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8608 pentode

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nhuwar

nhuwar

Member
Joined 2007
Hi all,


Just wondered if anyone has heard of this tube being used in audio applications ?
Any opinions of how the tube performed will be greatly appreciated?

I have 4 old amprex gold pin 8608 and I'm trying to think of something to do with them.
Thanks,
Nick
 
B

Bandersnatch

Member
Joined 2003
hey-Hey!!!,
With a significant part of the g1 plate curves above its plate dissipation, I'd want to run it at lower g2 voltages. beyond that, it looks like a fine audio tube. If you've got a linestage with balanced output a *VERY* simple amp can be built with just a two-tube, PP power stage. Looks like an easy 6-8W to mee...:) wishing I had several of them myself.
cheers,
Douglas
 
nhuwar

nhuwar

Member
Joined 2007
:Well I was thinking about using it as a driver for a 813.


I know it's probably a bit over the top but I think it would look cool to have a ll the tube have plate caps.


Oh and ya my linestage does have balanced outputs too LOL, how'd you know :D
Nick
 
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B

Bandersnatch

Member
Joined 2003
nhuwar said:
:Well I was thinking about using it as a driver for a 813.


I know it's probably a bit over the top but I think it would look cool to have a ll the tube have plate caps.


Oh and ya my linestage does have balanced outputs too LOL, how'd you know :D
Nick
Click to expand...

hey-Hey!!!,
813 driver sounds cool...:) I am driving mine with a 6H6Pi/FQP1N60 cascode. Let me suggest for you E-Linear at 20-25%, B+ of ~600 to plate and screen( the 813's ), and an 8k a-a load. 8608 g2 around 75V, with plate loads of 15-20k and idle current 15-20 mA per.

Or you could build a 'scope and use them for horizontal outputs.
cheers,
Douglas
 
nhuwar

nhuwar

Member
Joined 2007
I was going for 1kv on the plate of the 813 and running 6500 ohm plate load.

The idea has been in the works for a while it's just changing the driver tube is something new.




Oh this is a se amp though, not a push pull. I was toying with that idea a while back just didn't have the room LOL.


Nick
 
Wavebourn

Wavebourn

Member
Joined 2006
wavebourn.com
nhuwar said:
Gyrator loaded, I've never heard of that one. But then again there's a lot in this obsession I haven't learned yet.
Click to expand...

Here is the basic version that I used several years ago in a mic pre:

CS-Load-Servo-Wavebourn.gif


Here is another version Hearinspace implemented in his high-end amp:

http://wavebourn.com/forum/download.php?id=125&f=7
 
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B

Bandersnatch

Member
Joined 2003
nhuwar said:
Hey Douglas,

Did you try a 813 at a 40% ul tap? If yes how did it work?

Or is 20% the only way to go?


Thanks,
Nick
Click to expand...

hey-Hey!!!,
It worked very well, save for making about half the power. The low B+, minus 40% of the plate swing lowers the g1=0V line too far so swing w/o grid current is small. At 30% the envelope to work under is far larger, and I suspect 20% might just be better...soon enough, eh?
cheers,
Douglas
 
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