Locked Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýHalden, good information. I have not yet tried to understand the finals, bias etc, but I guess you are saying when going to STBY it takes a bit of time to unload the power draw, and it takes longer for the L26 to settle down to STBY current and /or ¡°off¡± current ? Re ¡°You ask the very important question:? "does it?"?¡±?? I¡¯m not sure about what you mean, however if it is about testing using the 6.3, I was meaning to test it going from STBY to OFF ?and/ or from MOX,,, ?with the normal pause. ?Depending on what you see you might shorten the pause, but don¡¯t do it for me. I can¡¯t say anything about the finals, and since it is the transformer that fails,? and might be related to the ¡°no pause¡± syndrome, my attention went that way. It is not clear to me ?that this is a swinging choke or not, and if it is ?just what the rating means[my lack of education], so when the tube resistance is added, the 3 seconds might be shortened, but the choke seems to ?cause the dominant ?time delay As an aside, in looking into power supplies, there is so much time/space spent on PS for old ?audio amps in radios etc etc that some ideas about PS get cast in stone, but it seems for Ham use and other two way stuff the PS needs to run for long periods mostly unloaded in standby, so some PS ¡°rules¡± don¡¯t apply here. ? From: [email protected] [mailto:[email protected]] On Behalf Of HF via groups.io
Sent: Saturday, August 17, 2024 3:09 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? Hi Don, Yep, the filaments are still loading the transformer so the voltage on one winding shouldn't go haywire by itself. You ask the very important question:? "does it?"? I actually have the equipment on hand and the radio opened up, so I could try it.? But the risk of damaging the transformer inside my HT-37 during that measurement is somehow of higher magnitude than my curiosity right now.? Now if I had more confidence in the protection diode idea, I might try it. And your other question - what constitutes "gradual" for removal of the blocking bias?? We have an inductor and 1000 ohms, then 5 nF, then the bias power source with 18k ohms feeding 10 uF.? From that, there's 47k to ground in MOX and open in STBY.? Switching from MOX to STBY removes the 47k + potentiometer setting and C98 fills through R63.? RC for this combination is 180 ms, much longer than the period of the 60 Hz hum L26 is supposed to filter out.? If the radio is turned off without spending 0.18 seconds in STBY, then the bias would rise and reduce the current a little bit but not fully.? Then it would decay and possibly allow some current to flow through the 6146s until C69 and C80 lose enough voltage that they can't push that current any more. RC for the HHV filter is 3 seconds, which is longer than it RC for the bias.? So a quick turn-off might allow the filtered HHV to discharge partially through the finals.? Could this damage anything? No, I haven't checked the -49V bias recently.? When I checked it a couple years ago, it was close. Cheers Halden VE7UTS _._,_._,_ -- don??? va3drl |
don Root