Dentron MLA-2500 Question
 

Gary Schafer wrote:
On 26 May 2006 03:09:34 -0700, wrote:


First, power you read on RF power meters is RMS power. Peak envelope
power is the peak value of short term RMS power, average power is the
short term average of RMS power. This is why for CW PEP and average
power is the same, while for SSB and AM it is not.

If you sustitute the word AVARAGE in place of RMS this will be
correct. There is no such thing as RMS power. :)

By RMS power, I mean the power derived from RMS voltage or current as
opposed to using the PEAK value of voltage and/or current to determine
power. I suppose I could have said effective or heating power, or power
derived from RMS values of voltage or current.

It gets too confusing when we say average power is the average of the
average power.

By the way, there is no such thing as avarage power. :-)

73 Tom

Dentron MLA-2500 Question
 

In article . com,
wrote:

Gary Schafer wrote:
On 26 May 2006 03:09:34 -0700, wrote:

There is no such thing as RMS power. :)

By RMS power, I mean the power derived from RMS voltage or current as
opposed to using the PEAK value of voltage and/or current to determine
power. I suppose I could have said effective or heating power, or power
derived from RMS values of voltage or current.

It gets too confusing when we say average power is the average of the
average power.

By the way, there is no such thing as avarage power. :-)

On average, anyway. 8-))

Chris.

Dentron MLA-2500 Question
 

Update,

My Dentron MLA-2500 has taken a back seat to my sons HS graduation, and
the 20th anniversary to my XYL. That said, I did sneak in a little time for
a few things:


1.) On 160 meters the 1000pf fixed loading capacitor is placed in parallel
with the 80 meter 1000 pf fixed loading capacitor. These are then in
parallel with the variable 500 pf (max) load control. Not much tuning range
here. The Dentron schematics are clearly wrong by not showing this. Sure
could use a bigger loading variable, and less fixed C for more tuning range.

2.) When replacing the RF PA plate load impedance with a carbon comp
resistor between 1500-2500 ohms and hooking my RF impedance bridge (Autek)
to the linear's 50 ohm output, I get a SWR null on all bands 160-10 meters
by tuning the pi-net for each band. This makes me want to reverse engineer
that pi net to figure out whatever the loaded Q may be, and to start
optimizing for my use with a 8877. I still agree with Tony that those
ceramic loading capacitors may be the crux of the problem because they are
not made of the right stuff for carrying hi RF currents; instead these are
made for bypass applications.

3.) The Alpha folks are trying to build a chimney for me with their Silastic
RTV material. I think they are either going to charge me an arm and a leg,
or kick the order back. This will be a custom design, and not an off the
shelf part. I may go back to the solid Teflon block idea, and try to find a
place that will machine it.


With SSB, or AM, doesn't a wattmeter show the average (over several
sylables) reading of the RMS power? :-)

Jim
WD5JKO

Dentron MLA-2500 Question
 

On Sun, 28 May 2006 13:47:35 GMT, "JC" wrote:



Update,

snip

3.) The Alpha folks are trying to build a chimney for me with their Silastic
RTV material. I think they are either going to charge me an arm and a leg,
or kick the order back. This will be a custom design, and not an off the


Ahhhh... That is just a pice of Silastic (TM) sheet wide enough and
long enough to form a chimney when wrapped around the tube. I can't
imagine it'd take much engineering. It's a very crude, but effective
design and easy to make if you have the material.

shelf part. I may go back to the solid Teflon block idea, and try to find a
place that will machine it.


With SSB, or AM, doesn't a wattmeter show the average (over several
sylables) reading of the RMS power? :-)

Some do and some don't. There are a number of watt meters including
at least one Bird model that are capable of measuring PEP. Even the
MFJ tuners have that capabililty but I don't know how accurage they'd
be.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com


Jim
WD5JKO

Dentron MLA-2500 Question
 

"Roger" wrote in message
...
On Sun, 28 May 2006 13:47:35 GMT, "JC" wrote:

Ahhhh... That is just a pice of Silastic (TM) sheet wide enough and
long enough to form a chimney when wrapped around the tube. I can't
imagine it'd take much engineering. It's a very crude, but effective
design and easy to make if you have the material.



Roger,

I proposed a single rectangular piece to wrap like they do on their 8874
amps. I even gave them dimensions, and a good picture of my 8874 mounted in
the amp. A round continuous piece would also work. So far two business days
have elapsed without a reply from Alpha. I hope to hear from them on
Tuesday. I'll keep you posted.

For my brief tests I used a 10" long X 2" wide X .02" strip of Mylar
wrapped around the tube. It worked fairly well, but got de-formed from the
heat. I later jumpered the fan resistor to speed up the cooling fan. For
some reason the MLA-2500 fan speed relay was not kicking in the high speed
mode when keying the amp. I need to look further into that wiring, and see
what is going on there. There is a button to enable the high speed fan
option, but it does nothing until the thermal Klixon OT-switch clicks on,
and then the fan goes to hi speed.

Jim

Dentron MLA-2500 Question
 

On Sun, 28 May 2006 19:41:21 GMT, "JC" wrote:


"Roger" wrote in message
.. .
On Sun, 28 May 2006 13:47:35 GMT, "JC" wrote:

Ahhhh... That is just a pice of Silastic (TM) sheet wide enough and
long enough to form a chimney when wrapped around the tube. I can't
imagine it'd take much engineering. It's a very crude, but effective
design and easy to make if you have the material.



Roger,

I proposed a single rectangular piece to wrap like they do on their 8874
amps. I even gave them dimensions, and a good picture of my 8874 mounted in
the amp. A round continuous piece would also work. So far two business days
have elapsed without a reply from Alpha. I hope to hear from them on
Tuesday. I'll keep you posted.

For my brief tests I used a 10" long X 2" wide X .02" strip of Mylar
wrapped around the tube. It worked fairly well, but got de-formed from the
heat. I later jumpered the fan resistor to speed up the cooling fan. For
some reason the MLA-2500 fan speed relay was not kicking in the high speed

I'm trying to remember how the fan was set up in the 2500. I think
you are going to need to pressurize the chassis to get enough air flow
through the fins of the 8874s and they do take more air with a higher
pressure drop than the originals. Those little suckers are expensive
too.

Good Luck,

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

mode when keying the amp. I need to look further into that wiring, and see
what is going on there. There is a button to enable the high speed fan
option, but it does nothing until the thermal Klixon OT-switch clicks on,
and then the fan goes to hi speed.

Jim