Anyone ever bias at VHT 2-90-2

  • Thread starter Thread starter yngzaklynch
  • Start date Start date
i havent messed with one personally. im not sure if it has the 1 watt 1 ohm resistor trick in them or if you have to do it by the pinouts of the power tubes.
 
Thanks for posting this Jim.

I am a little confused. I have a bias tester that plugs into one of the tube sockets. Do I leave the other tube in the socket as well (in that channel of course)? What measurement would I use if both tubes in the channel are running? I know how to adjust the little bias knob I'm just confused what the proper setting should be.

I'm running 6550's.
 
tcrash":y52mib3t said:
http://www.webervst.com/tubes1/calcbias.htm
This should give you all the numbers you need.
Yes, you do leave the other tube in the amp as your biasing it.
Click to expand...

Add to this: but you do take measurement of both tubes to be able to determine a happy medium between the two

Maybe it even turns out it's best to mix and match all four

Giga.
 
Where are the bias test points on the circuit board? Where is the bias pot? Anyone know?
 
Why don't you guys just call VHT and ask for biasing instructions? They've always been cool and helpful when I've called them - I'm sure they'd be happy to help... Just a thought...

Steve
 
sah5150":1vzis5fs said:
Why don't you guys just call VHT and ask for biasing instructions? They've always been cool and helpful when I've called them - I'm sure they'd be happy to help... Just a thought...

Steve
Click to expand...


You mean Fryette... :lol: :LOL: :lol: :LOL:
 
Not sure of your experience level so no intention to teach you to such eggs.
There is a sep bias adjust pot for each channel.
Use the nos. from the link and decide how hot or cold you prefer the tubes to run and bias to the chosen mVA. You must have tubes in all sockets when out of standby.
There are not bias probe points on the amp, so you'll need a bias tool.
I made one up, which takes a few materials, or you can buy one from Weber or others.
I would urge anyone with a little nonce to give your own amp biasing a go. It is quite simple (once you know how) and really satisfying. You'll be telling folk you service your own amps in no time LOL.
 
I checked it about 6 month ago.
I had to remove the fan to install the BIAS probes.

You can see the Bias pots in the red circles.
I set my BIAS on 30mA per tube. I talked to Steve at the Frankfurt fair,
in his oppinion to low, better would be 35mA.

But I sticked with 30mA, cause I wanted to be on the safe side.
 

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Worth considering buying/building a bias tool that sets the tube off at a 90deg angle to prevent the need for fan removal or other probs. Very few amps that will not be easier to bias with this 'bent' tool, ahem.
 
You do make a valid point, and anyone who can't be bothered with bias can just send a pair of the current tubes to a supplier who can rate them and send you equivalent matched sets. No bias needed. Watford Valves did this for me for a Boogie 2:90 as it doesn't have adjustable bias and I knew nothing about biasing at the time.

My 2-50-2 plate voltage is 505V, which, assuming the majority of EL34s are 25W, equates to optimum bias(70%) of 35mA. the Svetlanas that the amp ships with are 25W yet it comes set slightly hotter at 40mA.
Sorry, this stuff starts to look like gobbledigook pdq.
In short, for those tubes, biasing to 30 is cold, 35 bang on, and 40 hot.
You can use similar spread for the 6550s once you know their rating.
 
Major old bump on this one, anyone found an easier way to bias Fryette power amps without having to remove the fans?
 
saxxamafone said:
Major old bump on this one, anyone found an easier way to bias Fryette power amps without having to remove the fans?
Click to expand...
I used a Weber bias rite on mine before, it had L shaped adapters and I never removed the fan. I have a new 2/90 now and tubes haven’t needed changing, but I have a multimeter tube adapter from Eurotubes that has a short enough base that I should be able to fit in there.
 
My gigging rig for many years included a 2-50-2. To bias it I measured the resistance of the OT and then measured the voltage drop across it. IIRC it sounded best biased on the hot side and I used to run around 38mA.
 
saxxamafone said:
Major old bump on this one, anyone found an easier way to bias Fryette power amps without having to remove the fans?
Click to expand...
Yes you use a meter across the fuse holders in front. I would rather suggest you get in touch with Fryette, I thinik if they feel you know whats going on they will give you the instructions.
 
Thanks for the help guys - Yep I did contact Fryette too but they never got back to me.

cheers ?
 
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