[Hallicrafters] HT-33A Fan Assembly Needed

[Roger (K8RI)]

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)

> 73,
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
>
>
> On 4/16/2010 3:53 PM, garyislander wrote:
>   
>> Thanks Al,
>> Thats what it looks like to me.
>> A large dia. fan with about 8-10 blades.
>> It seems to be slightly larger in dia. than the tube and shroud.
>> It mounts below the PL-172 tube socket.
>> The case bottom vent plate is missing along with the fan assembly.
>> This amp probably had problems years ago.
>> But for free....I will try to salvage it if I can.
>> Most likely worth the effort.
>> Gary K1MQ
>>
>> ----- Original Message ----- From: "Al Parker" <anchor at ec.rr.com>
>> To: "Halliqth" <hallicrafters at mailman.qth.net>
>> Cc: "garyislander" <gary at garyislander.com>
>> Sent: Friday, April 16, 2010 3:40 PM
>> Subject: Re: [Hallicrafters] HT-33A Fan Assembly Needed
>>
>>
>>     
>>> The HT-33 fan is 6 or more inches in dia., not just a small muffin fan.
>>> It provides cooling air under some pressure to the tube, which is in a
>>> shroud.
>>> 73,
>>> Al, W8UT
>>>
>>>       
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