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Old 18th December 2009, 04:01 PM   #1
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Default NASA space-age tube for audio use

5876 is a high mu triode, price is reasonable, 20-30 $ around,NOS amplification factor 56, plate dissipation 6W so it can be one stage in gain and drive, even the power tube is in positive bias, I built one in 10 years ago, very simple circuit . it can deliver 8W (8ohm) with 1.5V in-put, if you want more sensitivity you can replace the 100K resistor with a 600 ohm 1 to 2 step up in-put transformer, than you will have 1V in-put to 8W out. this amp costs much cheaper than a 300B SE, but sound better to me
Tony KY Ma
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Old 18th December 2009, 05:54 PM   #2
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Is the basement 809 lake 2A3 for?
Is the heating of 809 DC or AC ?

Last edited by azazello; 18th December 2009 at 06:00 PM.
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Old 18th December 2009, 07:21 PM   #3
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Nice idea to use those UHF disc-seal triodes of yesteryear The types I used relied on heat conduction from the grid ring (which was ground in normal applications).
Haven't looked at the spec's, but maybe you could run a lot more steam with some heat-sinking.

How does it sound?
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Old 19th December 2009, 04:57 AM   #4
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809 is a radio transmitting tube, it's power is bigger than a 300B, in audio use you can let it works in negative bias with high voltage (1000v) and small current (3ma), but do not sound good, in other way, positive bias, voltage can be much lower and have a high current(similar to 300B SE) then sound wonderful. the only condition is need a power tube or semi power tube to drive, also need a interstage transformer to match the impedance .
no socket for 5876, I use a big fuse holder for it, quite hot at plate, make holder's metal change color, but use for 10 years problem free,
sound quality, it can challenge any other 8 watt class SE amp in negative bias, no matter how expensive they are
Tony KY Ma
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Old 19th December 2009, 07:14 AM   #5
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It's my understanding that most of those pencil, lighthouse, planar and etc. triodes had ugly curves (imagine 12AT7, flattened and mushed a lot worse). Nothing that matters when you've in class C anyway, and it's a nice way to generate gigahertz gain. As mentioned, the grid was ground, while the plate and cathode connections were made inside resonant cavities. You should probably consider bypassing the electrodes as close to the tube as possible (100pF plate to grid, let's say) to ensure it's not oscillating at UHF+ (and this is an oscillation that you well and truely will *not* see on the oscilloscope!).

Tim
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Old 19th December 2009, 09:00 AM   #6
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Quote:
Originally Posted by Sch3mat1c View Post
... You should probably consider bypassing the electrodes as close to the tube as possible (100pF plate to grid, let's say) to ensure it's not oscillating at UHF+ (and this is an oscillation that you well and truely will *not* see on the oscilloscope!).

Tim
After 10 years and a change of colour, they're probably no longer capable of UHF...
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Old 19th December 2009, 11:11 AM   #7
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After 10 years and a change of colour, they're probably no longer capable of UHF...
The stuff that's capable of UHF in them is held in a vacuum - the perfect preservative

Cheers!
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Old 19th December 2009, 11:37 AM   #8
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After 10 years and a change of colour, they're probably no longer capable of UHF...
Trying VERY hard not to make a fuss about "seeing" you again...
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Old 19th December 2009, 01:14 PM   #9
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Quote:
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The stuff that's capable of UHF in them is held in a vacuum - the perfect preservative

Cheers!
Which is why valves last for ever

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Trying VERY hard not to make a fuss about "seeing" you again...
Just play it , as ever Stuart..
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Old 19th December 2009, 09:30 PM   #10
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