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Old 16th June 2013, 01:25 PM   #1
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Default 6sn7 pse amp for altec lansing 604E

Hi would a 6sn7 pse amp be possible by tying the anodes for both halves together with the load being a hammond 125ase wired for 10k ohms with an 8 ohms speaker. However due to the speakers I am using with the amp being 604E, I can expect a load of 20k ohms on the primary of the transformer. Each cathode will have a Rk of 1k ohms and each grid will have a resistor of 470k ohms to ground.
I understand that this amp will only be capable of much less than a watt, however I would love to try this circuit out.
Thanks in advance.
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Old 16th June 2013, 11:41 PM   #2
ChrisA is offline ChrisA  United States
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Yes. It works. It has been done many times but more common to use the 12AU7 tube.

A common modern application is inside a guitar amp to drive the transformer that then drive a reverb pan. Usually 20K to 8 ohms. The pans only need about one watt or less.

But if you have room for an octal, I think you get all around better sound from a 6V6 in class-A so why bother with a doubled 6SN7?
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Old 17th June 2013, 12:11 AM   #3
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I think you'd want multiple tubes in parallel to get reasonable power, and an load impedance that is closer to say 3.5kohms.

Seems like 1 watt will be to little to make the 604 do much...

There is a nice little Russian pentode that is very linear when strapped for triode and does I think about 7-8 watts... there is a thread on it. It's inexpensive compared to a NOS 6SN7.

Something to think about.

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Old 17th June 2013, 11:04 AM   #4
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Thank you for your replies.
My reasoning for using the 6sn7 is due to my curiosity of an amp which utilized all the same tubes .
Along with that the tubes have to be true triodes (call me naive) however I have built (following textbook schematics) amps which utilized kt88s ,EL34s and 2a3s all single ended and triode strapped for the 2 non-triodes. With the 2a3 sounding the best to me.
As I already have most of the parts at hand this little amp will help to keep me from scratching my itch of building an amp utilizing those monster tubes I have sitting in my closet .
Besides would'nt a little amp with 3 6sn7s on it look extremely cute?
Finally this amp will be used with 604s for extremely low level background listening.
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Old 17th June 2013, 01:49 PM   #5
Cassiel is offline Cassiel  Libya
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I have built a SE and a PP 6SN7 amp. My vote goes to the push pull amp. B+ 420 volts, around 2 watts, great sound.
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Old 17th June 2013, 02:22 PM   #6
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Maybe biamp ur 604s?

I'd still vote for a method that brings the requisite plate load Z down to <5kohms... push pull parallel seems like the ticket.

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Old 17th June 2013, 02:32 PM   #7
Cassiel is offline Cassiel  Libya
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I did use a Hammond 1609 which is 10K but with the 'wrong' load it gets transformed to 20K.
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Old 17th June 2013, 02:43 PM   #8
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Hi!

That should work. It will probably not be the most refined amp but I am sure will sound nice. If you run them hot, close to the max plate dissipation you should be able to get a little over 1W out of two paralleled halves.

Depends on your listening habits and room size if its enough power. Most people way ovcer estimate the power need. I built a 45 amp with about 1.5W for someone who uses a 604 and he is more than happy.

Since you have that itch for this amp, go for it and built it. That is the only way to get that itch going away ;-)

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Old 17th June 2013, 06:46 PM   #9
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Thank you all for your replies.
ChrisA. Am I right in assuming that electrically both the 12au7 and 6sn7 are relatively similar?
Cassiel. Would it be convienient for you to share the schematic for the single ended amp? Haha as going p-p would require me to change my opt.
Bear. Bi-amping? Certainly! I am sure the 604s will benifit from being bi-amped. With the little 6sn7 amp on the highs and a 2a3 amp on the lows. Although I understand the reasoning for bringing the plate load impedance down, I have to stick with what I have as I do not wish to spend on this amp as I would prefer to conserve my funds for building an amp with either the 6c33cs or the 845s I have collecting dust in my wardrobe .
Vinylsavor. Hello . Well yes I have similar thoughts on power requirement as you do.
I am really confused as to how I am to calculate the plate dissipation . However I do know from the datasheet what the 6sn7 can take. Then again the 125ase is rated for 3watts 25ma thus I am assuming that if I do not exceed either 3watts of output and 25ma of idle current I should be safe. I understand that the tube's current is set by the cathode resistor (hope I am right) so how am I to calculate the current drawn ?
Thank you all once again.
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Old 17th June 2013, 07:16 PM   #10
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Hi!

You need to look at the plate curves and put the operating line in which is given by your primary impedance. I had a quick look. A good starting point would be to use 300V B+ and 12.5mA. This means 25mA with both halves in parallel. To get that you need -9V grid bias. A 360 Ohm cathode resistor will give 9V drop. This will be 7.5W plate dissipation which is the max allowed for both plates together. Make sure you have some of the later 6SN7 which can handle that dissipation. Once you have that running you can play a bit with the op point to get symmetrical clipping.

Best regards

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