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Re: Central Electronics BC-458 VFO low drive
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I decided I need two 1 watt resistors in parallel.
3 hours ago
Wednesday, March 25, 2020
Mr. Carlson Restores an All-American Five -- Tribal Knowledge! SITS! Flattening the Curve! (video)
It is always a pleasure to see a new video on Mr. Carlson's awesome YouTube channel, especially in these days of Staying-In-The-Shack (SITS). Obviously Mr. Carlson is doing his bit in this area. FLATTEN THE CURVE! Thanks OM!
My recent bout of S-38E madness has peaked my interest in the All American Five design, so this March 10, 2020 video was especially interesting to me. Mr. Carlson puts out so much great tribal knowledge. I didn't know about "rounder" resistors. I didn't know that you have to be careful not to short out (to the IF can case!) the 455 kc transformers. I really like his approach to dial cord restoration.
Mr. Carlson's discussion of the adjustment of the front end tuner circuit on this broadcast band radio was very interesting. Unlike the S-38 radios, there are no front end coils being switched in as you change bands. In fact, it appears that that big coil/antenna inside the back cardboard piece IS the front end coil. This discussion has caused me to question my front end alignment technique for the S-38E. Did I have an appropriate antenna or antenna substitute across the antenna terminal when I set the peak on the input LC circuit? I will check on this. Hooray! One more thing to do during the COVID-19 SITS period.
UPDATE: I checked on this using the test set up described in an earlier post, but this time with my antennas connected. First with a 40 meter dipole, then with my 130 foot doublet, then with a 50 ohm dummy load I was still able to see the resonance dips at exactly where I wanted them to be.
My favorite bit of Carlsonian wisdom from this video? Mr. C's confirmation that some hum in All American Five receivers IS NORMAL! (This may be too much for the folks who find normal band noise to be offensive.)
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Double check the Variac to be sure it providing isolation. Most Variac's and other similar products are autotransformers and provide no isolation.
ReplyDeleteChecking for isolation is simple. Inspect the wiring to see if the unit has two independent windings or perform a simple test. Set the unit to give about 60 volts out. Check each slot (blade slot) of the output for voltage to ground. (An analog meter is the best for this measurement.) If you measure more than a volt or two from either blade to ground, connect a 120 volt incandescent light bulb where you measured the voltage. If the light glows dimly or you measure many volts across the bulb, you do not have isolation.
Above comment is correct. If you will check Mr. Carlson's video where he describes his Variac, isolation, dim-bulb current-limiter
ReplyDeletesetup, you will find that it has both a Variac AND an isolation xformer.
Yea, I misinterpreted the comment about the isolation of the variac. Mine is NOT isolated. But I have placed isolation transformers in both my S-38Es. I took the incorrect line out of the blog post -- I don't want to mislead anyone. Thanks for the good catch. 73 Bill
ReplyDeleteI don't know why my previous comment (at 12:33 AM) showed up as Anonymous but that is a different issue. This is KN4BXI. With a previous employer we routinely tested the fuse links the oscilloscope manufacturers provided to go between the probe and ground. Had many of the leads open but never lost a 'scope.
ReplyDeleteNow the system is showing me as Unknown. Strange.
ReplyDelete