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#51
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Amp Design Concept -- Preliminary
Jan Panteltje wrote:
Telstar has been at it now for years..... At 4$ profit per amplifier you'd have to sell zillions. :-) Bingo. |
#52
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Amp Design Concept -- Preliminary
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#53
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Amp Design Concept -- Preliminary
Frank Gilliland wrote:
If I take your magic antenna and stroke it real hard with an old sock, will Barbara Eden spurt forth from the end and grant me three wishes? The 70's version, or the current one? ha |
#54
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Amp Design Concept -- Preliminary
On Thu, 21 Sep 2006 14:04:58 GMT, Jan Panteltje
wrote in : On a sunny day (Thu, 21 Sep 2006 05:38:08 -0700) it happened Frank Gilliland wrote in : On Thu, 21 Sep 2006 12:25:43 GMT, Jan Panteltje wrote in : snip Honestly. Damn are we honest today. That's friggin' twisted. I "found God" when I was in the USMC and lost a KY-57. Not a good thing to lose. I eventually found it, but ever since then I've been an atheist. Go figure..... LOL, maybe it was used in-between by the Russians. God -to me- is an experience inside yourself that causes bliss, stronger then all the reasoning and thinking we do. Yeah, I like Tequila too. But in those years (sixties) in the sense of 'well there must be one after all' and 'divine justice' etc. Or 'There but for fortune go you and I'. It looks somehow some people are destined for some things, it always works for them... Others do the same and fail. And noting in nature can stop that, or change that. Maybe that is cunning, some sort of awareness. Some become astronauts, some lose state secrets... some always end up with radio / tv equipment.... Maybe we have no free will, are a playing ball of all other forces in the universe, and can see in a clear moment where we are thrown. Nature/nurture, fate/volition, divine destiny or a dumb luck..... throw a handful of pennies in the air and you would expect half of them to turn up heads but they usually don't. One thing you be sure will happen and in which you can place your faith: They will fall. So we should not blame it on Telstar if anything is wrong with his amp. I have to admit his PCB looks the nicest of all the ones at that site. If an amplifier worked on 'nice looks' then I might have a different opinion. But they don't. They work on the well-established priciples of electronic engineering. |
#55
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Amp Design Concept -- Preliminary
True, if you expect the transistors to never be replaced. But that's
not the reality with CB amps. The owners like to swap transistors for more power. Either that, or they overdrive the transistors and blow them up. Replacing them tears up the board, which is why it's hard to find an old single-board amp with good traces. Point-to-point wiring eliminates this problem because both the transistors -and- the strips can be replaced. The servicable life of the amp is almost indefinite irrespective of the amount of work done to it. Transistors in amps normally have to be replaced because the amp has matching problems or inadequate cooling... or both. Almost all the bootleg amps I've worked with suffered from these problems. This causes the transistors to run red hot... and it cuts their life drastically. As for your statement about using point to point wiring... bad idea. This causes stray inductances and capacitances all over the place that cause RF oscillations. Oscillations contribute to failed power transistors, due to the tremendous power dissipation that is present during these oscillations. Many times these oscillations can't be heard on the air and do their damage without the operator ever knowing why the failure occured. http://www.telstar-electronics.com/S...202879ABTC.pdf |
#56
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Amp Design Concept -- Preliminary
If you say your modular design is reliable then you must first define reliable............HP's, Kenwoods, Motorolas that have been in use for thirty years or more will all have connector problems. On one of my benches I have an HP-1707B, an Eico 950B, and a Heathkit IG-72. All are older than 30 years. I let my nephews use this bench. Nothing on the bench has connector problems. If there is one general type of electronic equipment that has a wide variety of -lots- of connectors it's the reel-to-reel deck. I have a large collection of vintage decks including Akai, Rheem/Roberts, TEAC, Sony, Wollensak, Ampex, Concertone, Viking.....etc, etc. Most of them are more than 30 years old and none of them have, or had, connector problems except for the occasional loose phone jack. When I was in the USMC the only connectors I had to replace were on coax cables (the operators were quite rough with them) and the big, bulky interconnection cables used on the command amtraks (which had about 20-30 radios and intercom units and were heavily abused). None of the connectors inside the radios ever needed replacement. When I was working at the commercial radio shop the story was about the same; mostly coax connectors and the occasional power plug. During my time at the station, the only connectors that needed replacement were ones that had frequent and punishing use, mostly 1/4" plugs & jacks and XLR's. I don't suspect that the connectors in this amp will get that kind of use. So for you to categorically declare that any equipment that has "been in use for thirty years or more will all have connector problems" is complete and utter bull****. Attention. Sell your solder stock. It will fall drastically. If those same connectors were solder joints you would eliminate that aspect of reliability. Wrong. Interconnection wires that are soldered have a high rate of failure in abusive environments. That's why auto manufacturers use connectors, even under the hood (and out of the nearly two dozen vehicles I've owned, none of them had any connection problems, either). I'll repeat myself. SELL YOUR SOLDER STOCK |
#57
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Amp Design Concept -- Preliminary
On 21 Sep 2006 17:31:24 -0700, "Telstar Electronics"
wrote in .com: True, if you expect the transistors to never be replaced. But that's not the reality with CB amps. The owners like to swap transistors for more power. Either that, or they overdrive the transistors and blow them up. Replacing them tears up the board, which is why it's hard to find an old single-board amp with good traces. Point-to-point wiring eliminates this problem because both the transistors -and- the strips can be replaced. The servicable life of the amp is almost indefinite irrespective of the amount of work done to it. Transistors in amps normally have to be replaced because the amp has matching problems or inadequate cooling... or both. Almost all the bootleg amps I've worked with suffered from these problems. This causes the transistors to run red hot... and it cuts their life drastically. Most of the bootleg amps are usually overdriven. For example, the Pride 100 is rated for 100 watts output. But most ampheads don't know that 100 watts means the peak power output, and when running AM they need to reduce the input power until the output is only 25 watts (unfortunately, the word "attenuator" isn't part of the amphead lexicon). Then they key down for far longer than the designed duty cycle permits ("duty cycle" also not a part of amphead vocabulary). And -that's- why the transistors are frequently cooked. And -that's- why this amp is going to have a variable attenuator on the front end, a thermostatically controlled fan, and will include very detailed instructions on how to set up the amp for different operating modes. As far as "matching problems", if you are referring to mismatched gain in transistor pairs, that only causes harmonics. If the mismatch is great enough to cause one transistor to run hotter than the other, that would be due either to component failure or ****-poor quality control. As for your statement about using point to point wiring... bad idea. This causes stray inductances and capacitances all over the place that cause RF oscillations. Oscillations contribute to failed power transistors, due to the tremendous power dissipation that is present during these oscillations. Many times these oscillations can't be heard on the air and do their damage without the operator ever knowing why the failure occured. Not only are you repeating yourself, but you are -way- out in left field with this concern..... Power RF bipolars are inherently stable and not likely to oscillate (assuming no wiring errors) because (a) the input impedance is so low that stray RF is going to be heavily damped, and (b) the power gain isn't high enough to overcome the low impedance at the base. You have to intentionally force these things to oscillate, and even then they won't start without a solid kick. Ironically, the only bipolar amp I have seen that -did- oscillate was a single-board design that someone tried to modify for more power [insert Tim Taylor grunt here]. FET's are different because of the high input impedance at the gate. But point-to-point wiring has been used both successfully and reliably in commercial high-power RF transmitters ever since Molly Brown took a ride in a lifeboat. Oscillation problems were resolved long ago when tubes were the only choice. Damping isn't difficult, and shielding between the input and output circuits is a common practice with both FET's and tubes. All you need is a thin sheet of copper, aluminum, or even a blank PC board. Got tin snips? |
#59
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Amp Design Concept -- Preliminary
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#60
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Amp Design Concept -- Preliminary
Frank Gilliland wrote:
As far as "matching problems", if you are referring to mismatched gain in transistor pairs, that only causes harmonics. If the mismatch is great enough to cause one transistor to run hotter than the other, that would be due either to component failure or ****-poor quality control. No, I'm talking about impedance matching problems. On the input is not a big issue... only reducing the available drive... but a mismatch on the output is critical... and causes big problems with excessive transistor heating... leading to premature failure. www.telstar-electronics.com |
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