|
"Uwe" wrote in message ... I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. I think 200 V is enough. Someone here probably knows what the AC-1 design voltage was, but I'm sure it wasn't 300 V, and may be have more like 150 V. While the 6V6 can handle higher voltages, as a keyed crystal oscillator, you don't want to overdo it. You could fracture a crystal, too. There's quite a bit of AC-1 lore online. Use http://www.google.com/search?q=ameco+ac-1 to find it. I even found a copy of the original AC-1 manual, but it doesn't show circuit voltages. Congrats on getting your ticket and making your first QSO. Now it's time to put this antique away and build some safe, cool, solid-state gear! 73, "PM" |
Congrats on getting your ticket and making your first QSO. Now it's time to put this antique away and build some safe, cool, solid-state gear! I disagree somewhat. There is a lot to be learned from simple gear, tube or otherwise. Tube gear is more forgiving of the mistakes we inevitably make while learning. It will also bite you if you are not careful, so you learn respect. He should try the classic 6CG7 807 transmitter next - a bit more power and a lot less chirp. It can be a lot of fun making contacts with this kind of simple equipment, and it improves your code proficiency to the point you might even decide code is fun. Doug Moore KB9TMY |
Congrats on getting your ticket and making your first QSO. Now it's time to put this antique away and build some safe, cool, solid-state gear! I disagree somewhat. There is a lot to be learned from simple gear, tube or otherwise. Tube gear is more forgiving of the mistakes we inevitably make while learning. It will also bite you if you are not careful, so you learn respect. He should try the classic 6CG7 807 transmitter next - a bit more power and a lot less chirp. It can be a lot of fun making contacts with this kind of simple equipment, and it improves your code proficiency to the point you might even decide code is fun. Doug Moore KB9TMY |
Uwe wrote:
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Uwe I don't have the schematic, but if the screen voltage comes from the usual dropping resistor & bypass cap then it is probably dropping a little bit under load. This will cause the plate current & output power to fall a bit, and change the operating characteristics enough to chirp a little bit. As mentioned by another poster, this is the nature of a single-tube transmitter (or single-anything power oscillator, for that matter). No matter what you do the amplifier characteristics will be different for different RF outputs, so the frequency _will_ change. You can minimize it but you can't make it go away. --------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Uwe wrote:
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Uwe I don't have the schematic, but if the screen voltage comes from the usual dropping resistor & bypass cap then it is probably dropping a little bit under load. This will cause the plate current & output power to fall a bit, and change the operating characteristics enough to chirp a little bit. As mentioned by another poster, this is the nature of a single-tube transmitter (or single-anything power oscillator, for that matter). No matter what you do the amplifier characteristics will be different for different RF outputs, so the frequency _will_ change. You can minimize it but you can't make it go away. --------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Uwe wrote in message ...
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. Congatulations and well done! But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. That's correct. You won't see it much on a 'scope but you can hear it. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Several things to check: 1) If the receiver you are using to monitor the signal is overloaded by the strong local signal, it can make the signal sound like it is chirping or clicking even if no such chirps or clicks actually exist. This is particularly true if the receiver isn't really meant for CW use. What are you using to listen to the transmitter's signal? 2) Besides the power supply, chirp in that sort of rig can be caused by: a) the crystal - try a different one if you can b) the feedback capacitors (the one from the grid to cathode, and the one from cathode to ground). These control the feedback in the oscillator, and if there is too much or too little, chirp can result. c) the 6V6GT tube - try a different one if you can d) output tuning - maximum output is often not the best setting for chirp. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. It's 1-1/4 inches. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. That's to be expected. A common formula for the inductance of a solenoidal air-core coil is: L = (a * a * n * n)/ ((9 * a) + (10 * b)) where L = inductance in uH a = radius of coil winding in inches b = length of coil winding in inches n = number of turns Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Perhaps - but how do you know the caps are the same value? 73 es hope to CU on 40 Jim, N2EY Uwe |
Uwe wrote in message ...
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. Congatulations and well done! But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. That's correct. You won't see it much on a 'scope but you can hear it. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Several things to check: 1) If the receiver you are using to monitor the signal is overloaded by the strong local signal, it can make the signal sound like it is chirping or clicking even if no such chirps or clicks actually exist. This is particularly true if the receiver isn't really meant for CW use. What are you using to listen to the transmitter's signal? 2) Besides the power supply, chirp in that sort of rig can be caused by: a) the crystal - try a different one if you can b) the feedback capacitors (the one from the grid to cathode, and the one from cathode to ground). These control the feedback in the oscillator, and if there is too much or too little, chirp can result. c) the 6V6GT tube - try a different one if you can d) output tuning - maximum output is often not the best setting for chirp. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. It's 1-1/4 inches. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. That's to be expected. A common formula for the inductance of a solenoidal air-core coil is: L = (a * a * n * n)/ ((9 * a) + (10 * b)) where L = inductance in uH a = radius of coil winding in inches b = length of coil winding in inches n = number of turns Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Perhaps - but how do you know the caps are the same value? 73 es hope to CU on 40 Jim, N2EY Uwe |
In article ,
"Paul_Morphy" writes: "Uwe" wrote in message ... I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. I think 200 V is enough. Not really. The original design uses about 300-325 volts. Someone here probably knows what the AC-1 design voltage was, but I'm sure it wasn't 300 V, and may be have more like 150 V. Check the power transformer - it gave at least 300 volts with the 6X5 rectifier specified. The AC-1 was spec'd at 15 watts input, which means about 40 mA at 350 volts! While the 6V6 can handle higher voltages, as a keyed crystal oscillator, you don't want to overdo it. You could fracture a crystal, too. I ran a similar transmitter as a Novice. 350 volts on the plate of a 6V6GT, grid-plate circuit. Xtals were fine, both on 80 and 40 meters. Those were FT-243s, though. Smaller xtals need a bit more care. A 6AG7 is a lot easier on the xtal than a 6V6. There's quite a bit of AC-1 lore online. Use http://www.google.com/search?q=ameco+ac-1 to find it. I even found a copy of the original AC-1 manual, but it doesn't show circuit voltages. Congrats on getting your ticket and making your first QSO. YES! Now it's time to put this antique away and build some safe, cool, solid-state gear! Why? If it does the job, what's the problem? As another poster commented, the next step is a classic 6AG7/807 MOPA design (or similar tubes - lots of choices, like the 6BG6, 6DQ6, 1625, etc). With a few more parts than the AC-1, you can get 40-50 watts output. And learn a lot in the process. 73 de Jim, N2EY |
In article ,
"Paul_Morphy" writes: "Uwe" wrote in message ... I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. I think 200 V is enough. Not really. The original design uses about 300-325 volts. Someone here probably knows what the AC-1 design voltage was, but I'm sure it wasn't 300 V, and may be have more like 150 V. Check the power transformer - it gave at least 300 volts with the 6X5 rectifier specified. The AC-1 was spec'd at 15 watts input, which means about 40 mA at 350 volts! While the 6V6 can handle higher voltages, as a keyed crystal oscillator, you don't want to overdo it. You could fracture a crystal, too. I ran a similar transmitter as a Novice. 350 volts on the plate of a 6V6GT, grid-plate circuit. Xtals were fine, both on 80 and 40 meters. Those were FT-243s, though. Smaller xtals need a bit more care. A 6AG7 is a lot easier on the xtal than a 6V6. There's quite a bit of AC-1 lore online. Use http://www.google.com/search?q=ameco+ac-1 to find it. I even found a copy of the original AC-1 manual, but it doesn't show circuit voltages. Congrats on getting your ticket and making your first QSO. YES! Now it's time to put this antique away and build some safe, cool, solid-state gear! Why? If it does the job, what's the problem? As another poster commented, the next step is a classic 6AG7/807 MOPA design (or similar tubes - lots of choices, like the 6BG6, 6DQ6, 1625, etc). With a few more parts than the AC-1, you can get 40-50 watts output. And learn a lot in the process. 73 de Jim, N2EY |
Uwe wrote in message ...
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Uwe ---------------- Congratulations! I still have my original Ameco AC-1 15-Watt CW transmitter, completely intact with all original parts and accessories, all in perfect like-new condition, and a copy of the whole manual. If you want me to look at or measure anything for you (e.g. the coil you mentioned?), just let me know. I am at tomg AT fullnet.com . By the way, I think that I paid $14.98 for the Ameco AC-1 kit, new, back in about 1969. I built it, tested it, and then never used it. And I HAVE had people offer me hundreds of dollars for it, "out of the blue", several times over the last few years. There's a picture of it on my webpage (see URL, below). Good luck! Regards, Tom Gootee http://www.fullnet.com/u/tomg ----------------------------- |
| All times are GMT +1. The time now is 11:00 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com