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What tube exists in octal base to replace a 7247?
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In your circuit (Fisher 400),
the 6SL7 will work fine.
DanL
The high-mu section has nearly the same gain as in the 12DW7/7247. Gain as such in the low-mu section is not very relevant in a concertina splitter but you need to look at the plate resistances and slightly redesign the 7247 circuit. If you tell us more about your intended application, we can give more specific advice.
If you want to stay with a noval tube, there is the 6DR7.
I am replacing the deficient Fisher 400 PI. This application can be applied to the 500 & 800 series too.
Some background. I have been steadily improving the Fisher 400, 500 & 800 receivers over the last year using a group of listeners & some high-end speakers plus sources. Plus, I have been getting conformation on my mods as far as England.
The last obstacle is the PI. Using the stock 12AX7 these upgraded Fishers are stunning. But, I can get more performance.
If you're searching for the best sound, you'll need to use tubes designed for that purpose. It's hard to beat the 'SL7/SN7 series.
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Buy Chinese. Bury freedom.
Suggest you take a look at dual dissimilar triode vertical osc/output tubes such as 6DN7. Osc section mu run from ~20-70 and output sections are quite beefy. Not exact sub for 12DW7/7247 but may permit even better performance due to hefty output stage. VTV covered the possibilities nicely in issue 17.
VTV 17. Interesting read.
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