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Is there a 9-pin mini equivalent of 6AU6?

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rongon

rongon

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Joined 2009
#1
I have a gutted Dyna ST70 chassis with four 9 pin sockets ready to go. I was thinking of trying an E-Linear, but I'm hoping I can use a 9 pin mini pentode instead of the 6AU6. Is there a Russian pentode in the 9 pin mini package that will be pretty close?

Does anyone know of a different pentode that can be used instead of the 6AU6?

If not, I guess I'll just have to remove the 9 pin sockets and put in 7 pin sockets.

--

Can I sub EF86 (or equivalents) in the E-Linear PP amp?
 
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#4
rongon said:
I have a gutted Dyna ST70 chassis with four 9 pin sockets ready to go. I was thinking of trying an E-Linear, but I'm hoping I can use a 9 pin mini pentode instead of the 6AU6. Is there a Russian pentode in the 9 pin mini package that will be pretty close?

Does anyone know of a different pentode that can be used instead of the 6AU6?

If not, I guess I'll just have to remove the 9 pin sockets and put in 7 pin sockets.

--

Can I sub EF86 (or equivalents) in the E-Linear PP amp?
Click to expand...

if you want 9 pins, there is the 5879, 12by7, 6688, etc...
 
#5
Most of the purpose built single pentodes in a 9 pin bottle either have higher transconductance, or higher plate dissipation than their 7 pin brethren.

If you want a close match to the 6AU6 look at using the pentode half of a 9 pin triode - pentode tube like the 6U8.

If I were doing this I would use a higher transconductance single pentode like the common 6EJ7 and tweak the component values accordingly.
 
#7
tubelab.com said:
Most of the purpose built single pentodes in a 9 pin bottle either have higher transconductance, or higher plate dissipation than their 7 pin brethren.

If you want a close match to the 6AU6 look at using the pentode half of a 9 pin triode - pentode tube like the 6U8.

If I were doing this I would use a higher transconductance single pentode like the common 6EJ7 and tweak the component values accordingly.
Click to expand...

artosalo said:
Russian 6Ж9П (6J9P) and 6ЖП11P (6J11P) are very linear hi-gm pentodes near equivalent of E180F.

Prices are still quite fair: 6J9P-E: Long life E180F = 6688 Pentode Tube (5,000 hrs) Halo getter. Price for 4
Click to expand...


Yes, good ideas both. I have a bunch of 6J9P I can use for this. I guess I need to hit the books some more and learn how to tweak those values!

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#12
This is the circuit I'd like to put in my Stereo 70 chassis (attached). It's by Mr. Bandersnatch (Doug).

It uses an LTP made from two 6AU6 pentodes. I'm sure it could be made to use a pair of 6J9P-E instead. Would that be an improvement?

I'm thinking the resistor feeding the screen supply to the 6J9P-E's (Rg2) will need to be changed. What would the target voltage be at the 6J9P-E screen grids? I figure about 100V to 125V. (Max for 6J9P is 150V.)

I'd probably shoot for a plate voltage of about 200V. (Max is 250V.)

I need to read up on how to properly set operating points for a pentode.

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#15
Wavebourn said:
Leave it as is. 6J9P will work according to the current set by the CCS. In your particular case they will be able to swing more current and voltage that 6AU6.
Click to expand...

Now there's a reply I did not expect! A pleasant surprise. Now I have no excuse not to build this thing. It will be my first try at an amp with local feedback around the output stage.

Thanks!
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#17
Rongon,

If you haven't already come across this, Pete Millett had an e-linear SE amp article in the Apr. 05 AudioXpress. He explains a lot about e-linear theory and practice. He also has a bit about the amp here

E-linear amplifier

I'm very curious about your reaction to your e-linear amp when you get it built. I built 6SJ7GT 6550 SE and 6SL7GT 7591 PP e-linears and really liked the results for both.

Responses to your post have identified a bunch of potential drivers for another e-linear amp I'm considering.
 
#18
I've started to draw loadlines and run the circuit through LTspice, with 6L6GC output tubes using cathode bias instead of EL34 with fixed bias. I'm looking at it with about a 450V raw supply, so about 415V plate-cathode on the 6L6's. That would be with solid state rectification.

I have a couple of questions:

- Does the 6J9P draw much grid current if the bias voltage is more positive than -1.5V? The simulation predicts about -1.1V, which worries me. Should I try to re-jigger things so that the grid bias is -1.5V or more negative?

- What's a good voltage for the 6J9P screen grids? Is 90V OK, or does it have to be 100V to 120V?

- To get the screen voltage to about 100V, it looks like the screen grid resistor (Rsg in the original schematic) will have to be 50k to 56k ohms.

- Screen current looks like it comes out to 3mA per 6J9P. Is that OK?

The simulation suggests very fine performance with a pair of 6J9P driving the 6L6GC pair into the Dyna A470 OPT. I'm hopeful I can figure out what needs to be done, and then I'll start stripping out the remnants of the last experiment from my beater ST70 chassis.
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#19
I built this circuit on my ST-70. I used 6AU6, tried 12HL7's and a third pentode which I can't remember offhand but which was highly microphonic. My output tubes are Russian 6P3S-E with coin bases. I couldn't get the amp quiet. The general sound quality was good and quite lively, but it had a background hiss that I couldn't solve. Maybe I should try again with the 6J9P's.

Good luck and please share your results. I'd be happy to give mine another try.
John
 
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