----- 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 9:36 PM
Subject: Re: [Amps] QRO Heat management
> Carl wrote:
>> 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.
> But prior to the clarification the reg was only 1 KW average input.
> Even with the 1/4 second time constant I don't remember the reg
> stating any PEP limit.
They never came out that way to the general public. It was implied by
the time constant and average 60% plate efficiency. That was in the
letter they sent back.
>>
>> 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.
>>
> Right.
>> 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.
> I ran mine at "tilt" and never had a moments problem with either of
> them.
> OTOH, although it had nothing to do with the power level, I had a low
> voltage cap (bout 5/8" diameter and maybe an inch long) in the
> DTR-2000 blow and I do mean blow. It sounded like a 12 gage had been
> fired right next to me. The metal can hit the inside cover so hard it
> looked like a 38 wadd cutter that had hit a steel plate. Mushroomed
> out quite nicely.
>>
The DTR-2000 is possibly the most poorly designed QRO amp ever sold by a
real company.
Just for starters; how could anyone market an 8877 amp without a grid
current meter and no protection circuitry? And the list goes on.
OTOH Ive built up several for 6M at the stock power level and with a
3800VDC supply. Needless to say a lot of work was necessary to keep all
the smoke inside the coax.
>> 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.
>>
> When I finally moved on mine were still putting out the rated output.
> Sure was different picking up that MLA-2500 and then lifting an Alpha
> 76 <:-)) or an HT-33B
Ive a 76PA on the shelf and didnt notice it being that heavy but I work
out daily with weights. The Alpha 77 and HT33A/B is a lot heavier.
Or the HT-9 I just picked up. 100W out and only 150# !
I grunted lifting that out of the trunk! And got my weight lifting son
to help get it up the stairs and then down into the basement.
Carl
KM1H
>
> 73
>
> Roger (K8RI)
>> 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
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps@contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>
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>>>>
>>>>
>>>
>>
>>
>
>
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