Snip:
The 160 tab is under the most stress when the amp operates 80 meters. There
is almost 3kV peak across that 160 plate padding terminal to the switch
rotor. Every amplifier that switches a plate padding cap in has highest
peak voltage on that tab when on 80 meters.
To reduce the electric field gradient around all the pointed areas of the
contact, a washer is used. The washer acts just like one of those
anti-corona rings that used to be in TV sets, or that you see on HV power
lines. It spreads the field out, and reduces the chances of the corona
setting off an arc when you are on 80 meters.
Voltage between the switch rotor and that contact is highly dependent on how
you set the load control, because that sets the anode impedance. This is why
people should **always** tune an amplifier up for maximum possible power at
full drive and then back drive off to safe power. That reduces peak voltage.
I can, for example, make the anode of a 3-500Z reach 3 or more times the dc
supply voltage if I underload the amp. As a matter of fact if it is severely
underloaded, the voltage increases until something someplace absorbs the
energy. If it is a switch contact, then the contact goes away.
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On Tuesday, May 9, 2023, 8:21 AM, Bob <W4JFABob@...> wrote:
What is a corona washer?
Bob
On Tue, May 9, 2023, 8:08 AM Louis Parascondola via <Gudguyham=
[email protected]> wrote:
Bob, I refuse to change the band switch.? It will just happen again at some point with a new switch.? I see this problem all the time in fact just last week. The problem is too widespread to be coincidence. Heavy rtty on 160 seems? to be a common denominator.? It might even be 160 with poor antenna characteristics.? If you look back as far as the AL80A you¡¯ll see the same problem however the ¡° corona washer¡± seemed to be a fix on that?amp.? I¡¯m thinking that washer acted as a heat sink but JI mentioned corona voltages. ? Take your pick.
On Tuesday, May 9, 2023, 7:55 AM, Bob <W4JFABob@...> wrote:
I have two questions about this.
Lou, Do you just replace the band switch? If so, with what?
Adrian, What is "copper RL"?
Bob? W4JFA
On Tue, May 9, 2023 at 6:39?AM Louis Parascondola via <Gudguyham=
[email protected]> wrote:
That wire goes up to the two 170 pf doorknobs in parallel for padding the tune cap on 160.? That wire runs down to the bandswitch ?and is grounded through the switch completing the padding of the tune cap.? It¡¯s a point of high RF circulating currents .? This same issue was prevalent in the AL80A. SB1000 and LK500 amps with the small switch. ?
On Monday, May 8, 2023, 10:40 PM, Bob <W4JFABob@...> wrote:
Not sure if it'll fit but a solid spark plug wire may be a choice. They're designed not to arc and are running very high voltages. Just a possible option.
Bob? W4JFA
On Mon, May 8, 2023 at 10:00?PM Jim VE7RF <
jim.thom@...> wrote:
Lou, what's this... 'mystery insulated wire'? ?that runs down the inside of the bandswitch used for ??? ?It could always be replace, and some extra teflon tubing slid over it.?