I just built a one channel 5C8 tweed twin with two 6SL7 preamp tubes and 6L6 / 5U4 as usual. I love it probably because I lucked into a pair of quiet 6SL7s.
Question is, if you want the fat round tone of the octal where does it do most of it's tone shaping ? I have 2 octal preamp stages in series and the paraphase.
Where does the magic happen and is it in part due to the large value coupling caps ?
Where is the best place to put an octal preamp tube ?
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chopstuck
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Where is the best place to put an octal preamp tube ?
Heavens, an unused PI input !
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Stevem
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Re: Where is the best place to put an octal preamp tube ?
The best place to put a Octal preamp tube with there big plates and grids, especially the first gain stage in the amp is as far away from the power transformer as you can so as to not pick up 60 hz hum.
You also might want to bias up the filament string thru the heater center tap with about 48 volts DC, or at least run the first gain stage heater on DC if your looking for a super low noise amp.
The fat sound of Octals comes from there big internal structure and the fact that this added capacitance rolls off some of the unneeded high end as compared to a 9 pin tube.
All of this added mass is also why they last so long!
You also might want to bias up the filament string thru the heater center tap with about 48 volts DC, or at least run the first gain stage heater on DC if your looking for a super low noise amp.
The fat sound of Octals comes from there big internal structure and the fact that this added capacitance rolls off some of the unneeded high end as compared to a 9 pin tube.
All of this added mass is also why they last so long!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Andy Le Blanc
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Re: Where is the best place to put an octal preamp tube ?
I was gonna say in a tube socket.
Last octal based pre I fab'd I used a similar circuit but used a couple 12sl7 with the heaters run series as the cathode bias resistor for the 6l6 pair.
Free regulated DC for the heaters, lovely tone but the draw back is warm up time.
Second the recommendations so far. I would add that you mind the voltage applied to the pre. A lower voltage will be kinder to the NOS and tame some noise.
RCA gives RC gain tables at 300 180 and 90. Don't assume that a higher voltage and the most gain possible is the best tone.
Last octal based pre I fab'd I used a similar circuit but used a couple 12sl7 with the heaters run series as the cathode bias resistor for the 6l6 pair.
Free regulated DC for the heaters, lovely tone but the draw back is warm up time.
Second the recommendations so far. I would add that you mind the voltage applied to the pre. A lower voltage will be kinder to the NOS and tame some noise.
RCA gives RC gain tables at 300 180 and 90. Don't assume that a higher voltage and the most gain possible is the best tone.
lazymaryamps
Re: Where is the best place to put an octal preamp tube ?
So then, use a regular noval 9 pin for the PI for less noise and easier packaging without much loss of old amp goodness ?
Heavens, an unused PI input !
Re: Where is the best place to put an octal preamp tube ?
The 6SN7 makes a great PI or driver. I use them a lot and have no noise problems.
Tube junkie that aspires to become a tri-state bidirectional buss driver.