Biasing with Jan Philips 6l6 WGB's

liftman

Just ordered a pair of Jan Philips 6l6 WGB's for a Bandmaster RI 57,  going to take it to a tech for biasing. There's a bit a conflicting opinion online whether you should bias the amp as with 6l6 GC 's or differently. Anyone have any experience with these ? Cheers.

RiftAmps

Why not just bias the valves to run efficiently in the amp and measure operating condition afterwards? Seems to me a better way rather than picking a number off the internet and going with that.

ICBM

RiftAmps said:

Why not just bias the valves to run efficiently in the amp and measure operating condition afterwards? Seems to me a better way rather than picking a number off the internet and going with that.

+1. Ideally you should bias using a scope to look for crossover distortion, not by dissipation.

But if you don't have access to one, the 6L6WGB is rated for a maximum plate dissipation of 26W, so you should bias no hotter than 18W, or 44mA if the HT voltage is the same as a vintage 5E7 (410V). ~45mA if measuring cathode current. But I wouldn't bias GCs any hotter than that anyway, since the bias point is determined by the circuit and not by the maximum rating of the valve if you use a higher-rated type than the circuit was designed for.

Make sure the amp is set for 240V first, if it has that option. All Fender amps sold in Europe are set to 230V and run slightly too hot in the UK.

bandmaster188

I’ve had a couple of sets of the 6l6wgb’s in my bandmaster reverb heads and never had any problems. Different circuit I know, but have them biased around 28-30ma.

ecc83

Whatever bias point you choose it will shift! New valves these days seem to have excess grid current (not burned in long enough) so you set bias and leave the amp for an hour (I used to run bassy programme through them at 1/2 power) when you come back it will have moved, usually down a bit but sometimes up. Then, bias current depends on the drive "history". Drive the tits off it for ten, especially if you go into clipping, and Ia will be higher and take a minute to fall.

Bottom line, ain't that critical.

Almost all B's amps were biased for 25mA and I never had a request to bias one hotter.

Dave.

jpfamps

ecc83 said:

Whatever bias point you choose it will shift! New valves these days seem to have excess grid current (not burned in long enough) so you set bias and leave the amp for an hour (I used to run bassy programme through them at 1/2 power) when you come back it will have moved, usually down a bit but sometimes up. Then, bias current depends on the drive "history". Drive the tits off it for ten, especially if you go into clipping, and Ia will be higher and take a minute to fall.

Bottom line, ain't that critical.

Almost all B's amps were biased for 25mA and I never had a request to bias one hotter.

Dave.

I suspect JAN Phillips 6L6's are not new production valves.............

DJH83004

I had one in for service a while ago and I'm sure the anode volts were closer to 450v, looking at my notes I biased a set of JJ 6L6GCs at about 38mA off the cathode. Forgot to add I did the 240v voltage swap as well, but it's a cut and sleeve job, as there are no spare terminals  unlike say a HRD.

ecc83

jpfamps said:

ecc83 said:

Whatever bias point you choose it will shift! New valves these days seem to have excess grid current (not burned in long enough) so you set bias and leave the amp for an hour (I used to run bassy programme through them at 1/2 power) when you come back it will have moved, usually down a bit but sometimes up. Then, bias current depends on the drive "history". Drive the tits off it for ten, especially if you go into clipping, and Ia will be higher and take a minute to fall.

Bottom line, ain't that critical.

Almost all B's amps were biased for 25mA and I never had a request to bias one hotter.

Dave.

I suspect JAN Phillips 6L6's are not new production valves.............

Bias point will still shift with programme drive history.

Dave.

liftman

Thanks everyone!