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I just heard AM conversation on 75 meters... :)




 
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Author Topic: I just heard AM conversation on 75 meters... :)  (Read 23202 times)
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W1GFH
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« Reply #25 on: January 12, 2005, 03:22:23 PM »

Quote from: wavebourn
Are you going to donate it, Joe? Wink


Ha ha, no way, dude.  :grin:  But one shouldn't be hard to come by. All you gotta do is hang around hamfests and internet forums for a while. Eventually someone will unload one, thinking they are getting the better of the deal, but YOU will be the wiser.

BTW, one way to avoid the mute relay terminal zap might be to do like Bill N6PY suggests on the SX-28 (similar relay voltage).

He modifies the receiver to open the RF and IF cathode ground circuit at the RF gain pot to allow the tube cathodes to float up to around 50 volts and cut off these receiver stages - so the relay terminals will have no more than 50 volts on them when the receiver is muted during transmit.  This method of muting by opening the ground return on the RF, IF, and audio output tubes is less exciting - but much safer.
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wavebourn
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« Reply #26 on: January 12, 2005, 05:08:57 PM »

Here it is, as promiced.


Upon request of Jay, N3WWL the picture had been removed. You may see it going to the link, http://www.wavebourn.com/forum/viewtopic.php?p=2143#2143


B+ voltage depends on a bias voltage. Bias voltage increases while the capacitor C3 is charged by a load. When tubes are cold they draw small current. When they start conducting, they charge C3 faster. While bias voltage increases it increases B+ voltage until stabilizes. Both voltages depend on D3 zener, B+ depends also on R7 position.

D1, D2, R2, R4 - "fool proof" protection.

Attention: 315V source musn not be grounded! Why 315? Because I used industrial transformer, they are cheap on e-pay (120/240V)
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w3jn
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« Reply #27 on: January 12, 2005, 07:08:36 PM »

THis would also be a good circuit to rid the R-390 (non-A) and R-391 of those miserable 6082 regulator triodes.  The grid on those, however, is already regulated, IIRC.  I replaced both 6082s with one TV horizontal transistor.

Also great to regulate screen voltage on that leenyar!

Thanks for sharing the circuit, Tolly.

Gary - I nominate this circuit go in the Archives!

73 John
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FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
wavebourn
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« Reply #28 on: January 12, 2005, 07:27:12 PM »

Sure, why not?

But significant condition is, B+ current must be bigger than a bias current, othervise positive FB by B+ current will not work. Or you'll need to add a bleeding resistor to the output of B+ regulator to make it starting when switched on, but in such case it will not wait for tubes to warm up so patiently.

Actually, minimum input voltage may be no less than 12V + output voltage plus peak-to-peak pulsations on the filter cap plus about five volts to drop on a resistor that biases FET. Output voltage may be changed by varying feedback resistors R5-R6-R7. They may be cauculated by condition: voltage on the base of the transistor should be about 0.4 volt.
However, I myself don't believe in the "Cathode stripping on cold tubes", I just developed such a device to satisfy guys who actually do. Cheesy

Enjoy it!
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wavebourn
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« Reply #29 on: January 12, 2005, 08:49:15 PM »

Here is a filament voltage regulator. Speed of growth of output voltage depends on the C2 capacitor. It helps fo warm up cathodes slowly so filaments will live much longer. Thanks to Shottky diodes in rectifier and FET loss of voltage on open diodes and transistors is less than if to use ordinary diodes and bipolar transistor, so 12.6V AC from a filament transformer may be easily converted into the slowly increased 12.6V DC for less hum and longer tube life.

Upon request of Jay, N3WWL the picture had been removed (it is too big to post to the forum). You may see it going to the link,

http://www.wavebourn.com/forum/viewtopic.php?p=2143#2143
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wavebourn
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« Reply #30 on: January 12, 2005, 09:16:21 PM »

Quote from: W1IA
Quote from: wavebourn
Brent, I don't remember, who were in a truck? Someone in the team worked a mobile radio in a truck, if I understood well.


No Tolly...must have been someone else? Located in Derry, N.H.
To work the west coast is a treat with just a dipole.


Larry told, "that was probably Marv, kc9vf, on his cell phone ".
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wavebourn
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« Reply #31 on: January 12, 2005, 11:53:01 PM »

Wow!  :impact:
BC-348 has high enough voltage on heterodyne trimmers! I just lost my screwdriver under the table...  :badgrin:
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wavebourn
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« Reply #32 on: January 13, 2005, 01:42:51 AM »

Quote from: wavebourn
Wow!  :impact:
BC-348 has high enough voltage on heterodyne trimmers! I just lost my screwdriver under the table...  :badgrin:


But as the result, all circuits had been perfectly aligned, and I hear much better Frank W7ND from Seattle talking to Bill N6PY, right over my head, 800 and 360 miles wvay to opposite directions.  Cheesy
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w3jn
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« Reply #33 on: January 13, 2005, 06:57:15 AM »

Quote
Wow!  
BC-348 has high enough voltage on heterodyne trimmers! I just lost my screwdriver under the table...


Don't say I didn't warn you!  :lol:  :lol:

BTW I've *never* been able to align band 1 (the LF band) in a BC-348 to my satisfaction.  Most of the time the trimmers do nothing at all.

73 John
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wavebourn
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« Reply #34 on: January 14, 2005, 01:12:32 PM »

Quote from: w3jn
Quote
Wow!  
BC-348 has high enough voltage on heterodyne trimmers! I just lost my screwdriver under the table...


Don't say I didn't warn you!  :lol:  :lol:


No, you warned about Hammarlund's IF cans  :oops:

Quote

BTW I've *never* been able to align band 1 (the LF band) in a BC-348 to my satisfaction.  Most of the time the trimmers do nothing at all.


Looks like mine is in better condition. They act sharp enough. Wink
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w3jn
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« Reply #35 on: January 14, 2005, 01:22:16 PM »

Tolly - cheez... I thought I was warning about IF cans in general. :oops:

You're lucky with the BC-348... most of the ones I've had were ham-specialed to death, although I did have one that was 100% stock including the dynamotor.  *That* one wouldn't align at the upper end of any band.  IIRC it was something bad in the local oscillator... 'twas about 15 years ago so I'm kinda hazy on it.

73 John
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wavebourn
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« Reply #36 on: January 16, 2005, 04:50:01 PM »

Guys, who know where to order to print cheap but good PCB's?
I would make kits for power supplies...
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