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Chip647

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In Reply to: RE: The 6SJ7 is a single sharp cuttoff pentode tube, not compatable with 6SN7 posted by john635@earthlink.net on October 19, 2024 at 10:05:37

Tube Setup Guide
MP-401 MK3 supports EL34, 6L6GC, KT88, 6550 and KT120 power tubes, 6SN7,
6N8P preamp tubes, and 6N7, 6N7P driver tubes. Since MP-401 MK3 is auto
biasing design, users can change these tubes without any adjustment. Matched
pairs of tubes are recommended. All power tubes are placed at the back row.
6SN7 preamp tubes are placed at the center front row. 6N7 driver tubes are
placed at the outer front row. These need to be double checked and confirmed
before turning on.

Mentions nothing about 6SJ7 tubes. you are using them currently?

Follow Ups:

RE: website - john635@earthlink.net 04:13:24 10/20/24 (2)
Good morning Chip647!
This amp that you're talking about here, is a much newer amp.
Mine doesn't have the MK2 or MK3 designations printed on it.
I believe that my amp, is one of the first amps that Musical Paradise designed some 16 years ago.
Both the MK2 and MK3, are newer amps that superseded the one that I have.
I did write Garry, and asked him for a repair and user manual.
He tells me that, those manuals aren't available anymore.
So, I'm kind of stuck here.
But even without any manuals, sometimes, I can figure these things out.
But this thing, is stumpping me.
But as for that 6SJ7 tube, I've seen this tube before, but just not in any audio amplifier.
I first saw that tube, inside of an old radio receiver, that was made in 1937.
But it was in 1981 is when I was working on that old receiver.
And yes, that tube in deed is a sharp cut off.
There are some that are remote cut off tubes.
But they work really well in some RF applications.
But where this is stumpping me at, is how these tubes are used in audio applications.
I understand how to wire up tubes like the 12SL7 and 12SN7 tubes.
Which are higher voltage counterparts to the 6SL7 and 6SN7 tubes.
Just one family of tubes, you need 12 volts on the heaters.
The others, you need 6 volts on the heaters.
But truthfully, they are the exact same tubes.
It's just that, I don't understand the use of a 6SJ7 tube in an audio application.
But it looks like, a very uncommon tube these days.
- RE: website - Paul Joppa 07:20:55 10/20/24 (1)
  If both 6SJ7s (per channel) are wired as triodes, they can be replaced with a single 6SN7. You'd need to do extensive re-wiring.
  - RE: website - PakProtector 09:50:13 10/22/24 (0)
    Or a carefully executed adapter would serve.
    The type 6SJ7 is hardly an expensive one( Radio Electric Supply has them listed at $4 each ). The type 5693 Special Red from RCA being the possible exception.
    Douglas
    
    Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
    - 1948 RCA Special Red (Open in New Window)
    Edits: 10/22/24
RE: website - Paul Joppa 23:27:17 10/19/24 (0)
A quick search of the Almighty Web reveals that the MP-401 MK3 is push-pull (with four EL34s) but the MK2 is single-ended (with two 6L6's). Both claim that the use of cathode bias means you can substitute many other power tubes without adjusting the bias.

The MK2 has two 6SJ7s per channel, with numerous other options

The MK3 has one 6SN7 and one 6N7 per channel

I did not find anything on a plain MP401 or a MK1 version.

For further confusion, there is an MPA-401 amplifier made by Extron - completely different.

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