Lower gain substitute for a 6sj7?

[vintagekiki]

I have SK7's in 2 of my amps , so they will work .

Do your SK7's amps have grid leak bias or cathode bias?

[35L6]

Cathode bias . One is the input to a Silvertone floor model conversion .148V supply , 16k7 plate resistor , 56k screen resistor , 330r cathode resistor bypassed ,screen bypass .047 with switchable 22 for "deep" switch .73V at plate , 66V at screen , 2V at cathode . The other is the driver tube for a 35L6 in a radiola tabletop conversion . 107V supply , 10k plate resistor , 33k screen resistor , 1k cathode resistor bypassed ,.047 screen bypass , 74V on plate , 74V on screen , 4.4V on cathode . I don't know how to calculate grid leak bias other than plugging it in and measuring . Is there any way to tell if a simple tube swap would work ? If you try it , let me know what happened .

[J M Fahey]

while they all have a point at which they'll feed back, it isn't as low as 2 on the dial. That's why I think the problem is electronic, not acoustic.

It IS acoustic, the "number" on the dial means nothing.

If you use that amp on an open space and place it 10 meters away and set volume to 2, it will NOT howl, go figure.

Adjusting gain by "tube rolling" is a poor practice at best and anyway does not offer much gain reduction, a simple 10 cent resistor can offer any gain reduction you need with far more precision and repeatability, no need to rewire tubes, anything.

Please post amp schematic for suggestions and youŽll be able to set volume to š*any* number if you wish.

[vintagekiki]

I don't know how to calculate grid leak bias other than plugging it in and measuring .

About grid leak bias

https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/31280-grid-leak-bias-and-hum
Grid leak bias and hum...

https://robrobinette.com/Fender_Deluxe_Models.htm
Fender Deluxe Amplifier Evolution

https://www.tdpri.com/threads/tube-maximum-grid-resistance-and-grid-leak-resitance-generally.1007119/
Tube Maximum Grid Resistance and grid leak Resitance generally

https://tubes.njunis.net/?p=256&lang=en
Grid Leak Bias or Contact Potential Bias

https://www.diyaudio.com/forums/tubes-valves/272689-grid-leak-bias.html
Grid leak bias, how does it work?

https://www.ampbooks.com/mobile/classic-circuits/rickenbacker-m8e/
Rickenbacker Grid-Leak Bias

https://ampgarage.com/forum/viewtopic.php?t=29704
Further Grid Leak Bias Questions