Alex Eban wrote:
> Pardon my ignorance, but I was under the impression that we, as hams, are
> entitled to a maximum of 1500W input power; maybe 2000W or so in the States.
> What is all the talk on the monster transformers doing here on a ham related
> forum?
> Alex 4Z5KS
>
Well, just doing some fast math, running 1500 out on CW or better yet,
digital where the duty cycle approaches 100% for a few minutes with 60%
efficency GG the the transformer needs to be capable of 2500 watts CAS
with no head room. I'd want 3 KVA CCS for comfort. If running a
tetrode AB1 we're getting closer to 3 KW (or more)CAS or preferably 3.5
to 4 KVA CCS neglecting other losses. Most commercial ham amps run the
minimal amount of iron.
Were I to build and I may do so (I'd sure like to and I can still
dream), a GU84B which I believe is the equivalent of a 4CX-2500, I'd
certainly want to run it as linear as possible. I'd be willing to
settle for a 3 KVA transformer to keep it compact and I don't normally
run digital. OTOH I could use the same tube for six and two meters.
The thought of running one on two FM has crossed my evil mind, and I
tell the local guys my Henry 2002A is for packet <:-)), but I have an
aversion to splinters and feathers while I'm allergic to tar. Most know
I'm not serious, but the occasional outsider can get kinda feisty. OTOH
I'm not against running the legal limit on two-meters FM simplex. I'd
add a second 3CX-800 to the 2002A, but it doesn't have the power supply
to support it, nor am I sure how to modify the tuned circuit to handle
two tubes. I'm also limited by legal exposure levels even with the
antenna array at 130'. to 380 watts into the antennas at 100% duty
cycle. OTOH if I go to normal operation at 3 minutes on, 6 minutes off
it's 33% or 495 watts into the antennas. SSB which is 20% of that duty
cycle raises the power int he array to well over the legal limit for
exposure level limits. 160 through six-meters is limited only by the
legal limit even at 100 % duty cycle and that is with the big 7L C3i at
115 feet.
At any rate a 3 to 4 KVA transformer is not at all out of line for a
legal limit amp (1500 out) if it is going to be running heavy duty
digital or contesting although I doubt most commercial amps will come
near that.
73
Roger (K8RI)
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Ian White GM3SEK
> Sent: Sunday, March 01, 2009 10:17 AM
> To: amps@contesting.com
> Subject: Re: [Amps] "Big Iron" transformer source in UK?
>
> DAVE WHITE wrote:
>
>> Folks
>>
>
>
>> For any UK-based people on the list, this firm appear to be a good
>> source for custom-wound transformers: http://www.jmstransformers.co.uk/
>>
>
>
>> They recently quoted me GBP 525 (plus the dreaded 15% tax, unless you
>> can claim it back) for 4.5kv at 10kvA. That's by far the cheapest
>> quote I had recently. They can turn around orders in a week or so, but
>> do a maximum of about 5kV which is fine for my purposes.
>>
>
>
>> DOES ANYONE UK-BASED KNOW OF ANY OTHER GOOD SUPPLIERS?
>>
>
> There are two in: http://tinyurl.com/ukcomponents (go to the page and
> use your browser to find "transformers").
>
> SP Wound Components are excellent for small custom transformers - they
> made the multi-winding transformers that we used to supply for the
> Tetrode Boards, and are still happy to make one-off special orders.
> Their limit is about 1kVA.
>
> Harrison & Greenwood are more comfortable with larger transformers
> (presumably you got quote from them?).
>
> A couple of points to the group: transformer manufacturers tend to use
> the "kVA" rating as a headline figure to indicate the overall
> size/weight; but that rating is for a resistive load. It is not
> meaningful for our kind of load involving a rectifier and capacitor
> filter. For good HV regulation in a real-life amplifier, we need
> transformers with a much higher "headline" kVA rating than the rectified
> DC output.
>
> Thanks again to Steve G8GSQ for the link to the "PSU Designer" program
> by Duncan Munro M0KGK. When the transformer manufacturer comes up with a
> design proposal, you can use PSUD to check how it will perform in a
> real-life PSU.
>
>
>
>
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