Ahhhh yerself.
I take it then that you have never bothered to read the SB-220 front
panel or the tuneup procedure in the manual.
Or the NCL-2000, SR-2000, Hunter Bandit 2000's, and many others.
The meter time constant was put in the rules at the request of National,
Hallicrafters and others as well as getting an OK from the FCC that
advertising a 2KW PEP amp was OK by them with the above caveat. I was at
National when they formally asked the FCC for an interpetation.
It didnt require rocket science to realize that if the proper voltages
were selected that going from CW to SSB positions would double the
power and maintain the same plate load impedance. In order to save a few
bucks the xfmr iron was the limiting factor anyway for most products and
the manuals stressed using the Tune or CW position for tune up.
The MLA-2500 is a fine amp once owners realized the 8875's were only
rated at 300W dissipation and not 400 as with the 8874. If the input
resistor was not cut out and the amp run per instructions the tubes last
a long time. I use one as the amp for the 2nd station. Its fine at 1000W
in the button out position (labeled differently between versions) and
the regulation is as good as any other comparable amp.
Its mainly incompetent users that gave that amp a bad name while others
praised it. It was a popular DXpedition amp, mine had spent years
traveling around the world on its original set of tubes.
Carl
KM1H
----- Original Message -----
From: "Roger (K8RI)" <sub1@rogerhalstead.com>
To: "Carl" <km1h@jeremy.mv.com>
Cc: "Rob Atkinson" <ranchorobbo@gmail.com>; <amps@contesting.com>
Sent: Monday, November 10, 2008 6:33 PM
Subject: Re: [Amps] QRO Heat management
> Carl wrote:
>> What many also forget or are too young to realize is that many of the
>> older amps were built when the power was FCC regulated as 1000W CW
>> and 2000W PEP SSB INPUT. Those full legal power amps had a CW/SSB
>> switch for
>
> Ahhh... I don't remember any PEP limit on input. Just 1KW average
> based on a plate current meter with a 1/4 second time constant.
> My voice characteristics are such that I used to get over 2KW PEP
> output with the old 1KW average input which included the drive power
> in a GG amp.
>> that reason and I guess a few hams actually used them (;
>>
> I always used them. Tune in the tune position and go full bore for
> operation. The current and voltage ratios were such that the amp was
> properly tuned when switching to the high power position. Many hams
> couldn't get past the idea of tunning up at the power they planned on
> running to get maximum output but many old amps had such poor voltage
> regulation (such as the MLA2500) that you had several hundred watts
> more PEP out when running full bore after tuning in the tun position
> than you did when tuning up in the full bore position. I mentioned the
> 2500 as I had several and they all put out at least 200 watts more
> when tuned in the tune position and then switching to the full power
> position. That means they were also tuned properly and running more
> efficiently at the full power position.
>
> 73
>
> Roger (K8RI)
>> When run at full bore of 1200-1800W OUTPUT on CW the duty cycle warms
>> things up a bit more than at the old limit which is roughly 600-700W
>> output.
>>
>> Wassamatter with AM? Properly adjusted 1500W output linears work fine
>> at 375W carrier which is 1500W PEP. Thats easier on them than RTTY
>> and if using controlled carrier AM its even lighter duty. A DX-60
>> with some audio mods sounds great with a SB-220.
>>
>> Carl
>> KM1H
>>
>>
>>
>>
>> ----- Original Message -----
>> From: "Rob Atkinson" <ranchorobbo@gmail.com>
>> To: <amps@contesting.com>
>> Sent: Monday, November 10, 2008 12:36 PM
>> Subject: [Amps] QRO Heat management
>>
>>
>>
>>> Heat can be an issue with some ham amps built over the past 30 or 40
>>> years (can't say that about all of them since I have not owned all
>>> of
>>> them). There are several reasons for this. When SSB became the
>>> popular voice mode, designers realized they could come up with amps
>>> that would work okay for most users operating ssb and cw (duty
>>> cycles
>>> of no more than 50%) because most transmissions were no longer than
>>> a
>>> few minutes. They could build amps with lighter power supplies,
>>> make
>>> them compact and relatively light weight to sit on a table top, and
>>> pass the lower costs on to the customers.
>>>
>>> These amps were cooled adequately, but some hams complained about
>>> noisy fans. Now we have some ham amps with whisper quiet fans to
>>> make these users happy. I've seen amps advertised and reviewed
>>> positively for being quiet. They work okay for the above described
>>> operation such as a typical ssb ragchew where no transmission is
>>> longer than 5 minutes but if you run RTTY or heaven forbid AM, with
>>> one it will darn near melt down pretty quickly. Another practice
>>> that I think Dentron among others got into, was to try to cram as
>>> much
>>> as possible into the smallest cabinet possible, which never made
>>> sense
>>> to me, but maybe some users thought a compact amp was a good thing.
>>>
>>> So anyway, there's nothing wrong with augmenting the cooling and in
>>> fact you may have to if you have one of these desktop "quiet" amps
>>> and
>>> you want to run slow scan or make long transmissions on cw. In my
>>> opinion the trick is to not have the added fans somehow obstruct
>>> airflow rather than increase it. The goal should always be moving
>>> air
>>> in and out of the cabinet. If the chamber to be cooled is sealed,
>>> you have to be sure the amount of air at any instant being pushed
>>> in,
>>> is the same amount as that being sucked out, otherwise a fan is
>>> going
>>> to be worked against or pushed. This is usually an easy problem
>>> to
>>> fix by adding some vent holes, or having all fans blowing in or
>>> drawing out. The best amps have big cabinets with lots of space
>>> around all the components. I think these days, if you want an amp
>>> like that you have to build it yourself.
>>>
>>> 73
>>>
>>> rob / k5uj
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>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
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>
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