6HF5 testing

[rsumperl]

Hello everyone,
Did some 6HF5 testing. Plate = 500v, G2 = 170v, G1 = -70v. P-P is 3.3KΩ.
So, initially had some problems getting Ib under control. I started with G2 at 215v and with -70v on G1, Ib for 2 tubes was at 160ma. So, with -70 on G1 and G2 at 170v, I get 42ma/tube.
As with previous testing, I am feeding the tubes with the driver from a Dynaco Mark III.
I have not been able to find any graphs for the tubes, If someone can point me in the right direction, that would be great.
Anyway, not a bad tube. I can't give any numbers as to max power or distortion, but they sound fairly decent.

Ray

[smoking-amp]

The 6HF5 appears to be the same tube as the 6JS6/A/B but with slightly different pinout.

I only see the 6JS6C datasheet with curves, presumably very similar.

http://scottbecker.net/tube/sheets/123/6/6JS6C.pdf

[davorin]

Halo, Ray!
I have complete curves for 6HF5 tube, but file (PDF) is ~5MB, so plese send me Your direct e-mail address, and I'll send You.

[Tony]

Originally Posted by smoking-amp

The 6HF5 appears to be the same tube as the 6JS6/A/B but with slightly different pinout.

I only see the 6JS6C datasheet with curves, presumably very similar.

http://scottbecker.net/tube/sheets/123/6/6JS6C.pdf

hi don, the 6HF5 spec shows a positive bias for G3, do we need to bias this grid positve also for audio? i have a hunch that we need that positive bias...

[Tony]

@davorin, sent you pm, please send me your files also...thanks

[Tony]

Originally Posted by Tony

hi don, the 6HF5 spec shows a positive bias for G3, do we need to bias this grid positve also for audio? i have a hunch that we need that positive bias...

oopss...i was thinking another tube.....please disregard...

[rsumperl]

Davorin, thank you for the curves.
So if I am reading this one correctly, 3.3KΩ is not a good P-P load for these tubes. I'm seeing 2.5KΩ as the better choice when the plate is 500V. Anyone else agree with me on this?

Thanks,
Ray

[davorin]

Maybee 2,2-2,3 KOhm including SAG of PS.

[tubelab.com]

So if I am reading this one correctly, 3.3KΩ is not a good P-P load for these tubes........Maybee 2,2-2,3 KOhm including SAG of PS.

That number sounded familiar so I used the SEARCH feature.

The 6HF5's met the red board in post #168. With 520 volts of B+, 150 volts on the screen, and a 3300 ohm load I got 125 WPC out of 6HF5's.

In post #218 I tested the same tubes with a 2500 ohm load. Power did not increase, distortion went up and redness appeared.

hi don, the 6HF5 spec shows a positive bias for G3, do we need to bias this grid positve also for audio?

Many sweep tubes allow for a small positive voltage on G3 to stop Barkhausen Oscillation. This is not needed in audio.

[Tony]

thanks george, that's one concern out of the way......