The AM Forum

I'm in process of building a HB PA using an Eimac (PL-172) / 8295A tube.

The PA will be similar to the Hallicrafters  HT-33A/B that uses that particular tube.

While reviewing eham.net reviews for the HT-33A/B, there is reference to a metallic "Heatsink" that is affixed to one of the socket base pins....the reviewer cautions about dire tube consequences if this heatsink is not installed.

Both the Eimac spec sheet for the 8295A  and the Penta PL-172 spec sheet (1962 version)  do not refer at all to this heatsink, therefore, this appears to be a specific Hallicrafters design requirement to keep this pin cool.

Wondering if someone can describe or otherwise provide a picture of this heatsink on this pin ??  Which pin is this heatsink attached to ??

Thanks in advance.

Bill

That amplifier was badly under cooled. Instead of using a squirel cage blower.. There was an anemic bladed fan located under the socket. Down load the Eimac spec sheet for an 8295. Use the recommended socket and chimney.  Ensure that the blower you use provides the proper CFM at that stated water column. That tube will make a lot of power if cooled properly.
 
Johnathan N8QPC

Department of "free advice"?
If you have only ONE tube?
Probably best if you do not go through all the time and effort to build with
that one tube. They are extremely rare.

Suggest using a Ruskie tube of equal Pd or two Ruskie tubes making up a similar
Pd?

                        _-_-bear

It was interesting that Penta said tube is not to be supported by the base/pins, but by the anode preferrably, or the screen grid ring. Hey just one of those tubes with which extra care must be taken, and a 1KW plate is worth some work.

If I had to guess I'd say hallicrafters was heatsinking the control grid.

I understand why some desktop amps use a fan/fans when a blower is indicated. That and plate-transformer undersizement are the two main sins of the form factor.