Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on February 06, 2020, 09:57:35 am
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Hi,
Another day, another question. After mostly finishing up the surprise gift 4X6L6GC AB763 amp (no tremolo, one channel), I think I'd like to have one for myself as I'm really happy with it.
But I like tremolo also and would like to use bias-shifting tremolo in it as opposed to the AB763 version. I notice that Doug has schematics for the AB763 with this bias shift circuit.
I would love to do it but am wondering how effective it would be in a high powered 4X6L6 amp. I have heard that tremolo works better in lower powered amps; is that because the amount of bias shift induced on the output tubes is greater, percentage wise, on a small tube biased around 20ma as opposed to a 6L6, where the bias is set somewhere around 40-45ma?
Thanks!
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The bias trem circuit works well with 6V6 tubes but can be finicky with 6L6s. It can be difficult to get a strong good sounding trem at your preferred bias point. And when you change tubes you will get to tweak it all over again. If you search through this forum you will find plenty topics about weak tremolo and some good ideas about increasing the tremolo intensity. Probably the best idea is using a red LED on the cathode of the LFO oscillator. I would not use this trem circuit in a 6L6 amp and I don't recommend this circuit to anyone else either.
There is a simple alternative. Read this thread...
http://el34world.com/Forum/index.php?topic=24334.msg261229#msg261229
Then read this web page for my final version as used in a '67 BandMaster. You would use this exact circuit in a 4X6L6 AB763 amp...
http://sluckeyamps.com/trem/trem.htm
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Awesome, much obliged. If I can scrounge up some money for transformers etc. I may start in a few weeks. Looking forward to giving it a go,
Ted