VHT deliverance D120

  • Thread starter Thread starter Michiel Kemper
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Michiel Kemper

Michiel Kemper

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Hi,

I got a 2004-2007 VHT deliverance D120 and want to bias a new quad of KT88’s.
I do see something about power and percentages on the pcb but was wondering what you prefer to bias your vht deliverance d120 to? How much mA per KT88?
 
Thanks but I don’t seem to be able to register as I don’t receive a confirmation email 😞
 
Michiel Kemper said:
Yeah but I’m not sure how to calculate it and get to the proposed mA per KT88
Click to expand...
Take it to a tech before you electrocute yourself. You don't have to calculate anything, just know how to use a multimeter. If you don't have that skill yet it's best not to be poking around in a tube amp.
 
Kelly said:
Take it to a tech before you electrocute yourself. You don't have to calculate anything, just know how to use a multimeter. If you don't have that skill yet it's best not to be poking around in a tube amp.
Click to expand...
I have biased multiple 6l6 and el34 amps to spec and installed my own bias pots.
Most of the information can be found online or received from the amp builder or manual.
It is set at 54 mA and I saw in above mentioned thread that is what I should aim for.
 
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I tried to link the post but it only showed one entry instead of the link to the thread. That’s also from the same time period as yours.
 
take a pic of the info on the PCB ....... and post it ....

do you know what your plate voltage is ??
 
The D60/120s I've had, I biased the 88s/6550s to 50-60 ma...whichever number sounds best..If I remember right the info on the PCB is similar. Those transformers are designed for those tubes..vs a vintage Marshall that comes with 6550s, there I would bias the 6550s as a 34 in the 30-40ma range since those transformers are designed for EL34s.
Just to be safe.
 
Racerxrated said:
The D60/120s I've had, I biased the 88s/6550s to 50-60 ma...whichever number sounds best..If I remember right the info on the PCB is similar. Those transformers are designed for those tubes..vs a vintage Marshall that comes with 6550s, there I would bias the 6550s as a 34 in the 30-40ma range since those transformers are designed for EL34s.
Just to be safe.
Click to expand...


If your biasing KT88 tubes in the D 120 and your plate voltage is 500 VDC ,
( let's just say , )
what ma would you dial in for
a 60% idle condition ? What maximum watts plate dissipation is used in your formula ?
 
I think you've already answered my question in your last post but I'll back math it later .
 
griff10672 said:
take a pic of the info on the PCB ....... and post it ....

do you know what your plate voltage is ??
Click to expand...

I didn't click on any links in this thread but this is what I came to say. You need your plate voltage first as that can vary. @Michiel Kemper if you've biased amps before as you said then grab your plate voltage and then back into your cathode milliAmp target either by % or by ear. Ear is better honestly, but don't play the amp with a probe attached (assuming your are using a probe), your volume should actually be on zero.

I wrote up a tutorial for EL34 based amps but the math works the same. Just replace the EL34 25w with whatever tubes you are using.



MilliVolts is a constant that we captured earlier. (475 was my plate voltage)
Cathode bias is a variable that we will be adjusting.
Plate dissipation % we decide on up front but only as a guide. (60%)
Tube wattage is a constant. EL34s are 25 watts each. (25w)

If you take your tube watts and divide it by your plate voltage you will get your cathode reading in milliAmps. You then take this number and multiply it by your desired plate dissipation %. This will give you your cathode bias 'ball park' starting point. We will adjust the variable resistor up or down from this number but more importantly - we will adjust it to the best tone.

Here is the formula with my readings using EL34 tubes:

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25 watts per EL34 tube / 475 plate voltage = .052 amps
so 52 mA x .60 plate dissipation = .031 or 31 mA

bias amp to 31 mA to start
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So, as you can see - I want to shoot somewhere in the 30 - 34 mA range.


(I made a few adjustments to call out EL34). Honestly not sure what yours are but easy to find out.)
 
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