开云体育

S-38B Power Consumption

Ron Sharp All Messages By This Member #32130 Hi folks, I am restoring a Hallicrafters S38-B receiver and want to add an isolation transformer. So that I can select the correct transformer, I need to know the actual current the S38-B draws. I note in a PhotoFact Folder on the first model (the S-38) the current drain is shown 0.245 Amps @ 117V AC. This is cutting it fine with the transformer that I have (30VA), but as there is no BFO tube in the S-38B, I figure there may be less current drain overall. I recognise that the heater chain will still draw 150mA, but there should be a reduction in the DC (B supply) due to one less tube. ? Would someone please advise the actual current drawn by the S38-B operating with an AC input? ? Cheers Ron VK2IRS
Don VE3IDS All Messages By This Member #32131 Ron,? I just measured my s38b and it draws 208 mA with a supply voltage of 121 VAC. I think I would use a transformer with a good safety headroom. Maybe 50 VA so it doesn't get hot.? 73 Don ve3ids? toggle quoted message Show quoted text On Fri., Apr. 11, 2025, 2:31 a.m. Ron Sharp via , <vk2irs=[email protected]> wrote: Hi folks, I am restoring a Hallicrafters S38-B receiver and want to add an isolation transformer. So that I can select the correct transformer, I need to know the actual current the S38-B draws. I note in a PhotoFact Folder on the first model (the S-38) the current drain is shown 0.245 Amps @ 117V AC. This is cutting it fine with the transformer that I have (30VA), but as there is no BFO tube in the S-38B, I figure there may be less current drain overall. I recognise that the heater chain will still draw 150mA, but there should be a reduction in the DC (B supply) due to one less tube. ? Would someone please advise the actual current drawn by the S38-B operating with an AC input? ? Cheers Ron VK2IRS
Jim Whartenby All Messages By This Member #32136 Not sure that a higher VA rating is really necessary for this small of an isolation transformer. "It is possible to estimate the output voltage at intermediate loads since load regulation varies in an almost linear manner. For example, the 241-8-16 has a full-load rating of 16 V @ 6.25 A and a regulation of 10%. Its no-load output would be 10% more than 16 or 17.6 V. At half-load (3.12 A) its output would be 5% more than 16 or 16.8 V. Similar estimates can be made for any % load. Another factor to bear in mind is that it is possible to safely exceed the VA rating of many small power transformers. If the added regulation (drop in output voltage) is acceptable, an “overload” may be permissible because the design is regulation-limited rather than heat rise-limited."? This is from:? In other words, if a lower output voltage is tolerable say 95% worse case of 120 vac or some 114 vac then a 25 VA transformer operated at 100% of it's VA rating does no harm.? I doubt that the isolation transformer will be too warm to touch. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy On Friday, April 11, 2025 at 01:14:48 PM CDT, Don VE3IDS via groups.io <ve3ids.don@...> wrote: Ron,? I just measured my s38b and it draws 208 mA with a supply voltage of 121 VAC. I think I would use a transformer with a good safety headroom. Maybe 50 VA so it doesn't get hot.? 73 Don ve3ids? toggle quoted message Show quoted text On Fri., Apr. 11, 2025, 2:31 a.m. Ron Sharp via , <vk2irs=[email protected]> wrote: Hi folks, I am restoring a Hallicrafters S38-B receiver and want to add an isolation transformer. So that I can select the correct transformer, I need to know the actual current the S38-B draws. I note in a PhotoFact Folder on the first model (the S-38) the current drain is shown 0.245 Amps @ 117V AC. This is cutting it fine with the transformer that I have (30VA), but as there is no BFO tube in the S-38B, I figure there may be less current drain overall. I recognise that the heater chain will still draw 150mA, but there should be a reduction in the DC (B supply) due to one less tube. ? Would someone please advise the actual current drawn by the S38-B operating with an AC input? ? Cheers Ron VK2IRS
don Root All Messages By This Member #32138 开云体育 Ron, Perhaps you are ?wanting a 240-120 nominal step-down transformer? for use in Australia? And want it to be isolating Perhaps it will be located nearby the radio in open air? Or within the radio where mutual heating should be considered? Have you decided on grounding for the radio, which in the original incarnation has a possible “hot chassis” ? -- don??? va3drl
Ron Sharp All Messages By This Member #32140 Hi folks, Thanks for the good information on the current drain of the S-38B. ? My intention is/was to use a Triad Magnetics TR6-120 transformer that has a 230VAC or 115VAC input and an output of 120VAC at 0.25A, which is available from Element14. Also, I was intending to place the transformer inside the radio and also use a ground connection to overcome the hot chassis issue. Australian 240V?mains supply provides for a ground connection at the wall socket. ? I want to avoid using an external transformer, so will see what else is available. ? Cheers Ron VK2IRS
don Root All Messages By This Member #32141 开云体育 Ron, Do Australia houses use a hot wire, + a grounded neutral, + a safety ground [three prong plugs] so will you use a three prong ?plug. an auto-transformer ?should be more efficient. How do you intend to handle the ON/OFF switching? ? toggle quoted message Show quoted text From: [email protected] [mailto:[email protected]] On Behalf Of Ron Sharp via groups.io Sent: Friday, April 11, 2025 7:02 PM To: [email protected] Subject: Re: [HallicraftersRadios] S-38B Power Consumption ? Hi folks, Thanks for the good information on the current drain of the S-38B. ? My intention is/was to use a Triad Magnetics TR6-120 transformer that has a 230VAC or 115VAC input and an output of 120VAC at 0.25A, which is available from Element14. Also, I was intending to place the transformer inside the radio and also use a ground connection to overcome the hot chassis issue. Australian 240V?mains supply provides for a ground connection at the wall socket. ? I want to avoid using an external transformer, so will see what else is available. ? Cheers Ron VK2IRS _._,_._,_ -- don??? va3drl

Previous Topic Next Topic