[Amps] GU-84B Conversion (Re-thought)

[Roger (sub1)]

On 4/13/2011 8:31 PM, Gudguyham at aol.com wrote:
>
> In a message dated 4/13/2011 8:22:42 P.M. Eastern Daylight Time,
> km1h at jeremy.mv.com writes:
>
> If you  can find PL-175A's they will equal a 3-500Z watt for  watt..
>
>
> Carl, I know you have a few years on me, so when I came on the scene the
> 3-500's were so popular that the PL-175A tubes were history by then. Sure, I
> have tried 4-400's in place of 3-500's so I know that they work OK in GG
> with a  little less gain.  I have never tried a PL-175.   As I recall  didn't
> Hallicrafters make an amp with that tube?  I looked up the 175 and  it seems
> it is a tetrode.  When you mentioned it before, did you mean "watt  for
> watt" in GG or AB1?
>

Hallicrafters sold the HT33A and HT33B which are different iterations of 
the same amp. They used the PL172/8295A which was a glass/metal external 
anode pentode with a 1 KW anode dissipation.  The anode is quite large 
with a coarse fin structure making them easy to cool without a lot of 
back pressure.  The PL172 with the glass to metal seals tend towards 
getting gassy and particularly so if they just set around.  There is 
also a straight 8295A which is the ceramic/metal version of the same 
tube.  IIRC they are almost double the size of the 8877 and tested used 
ones may bring more than a new 8877. They are easily worth more than the 
price of the HT33B.  They were brining $2400 USD for a tested and 
guaranteed used one a couple years back.

Tested good used ones (without the guarantee) are considerably cheaper, 
but OTOH still expensive.

73

Roger (K8RI)