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Old 23rd April 2011, 02:17 AM   #1
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Default 6HF5 testing

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
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Old 23rd April 2011, 03:47 AM   #2
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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
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Old 23rd April 2011, 08:06 AM   #3
davorin is offline davorin  Croatia
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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.
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Old 23rd April 2011, 09:26 AM   #4
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Quote:
Originally Posted by smoking-amp View Post
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...
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Old 23rd April 2011, 09:47 AM   #5
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@davorin, sent you pm, please send me your files also...thanks
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Old 23rd April 2011, 10:45 AM   #6
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Quote:
Originally Posted by Tony View Post
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...
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Old 23rd April 2011, 04:24 PM   #7
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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
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Old 23rd April 2011, 06:40 PM   #8
davorin is offline davorin  Croatia
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Maybee 2,2-2,3 KOhm including SAG of PS.
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Old 23rd April 2011, 07:12 PM   #9
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Quote:
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.

Quote:
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.
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Old 23rd April 2011, 11:30 PM   #10
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thanks george, that's one concern out of the way......
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