Biasing a Blackstar HT Venue amp

[ecc83]

Did somebody try to use 6l6? G1 voltage can be -50. It's more than enough, but does transformer endure "torture"?

Are you asking ProgM if the output transformer will be ok with 6L6's? I have no reason to suppose otherwise.

Additional: The 6L6 has only 1/2 the gm of a '34 which means it will need much more drive for the same power output. This is almost certain to change the driver stage characteristics but again no harm that I can see.

Dave.

[ProgM]

I mean the power transformer, as the current increases from 100 mA (EL34) to 170 mA (6L6).

[ecc83]

I mean the power transformer, as the current increases from 100 mA (EL34) to 170 mA (6L6).

Why bias the L's so hot? Is this some edict from the "Amp Gurus in the Sky"?

Short answer is I don't know! The traff will probably stand it for a very long time but that is a considerable over rating (about 80W Pa from~ 50W) . It will also I think compromise the maximum power output of the amplifier.

Dave.

[ProgM]

4xEL34 have bias 100 mA. Thanks for your answer, Dave.

[ecc83]

4xEL34 have bias 100 mA. Thanks for your answer, Dave.

1) Yes I know.

2) Why 170mA?

Dave.

[ProgM]

1) Yes I know.

2) Why 170mA?

Dave.

Oh, sorry, I thought you mean EL34. I use this link:
http://www.ax84.com/contrib/biascalc.php and choose 6L6GC. But realy 6L6 current is less than El34. But heater current of EL34 is 1.5 A and of 6L6 is 0.6 A.
Still I arrive at a conclusion I have too little knowledge that carry out such experiment.
Once more thanks.

[ecc83]

Oh, sorry, I thought you mean EL34. I use this link:
http://www.ax84.com/contrib/biascalc.php and choose 6L6GC. But realy 6L6 current is less than El34. But heater current of EL34 is 1.5 A and of 6L6 is 0.6 A.
Still I arrive at a conclusion I have too little knowledge that carry out such experiment.
Once more thanks.

-The heater current of the 6l6 is in fact 0.9A.
I don't agree with that table of bias points but if the only way a set of 6l6's can be made to sound good in an HT-100 is to bias them that hot I do not advise their use!

Dave.

[JCA2550]

Anyone know where I can readily get hold of the little white 2 prong connector I would like to rebias my HT-60? I've just fitted a matched pair of Tung-Sol EL34bs and want to get it into the sweet spot.

[ecc83]

Anyone know where I can readily get hold of the little white 2 prong connector I would like to rebias my HT-60? I've just fitted a matched pair of Tung-Sol EL34bs and want to get it into the sweet spot.

You can't actually "get hold of" the connector, you have to find a gash plug, butcher it and make up the test lead.

But there really is no point unless you are servicing the amps! Just croc' onto R207 (1R 1W) or D27 and set for 50mV. I strongly advise you not to bias hotter than that.

And don't forget to set the balance control for minimum hum.

Whilst you are in there, TAKING THE GREATEST CARE! Check the the grid lead to the op valves is secure both ends and a couple of cable ties are a good idea here.

Dave.

[JCA2550]

Cheers Dave!