The AM Forum

Did some cosmetic work on the PA and modulator sections using dark gray hammer tone paint finish. 

looks great! :D

VERY NICE! I really like the hammered paint look. 
The hammered black looks great also.

Looking good Bob, gee I remember standing in that spot not long ago. Guess you rolled the rig over for pictures. Nothing like a background of spare parts..

Thanks guys.

Working that hammertone paint was a PITA. I never worked with it before.  The first panel I had to strip 3 times because it didn't come out right.  The first time I used white primer, bad mistake. Plus, I think there was an incompatibility between the primer and final coat. The primer bubbled in some places. Also, the primer coat would show through in some of the larger dimples, so off it came. So I went to a dark gray primer.  That worked but still the dimples were not right. So off it came again. A third attempt and got the same result.  I finally figured light coats are the best way to go.  Trying to lay it on heavy initially gives a nice look but as it dries then it goes to crap. 

The second panel I had to strip once because I painted it when the temp was not optimum (too cold).  The hammertone pattern came out very rutty looking.  Again, light coats and temp above 40 seem to be best. 

Frank, Things have advanced a 10 fold since you were over last.  I got the modulator off the bench and reworked the PA.  I incorporated some of your suggestions into the PA.  I got rid of that hokey coil and wound a new one out of 1/4" tubing.  It's positioned horizontally rather than vertically.  I put an input tuning network underneath and it's well shielded.  I learned that working with sheet metal is something I'm not very good at unless one has good tools for doing so.

Next step is the bias and screen supply.  I've got the chassis somewhat assembled.  I'll work on that this weekend.  I also need to build into the rig some safety features.

I think the 813 rig has advanced the most in the last month that it has in the last 6 or 7 years combined when I took on the project.  I'm looking to squeezing some RF out of this thing in the not to distant future.

Not to worry on the beer and HV.  I probably shouldn't even be handling power tools with beer around but that's not fun.

Rich, yes, to the question on the mod section, it is on top.

Question for everyone:  Do you think I should paint the outside of the rack to match the front panels?

black or gray works for me.

Added another section to the 813 rig today.  The bottom section is the screen and bias supply.  It tested good under load today. It's the first component in the xmitter that has had voltage applied to it and it passed with flying colors.  So far things are looking good and getting closer to finality.

Hi Bob,

 Looking Good OM... :D

Way to go Bob! 

73,
Ellen - AF9J

keep going and dont stop until you strap.

Looking good Bob!

guess buddly aint around so ill say it

he said "PITA"  hu hu

Very nice job Roberto.
Mine's about done now and will post pix shortly.
It'll have a reverse color scheme than yours   - black panel, hammertone grey  cabinet.

you have Nice iron too...

Hi Rick,
Thanks. I'm itching to get power to this thing.  I'm so close I can taste it. My goal is by the end of this month to be spewing RF. Hopefully it will spew cleanly.  Look forward to seeing some of your pix.

Great sounding rig! I wonder what your audio chain is,that you will be feeding the 813 Xmitter? Have you swept the modulator for frequency response withe the CVM-4? I am curious as to how that mod iron performs.
Again,Great job on the 813 rig!

Nick,KG2IR :)

I agree with all Bob.  Great looking rig.  I'm interested in how your modulator works out.  Drive chain, etc. Final freq resp...  I have a couple of choices with the mod iron -- the RCA iron or the CVM-4.

The aluminum rack with the blue panels will take some thinking / color matching with it comes to the front panels.  Some have suggested Black Crinkle -- that will be tons of fun.  I'm goin to "dead bug" a lot of the really heavy stuff on the bottom of the rack.

Great ideas Bob.  I'll be following your progress closely.  Any chance of emailing detailed pics of the "guts?"  I'm good in QRZ.

Al

Nick, Al,
I did sweep it early on but haven't lately since some tweaks.  The last time it was swept the response was not flat. Lows rolled off around 120cps. High end was not as extended as I was hoping either then.   Low end isn't what I was expecting then but I don't know now since tweaking and learning how to load it.  I'm sure I still have some tweaks to do but will find out as time goes on when it is on the air more.  I'll sweep it again at some point.

Also, Nick, I neglected to mention the modulator is configured as a Heising modulator. JJ's circuit uses 50H. I could only muster 30H for the Heising chokes so that is one of a couple of departures from the original 813 JJ Maul design.

Audio chain: Audio Technica AT2020 Mic, Behringer 12ch mixer, Samson compressor limiter, Urei EQ. Audio amp is a homebrewed solid state amp using an LM1875 which drives a reverse audio transformer that tickles the triode connected grids of the 813 modulators.

I'll provide some updated pictures this evening. And yes, Al, I can send to pics of the guts.   Need to beat the rain and get a little yard work done.

Thanks for the compliments. Hope to catch you on the air again soon.
Bob

Beautiful job on all your rack wiring Bob. It (almost) makes me want to pull out all my JS alligator clip-lead connections inside my big rig! Do you ever find fried mice or cats in the bottom of the rack?

Hi Rob,
Please realize that wiring was about 30% of what's in there last year. See  new pix for final (or close to final) product.  There's more wire and stuff in the rack now. No on the mice and critters.  Don't have to much of a problem with little critters   around here. Miss Pigs takes care of the mice and the back of the rack has a door to keep critters out and my curious fingers.

1st: Modulator - Pair of 813s. HB solidstate audio amp. CVM4 mod transformer wired as an autoformer per HenryLR.
2nd: Final PA - pair of 813s. Pi network set as 75m mono operation. The 2 small knobs on the front control the input tuning and neutralization.
3rd: Screen and Bias PS - Variac to set screen supply output voltage.
4rd: HV supply control. Meters monitor Vplate and Vscreen
5th: Fan air intake to pull filtered air into the rack.
Bottom of rack (interior): Plate supply and Heising chokes. Fuse box with blown fuse indicators in the little gray box.  Contactor above fuse box for AC of entire rack tied to Emerg. cutoff switch.

Al/VTP, I'll get some internal shots of each chassis in the next few weeks.  I still have to label the front panels at which time I'll pull each chassis and open them up for you.

Those are the latest pix of my first big rig or first HB'ed rig in general.

Very nicely done! I like the unistrut for shelf rails. I may have to try that for some test gear.

Thanks. I ended up using that to support the modulator because trying to support the mod transformer by the faceplate didn't bode well for the front of the chassis.  In the long run I'm glad I did it because it works out good for troubleshooting. I can simply rest the chassis on the strut without constantly having to remove and install the faceplate screws.

Rob,
Joe,  W1AIU told me to tell you to lighten up on the cat and mice comments  ;D

Bob

I think my newest 813 xmtr will end up something like yours.  My first 813 xmtr (some 30 years ago) actually had chassis for the modulator and power supply.  This time the iron is just going to be too heavy. All the iron HAS to go on the bottom.  So, I'm planning on putting some sort of protection on the back.  I'm thinking about some sort of frame with cane metal just to keep the critters out. The front will have panels of various sizes just to cover things up. My last 813 xmtr even had interlocks on it with a contactor just in case I got crazy and tried to work on it with the AC engaged.

Keep us posted with pics

Al

Heh, Joe just hit me with an email challenging both of us to work his K3 on AM. I'll look forward to working both you and Joe on that one! Seriously, you did a beautiful job on that rig and I'll bet it sounds as good as it looks!

Rob

    Looks great Bob, a worthy achievement! Can't wait to work you on it.......Larry

I particularly like the "transmitter builder cooling system" on top of the transmitter. I count 5 containers; does that mean you are one beer short of a 6-pack?

Bob, It's BUI - Building under the influence. And those cylinders kept the builder cool.

Got to clean up the operating position and work area so I can operate the rig.  The hamshack is an absolute mess.