[Heathkit] AT-1 nearing completion

[kwylow zinjanthropus]

For those of you who have been following my rebuild process on the AT-1, the unit is nearing completion! 
 
I finished with the amplifier section last week. The next step was to refurbish the tank circuit section. As you recall, I stopped on this section because my old 25 watt irons couldn't melt the solder on some of the critical wire to hardware points due to the metal of the condensers and hardware components sinking away the needed heat. 
 
Yesterday, I decided to "splurge" on another Weller soldering gun. While not as high wattage as my old dual 120/240 watt beauty with spotting light bulb, the new one is an abbreviated version with a smaller footpring and rated at 75 watts. It was good enough to melt the solder on the variable condensers and other hardware to wire interface where the 25 watt pencils couldn't hope to melt those solder joints. 
 
After I ensured that all joints were resoldered and touched up, I turned my attention to the mica capacitors on three of the four tank coils. The 40 meter coil had a 68 pf mica that had looked like it was burnt and deforming from within! Generally, these caps don't seem to do very good in their "later years" as a result of material degradatio. Hence, the failure. I suspect that this may have been a reason why the transmitter was taken out of commission. Well, I pulled out a couple of 68 pf 1kV ceramic replacements. I also took out a 24 pf 1kV replacement for the 20 meter tank coil. I felt that since the rest of the transmitter was filled with new components, why not the tank circuit? So, out came all the postage stamp micas and in their place, equivalent ceramics (with a much smaller footprint) were soldered in. 
 
After removing the coil bracket and putting in all of the coil clip holders to the bracket, I took a little time to fit the entire assembly to the transmitter. Of course, I used new hardware to bolt in both the grid and plate caps to the front panel. I also soldered in the plate blocking cap from the 6L6 final to the plate tune cap. That plate blocking cap (a 100 pf 1kV unit) was also a replacement for another postage stamp mica. I ensured that this rebuild won't be faulted by an bad or questionable component and by putting in new caps and resistors, I should actually lengthen the service life of the AT-1 for many more years to come. 
 
For a finishing touch, I installed the knobs. I bought several of those Dakaware knobs from Chuck Talbot on Ebay (the guy that sells the aluminum inserts for the Heathkit and Collins gear). These were also replacement knobs for the older AT-1 (which my unit was). They also happened to be NOS items! I missplaced the setscrews so I salvaged them from the old knobs. I also put the "AT-1" specific knobs on the bandswitch and the meter switch. I ensured that these items were polished and cleaned before mounting. Needless to say, the new and refurbished knobs along with the repainted and cleaned front panel meter really set the AT-1 looking nice again!
 
Today, before going to my duty station at Ord Military Community, I took some time to wire in the meter. I wanted to ensure that the wiring was sanitary so I got a long strand of black insulated wire and twisted it. I also removed the solder tabs from the meter and removed all of the remaining wire residue from the previous harness. Then, I soldered in the new wires and a new .001 mfd cap. However, I didn't solder the wires to the meter switch. I need to get my DVM and see which wire goes to where and compare that to the wiring shown in the manual copy. I don't want a backwards reading meter when I'm going to test the AT-1 out! 
 
Remaining tasks to be done: installing the power cord and fuse (I wonder why Heathkit and some other BA equipment manufactures never did that), and putting on the case (which is currently being refinished in a dark grey powdercoat krinkle finish). 
 
Later follow on project is to plate modulate the AT-1 (which is another story). 
 
Cal N6KYR. 


---------------------------------
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software

--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---