VH4 Tube Biasing

[acebick]

This is my first tube biasing in 30+ years of owning tube amps. I'm tired of waiting 3-6 weeks for a tech to get to my amp. I've been reading all day on this web site about Diezel biasing on the Einstein, Herbert and VH4. I'm convinced that this is simple. I've been reading on some other web sites about biasing tube amps in general which may be confusing me, but I just want to clarify.

Question 1: If I use the transformer method for measuring Ma for the VH4 using a DMM, then I don't need a Bias Probe? All I need is a DMM and my new power tubes?

Question 2: The official VH4 instructions on Diezel website don't mention removing the fuses if I'm using a DMM. If I use the DMM, should I remove all 4 fuses (one for each power tube) and keep the main fuse in (I would think so)?

My VH4 is a 2003, so it sounds like it won't have an external bias point. ALL of the other instructions seem pretty clear with number one being CAREFUL.

I would appreciate any further clarifications. Thanks

 

[duesentrieb]

You can find the DMM/Outputtransformer-Biasing method on the official website.

If you are not familiar handling more than 500 Volts:
Get a bias probe by http://www.tedweber.com !
I'll post instructions then.

In both cases: DMM/OT and BiasProbe: don't mess around with the fuses.

Olaf

 

[acebick]

ok. So I got the Ted Weber Bias Rite Tool. My understanding is that the tool will read the cathode current (which includes the screen current). So my bias reading should be 5-10% higher than the plate current recommendations. I'm installing SED EL34's in a VH4. So, if the plate current recommendations are 60-70mA for a pair of EL34s, then with the bias rite my range is 66-77mA per pair or a range of 33-38.5mA per tube. Is this correct?

Somewhere in this site I read that I shouldn't bias higher than 34mA per tube with the bias rite. Why? If that is about 65% of maximum dissipation?

 

[duesentrieb]

33-35mA per tube is perfect IMO.

Here's a chart for ya:

plate voltage is 480V

 

[Axegrinderturbo]

Hi,

I checked the bias on my VH4 a couple of days ago and it was 64-65ma so I haven't adjusted it as on the website it says 60-70ma is correct. When I checked the bias, all of the volume knobs were set at zero, is this right or should they be turned up???

Thanks!

 

[acebick]

Excellent. Thanks for the info. A picture is worth a thousand words!

 

[acebick]

Out of curiosity, I took bias readings on the existing 6L6s in my VH4 with the Bias Rite (tubes are a good year old but not with excessive playing time on them

23.0
22.1
22.3
21.7

Don't these measurements look awefully low?
And don't they seem to be too far apart to be considered a matched Quad?


Any feedback would be greatly appreciated.
I don't know if I'll ever go back to that tech again.

 

[duesentrieb]

Matching: within a range of 5 mA.

6L6 should be biased between the blue and red line - close to the blue line.

 

[duesentrieb]

Hi,

I checked the bias on my VH4 a couple of days ago and it was 64-65ma so I haven't adjusted it as on the website it says 60-70ma is correct. When I checked the bias, all of the volume knobs were set at zero, is this right or should they be turned up???

Thanks!

If you like the sound, keep it. If you want more overtones (tubes harder driven, faster tube wear) put them up a bit.
I take it that we are talking about (biasing - valuewise) pairs, right?

 

[Axegrinderturbo]

Yes, i've just checked the Diezel website as I followed their instructions and it says it is for 2 tubes

Does it make any difference where the volumes are set when checking the bias???

Thanks

 

[acebick]

I got the EL34s installed, burned the new tubes in for a few hours and then re-adjusted the bias. It was a piece of cake and my VH4 sounds great. Thanks for all the help.