Re: [Amps] Re: Drake L7 newbie - Summary

[rlm <r@somis.org>]

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

>  The aforementioned ECBS obviates the need for the relay.
>  
> You could install QSK without changing the biasing method, or change 
> the biasing without installing QSK, right?

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

>  Glitch resistors are not supposed to open. Their job is limit peak 
> discharge current during a fault. The trouble with the stock 0.82-ohm 
> resistor is that it does not limit current to a reasonable amount.

> Suppose you have the worst case fault (shorted tube?). 3000 V across a 
> 10 Ohm resistor means 300 Amps. Not much of a current limiter. Should 
> the Glitch resistor be a higher value?

  With smallish tubes, yes.  With the typical amp, there's c. 5-ohms 
of ESR in the filter caps, so the total = 15-ohms-ohms, which limits 
peak fault current to c. 200A, a value that 3A diodes can tolerate.
>  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 
> although I know the relays used in QSK would last longer than the open 
> frame type.

  All modern radios switch so fast that the amp needs quick relays to 
avoid hot-switching -- even if PTT is used.
>  
>  Adding a 0.39-ohm shunt R will change the meter calibration. 3A 
> diodes won't.
> I believe the resistor and diode are in series and then placed in 
> parallel with the meter movement. I don't see that changing the 
> calibration.

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

  I agree.  cheers, Tom
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