Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Recent Posts

The AM Forum
February 18, 2020, 01:44:58 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1] 2 ... 10
 on: Today at 01:16:00 AM 
Started by W8ACR - Last post by Ed - N3LHB
This is an easy one, pull the connectors from the audio deck and fire the 390A up, my bet is that one of the plug in electrolytics are bad. If the fuse doesn't blow, check the plug in electrolytics in the audio deck for shorts. Don't put in bigger fuses as you will cook 1 of the inductors on the audio deck. 26Z5's are getting pricey, if you don't have any spare, just tack 2 diodes in place in the PS module until you get the issue fixed.

 on: Yesterday at 10:00:06 PM 
Started by WB2EMS - Last post by AG5UM
Not knowing anything about 630 meters myself, I've enjoyed your posts.
You make 630 meters look like alot of Fun. When I saw my ARRL chart showing 5W EIRP max,
I thought I would'nt be able to get out very far at that power.
Your running "200W", and making contacts in New Mexico, great.
I'm going to have to check this out and Learn something about it, 630 meters sounds fun..
I've got room for "lots of wire", Keep us posted,

 on: Yesterday at 09:37:19 PM 
Started by AJ1G - Last post by KK4YY
Looks like you're getting more low-angle radiation from the inverted L at 8+33 feet than the inverted V dipole at 43 feet. Might be a good DX antenna for those of us (most of us) that can't get a dipole up at 100 feet. I think you're on to something. Well done!

 on: Yesterday at 09:19:48 PM 
Started by KA3EKH - Last post by WU2D
I have an idea but it is a gimmick. No it is a gimmick. Solder a piece of # 22 solid insulated wire to the grid about 2 inches long. Wrap it around the wire going to the plate with about 6 turns.

 on: Yesterday at 09:06:23 PM 
Started by WB2EMS - Last post by KB2WIG


I hope u waterproofed the coax/ant connection.......  woodent hertz to point the coax towards the gnd so the drippage  has a harder time gettin' into the coax.


 on: Yesterday at 08:59:57 PM 
Started by KA3EKH - Last post by DMOD
Have been playing around with this oscillator circuit in my MAK transceiver for a while now and have been having an issue or two. The problem is that the MAK is intended for use in the field powered by a car battery. I do not have the original power supply that provided +175 to the receiver and the TX oscillator and built up a solid state supply for both the B+ and the HV for the PA and modulator.
I am running around 150 volts for the B+ and with 13.5 volts on the input of the power supply the radio works without issue but below 11.5 or so the B+ drops down to 125 volts and the transmitter oscillator will not start every time. At 10.5 the oscillator fails to start at all.
This radio has a crystal in the receiver also and the receiver works without issue down to 10 volts although itís not as loud it still works. The issue is with the transmitter.
The question is am I dealing with a B+ issue or something else? At first I thought it was B+ related but not one hundred percent of that. The original transmitter oscillator used huge primitive crystals and now I am using modern rocks and am wondering if this is not a crystal capacitance issue that causing the oscillator not to start under less than ideal conditions?
I am attaching a copy of the schematic of the oscillator. Itís a 12A6 tube with a grounded cathode and a tuned resonance circuit in the plate that directly feeds the PA tube grid. There is no directly visible feedback path at least that I can see but I have seen this same approach used before in prewar and ww2 design. Did designers back then count on the added capacity of the huge primitive rocks and the modern crystals just donít provide that? Would a small amount of capacity across the crystal help it start osculation? Or is this just an issue due to the reduced B+ voltage?
Or maybe itís something completely different like reduced filament voltage cuts the gain of the tube below the point of self-exciting?
An additional item of interest is that the PA plate tuning affects oscillation. If I tune dead center on the plate tank dip the oscillator will not fire up the next time I key the microphone but by tuning a little on either side of the dip the oscillator works just fine, except the plate voltage issue.
Maybe when you consider the PA and its tank that is what is kicking this thing into oscillation in kind of some weird form of Armstrong oscillator? Although there is tons of shielding between the PA tank and the oscillator tank.

You can try these three things 0NE at a time.

1) Reduce the capacitance from the screen grid to B+. It is usually 100 pF or so but may need reducing.

2) Place a 33 pF capacitance across the 50k grid resistor.

3) Increase the grid resistance to 68k or higher.

Phil - AC0OB

 on: Yesterday at 06:46:54 PM 
Started by K1JJ - Last post by nq5t
Over the years I've read the arguments for and against.  Worse in many ways than the state of modern politics.

I joined the ARRL sometime around 1958 as a kid.  Was a member continuously until ham radio became a sideline during an unfortunate divorce, and I was forced to sell all my radio gear to eat.

But in the early 80's I joined again, became a Life Member, and never looked back.  You may not like the positions du jour, but they will change, like they always have.  It's all we've got Ö a voice you don't like is at least a voice. ANY voice is better than nothing Ö when you're fighting corporate money.

 on: Yesterday at 05:49:47 PM 
Started by WB2EMS - Last post by WD5JKO
Kevin, Now that this info is in the public domain, prepare for some Sap like the Grandson of Euell Gibbons to come knocking on your door!

I am enjoying this thread.


 on: Yesterday at 04:54:48 PM 
Started by n4joy - Last post by n4joy
I had the front panel and cabinet sand blasted and powder coated (hammertone gray/silver).  The most challenging part of the project, so far, was measuring and drilling out the front panel!  It took hours!  I used step bits of various diameters for the drill and the holes for the meters required a fairly large step bit.

I am waiting on a variac I ordered from eBay and will begin testing soon!

 on: Yesterday at 04:53:24 PM 
Started by WB2EMS - Last post by W6TOM
  Sound like a reasonable story, plausible deniability, after all, all us old farts need to stick together, wish I had the space to play 630 meters.

Pages: [1] 2 ... 10
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.034 seconds with 14 queries.