Hi all,
This is my first post, glad to be here! Wondering if DIY audio members can help me with a question about power switches on SE tube amps. The power switch on my 8 watt, tube rectified EL34 amp just broke, and instead of replacing it, I'm thinking of just getting rid of it altogether (so that on/off is just controlled by plugging in and unplugging the amp). I am in the practice of unplugging the amp every time I turn it off anyway, so it's not going to be any inconvenience.
My question is: Would I run a risk of damage to the amp and/or tubes by controlling the on/off via just plugging in and unplugging the amp? I'm pretty sure there was a current rush to the transformers and tubes anyway when I would control this with the on/off switch (as evidenced by a brief hum when the switch was flicked on). I know sometimes when I plug things in to the wall there is a slight blue flash on the plug prongs--might this indicate current that would harm the amp?
Many thanks in advance!
This is my first post, glad to be here! Wondering if DIY audio members can help me with a question about power switches on SE tube amps. The power switch on my 8 watt, tube rectified EL34 amp just broke, and instead of replacing it, I'm thinking of just getting rid of it altogether (so that on/off is just controlled by plugging in and unplugging the amp). I am in the practice of unplugging the amp every time I turn it off anyway, so it's not going to be any inconvenience.
My question is: Would I run a risk of damage to the amp and/or tubes by controlling the on/off via just plugging in and unplugging the amp? I'm pretty sure there was a current rush to the transformers and tubes anyway when I would control this with the on/off switch (as evidenced by a brief hum when the switch was flicked on). I know sometimes when I plug things in to the wall there is a slight blue flash on the plug prongs--might this indicate current that would harm the amp?
Many thanks in advance!
Should be ok if done quickly and deliberately, or use a switched outlet strip.
I could not recommend operate without power switch, even also I unplug my audio equip and PC from the wall to avoid lightning.
Do your amp have soft start to slow heating the tubes or have tube rectifier?
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This is not necessary in tube amps using the 5AR4/GZ34 rectifier tube, which has a slow warmup filament.
For an example, the Dynaco Stereo 70, which is extremely reliable.
Yes, you could ha a problem by unplugging.
Reason is that plugging in or out is a inprecise action that often bounces , this
intermittent on-off-on or off-on-off can make tubes flashover.
I would recommend a mains switch, switching both leads and proper fuses.
The Dyn70 can be a reliable amp but the tubes from a late friend used to lasts only around 6 months at an point he tired to buy tubes and sold the amp.
I built, modified, and sold hundreds of Dyna Stereo 70s, and they have been extremely reliable.
If an output tube cannot last for years in this amp in normal use, it must be a poorly manufactured tube.
Thanks everyone for all the replies. The amp has a 5Z4P (5V4G) rectifier--I'm not sure if this is similar to the 5AR4/GZ34 rectifier mentioned by rayma that has a slow warmup filament. Thanks also to rayma for the idea of using a switched outlet strip--I can't imagine that this would introduce much more of a current spike than the basic SPST power switch that was on the amp. So, I think I'm gonna try just joining the leads that were on the power switch and running the amp without a chassis power switch, but on a switched outlet strip. I'll try to report back on how this works out once I get the strip. Thanks again everyone and any other input is very welcome 
The 4 Ohm speakers wouldn't be a problem, since there are matching output taps.
The amp doesn't care which tap you use. If several new tubes had the same problem,
the bias could have been not properly adjusted, or the tubes were not a properly matched pair.
About the only other possibility is a leaky coupling capacitor, if the amp were really old, from the 50s.
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Not necessary for domestic amplifiers. One switch is fine; even soft start is more optional than many people realise. If you need power sequencing (which you don't for domestic systems) then this should be automatic and not rely on users getting it right.FullRangeMan said:
An amp needs a switch. This is because you need to avoid a messy break or make, which is what you get when you unplug a live connection. Switches are designed to make or break quickly. The switch need not be part of the amp chassis, but it should be somewhere in the mains supply.
Wow… did anyone yet comment on WHY both switches fail, and pulling out power plugs emits a blue-white spark?
Power transformer inductance is at the core.
Whether a transformer is just sitting there free-wheeling or actually delivering transformed power to the downwind circuit, the relationship between voltage and current phase remains that of an inductor: current LAGS voltage. And the total amount of power stored by the inductance of the transformer is significant. And when one breaks the circuit during current flow, there is a very large reverse EMF voltage spike … that bridges gaps.
Switches, flipped off, introduce such a gap.
Pulling out the power plug … same thing.
So. Just replace the switch with a higher-amperage one. Seriously.
End of discussion in my book.
Holey Moley.
GoatGuy
Power transformer inductance is at the core.
Whether a transformer is just sitting there free-wheeling or actually delivering transformed power to the downwind circuit, the relationship between voltage and current phase remains that of an inductor: current LAGS voltage. And the total amount of power stored by the inductance of the transformer is significant. And when one breaks the circuit during current flow, there is a very large reverse EMF voltage spike … that bridges gaps.
Switches, flipped off, introduce such a gap.
Pulling out the power plug … same thing.
So. Just replace the switch with a higher-amperage one. Seriously.
End of discussion in my book.
Holey Moley.
GoatGuy
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