[Amps] LK 550-ZC

[Dick Green WC1M]

I use mostly CW, with varying lengths of transmission. But there's a big
difference between the modes I use for operating and what I did to test the
tube temperature before and after the mod. I transmitted continuous CW; I
went key down, continuous RF for as long as I could at full power; I reduced
power and transmitted even longer, as I would if I was doing a typical RTTY
QSO, and repeated the sequence for several minutes. I also measured the tube
temperature while operating in CW contests. I did my best to simulate the
toughest conditions I expected the amp to endure, driven not just by me but
by subsequent owners, without exceeding the tube ratings.

I wouldn't be surprised if my testing was more rigorous and my measurement
equipment was more accurate than what Denny used when he designed the amp.
No way I wanted to replace three 3-500Zs or any other components in the amp.

73, Dick WC1M

> -----Original Message-----
> From: Rob Atkinson [mailto:ranchorobbo at gmail.com]
> Sent: Saturday, March 17, 2012 1:14 PM
> To: Dick Green WC1M
> Cc: AMPS
> Subject: Re: [Amps] LK 550-ZC
> 
> What modes do you operate?  How long are your transmissions?
> 
> 73
> 
> Rob
> K5UJ
> 
> On Sat, Mar 17, 2012 at 11:29 AM, Dick Green WC1M <wc1m73 at gmail.com>
> wrote:
> > Are you basing this on fact or speculation?
> >
> > I was very careful to measure the tube temperatures at the highest
> > acceptable duty cycle both before and after the mod. I'm confident
> > that the modification I made is both safe for the tubes and
> > acoustically superior to the original design.
> >
> > Remember, my LK-550ZC has a thermal sensor that will kick the fans
> > into high speed as needed. If it's not switching to high speed because
> > I increased the fan speed at the low-speed setting, then that's a good
> > thing. If my reduction of speed in high-speed wasn't effective, then
> > the amp would spend more time at high speed. It doesn't.
> >
> > 73, Dick WC1M
> >
> >> -----Original Message-----
> >> From: Rob Atkinson [mailto:ranchorobbo at gmail.com]
> >> Sent: Saturday, March 17, 2012 8:19 AM
> >> To: Dick Green WC1M
> >> Cc: Carl; Paul Kraemer; AMPS
> >> Subject: Re: [Amps] LK 550-ZC
> >>
> >> If you have 3 3-500s to cool and you operate any serious duty cycle
> >> at what the amp is capable of you probably need the high speed and
> >> accept the noise problem.
> >> hams obsess about fan noise far too much if you ask me.
> >>
> >>
> >> 73
> >>
> >> Rob
> >> K5UJ
> >>
> >> On Sat, Mar 17, 2012 at 12:16 AM, Dick Green WC1M <wc1m73 at gmail.com>
> >> wrote:
> >> > Guess I have a real late one: it has the fan speed temperature
> sensor.
> >> > The stock fan speed is too slow in low-speed mode, so the fan
> >> > cycles low-high constantly. And it's like a freight train at
> >> > high-speed. I increased the RPM at low-speed so it goes to high
> >> > speed much less often. That didn't raise the noise level very much.
> >> > I also decreased the RPM in high-speed mode, which reduced the
> >> > sound considerably, but didn't appreciably affect the cool-down
> >> > time to low speed. I used a temperature probe to make sure the tube
> >> > temperatures stayed well
> >> within spec.
> >> >
> >