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Old 31st January 2017, 05:28 PM   #1
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Default Advantage of pentode for LTP?

Advantages and disadvantages of small signal pentodes for LTP or output stage drivers?

Mike
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Old 31st January 2017, 06:15 PM   #2
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High gain, excellent PSRR when utilized correctly, such as using a stable reference voltage at the screen, and a CCS tail load.

Some resistively loaded Pentode can pick up noise or hash if they aren't given a healthy current. Capacitance can be an issue, especially at lower currents.

6AU6 are a very nice Pentode that is woefully underutilized these days. The 6V6 makes a great beefy Pentode, and has only a .45A filament when you want to push a good dreal of current. The D3A and EF86 are very nice too, in fact for many the D3A is *the* Pentode.

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Old 31st January 2017, 09:09 PM   #3
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Good afternoon,
What would you think about using a 6360?

Ray


Quote:
Originally Posted by Lingwendil View Post
High gain, excellent PSRR when utilized correctly, such as using a stable reference voltage at the screen, and a CCS tail load.

Some resistively loaded Pentode can pick up noise or hash if they aren't given a healthy current. Capacitance can be an issue, especially at lower currents.

6AU6 are a very nice Pentode that is woefully underutilized these days. The 6V6 makes a great beefy Pentode, and has only a .45A filament when you want to push a good dreal of current. The D3A and EF86 are very nice too, in fact for many the D3A is *the* Pentode.
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Old 31st January 2017, 09:16 PM   #4
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Originally Posted by rsumperl View Post
Good afternoon,
What would you think about using a 6360?

Ray
I'd rather use it for a ~3-6w push pull output stage, but it would probably do well in a LTP as a driver. Common screen grid restricts you to true Pentode operation, but would work well with a VR tube screen supply.

Click the image to open in full size.

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Old 1st February 2017, 12:08 AM   #5
Junm is offline Junm  Philippines
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Some dual Pentodes will be of interest...12L8 and 28D7 and russian 6R2P...
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Old 1st February 2017, 01:56 AM   #6
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Then we have my favorites, the Compactrons 6BN11 & 6J11, any thoughts on these????
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Old 1st February 2017, 09:06 AM   #7
DF96 is offline DF96  England
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That data for 6360 in post 4 is for Class C, so not relevant to audio.
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Old 1st February 2017, 09:50 AM   #8
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Advantages and disadvantages of small signal pentodes for LTP or output stage drivers?

Mike
The only "advantages" are aesthetic: glowey bottle coolness or the desire to avoid solid state for nostalgic reasons. Otherwise, it's all downside: another hole in the chassis, a high negative rail voltage, poorer performance.

For active tail loads, I like a cascode of BJTs: no extra holes required, and the negative rail doesn't need to be all that high, and could be derived from a heater winding. The gm is much higher, cascoding reduces Early Effect, and therefore this circuit comes closer to perfection than does a pentode, with a significantly higher effective impedance for the tail that improves on AC balance.
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Old 1st February 2017, 02:37 PM   #9
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Most of small signal pentodes, say 6CB6 6AU6, EF184 can give a high plate impedance, more than 1MΩ with a -100 V supply. A 12AX7 triode with 300V can give more than 47MΩ, but with an extra heater winding.
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Old 1st February 2017, 02:48 PM   #10
rmb is offline rmb  United States
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The 6360 was used as an output tube in the very early Gates FM transmitter exciters...
The 829B was also used at VHF frequencies in the 40 watt range...
Haven't tried them with audio...
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