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Any thoughts on this circuit?

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M Gregg

M Gregg

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Joined 2010
Just for interest.

I came across this circuit has anyone ever used it?

The reason I ask is I am looking at a possible Miniwatt using inverter and 3 tubes 2x EL34 1x ECC81 just for fun!
:)


Regards
M. Gregg
 

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leadbelly

leadbelly

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Joined 2002
What's going on? The schematic you posted is of an ECC81 driving a triode strapped EL34. The Miniwatt amp you linked to (as inspiration?) is a 12AX7 driving an EL84, and it's definitely not triode strapped or it wouldn't make 3.5W. What are you trying to achieve?
 
M Gregg

M Gregg

Disabled Account
Joined 2010
leadbelly said:
What's going on? The schematic you posted is of an ECC81 driving a triode strapped EL34. The Miniwatt amp you linked to (as inspiration?) is a 12AX7 driving an EL84, and it's definitely not triode strapped or it wouldn't make 3.5W. What are you trying to achieve?
Click to expand...

The idea is to get an "improved" miniwatt. Using triode EL34 to get the same output power.:)
Or switchable pentode to get more power! If you have any improvements please post!
 
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leadbelly

leadbelly

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Joined 2002
M Gregg said:
The idea is to get an "improved" miniwatt. Using triode EL34 to get the same output power.:)
Or switchable pentode to get more power! If you have any improvements please post!
Click to expand...

It's hard to talk in generalities since the devil is in the details, but one aspect is that a pentode EL84 is so much easier to drive than a trioded EL34 that you might be very well be taking a step backwards rather than forwards.

There are SO many choices out there. Have a look at the Simple SE for one.
 
artosalo

artosalo

Member
Joined 2010
Why is the screen grid connected to the OPT center tap instead of the plate of the EL34?
Click to expand...

When screen is connected this way, the circuit is called as ultra-linear.
This kind of circuitry gives low output impedance and good linearity like triode connection. It is also not very sensitive to load impedance variation and thus again resembles triode output stage.
On the other hand it has high(er) output power and requires less driving voltage like pentede connection.

According to some Mullard test report, UL-connection is more linear and produces less harmonic - and intermodulation distortion than triode connection.
 
T

toprepairman

Member
Joined 2010
Agree with Leadbelly, stick with EL84, but thats ne reason not to experiment with others, like 6BW6. Keep it in pentode mode but include the secondary winding in the EL84 cathode ciruit, ie remove the 1000uF neg end off the ground, attach it to secondary, with the other end of the secondary to ground. You'll have to experiment with this one as one way it will work and the other it will oscillate.
Regards
Henry
 
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