> 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".
A well designed amplifier using 8 VRF-2933 or a pair of the Motorola/
Phillips 1200W TV transmitter "bricks" could be done commercially at
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.
> 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)?
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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