Biasing Help...From The Ground Up

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
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iceman823
Posts: 2
Joined: Tue Feb 21, 2017 7:44 pm

Tue Feb 21, 2017 7:59 pm

Hello,

I've looked around a lot and while I've found some info regarding biasing the HT series amps, I'm hoping someone can help me understand a few things.

The amp in question is a HT Club 50 head.

1) Are these cathode biased, fixed non-adjustable bias or fixed adjustable biased?
2) If cathode, will any rating of EL34 work?
3) If biasing is needed, do I need anything other than a multimeter?
4) What are the recommended values for the bias?

Any and all help is greatly appreciated!

My only experience biasing is with a handwired Port City Pearl head and I had the designer walking me thru that via email. The Club 50 is bound to be a very different beast though. Just trying to get as much info as I can since I can't even find the right link to ask Blackstar about it. Detailed biasing info for these amps seem to be very limited.

Thanks!

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8len8
Posts: 61
Joined: Sun May 08, 2016 8:26 pm

Tue Feb 28, 2017 12:38 am

If you don't know how to bias an amp properly you can literally kill yourself. There are hundreds of volts in the chassis.

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thephantum
Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Tue Feb 28, 2017 6:43 pm

Voltage isn't the issue, it's the amperage. Sure, there's hundreds of volts in a guitar amp, but there's tens of thousands in a static electric shock. The difference is in the current levels. A static shock has high voltage, but very low current. Guitar amps have lower voltage, but the current levels can kill you.

To answer the specific questions:
  • 1) With the exception of the HT1, the Venue series are all Class AB amps in a pull pull configuration with fixed adjustable bias.
    2) You can use any pair of EL34's, 6CA7's or KT77's, but they must be manually biased.
    3) One multimeter will do the job, but it's much quicker to use at least two so you can take a measurement on both tubes simultaneously (makes setting balance much easier)
    4) There is no such thing as "recommended values" for bias. Anyone who tells you there is does not know what they are doing
.
Personally, I use bias probes and four meters so I can see plate voltage and bias current, at the same time, for a push pull pair. Makes dialing in an amp really quick and easy.

You also need to insert a 1w, 1 ohm resistor between the Cathode (pin 8) of each tube and ground to do the bias measurement. That's another reason I prefer probes since they do that for me and I don't have to modify the amp.

Read this post for more info.
http://www.blackstaramps.com/forum/view ... 093#p24420

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