[Amps] Re: Drake L7 newbie - Summary

[rlm]

On Mar 31, 2004, at 5:27 AM, Thomas R. Williams wrote:

>
>
> =F0 The aforementioned ECBS obviates the need for the relay.
> =CA
> You could install QSK without changing the biasing method, or change=20=

> the biasing without installing QSK, right?

=F0  A conventional bias relay is too slow to keep up with the =
high-speed=20
RF relays.
However, an ECBS can be used with a slow RF relay.

> =F0 Glitch resistors are not supposed to open. Their job is limit peak=20=

> discharge current during a fault. The trouble with the stock 0.82-ohm=20=

> resistor is that it does not limit current to a reasonable amount.

> Suppose you have=CAthe worst case=CAfault (shorted tube?). 3000 V =
across a=20
> 10 Ohm resistor means 300 Amps. Not much of a current limiter. Should=20=

> the Glitch resistor be a higher value?

=F0  With smallish tubes, yes.  With the typical amp, there's c. 5-ohms=20=

of ESR in the filter caps, so the total =3D 15-ohms-ohms, which limits=20=

peak fault current to c. 200A, a value that 3A diodes can tolerate.
>
>
> =F0 But still not fast enough to keep up with modern transceivers.
>
>  I operate 95% CW and almost never QSK. Don't really care for the mode=20=

> although I know the relays used in QSK would last longer than the open=20=

> frame type.

=F0  All modern radios switch so fast that the amp needs quick relays to=20=

avoid hot-switching -- even if PTT is used.
> =CA
> =F0 Adding a 0.39-ohm shunt R will change the meter calibration. 3A=20
> diodes won't.
> I believe the resistor and diode are in series and then placed in=20
> parallel with the meter movement. I don't see that changing the=20
> calibration.

=F0  There is a sound reason not to put any R in series with the diode.
>
>
> cheerz, Tom
> =CA
> Thanks for the input. After 32 years in ham radio, I still find it=20
> exciting and rewarding. Plus a great bunch of guys (for the most=20
> part).

=F0  I agree.  cheers, Tom