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Old 22nd March 2016, 11:26 PM   #1
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Default 6HJ5 SET

I just wanted to share my successful build using the 6HJ5 wired as a triode. These tubes are cheap and rugged, and oh yeah they sound great. The driver is a 6N7 with both triodes in parallel.

I have a SS Slewmonster and Mullard 5-20 monoblocks so this amp is my "colored" sound amp. It has that warmth of a 300b amp. I highly recommend people to go ahead and not be afraid to use this tube for audio. I know George has used them in Pete's big red board but I wanted to share the success of it wired as a triode.

-bird
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Old 23rd March 2016, 12:24 AM   #2
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nice, what operating point did you use for the output tube and what OPT? thanks...
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Old 23rd March 2016, 01:34 AM   #3
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Very cool! I'll guess Transendar OPT's. Same questions re: operating point, B+ etc.

jeff
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Old 23rd March 2016, 01:53 AM   #4
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Yes those are 3k:8 10 watt Transcendar OPT.

Operating point is, Va=310, Va-k=260 @ 85mA.


6N7 has a 10M45S @ 10mA loading the plates and a yellow LED @ cathode.

I will post the full schematic soon. I am really enjoying this build, the sound is so beautiful.
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Old 23rd March 2016, 02:44 AM   #5
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Thanks for the update.

jeff
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Old 26th March 2016, 10:14 PM   #6
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For anyone still interested here are some more details.

Pout= 5 watts

Power supply is a CLC and then I branch off separately to each channel via RC networks. The supply is tube rectified via 5U4GB. The choke is Triad C-14X, 6H 150R. The 50uF electrolytic cap value is for two 100uF 350v in series with 470k balance resistors. The reason is for using the 5U4GB and the B+ jumping up to 460v during turn on. I used the 5V winding center tap to feed B+ to the power supply filters. The power transformer is a Hammond 272HX. Current source for the 6N7's is a 10M45S module with a 1k CC resistor up very close to pin "G" and a 380R current set resistor.

Actual Measured data:

C1 (50uF) V=356
C2 (50uF) V=326
C3 & C4 (50uF Electrolytic | | 45uF Polypropylene motor run) V=318
C5 & C6 (22uF) V=297

6N7

Va=170

Vk=2



6HJ5

Va=295

Vk=50 Rk=620

Ig2=4mA

g3 is tied to cathode


With my ear directly up against my Klipsch La Scala's there is zero audible noise or hum, dead silence.
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Last edited by famousmockingbird; 26th March 2016 at 10:16 PM.
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Old 26th March 2016, 10:59 PM   #7
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Really great engineer aesthetics with the metal tubes and the fat bottle sweep tubes, and the chassis as a whole!

I gotta make an all metal tube amp some day...
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Old 26th March 2016, 11:24 PM   #8
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Thank you MrCurwen! The metal can tubes get no love because you can't see the filament. That's fine by me, that makes them cheap and easy to find

I was worried about using a sweep tube but they seem very stable. I figured it was time to reveal it knowing there hasn't been any issues. I used CC resistors right up against the sockets to prevent oscillation. No runaway tubes so far. The 6HJ5 g2 is rated for 6 watts! That's almost 3 more watts than the more popular 6CB5a. It is also rated for slightly higher voltage. I started out pushing these tubes and I didn't have any issues but I settled on a pretty relaxed operating point. I don't require tons of power with this amp paired to Klipsch La Scala's which I believe are 104db efficiency. At the price of these tubes ($4) I am surprised they aren't more popular.
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Old 27th March 2016, 01:16 AM   #9
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A couple of 6HJ5 tubes in triode. Usually very consistent. Raytheon tubes. (Argh, just found the zero was off by 2V on the left picture, left most curve is -2V then 7 V steps down from that.)
50 mA/div Vert., 50V/div Horiz., 7 V steps on grid 1
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Last edited by smoking-amp; 27th March 2016 at 01:32 AM.
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Old 27th March 2016, 01:17 AM   #10
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Most hobbyists don't really do much design, they build schematics they find online. I guess there's not that many sweep tube schematics around, other than maybe nowadays on this forum.

Regarding stability: You can always decrease gm by putting an unbypassed resistor (22, 33 or maybe 47 ohm) under the cathode. Also a bigger g2 to plate triode strapping resistor helps; I didn't get my 6E5P balanced amp stable until the triode strapping resistor was 8.2k. I used 10k straight away in my SE build. These tubes have a lot of gm so in my opinion doesn't hurt at all to lose some, especially if power is not a priority.
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