How much capacitance is allowed to use for amp's switch to eliminate speaker thump? Would 1uF is ok?
I usually use about .047uf across the power switch,and it works alright for me. 🙂 1uf seems a bit big to me..
Or even a 10nF 1-2kV works well also. Mainly to prevent the switch contacts from arcing or welding together. I've often seen a 130R resistor and a 10nf-22nf cap in series in a little package mounted across the mains sw. I think the ones I've seen were manufactured by NCC, who-ever they are. Nippon Chemical or Condenser Corporation/Company? Having a cap across the mains sw also allows a small amount of current to pass when the switch is in the off position, so you don't want a too big of a cap!
I've seen in some of the older tube amps from long ago that had a 47nF cap across the pwr tranny primary. And sometimes a resistor, 2.2meg carbon composition and/or a cap 47nF from one side of power cord to chassis ground. This was back in the days (here in US) when they used mostly two conductor, nonpolarized power cords, though one side of the zip cord insulation was sometimes ribbed. In modern equipment that have a polarized power cord that 2.2meg resistor is usauly found on the wide blade-white stripe-ribbed (neutral) side, along with a noise filter (VCR's and TV's etc.).
Wayne
I've seen in some of the older tube amps from long ago that had a 47nF cap across the pwr tranny primary. And sometimes a resistor, 2.2meg carbon composition and/or a cap 47nF from one side of power cord to chassis ground. This was back in the days (here in US) when they used mostly two conductor, nonpolarized power cords, though one side of the zip cord insulation was sometimes ribbed. In modern equipment that have a polarized power cord that 2.2meg resistor is usauly found on the wide blade-white stripe-ribbed (neutral) side, along with a noise filter (VCR's and TV's etc.).
Wayne
for a cheap solution, I used those HV ceramic caps from PC PSU's (blue ones, about 2.2nF) and connected across the mains switch. works well for a guitar amp.
cogsncogs said:
hi cogsncogs, wanted to know if this(cap across switch) is recommended if i have a switch on HT side for delayed B+ switching?
schematic below, switch at 480-0-480 side:
An externally hosted image should be here but it was not working when we last tested it.
thanks.
garbage
Thanks guys. BTW, does it need to put cap on both power and standby switch?
So, 0.01uF/2KV will be ok?
So, 0.01uF/2KV will be ok?
Yep, Yup, Yes Sir! A 0.022uF 2kV will be fine also. If you still get a pop coming from the spkr or switch try a 100R - 150R 1/2 watt in series with the cap. Also try a 2.2meg carbon composition (both resistors must be carbon comp. tho, low inductance) resistor from the neutral side of the mains to chassis ground near where the mains enters the amp. Carbon comp resistors handle pulses well.
A 0.47uf 630V (250VAC) metal film cap across the power transformer primary may help, but I've seen situations where it may cause hum.
Place a 0.01uf 1kV ceramic cap across the secondary of the filament supply for the 300B, before the sand bridge. It may help with rectifier switching noise. 😉
Wayne
cogsncogs said:
What you describe is a product manufactured by Mallory called a "Quencharc" -- for relays and switches the contacts can be viewed as "capacitor plates" -- as they come into closer proximity the capacity increases until the air dielectric is breached -- causing the spark. Eventually the arc-over or spark oxidizes the contacts, reducing their conductivity, or even blowing the contactor right off ! Another manufacturer is Microcube. The Mallory is shown below:
An externally hosted image should be here but it was not working when we last tested it.
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