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-   -   Why use a pentode? (http://www.diyaudio.com/forums/tubes-valves/236769-why-use-pentode.html)

M Gregg 29th May 2013 02:20 PM

Why use a pentode?
 
Why,

did early tube amplifiers use pentodes in the first stage?


Regards
M. Gregg

TheGimp 29th May 2013 02:31 PM

Gain and economy.

Multiple triode gain stages cost more than a single pentode gain stage.

Distortion levels were low enough to be acceptable.

SY 29th May 2013 02:39 PM

Lots of open loop gain mean more distortion reduction closed loop. Great voltage swing as well. Low input capacitance.

A pentode is ideal for the input of a power amp.

M Gregg 29th May 2013 03:07 PM

1 Attachment(s)
I was looking at this old text..

However we don't seem to use pentode input...The EF86 is not so popular these days..



Regards
M. Gregg

artosalo 29th May 2013 06:55 PM

Quote:

Originally Posted by M Gregg (Post 3508179)
...The EF86 is not so popular these days...

It is strange today that many DIYers think that EF86 is the only choice if pentode voltage amplifier should be built.

I try to balance the situation so that I never use EF86, but all the rest.

Frank Berry 29th May 2013 07:04 PM

5879 is a good, low-noise pentode. It was used in many microphone preamps.

SY 29th May 2013 07:16 PM

You don't need super low noise at the input of a power amp, though it's certainly not a disadvantage! I'd look at higher gm pentodes. C3g, D3a are superb. I'm playing with some compactrons like 6M11 which seem to be inexpensive and high performance.

Rundmaus 29th May 2013 07:26 PM

Quote:

Originally Posted by SY (Post 3508450)
I'm playing with some compactrons like 6M11 which seem to be inexpensive and high performance.

How much of the compactron is really usable/used then, do you leave many sections 'idle'? I think I remember reading something about the limited possibilities with compactrons due to the often shared cathode...

Rundmaus

SY 29th May 2013 07:33 PM

You could leave sections idle, but why? If you're doing something along the lines of a 5-20 topology (which is what I'm doing), the extra two triodes are perfect for the long tail phase splitter. If you're doing a Dyna style circuit, they can be paralleled.

Rundmaus 29th May 2013 07:44 PM

OK,

just looked up the 6M11 datasheet and what I said does not apply here. In this nice compactron, each electrode of all three systems is accessible separately. Looks very useful!

Rundmaus


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