ka1tdq
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« on: April 22, 2011, 01:51:00 PM » |
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I'm building this for the heck of it. It's a 4 watt RF deck using a pair of 6L6's. I'm using two tubes for a lower plate impedance. The thing on the right is a mercury keying relay and the coil in back is a homebrew transformer for the 50 ohm driver to the grids.
I wanted it to be small so I will skip the variable loading capacitor and go with a fixed value cap. I'll heising modulate the power supply.
Jon KA1TDQ
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It’s not just values, it’s business.
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KK4RF
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« Reply #1 on: April 22, 2011, 04:39:35 PM » |
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Jon,
Project looks neat. If you could, post a schematic and let us know the power supply voltages, as well as your driver and modulator info. Nice metal work, too. ---Marty, KK4RF---
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W4AAB
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« Reply #2 on: April 22, 2011, 07:58:14 PM » |
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I assume this is the final amp. One could drive them with a single 6V6 or 6AG7. Somewhere in Electric Radio, there is an example of such a rig. Good luck with your project!!
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ka1tdq
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« Reply #3 on: April 23, 2011, 11:23:56 AM » |
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I drew up a sketch of the schematic. Plate voltage is 240 volts and I will use a solid state audio amp to drive an audio output transformer in the heising circuit. For 4 watts I have plate impedance at 2500 ohms.
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kb3ouk
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« Reply #4 on: April 23, 2011, 12:46:57 PM » |
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would probably work real nice to drive an amp with
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
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Ralph W3GL
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« Reply #5 on: April 23, 2011, 01:30:09 PM » |
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Wont work as drawn, the b+ is shorted to ground and only on the screens of the tubes !    And what's with the grid, plate and safety chokes being indicated as iron core? Perhaps more inductance? No, the choke hanging there on the output line is labeled as 2.5mh  |
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73, Ralph W3GL
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other" Ed Morrow
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Steve - K4HX
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« Reply #6 on: April 23, 2011, 01:49:06 PM » |
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The plate blocking cap just needs to be moved to the right a little - other side of the junction with the B+ line. Good catch Ralph.
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ka1tdq
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« Reply #7 on: April 23, 2011, 04:08:52 PM » |
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Oh, you know what I meant... |
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W4AAB
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« Reply #8 on: April 23, 2011, 05:39:12 PM » |
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I am reading his writing as 2.5 mH, which is what all three RFC's should be. I have several axial-lead 22 uH inductors if anyone wants to wind the 5 turn on the outside(the input RF transformer).A similar rig is in Electric Radio #194(July 2005) by K4JEJ. A 6AG7 is the oscillator that drives ithe 6L6's. I love seeing folks building stuff!! I am trying to finish my new antenna so I can put the tower back up.
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KC2ZFA
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« Reply #9 on: April 23, 2011, 06:55:38 PM » |
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the input circuit looks like one half of a bandpass inter-stage coupling scheme.
I thought with link input you would need to put the rfc+leak to the bottom of the tuned circuit to ground with a bypass between the rfc and the leak resistor (instead of grounding it directly) and do away with that 100pF coupling cap (i.e., the top of the tuned tank should go straight to the grid.
Please let us know how it works.
73 de Peter
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W4AAB
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« Reply #10 on: April 23, 2011, 10:36:52 PM » |
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Been looking at similar setups. There is no need for an RFC from cold side to ground. The coupling cap could even be higher( 220 to 470 pF) if you need more drive. I am anxious to see how it works as-is.
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K1JJ
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« Reply #11 on: April 23, 2011, 11:07:43 PM » |
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Nice job, Jon.
Couple more suggestions - I would add a 100K resistor across the PTT contacts from the cathode to ground. This will keep a reference cutoff bias on the tube instead of an infinite all or nothing. Less circuit shock when keyed up or down this way.
Also, add individual .01's from each screen socket pin to ground. Short leads and plenty of bypassing for the screen is key for stability.
With the other suggestions as given, looks like it shud work FB!
T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed. Easily done in DSP.
Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."
There's nothing like an old dog.
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VE3GZB
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« Reply #12 on: April 25, 2011, 03:01:19 PM » |
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That is cute!!!  Good job! |
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ka1tdq
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« Reply #13 on: April 25, 2011, 03:06:57 PM » |
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I've built something similar using with the grid tank grounded and it seemed to work fine. Besides, I've already done my welding and things are kinda almost permanent. I borrowed this setup from a PW AMWindow.org setup. Thanks for the tips on the screen bypass caps and cathode resistor on receive. And yes, it is kinda cute if I may say so myself. Jon |
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It’s not just values, it’s business.
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