should't be a problem. But I'd like to check bias on my Hagen and the new VH4 when I get it.

Last year, Herbert has been seen by a tech for tubes change and he'd told me that the bias was wrong and that could happen when amps are moved or with time passing. It has never been checked since I got it new in 2007.

To make it easy, I think to use TAD Bias Master and an insulated screwdriver…and only one hand handling the screwdriver (the other hand in the pocket).

There are tutos on the net and I will compile them but I'd like to know what are common errors that I should avoid, what parts of the amp are dangerous to touch.

I should only touch the bias plot but where lay the deadly volts ? Everywhere in the amp ? Only in transformator ?


Best Regards

 

[webrthomson]

My understanding is that it is mainly the capacitors that can be the issue in terms of remaining charge - to drain then you need to turn the amp off with out switching it to standby, this should do the job (PS - if anyone has better way please chime in!).

In terms of what you do then it varies by amp; the VH4 guide is here:

http://www.diezel.co.uk/VH4 Biasing.pdf

And the Hagen I *think* is like biasing the Herbert and there are some instructions here:

http://www.diezel.co.uk/Einstein & Herbert Biasing.pdf

It's worth noting that these instructions are not up to date for the latest Herbert's and that may be the case for the Hagen's too. However my Herbert (which is pretty new) has pretty clear instructions on the PCB (I think from memory near the trim pots for the bias).

Happy to be corrected on any of this - I've not owned a VH4 since 2008 and, although I want a Hagen, I've never owned one of those either

In terms of the bias wandering as you touched on this can happen over time, movement of the amp etc. so it's always a good idea to bias your amps once or twice a year. Also, I've noticed with the Herbert that I need to go back and check it a week or two after setting the bias as it can wander a little immediately after being set - hope some of this helps and let us know how you get on!

 

[docben]

thanks a lot

 

[webrthomson]

No problem - BTW if you are planning on biasing the amps internally you will need to get a digital multimeter. The TAD Bias Master, I believe attaches to the valve sockets, and I don't think this will work doing the bias the internal way

Again, not 100% on this as I don't use one!

 

[Black Sabbath]

. . . to drain then you need to turn the amp off with out switching it to standby, this should do the job (PS - if anyone has better way please chime in!).

Simple: gather your favorite rubber gloves, plastic screw driver & tennis shoes and your golden.

Always shoot hot as in the late Robert Palmer.

 

[Bayside]

OK for Dummies . . . research your amp. . watch Eurotube YouTube. . . follow their instruction. there are dangers inside a tube amp, but it's like a fan belt on a car engine, don't touch it. What not to touch ? Anything, except that little tiny, slotted, adjustment screw that adjust the bias
resistor. Where to set the bias, see above video, research your amp, ask tube sales person about typical spec's for the tubes, your buying from them as well as the biasing socket adapter to read mA values. Hope this helps.

 

[adr1anos]

Also when working/measuring on a live amp, always keep your left hand in your pocket, a surefire method to keeping it away from danger. An electrocution through the left hand tends to go through the heart, with obvious dire results. Always use your right hand for measurements, while wearing an clean, dry rubber glove or equivalent.

 

[andiggity]

Dont cut the blue wire.

 

[RJF]

Herbert with external points is so easy it's not even funny. There is even directions on the amp.

1. LEAVE the amp IN the chassis.

2. grab multi meter and short small flat head screw driver.

3. Set your multimeter to the highest mA setting (around 200mA)

4. Pull old tubes and install new ones.

5. Make sure master volume is on 0

6. Flip on the power switch, wait 30 seconds, then flip stand by.

7. Pull out the fuse for 1&6. The blue light should come on

8. Put your COM or black prob in the black socket, put the red probe in the first red socket. The blue light should go off, and you should get a bias reading. Put your screw driver into the bias adjustment whole for 1&6 and turn it until you feel your screwdriver fall into the notch, then turn to adjust bias. You want 60-70mA.

9. Put the fuse back in, then pull the fuse for 2&5, and repeat the process as the directions say on the amp with all three pairs of tubes.

10. DO IT ALL AGAIN, the bias on 1&6 and 2&5 will drastically change as you go through this procedure since adjusting one pair of tubes effects the other two pairs. Think of it as trying to tune a floyd rose equipped guitar after installing new strings. Once you get it adjusted the 2nd time to the proper bias, you should be good to go.