Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Boots Deville on October 31, 2011, 05:17:20 pm
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I've used the 5G9 tremolo circuit in a couple 6V6 amps and like it a lot.
http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_5G9.pdf (http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_5G9.pdf)
I'm about to embark on a new 2 x 6L6 AB763 build. I'd like to use the 5G9 tremolo with it, but since it was designed around the 6V6, I'm wondering if there is anything I should consider when using it with a 6L6 power section.
The 6G16 Vibroverb and 6G9A Tremolux both use a similar tremolo but designed around a 6L6 power section. Should I opt for one of these, or can I splice in the 5G9 trem to the 6L6's without a worry?
http://www.el34world.com/charts/Schematics/files/fender/vibroverb_6g16_schem.pdf (http://www.el34world.com/charts/Schematics/files/fender/vibroverb_6g16_schem.pdf)
http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_6G9A.pdf (http://www.el34world.com/charts/Schematics/files/fender/TREMOLUX_6G9A.pdf)
-John
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The 6G16 Vibroverb and 6G9A Tremolux both use a similar tremolo but designed around a 6L6 power section. Should I opt for one of these, or can I splice in the 5G9 trem to the 6L6's without a worry?
I'd start with the later brown tremolux (6G9B) LFO circuit. I find the 6G16 trem is smooth, but doesn't have as much intensity as a 6G9B trem (probably to do with the plate-shunt cap in the 6G16 trem).
A 5G9 trem is designed for 6V6 grid voltages (as you infer), and you could adapt it for 6L6s (it is basically the same circuit topology after all). The main difference is the voltage output swing is different (but that's easy to tweak).
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In ARCHIVES, there is a thread about modding a tremolo for 6L6 use.
http://www.el34world.com/Forum/index.php?topic=604.0 (http://www.el34world.com/Forum/index.php?topic=604.0)
With respect, Tubenit
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Thanks for the tips guys.
Regarding the 6G9B circuit. That amp has a published plate voltage of 365V. My amp will have a 360-0-360 PT, so, with a GZ34, the plate voltages will be about 100V higher. I don't understand these tremolo circuits well enough to know how this will effect the operation of the tremolo. Will I need to tweak some component values to accommodate the 100V plate increase?
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Will I need to tweak some component values to accommodate the 100V plate increase?
Depends on the voltages you get. Ideally you want the trem voltages to be somewhere between a 6G9B and a 6G16. The CF driving the trem voltage swing on the output tube grids will work well with either with a 100k, 220k or 470k cathode resistor, and the deciding factor here will probably be the heater-to-cathode voltage you get. But if you use 470k with about 450V HT, you you be approximately right. (You can always level-shift - by way of a voltage divider - between the LFO output and the CF stage's input in order to get the CF stage to run at a lower heater-to-cathode voltage). Similarly, you can always reduce the voltage swing going into the output tube grids by adjusting the voltage divider that comes between the CF output coupling cap and the output tube grid load resistors. (In the 6G16, this voltage divider consists of a 470k bleed-out resistor and the 250k depth pot, or 220k and 250k in the 6G9B). You want the trem voltage swing such that it doesn't cause 'helicoptering' with the depth pot at maximum (this is caused by too much trem voltage swing driving the output tube bias into the cutoff range)
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Excellent, this is exactly the info I needed, Tubeswell, thank-you much!
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FWIW here's what I ended up with in a Super Reverb that worked well.
Cheers,
Chip