6T9 push pull with Cathode Coupled input

Brit01 · 14th January 2009, 03:15 PM

I'd like some Opinions on this design. It's my first attempt of integrating a couple of designs to build a really econonical integrated amp.

I have incorporated a cathode coupled input with 5687 (I have a couple spare), and a 6T9 Compactron push pull with zener diode bias.

The 6T9's are appealing because you can buy them for 3 USD. This will be my first attempt with power tubes. I have just about finished my Aikido and would like to proceed with my next challenge but keeping it really cheap.

I would prefer to add a couple more 6T9's for more power but this is above my head.sorry about the drawing. I will try and get a better one done later. I was scribbling at work under cover!

Brit01 · 14th January 2009, 08:11 PM

first stage with 5687 (Cathode Coupled):

Brit01 · 14th January 2009, 08:14 PM

power stage with 2 6T9's per channel:

leadbelly · 14th January 2009, 08:21 PM

IMHO you would wind up with much better amp if you made a phase splitter with the 6T9 triodes, then used the 5687 as cathode followers, then the 6T9 pentodes. I don't really know why you threw in the 5687 as a gain block, as it shouldn't be needed with line level sources. If you did it because you actually need extra gain, going 6T9 triode -> 5687 -> 6T9 pentode is still much better.

Brit01 · 14th January 2009, 09:18 PM

Hi leadbelly,

Yes you're totally right. Studying it more now I realise what is happening.

The cathode follower will basically isolate the 6T9 triode from its pentode right? Almost like a buffer with no gain.

Also I was thinking I could run pin 10 from the pentode to an UL tap on the output transformer.

Would it be possible to use one pair of 6T9 triodes as the phase splitter and then various 6T9's pentodes in parallel to increase output? eg. pin 8 from 6T9 pentode would follow on to the next pin 8 of 6T9 pentode and so on..

I have a very similar design from Carver where he used 6 KT88 pentodes per channel with 12 AT7 triodes as the drivers.

Thks

Brit01 · 18th January 2009, 11:58 AM

6T9's seem to be hard to get hold of.

Think I'll try a simple SE design to start with easily available tubes.

I'd like to use KT88 or EL34 driven by a 6N1P. 6N1P has an mu of around 35.

Would this be enough to drive the kT88 or EL34? Or better of buying a higher mu tube such as a 12AX7

14th January 2009, 08:21 PM	#4
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	IMHO you would wind up with much better amp if you made a phase splitter with the 6T9 triodes, then used the 5687 as cathode followers, then the 6T9 pentodes. I don't really know why you threw in the 5687 as a gain block, as it shouldn't be needed with line level sources. If you did it because you actually need extra gain, going 6T9 triode -> 5687 -> 6T9 pentode is still much better. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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14th January 2009, 09:18 PM	#5
Brit01 diyAudio Member Join Date: Jul 2008	Hi leadbelly, Yes you're totally right. Studying it more now I realise what is happening. The cathode follower will basically isolate the 6T9 triode from its pentode right? Almost like a buffer with no gain. Also I was thinking I could run pin 10 from the pentode to an UL tap on the output transformer. Would it be possible to use one pair of 6T9 triodes as the phase splitter and then various 6T9's pentodes in parallel to increase output? eg. pin 8 from 6T9 pentode would follow on to the next pin 8 of 6T9 pentode and so on.. I have a very similar design from Carver where he used 6 KT88 pentodes per channel with 12 AT7 triodes as the drivers. Thks

18th January 2009, 11:58 AM	#6
Brit01 diyAudio Member Join Date: Jul 2008	6T9's seem to be hard to get hold of. Think I'll try a simple SE design to start with easily available tubes. I'd like to use KT88 or EL34 driven by a 6N1P. 6N1P has an mu of around 35. Would this be enough to drive the kT88 or EL34? Or better of buying a higher mu tube such as a 12AX7

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