Hallicrafters HT-33A Power Amplifier
The amplifier is now being worked on. No idea if it can be salvaged.
This unit has been modified to a HT-33B by a quick look along with several additional modifications.
If the PL-172 final is bad, it will probably be parted out in the future.
May 12, 2010 - Found that the filament transformer is fried. I disassembled the transformer and found the primary was shorted to the core. Looks like there is a real possibility that the PL-172 has gone south.
I am in the process of trying to locate a used transformer. It has a 2.5 VAC secondary that draws 10 Amps that feed the 866A rectifiers for the 2700 Volt HV PL-172 plate supply. A replacement transformer can be custom made, but the price of this transformer in 1963 was $145.00. Todays price is way more than I would spend to get this amp operational.
Since this transformer was replaced once already, it could be a design problem with the amp. This is a 3 winding transformer that supplies the 350 Volt bias supply and the 6 Volt tube filament line along with the HV rectifiers. The cost of this transformer and a PL-172 replacement would definitely be prohibitive.
Case closed unless I can find a filament transformer to experiment further.
This unit has been modified to a HT-33B by a quick look along with several additional modifications.
If the PL-172 final is bad, it will probably be parted out in the future.
May 12, 2010 - Found that the filament transformer is fried. I disassembled the transformer and found the primary was shorted to the core. Looks like there is a real possibility that the PL-172 has gone south.
I am in the process of trying to locate a used transformer. It has a 2.5 VAC secondary that draws 10 Amps that feed the 866A rectifiers for the 2700 Volt HV PL-172 plate supply. A replacement transformer can be custom made, but the price of this transformer in 1963 was $145.00. Todays price is way more than I would spend to get this amp operational.
Since this transformer was replaced once already, it could be a design problem with the amp. This is a 3 winding transformer that supplies the 350 Volt bias supply and the 6 Volt tube filament line along with the HV rectifiers. The cost of this transformer and a PL-172 replacement would definitely be prohibitive.
Case closed unless I can find a filament transformer to experiment further.