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Author Topic: 6m amplifiers  (Read 15618 times)
N8IK
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« on: August 20, 2003, 11:43:13 AM »

There are several mfgs. that sell HF amps that also do 6m. But Alpha and ACOM also sell dedicated 6m amps.  What's so special about a 6m-only amplifier?  Pretty pricey for a single-band amp!
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CW559
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« Reply #1 on: August 20, 2003, 12:52:49 PM »

Like anthing else, they charge what they can get for them...whatever the market will bear. As far as I know, only Icom and ACOM offer amps that operate on both hf and 6 meters.
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WB2WIK
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« Reply #2 on: August 20, 2003, 05:04:38 PM »

Commander also makes a "6m only" high-powered amplifier, and so does Henry -- in fact, they make a few models from about 750W PEP to >1500W PEP output.

Considering most of the cost of such an amplifier is in the enclosure, power supply components, tubes, tube sockets and chimneys, metering, cooling elements and T-R switching components and *not* in the RF circuitry, it's not surprising a 6m high-powered amplifier should cost just a tad less than a bandswitched HF amp.  In a 6m-only amp, the only cost savings are the bandswitch, a few inductors and a few capacitors...all of which might cost $100.

WB2WIK/6

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N8IK
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« Reply #3 on: August 21, 2003, 09:52:46 AM »

But what's the advantage of a 6m-only amp as opposed to using a 160-6 amp on 6m?  What is optimized for 6m that would really make a difference on the magic band?
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WB2WIK
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« Reply #4 on: August 21, 2003, 11:45:03 AM »

The only advantage I can think of for a "6m only" amplifier is improved efficiency, which results from the elimination of parasitic components not required for 6m operation.  

For example, by eliminating a bandswitch and all its interconnections, we reduce unwanted series inductance as well as stray capacitance which will improve overall efficiency because the Q of each component can be higher.  By optimizing the plate RF choke, plate coupling (DC block) capacitor(s), filament chokes (if used, as in a GG circuit) and other items specifically for 6m, the amplifier is not only likely to be more efficient, but also more stable as it is very unlikely that VHF components will have undesired (parasitic) resonances.

When I build a 6m only high-power (tube) amplifier, I always use a very high-Q and small-range (c. 2-30 pf) vacuum variable capacitor for plate tank tuning; an "HF+6" amp may not use such a stellar component, and as a result may be tricky to tune.

However, the improvement in efficiency might only be 10% -- I wouldn't expect miracles.  (Still, 10% at 1 kW is 100W less to be dissipated as heat in various parts.)

A "6m only" amp is also less likely to fail, assuming proper design, since it's a lot simpler.

WB2WIK/6
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CW559
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« Reply #5 on: August 21, 2003, 11:52:01 AM »

One advantage of the 6 meter only amps is that if someone wants to run full legal power...only some of the single band 6-meter amps offer it...such as Commander and Henry. Another advantage would be the slightly lower cost. Another would be if the operator only operates on 6, there would be no need for the hf bands...if only operating on 6...the additionally switches/controls would be nothing but clutter and/or something else something to failure. Also, a single band amp, for any band, is likely to be more effecient than something built to be a "compromise" for multiple bands.
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WW1Z
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« Reply #6 on: August 21, 2003, 02:15:22 PM »

Back when I was in the working for a printer manufacturer I was really surprised by the difference between what they cost going out the plant door and what they cost at the computer store, this was 20 years ago. There are lots of "hidden" costs to things that will be the same for a multiband or single band amp. Plus they don't sell anywhere near as many 6m only amps, raising the unit cost. Which can easily erase the savings of a bandswitch etc. of a multiband amp. Back in the 80's Celestron sold a 5 inch version (C5) of their still popular 8 inch C8. Not selling anywhere near as many C5s meant they cost more to make than the bigger C8, but, they had to sell for less!
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K7VO
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« Reply #7 on: August 21, 2003, 11:24:29 PM »

Tokyo Hy-Power make both HF/6m amps (the HL-2KFX is 1.5KW on HF, 1KW on 6m) and dedicated 6m amps.  Yaesu also make an HF/6m amp.

73,
Caity
K7VO
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WA9SVD
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« Reply #8 on: August 22, 2003, 03:59:42 AM »

As Steve, WB2WIK said, a single-band 6 M (or any single band, for that matter) WILL be more efficient that a multi-band amplifier, because the amp design is optimized for use on that single band.
    As K7VO pointed out, Tokyo Hypower makes a combination HF/6M amp. with 1500 W. out on HF, but only 1000 Watts out on 6M.  Whether the reduced power is because the additional power goes up in heat (reduced efficiency) or because the circuit has to be de-rated because it is not an optimum design for 6M, it points to a compromise design, and it's 6M that has to make the concession.
    Granted, the difference between 1000 and 1500 watts OUTPUT is probably not significant, but if it's going up in heat due to inefficient circuit design on 6M, it is a LOT of electricity to waste!
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WB2WIK
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« Reply #9 on: August 22, 2003, 12:10:30 PM »

In that case, if the extra 500W is just heating the room, I would worry a lot more about what else it's heating, rather than the electric bill!

WB2WIK/6
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W8MW
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« Reply #10 on: August 22, 2003, 12:38:17 PM »

FCC emission standards get much tighter on amplifiers operating above 30MHz.  The HF spec for spurious emissions is -40dBc and it becomes
-60dBc on 6 meters.  In many cases monoband amps achieve better harmonic output specs. ACOM for example shows the 6 meter monobander 4dB cleaner than their 160-6 unit.

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WA9SVD
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« Reply #11 on: August 23, 2003, 03:34:15 PM »

<<by WB2WIK on August 22, 2003
                                                                                              "In that case, if the extra 500W is just heating the room, I would worry a lot more about what else it's heating, rather than the electric bill!"  >>

    You mean the plate tank circuit ISN'T supposed to glow "cherry red?"   <GRIN>

    I'm sure the HF/6M combo amps reduce the power input on 6M, BECAUSE of inefficiency in the RF circuits, meaning they can't operate at the full input to supply 1500 W. out, but also because the output devices and/or power supplies (especially in solid state amps) can't withstand or develop  the additional input power necessary to provide a full 1500 W on 6M, even if they CAN on the lower bands.  It's just not reasonable to think a design that works at 160M will perform as well on 6M. There is ALWAYS a compromise, and that's usually at the expense of 6M, as that's probably used less often that the other bands, if one uses an amp.  And as frequency increases, circuit loss and efficiency go down.  So 6M suffers, unless an amp is optimized for 6M.
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OBSERVER
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« Reply #12 on: September 01, 2003, 12:54:24 PM »

Market demand and profit margin.  Up until a few years ago a majority of Hams did not have radios that could effectively drive a kW class amplifier. Additionally, 6m for many years has been evil taboo for neighbor relations (RFI,  TVI).  With all of the CC&R problems these days, many Hams would prefer to remain low key.  So, if the market does not demand 6m power amplification why add the necessary circuitry if it probably won’t be used?  Almost any technical issue can be overcome if the market demands.  Adding 6m circuitry to a HF amplifier design is pretty simple.
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