Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: phsyconoodler on December 13, 2021, 11:01:08 am
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One question. Is Traynors method of simply lifting the secondary center tap a viable standby method for all amplifiers
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One question. Is Traynors method of simply lifting the secondary center tap a viable standby method for all amplifiers
One answer. No.
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Can you elaborate on that?
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Leaving the screen grids energised whilst the anodes aren’t will probably result in them passing excessive current and overdissipating.
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I went and looked at Valve wizards page on this and it really helped. I'm using a valve rectifier so I just think it's best that I don't implement the standby switch.
Just think now of what else I can use the switch for. Hmmm...
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FWIW;
my last build I did 2 different NFB schemes, used a switch to choose which one
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Can you elaborate on that?
OK. I'm using this schematic as a reference. The bias circuit is the same as the Traynor YBA1 except slight component value differences...
http://sluckeyamps.com/phoenix/phoenix.pdf
The bias voltage at the first filter cap is normally -56V. (I just checked all this stuff a few minutes ago.) Then I disconnected the PT CT from ground (simulating a STBY switch). This killed all the B+ voltages as expected ***BUT*** the bias voltage started climbing and after 30 seconds it had settled at -104V!!! No big deal for the tubes but the bias filter caps are at risk if not rated for higher voltage. My caps are rated for 150V, so no harm. And the YBA1 bias caps are rated for 250V. See schematic...
https://el34world.com/charts/Schematics/files/Traynor/Traynor_bassmaster_mkii_yba1.pdf
So switching the PT CT will work in my amp or the YBA1 amp. But think of something like a Princeton Reverb that has a bias cap rated for 25µF/50V. Guess what will happen to that cap if you switch the PT CT? :think1:
https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_bf_aa1164.pdf