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Post by bluemax on Nov 28, 2017 15:15:06 GMT -5
Meter swings backwards on key up. I'm assuming someone tried something that didn't work. There are incriminating marks on the schematic. I am going on the assumption that the carrier and modulation are out of balance. My parts list only reveals a few variable resistors; 1-6 if I remember. #1 being the volume control and #2 squelch. The others are un-named and their relative location doesn't really help me i.d. them. I would expect one regulates basic output power and one adjusts modulation.
And since a screwdriver probably messed it up in the first place, I though I might get lucky and be able to reverse the mistake. Sure isn't worth a repair shop, and I don't have the equipment or knowledge to do a complete alignment. And I'm not really sure if the meter reaction really means I need to do ANYTHING. I only keyed it up a couple times without a contact. I have a couple radios that have mis-functioning parts, but that doesn't stop me from using them!
Anybody have experience with this? I didn't want to upload the layout if it wasn't necessary. This seems a likely radio for experimenting.
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Sandbagger
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Post by Sandbagger on Nov 28, 2017 22:08:36 GMT -5
Meter swings backwards on key up. I'm assuming someone tried something that didn't work. There are incriminating marks on the schematic. I am going on the assumption that the carrier and modulation are out of balance. My parts list only reveals a few variable resistors; 1-6 if I remember. #1 being the volume control and #2 squelch. The others are un-named and their relative location doesn't really help me i.d. them. I would expect one regulates basic output power and one adjusts modulation. And since a screwdriver probably messed it up in the first place, I though I might get lucky and be able to reverse the mistake. Sure isn't worth a repair shop, and I don't have the equipment or knowledge to do a complete alignment. And I'm not really sure if the meter reaction really means I need to do ANYTHING. I only keyed it up a couple times without a contact. I have a couple radios that have mis-functioning parts, but that doesn't stop me from using them! Anybody have experience with this? I didn't want to upload the layout if it wasn't necessary. This seems a likely radio for experimenting. We'll talk about this during the Roundup tomorrow night. We can cover more ground that way...... |
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Post by BBB on Nov 28, 2017 22:18:17 GMT -5
Do you have an watt/power meter? That would be helpful too.
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Post by bluemax on Nov 29, 2017 11:07:52 GMT -5
Yes, the obligatory Radio Shack SWR/RF Power combo. Not saying it's extremely accurate, but neither am I.
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Post by bluemax on Dec 12, 2017 10:55:41 GMT -5
Well, the result of trying the radio a couple weeks ago was convincing, although not the ideal outcome. It seems as though we lost a final by all reasonable deductions. But I suppose that also points to why the meter swung backward; rather than the modulation set too high the output power was fading drastically causing the same imbalance. Just for fun, I checked the parts list and that transistor isn't available readily on EBAY or a few broad searches. What I find are a bunch of sites selling newer transistors as replacement "or equals".
Can anyone recommend a reliable source for a novice to search? It appears that there might be a few parts that MAY work, but at the cost of buying them all (and risking more potential damage) I'd rather have confidence in what to buy.
And just a side note, apparently this radio was built with "smokeless" parts. Too bad, since my shack could use the release of some "Magic".
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Sandbagger
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Post by Sandbagger on Dec 12, 2017 12:19:24 GMT -5
Well, the result of trying the radio a couple weeks ago was convincing, although not the ideal outcome. It seems as though we lost a final by all reasonable deductions. But I suppose that also points to why the meter swung backward; rather than the modulation set too high the output power was fading drastically causing the same imbalance. Just for fun, I checked the parts list and that transistor isn't available readily on EBAY or a few broad searches. What I find are a bunch of sites selling newer transistors as replacement "or equals". Can anyone recommend a reliable source for a novice to search? It appears that there might be a few parts that MAY work, but at the cost of buying them all (and risking more potential damage) I'd rather have confidence in what to buy. And just a side note, apparently this radio was built with "smokeless" parts. Too bad, since my shack could use the release of some "Magic". If my memory serves correctly (an increasingly dubious claim the older I get) that radio should have a 2SC756 as the final. I'm sure someone has one of those in a junk box radio somewhere. |
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Post by bluemax on Dec 13, 2017 9:53:49 GMT -5
That's scary...and yes you're right. You obviously opened a few of these. And it's not what I expected to see. It's metal piece the size and shape of a pencil eraser. And it appears to be mechanically connected with a sort of saddle clamp. I didn't remove it yet...is that the case? no solder direct to the board? I expect to see that with computer chips today, not radios from the 70's.
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Post by 2600 on Dec 13, 2017 15:57:13 GMT -5
If this is the "WV23" model, and not the"WV23A", the final transistor shows up as a 2SC778 in Sams CB67. The mount flange is welded to the metal can of the transistor, same size as the "TO-5" transistor case that was popular in the 60s and 70s, before plastic-body transistors became common. All-metal final transistors gave way to the metal-tab/plastic-body TO-220 types a few years later.
Seems to me we were taking the cheaper and easier-to-get plastic final transistor like 2SC2078 or 2SC2166 and mounting it to the old heat-sink bracket with a mica and an insulated shoulder washer on the mount screw. The leads would reach the pc board pads okay with the transistor bolted to the underside of the original mount bracket.
Even with a good final transistor this one was not a "swing monster" radio. The driver stage is set up as an emitter-follower circuit. Tends to limit the peak RF drive to the final transistor on modulation peaks.
Not a terrible radio, but nothing special in comparison to the other three-knob radios on the market in 1974. 23-channel radios like this one tended to end up on closets and landfills when 40-channel radios got cheap a couple of years later.
One last thought. The letter suffix "A" on the 2SC756A was a make-or-break difference. The "2SC756" without the letter "A" suffix was an audio transistor. No gain to speak of if you try to use it to amplify RF. The "A" version was the RF-final version. If you find some of these under a rock, remember that the "A" matters on this part.
73
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Post by bluemax on Dec 15, 2017 10:26:21 GMT -5
I double checked myself, and it is definitely WV23, and the Owner's manual says TR14 is the final, and the part number is just 2SC756. The existing component has no stamped markings visible. I did locate a new one which is stamped C756, but would I do myself a favor to look for the 2SC756A? Is the latter going to fit the location physically as well as the circuitry? Or do I just stay with original? I don't need a Lamborghini out of this one!
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Sandbagger
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Post by Sandbagger on Dec 15, 2017 12:55:12 GMT -5
I double checked myself, and it is definitely WV23, and the Owner's manual says TR14 is the final, and the part number is just 2SC756. The existing component has no stamped markings visible. I did locate a new one which is stamped C756, but would I do myself a favor to look for the 2SC756A? Is the latter going to fit the location physically as well as the circuitry? Or do I just stay with original? I don't need a Lamborghini out of this one! If you have a 2SC756 on hand, I would try it. The worst that could happen is that it puts out even less power than before. Before you even change the final, have you tried aligning the transmit section to see if, perhaps, it had been misaligned by the previous owner? If the radio turns out to be misaligned, and you replace the final, it will not work any better, and you will think that the final you replaced was not a good one. It pays to verify that the part is actually bad before you replace it. |
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Post by bluemax on Dec 15, 2017 14:15:05 GMT -5
Well, the suggestion is valid, and I would if I could. But I can't and it's not worth spending money to have a pro align it for the test or to buy equipment myself. At this point the transistor is $12 for a pair. That's cheaper than the cheapest piece of test equipment on the list of what I would need.
And as long as I'm getting 2 brand new, I would hope at least one works. I suppose the only way to test a transistor is to apply the exact voltage it requires to open...no more or less. Is that a true assumption?
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Sandbagger
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Post by Sandbagger on Dec 15, 2017 19:45:59 GMT -5
Well, the suggestion is valid, and I would if I could. But I can't and it's not worth spending money to have a pro align it for the test or to buy equipment myself. At this point the transistor is $12 for a pair. That's cheaper than the cheapest piece of test equipment on the list of what I would need. And as long as I'm getting 2 brand new, I would hope at least one works. I suppose the only way to test a transistor is to apply the exact voltage it requires to open...no more or less. Is that a true assumption? No, you don't test transistors that way. Typically the easiest way to test for common faults like opens or shorts is to use a VOM to test the resistances between each leg of the transistor. Between the base and emitter and base to collector, you should have a fairly low resistance one way and a near open the other. There shouldn't be any resistance measured between the collector and emitter either way. Bear in mind that this only tests for opens and shorts, not if the transistor has any gain. For that you would need a transistor tester. But it's rare that a transistor would pass the VOM test and not have any gain (I have seen it maybe 2 or 3 times in 40 years). |
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Post by bluemax on Dec 17, 2017 11:36:20 GMT -5
I can figure that out. I'm having trouble finding leg identification for the can style BJT. I found the 2SC756A (attached). I would guess the 756 is the same leg configuration? p5 data 2SC756A.pdf (41.73 KB) Also, can the transistor be tested in the board, or will other components foul that test. It would be nice to test without removal if possible. |
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Sandbagger
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Post by Sandbagger on Dec 17, 2017 12:53:09 GMT -5
I can figure that out. I'm having trouble finding leg identification for the can style BJT. I found the 2SC756A (attached). I would guess the 756 is the same leg configuration? View AttachmentAlso, can the transistor be tested in the board, or will other components foul that test. It would be nice to test without removal if possible. Transistors must be checked out of circuit. The basing for the '756 is collector is tied to the metal can. Base is the lead in the middle. The one remaining is the emitter. |
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