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#1
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RF amp help
I am trying to build a small class C RF amp for 160 AM. The amp is to be
plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie |
#2
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RF amp help
Jimmie D wrote:
I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. With only 12 watts of audio available, I would be tempted to use grid modulation on a pair of 6146's. -- 73, Cecil http://www.w5dxp.com |
#3
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RF amp help
"Jimmie D" wrote in message ... I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie Sorry, meant to send this to 'homebrew'. would still appreciate the help. |
#4
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RF amp help
"Jimmie D" wrote in message ... I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie You have about enough audio power to plate modulate a 25 watt input amp. Maybe something using a 2E26 or a 6DQ6 tube. As Cecil mentioned you may want to modulate the screen of a pair of 6146 tubes or similar to get enough power out to make it worthwhile. |
#5
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RF amp help
"Jimmie D" wrote in message ... I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie I presume you mean 160 KHz, not MHz. Almost any of the N channel power FETs intended for switching power supply use will work at 160 KHz.. Forget about the 12W amp; you would need a low impedance modulation transformer for that. I would start with a non regulated power supply at about 30 volts, and run that to a buck regulator. Set the quiescent voltage to 12 V. Now, AC couple the audio ( a few milliwatts) into the regulator reference input, and adjust the audio amplitude so that the regulator output swings between 0 and 24V. That is the supply for the power FET. To operate in class C, you will want to drive the gate with a rectangular waveform. I would start with about 25% duty cycle. There will be a tuned circuit at the output of the FET; that has to have a fairly low loaded Q, or you will cut off the sidebands. Actually, It should be possible to do this without even having a separate RF amplifier. Run the buck regulator at 160 KHz with almost no filtering at the output. The regulator output will be AM modulated 160 KHz. Filter it in an LPF. If you meant 160 MHz, the first paragraph still applies. Use the regulator output to power an RF transistor operating at 160 MHz. Tam |
#6
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RF amp help
Tam/WB2TT wrote:
I presume you mean 160 KHz, not MHz. Probably neither - probably 160m. -- 73, Cecil http://www.w5dxp.com |
#7
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RF amp help
"Cecil Moore" wrote in message et... Tam/WB2TT wrote: I presume you mean 160 KHz, not MHz. Probably neither - probably 160m. -- 73, Cecil http://www.w5dxp.com Makes sense. Forgot this was a ham site. He would need an RF transistor. Tam |
#8
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RF amp help
On Apr 9, 11:07 am, "Ralph Mowery" wrote:
"Jimmie D" wrote in message ... I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie You have about enough audio power to plate modulate a 25 watt input amp. Maybe something using a 2E26 or a 6DQ6 tube. As Cecil mentioned you may want to modulate the screen of a pair of 6146 tubes or similar to get enough power out to make it worthwhile. Thanks, I have a couple each of 2E26s and 6DQ6s I think I can come pretty close to the impedance values I need by driving one of my LS-55 transformers witth a solidstate amp using one of the low impedance connections as the primary of a modulation transformer. Jimmie |
#9
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RF amp help
"JIMMIE" wrote in
oups.com: On Apr 9, 11:07 am, "Ralph Mowery" wrote: "Jimmie D" wrote in message ... I am trying to build a small class C RF amp for 160 AM. The amp is to be plated modulated and I have about 12 watts of audio available. I have built amps before(30 years ago) but I have never built one around a modulator, previously I built the modulator to suit the amp. Any help with tube and voltage selections would be greatly appreciated. Jimmie You have about enough audio power to plate modulate a 25 watt input amp. Maybe something using a 2E26 or a 6DQ6 tube. As Cecil mentioned you may want to modulate the screen of a pair of 6146 tubes or similar to get enough power out to make it worthwhile. Thanks, I have a couple each of 2E26s and 6DQ6s I think I can come pretty close to the impedance values I need by driving one of my LS-55 transformers witth a solidstate amp using one of the low impedance connections as the primary of a modulation transformer. Some thoughts: If you have 12W of audio and you want to use plate and screen modulation, you have enough to cover 24W of DC input at 100% modulation, but it wouldn't hurt to have a slightly higher powered final with 60% to 80% modulation. That would suggest up to about 36W input, which at 66% efficiency would give you a 24W carrier, 66% modulated. In that case, you would need a PA tube with more than 12W of anode dissipation. The 2E26 has an ICAS plate dissipation of 12W. One approach is to choose a tube that is likely to remain available due to its widespread use and the consequent replacement demand. I don't think the ones you nominate would be high on that list. Although a 6146B might seem overkill, it is cheap, can run comfortably from a 500V supply at good efficiency, and will idle along at about 60% of CCS ratings. Important factors will be the supply voltage and anode current compatibility with your modulation transformer... otherwise your 12W of audio might not go very far at all. The 2e26 has less room to move in accomodating your mod tranny than the 6146B. Owen |
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