On 4/29/2012 8:43 PM, Joe Subich, W4TV wrote:
>> Yes, I prefer SS over tubes *but* I want one that is capable of at
>> least 2 KW nominal CCS or 2.5KW PEP to run the legal limit on any
>> mode contest style. To me that would be a valid comparison.
> No, that's an apples to oranges comparison since you want a solid
> state amplifier to be capable of 65% "headroom".
No, it's exactly what I expect out of a tube amp, and I have one that
will do it. So it's a valid comparison if I want the same thing out of SS.
>
> A well designed amplifier using 8 VRF-2933 or a pair of the Motorola/
> Phillips 1200W TV transmitter "bricks" could be done commercially at
I don't want a 1200 watt amp that has to be derated for digital.
> a price that is competitive with the top of the line Alpha but FCC
> rules make it very impractical for any US manufacturer to bother to
> do so.
FCC rules mean I have to import a 2KW nominal, 2.5KW PEP amp to have an
amp that will run the legal limit any mode key down.
>> BTW I had ah HL1.5KFX for a few months and nary a complaint, *except*
>> It needed a very low SWR to let it output full power. I replaced it
>> with a manual tune, amp that will run 2 KW nominal and so far am very
>> happy with it.
> Again, apples to oranges ... you would never run your manually tuned
> amplifier into a high SWR without tuning it for that SWR. Why would
> you expect an untuned solid state amplifier to handle a high SWR
> without adding a tuner (either manual or automatic)?
Please note, I said, very low SWR. I can move 40 or 50 KHz on 40
without having to touch the amp or line tuner.
With the HL1.5KFX I'd have to retune. I can currently go from a 1.1:1 to
a 1.3:1 and see no difference in output.
I could not do that even at 1.2:1 with the SS amp.
73
Roger (K8RI)
> 73,
>
> ... Joe, W4TV
>
>
> On 4/29/2012 8:24 PM, Roger (K8RI) wrote:
>> On 4/29/2012 9:58 AM, Joe Subich, W4TV wrote:
>>>> I'm an ardent "tube" amp man for this reason. They're significantly
>>>> more robust and bullet proof in the longevity stakes.
>>> I don't believe that for a minute if you compare apples to apples.
>>>
>>> Most of the tube designs have been significantly "over engineered".
>>> That is, the tubes have excess plate dissipation for the power output
>>> and grids that will take a significant beating.
>> Which is a plus for tubes.
>> And the protection circuitry for a SS amp is extremely elaborate.
>> Add to that the aging of the transistors. On an hour by hours basis,
>> transistors "operated well within their limits" will last many times an
>> equivalent tube.
>> Semiconductors do age. The dopant material migrates across junctions and
>> as the power density goes up so does the cooling requirements and they
>> are still limited by the delta T internally.
>>
>>> If one looks at amplifiers like the MLA-2500 or Alpha 76 series with
>>> tubes that have grid dissipation in the 10 watt range and no grid
>>> protection ... tubes that have become unobtainium ... there are plenty
>>> of owners that have been reduced to tears at the cost (or lack) of
>>> replacements.
>> But had they operated those tubes well within their ratings they'd still
>> be running strong.
>>
>>> Even the 8877 is not exactly an "unforgiving" tube
>> I've always considered it to be a fragile tube, but never had one fail
>> and I only had the old amps that had no protection in them except a main
>> fuse.
>>
>>> when used in designs that lack proper grid protection and the 3-500Z
>>> are not safe in an unmodified TL-822.
>> I've seen 3-500s last many years with no protection at all in some of
>> those old amps as long as they weren't over driven.
>>
>>> Given proper design and protection, modern solid state devices will
>>> last a lifetime unlike tubes that *will* need to be replaced due to
>>> filament/cathode aging. Transistor amplifiers don't suffer from
>>> catastrophic arcing and certainly don't represent the electrocution
>>> danger of tube amplifiers.
>> But they are very sensitive to nearby lightning strikes or plain old ESD
>> from walking across a carpet.
>>
>>> There are pros and cons on both sides of the solid state vs. tube
>>> debate but choose the appropriate amplifying device, operate it
>>> within its design parameters, keep it cool and provide the proper
>>> protective circuits and either will provide years of trouble free
>>> service.
>> Agreed, but I also agree with Carl in that the SS legal limit amps with
>> plenty of overhead have a ways to go before prime time.
>> I'd not compare them to tried and true, top end designed tube amps like
>> Alphas, or any of the other properly engineered amps. Performance,
>> including overhead, the SS amps are new designs of which most are
>> pushing the ragged edge and on a price per watt the SS are about twice
>> the tube amps. OTOH some tubes are becoming very expensive due to lack
>> of demand.
>>
>> Yes, I prefer SS over tubes *but* I want one that is capable of at least
>> 2 KW nominal CCS or 2.5KW PEP to run the legal limit on any mode contest
>> style. To me that would be a valid comparison. I know of no SS amps
>> available for amateur service that will do that. So for the time being
>> I am far more comfortable with tubes.
>> BTW I had ah HL1.5KFX for a few months and nary a complaint, *except* It
>> needed a very low SWR to let it output full power. I replaced it with a
>> manual tune, amp that will run 2 KW nominal and so far am very happy
>> with it.
>>
>> 73
>>
>> Roger (K8RI)
>>
>>> 73,
>>>
>>> ... Joe, W4TV
>>>
>>>
>>> On 4/24/2012 9:32 PM, Leigh Turner wrote:
>>>> It's a pity vendors of solid-state QRO amplifiers don't offer
>>>> purchasers an
>>>> accompanying low-cost insurance policy to cover them against the
>>>> inevitable
>>>> day when the finals blow up for whatever reason and reduce the owner to
>>>> tears at the huge expense of carrying out out-of-warranty repairs.
>>>>
>>>> I'm an ardent "tube" amp man for this reason. They're significantly more
>>>> robust and bullet proof in the longevity stakes.
>>>>
>>>> Leigh
>>>> VK5KLT
>>>>
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