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 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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