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154.3.129.56
In Reply to: RE: 6SN7 Substitute for 5670 - Request Insights posted by svisner on June 20, 2024 at 10:51:58
The 5670 is a high quality modern tube released about 1955 and made by many of the best tube producers such as Tung Sol, RCA, Ericson (2C51) and Western Electric (396A). It has a different plate resistance, transconductance and amplification factor than the 6J5/6SN7; a higher performing tube with much greater transconductance and lower plate resistance.
As such, the 5670 has very different operating points, so that a 6SN7 plugged into a circuit (with an adapter) intended for a 5670, will give very unsatisfactory performance. So any competently engineered circuit using the 5670 should be very high quality. It would be a mistake to seriously degrade the performance by inserting the wrong tube.
Follow Ups:
Thanks.
substitute a 6sn7 for a 5670 without redesigning the circuit first.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Since there is an adaptor for it on epay, the assumption is that it will work without any redesign. Other specious assumptions are: my preamp has too much gain with a 12AX7 so I will put in a 12AU7 for less gain. It seems that Gm and Rp are not even considered relevant.
As you know, those are some really bad assumptions.
There are manufacturers that claim their power amps can use all the different beam power and power pentode tubes but that is nonsense.
If the amp is optimized for any one of those tubes, it will not be for the rest.
As for gain stage tubes. Pretty much the same thing. Even if you can plug a 12ua7 into a circuit designed for a 12ax7 without it blowing up it doesn't mean you should. Unless you don't care about distortion (or maybe you are looking for distortion?)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
...the 12AU7 is certainly the place to find it! I think back on how many times I glossed over your (as well as Eli Duttman's, among others) posts about the non-linearity of the 12AU7.
Meanwhile I was trying different coupling caps, improvements to the power supply, even different resistor types to try and coax some music out of my ST-70 with a 12AU7 circuit.
Then one day, after reading one of your posts about the clear superiority of the 6CG7 for who knows how many times, I finally paid attention. But rather than cutting board traces, and since I already had a few 6SN7s, I bought an 12Au7 socket to 6SN7 tube adapter to try in the circuit's voltage position. After so many previous disappointments I wasn't expecting much, but couldn't quite get over the level of improvement. I could finally listen to this amp for musical pleasure.
When I think of how much time, money and frustration I wasted, when the problem was the 12AU7 in the gain position all along. Ugh! What an awful tube to use for amplification.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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