I can buy some 6U9's cheap - are they any good, and what could I build? - diyAudio
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Old 20th April 2014, 11:53 PM   #1
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Default I can buy some 6U9's cheap - are they any good, and what could I build?

Hi all,

I've mainly played with solid state amps until now, but I've the opportunity to pick up some tubes/valves cheap, and I was thinking I could have a bit of a play with them and see what I could make. However I'm struggling to find a datasheet for this part and thought I'd ask here as to whether these parts would be any good for an amp.

A quick search here suggests that this is quite a non-linear part and might be better suited to an instrument amp - is this the case?

Whilst we're about it these are on clearance as well...
6HS8/6BU8

and if anyone happens to have a schematic...
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Old 21st April 2014, 12:13 AM   #2
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I have heard that 6U9 is a remote cutoff pentode + triode. And it has a wacko 10 pin socket requirement. So unless you can get them for $0.05 each for fishing bobbers, I would forget about them.
The 6HS8 doesn't look much better.

Is this where you are looking? There are some decent tubes there.
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Old 21st April 2014, 12:35 AM   #3
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Fair enough then!

I have been putting together an order for a supplier down in my neck of the woods and these happened to come up on their clearance page - so the additional postage cost to me would have been zero basically, hence the question.

I suppose it's a false economy anyway - I live in Perth, Australia, which is the worlds most isolated city. Postage of output transformers to here would be a riotously expensive exercise - far outweighing (bad pun - sorry!) the savings on tubes.

Er, forgive my ignorance, but what is a remote cutoff part? and what would you use pentode/triode part for exactly?
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Old 21st April 2014, 01:12 AM   #4
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Remote cutoff is a purposely non-linear design used for AGC (automatic gain control) on radios. The grid wires are non-evenly wound on the support rods to make it have a slow turn off, so the gain steadily drops with large signals to keep the RF level near constant.

The doubled up pentode and triode in one evelope could be useful for the first two gain stages of an audio amplifier if it were not remote cutoff. For a radio, probably was for two gain stages in the IF chain.
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Old 22nd April 2014, 03:48 AM   #5
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Always good to learn something new - thanks!

I'm tempted to grab some anyway and maybe put together a guitar amp for a friend of mine just for fun... If I didn't have quite so many other unfinished projects kicking around.

Thanks for the answers - again, much appreciated.
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