16-07-2015, 08:11 AM
(This post was last modified: 16-07-2015, 08:12 AM by Radio Fixer.)
This was interesting to me in Alan D's ARF posting.
"The originals were often wet electrolytics, which would purposely leak above their rated voltage and hold the voltage down. They could absorb tens of milliamps without harm, being "liquid-cooled" so to speak. In the 1940s there were "wet replacements" available that were dry but could still handle the initial surge."
Its one of the reasons we fit 450 to 500V reservoir capacitors for, as with a directly heated rectifier the HT soars skywards (420V in one measurement) whilst the indirectly heated other valves, and particularly the output take there slow warm up. In some cases an indirect sub. can be used for the original directly heated type. HT only climbs slowly (to 340V in the same tests) and is lower by say 10%, (as the indirect will have a larger drop across it)which can be useful.
Gary
"The originals were often wet electrolytics, which would purposely leak above their rated voltage and hold the voltage down. They could absorb tens of milliamps without harm, being "liquid-cooled" so to speak. In the 1940s there were "wet replacements" available that were dry but could still handle the initial surge."
Its one of the reasons we fit 450 to 500V reservoir capacitors for, as with a directly heated rectifier the HT soars skywards (420V in one measurement) whilst the indirectly heated other valves, and particularly the output take there slow warm up. In some cases an indirect sub. can be used for the original directly heated type. HT only climbs slowly (to 340V in the same tests) and is lower by say 10%, (as the indirect will have a larger drop across it)which can be useful.
Gary
