>> If there ever were candidates for a tube swap the HT-33A & B's are right
>> up there with the MLA-2500 and HT-41. There is nothing wrong with the
>> tubes except availability and cost.
>>
>> The sraight 33 uses a pair of 4CX300A's which are another variant of the
>> 4CX250's. One of a kind twist lock socket and about 100W more than the
>> 250. They have a reputation of seal leakage over time.
>>
>> I have a SX-115/HT-32A and might look for a tubless HT-33A/B to
>> experiment
>> on. The 8877 would appear to be a "natural" in place of the Penta which
>> had a reputation of being extremely clean; I never tested one.
>
> The 8295A is much larger than the 8877 although it only has 1000 watts
> plate
> dissapation compared to the 1500 for the 8877. OTOH the fins are coarse
> with lots of space so the tuve is easily cooled with a fan rather than
> requiring a squirrel cage blower to produce plenty of back pressure. Those
> fins are very soft and easily bent, but they are easily straightened as
> well
> so. In a way being so soft they protect the insides from damage from some
> pretty good bumps. The biggest problem with that conversion as I see it
> would be adding suficient cooling in an unobtrusive manner. That and the
> plate transformers all have 110 VAC primaries only.
>
> 73
>
> Roger (K8RI)
The Dentron original DTR-2000L had only a muffin fan on the 8877. Not good
for heavy use as it was replaced by a small squirrel cage in later models.
In the HT-33 anode temperature testing would tell if it would be safe to use
at a somewhat reduced output with the existing fan. I suspect that 800-1000W
would be OK; the Dentron could get up to 1700 or so.
Many other KW output amps work OK at 120V as long as a stiff line and a
heavy cord are used. All my operating positions have a 25A 120V outlet as
well as 25A 240V. My idea is to use it only for occassional non processed
SSB ragchews.
It's not an instant swap as metering, bias and protection circuitry have to
be changed/added; filament also? The socket would go on a plate bolted to
the original socket holes. Id make the conversion as unobtrusive and
reversible as possible in case someone 50 years from now thinks its a
collectors item.
Carl
KM1H
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