Monday, December 31, 2012

New Year's Eve II

My office is quite a mess at the moment. I brought out a bunch of old file boxes looking for my old ham radio project files. In the photo below, you can see the view of my office from the door.  I've got three folding tables arranged in a U shape, with the grey chair in the center and bookshelves to the rear.  There are file boxes on the tables, and more unseen on the floor.  I've got to get these sorted and put away.  On the far wall, under the window, is the small table where I was working on the Leader o-scope.  You can see the scope pushed under the table.  You can see my own scope near the lower right corner of the window.  There's a dead capacitance meter on the left side, but it's hard to make out if you don't know what you're looking for.
 
 
I am hoping to get Josh's FT101 up on the bench maybe this evening. I don't know what's wrong with it, how long it will take to fix, or what it will cost.  But it's probably something simple ;-).
 
My projects for today are to install the wood floor in the XYL's office.  You can see below.  I've got the old carpet removed and still need to pull up all the tack strips. Then vacuum and maybe level the floor. The room is 165 square feet.

 
Here's the engineered hardwood flooring.  Five boxes at $109 per box. 

New Year's Eve

Worked on the dead Leader o-scope last night.   The problem is in the high voltage circuit that provides bias for the trace of the CRT.

The circuit is shown below and copied from the service manual.  The 930 AC RMS volts on the power transformer secondary winding produces peak voltage of +/- 1315 volts (930 times 1.414 converts from RMS to peak volts).  On the positive cycle, V1 is +1315 and V2 is approx 0 volts because the diodes at V2 are forward biased.  So C1 is charged to 1315 volts at V1.  On the negative cycle V2 is -1315 volts.  Now current doesn't flow in the diodes at V2 because they are reverse biased. So the voltage at V2 is the voltage at V1 (-1315 volt) plus the voltage on C1 (another -1315 volts), so -2630 volts.  This voltage charges C2-C3 through the diodes between V2 and V3.  The voltage is filtered by C2-C3 & C4-C5 and the two 270 kohm resistors. Finally the two series 1000 volt zeners regulate the voltage  down to  2000 volts.

I found that C1 was dried out and no capacitance.  I replaced that capacitor and now the voltage comes up to -1600 volts or so.  There is a faint sound of arcing, so I suspect one of the other capacitors have dried out as well.  When I went to check the capacitance with my capacitance meter, I forgot to discharge the capacitors first, so there was still some charge on them.  So I blew the fuse on the capacitance meter.  I'll have to order a new fuse and order some more capacitors as well.  I can't get oil capacitors any more but have to order polypropylene capacitors, which are about $10 apiece.  So we're looking at a $50 to get it running, for a scope I paid $35 for.  If I had some patience and went to a few swap meets I could probably pick up the caps for a few pennies. 

However, if the scope runs, it should be worth at least $100 on Ebay, so it's still not a bad investment.  I may still be able to find some replacement caps from another source. 

For now, I've put the scope under the bench and will get to it after I get the parts.

Buying old equipment is kind of an adventure and a gamble.  Usually the equipment is simple to troubleshoot and easy to fix, but occasionally, it's impossible to get replacement parts, or the parts cost more than the cost of the equipment.  But that doesn't happen that often.

Sunday, December 30, 2012

I scanned the old article I wrote on the NE602 40 meter receiver.  The link is below.

https://www.box.com/s/8d1a0rca4du2zubx96ir

Here's a grainy photo of my sons Harvey, 9, and Sam, 7, posing with the little rig.  Last month Harvey turned 35, Sam is 32.

 
Below is a shot of the interior of the rig.



Cancelled auction

The auction for the Yaesu 757 that I was bidding on go cancelled.  I need to set up some really smart ebay notifications to alert me when something new comes out.  There must be a way to do that for Craigslist.com too.

Better luck next time. ...

Saturday, December 29, 2012

oscope problem

The Leader O-scope has a dried capacitor in the 2000V supply.  I'll have to order a new one. 

Sorting old stuff

I have been going through my files to find old ham radio projects.  I am looking for the cardbox trans-receiver that I built, as well as a couple of other projects. 

I found a lot of the old files at the bottom of box, everything except the cardbox rig.  I have a very nice article that I wrote concerning the small NE602  40 rx that I built. I guess I wrote it up and didn't submit the article to anywhere.  At any rate I think we should use that rx for another carbox rig, rather than the 1496 rx.  It's much smaller.  When the NE602 first came out in the late 80's I ordered samples through my company and built that little rx.  It would have been one of the first NE602 rigs.  There's a zillion of them out there now.  

I am thinking of modernizing this circuit and producing about 10 of them. The circuit board is 1.5 inches by 2 inches.  



Friday, December 28, 2012

My Brothers regenerative rcvr & QSL card.

Daniella and the Card Box QRP rig

My 1st Transcvr

Code practice machine

Post card from Ft. Gordon Sig School

Here is a photo of my old Swan 350 that was my main rig during my old ham days.  This is January of 1987.  My call sign was N5JBB.
 
This is a photo during the Jan 1987 Antique Wireless Association's Old Time CW contest.   I used a replica regenerative receiver, a simple power supply, a 6L6 crystal controlled transmitter (about 12 watts IRRC).

Thursday, December 27, 2012

Need a HV meter....

I got the covers off and started testing the power supply.  The +/- 15 volts, 200 volts and 320 volts are all good.  I don't have a high voltage probe to test the 2000 volt supply.  Now I'm going to Radio Shack to pick up a package of 1 Megohm resistors to make a voltage divide to check the 2KV line.

Back in a flash....

O-scope repair

Here's the first project for this blog:  Mike's 20 MHz Leader oscilloscope. 

It's not showing any trace right now, so I've got it up on the bench and am working on it.  I picked it up for $35 on Ebay, it ran for all of 10 minutes then died....

I've got the operator's manual as well as the service manual, so it shouldn't be difficult to get it going again.

First post. 40 meters cardbox

Okay,

I've created a new blog called "QRP Brothers" for sharing stuff and commenting and other stuff. 

I scanned the Cardbox Trans-receiver article and posted it in the QRP Brothers folder on my box.net account.

Here's the link.