On Wed, Jul 17, 2024 at 12:12 PM, Jim Whartenby wrote:
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You said: "An advantage of freeing up a 5V filament winding is that one can then use it to "buck" the primary so as to accommodate increased AC line voltage.? (I don't have enough auto-transformers [VARIAC's] to go around!)"
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If the power transformer used in the HT-37 is prone to a hard short circuit between the 5 volt heater supply and the associated high voltage winding, then the use of the 5 volt winding to buck the line voltage is a solution which could do real damage.? One would have to do a high voltage test for leakage resistance between the two windings and then hope that the two windings will remain isolated when the 5 volt heater winding is then used to buck the AC line.
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Regards,
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
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I would venture to guess that if an HT32 or HT37 transformer has NOT had a FIL-->HV short after only 60 years or so,??? If probably never will.? I would submit that a HIPOT test wouldn't be required.? If it didn't short @ 700+ volts DC, it probably won't at a line voltage peak of only 170V .
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But enough Collins 516-F2 power supply tube rectifiers have internally "flashed" and prompted a LOT of people to consider using solid state rectifiers. to make me at least a little wary any up to 60 year old 5U4, 5V4 , 5R4 and quite frankly most all vacuum diodes.???
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Certainly not all of them fail and they're easily replaceable.? Transformers OTOH are well,? replaceable too but they seem to cost a tad more!
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I am of course not suggesting the solid state rectifier swap is a complete cure-all.? But it is a good alternative if done right.
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ymmv
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73/Rick
W4XA
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Rick W7IMM