[Hallicrafters] HT-33A Fan Assembly Needed

[Carl]

>
>
> Al Parker wrote:
>> Hi Gary,
>> Yup, you've got it.  I think some of the guys haven't realized that
>> this tube is an external anode, finned, air cooled, tube similar in
>> configuration, but bigger, to  a 4CX350 series, etc.  It requires a
>> specific air flow to properly cool it, and that necessitates more
>> pressure than what's required to cool glass 3-500's, 4-400's, etc.
>> I had a "modified" HT-33 for several yrs, but sold it last yr due to
>> acquiring a Henry 3-KA which replaced it.  You can see at
>> <http://www.boatanchors.org/HT-33hb.htm>  I thought there might be a pic
>> of the bottom, showing the fan, but guess not.  I do have a complete,
>> nearly original, HT-33B that I can drag out & get pix or info if you
>>
>
> The stock fan in the HT33A and B does not move a lot of air, nor does
> the PL172/8295A need a lot with much back pressure.  It'd take one whale
> of a fan to get much back pressure with that tube.  The tube has a very
> large anode, almost twice the size of a 8877, and has a very coarse fin
> structure. It is rated at 1000 watts plate dissipation, can be run from
> class A to C in the 33A and B series with front panel bias adjust. In
> class B at the old legal limit the tube was loafing along and in mine
> only gets warm. IOW at 1000 watts DC input, or 2 KW PEP the tube is
> running only 400 to 500 watts of dissipation, or half it's design max.
>> need.  It's a future project, I do have one good tube for it.  There've
>> been threads on the Halli & BA reflectors every so often abt those
>> tubes, and the fact that most glass ones are gassy by now.  It's said
>> that keeping filament voltage on them every month or 3 is helpful,it
>> might be, but it won't restore a real flat one (experience).
>>
> I've found a lot of duds that died from lack of use. I've also found
> some very old ones that worked just fine. If it hasn't been run in a
> long time, just plug it in and let the filaments run for a few days
> before turning on the plate voltage and hoping for the best.
>
> So far I've had very good luck with the 33Bs but just remember they are
> built for 1 KW DC input, not 1500  out.
> They are also Pentodes and not triodes.
>
> 73
>
> Roger (K8RI)

That will work only if the cathode is the getter. If it is the plate it will 
have to be run. One way is to run low HV and enough positive bias to get 
sufficient idle current; many gassy tubes (not leaking air) can be restored 
that way.

Carl
KM1H