[Heathkit] AT-1 rebuild update

[kwylow zinjanthropus]

All:
 
Last night, I took a break from doing my daily exercise to do some major wiring of the AT-1.
 
Quite frankly, after mounting the transformer into the chassis, it didn't quite look right. What I mean was all of those loose wires splayed out. So, I broke out the manual copy and took a good hard look at the wiring diagram and the kit steps. Remember from my earlier posts that the transformer used is a replacement Thordarson. Sometime before, the old Heathkit original xfmr probably fried. I heard that this was a common occurence. No matter. The refurbished transformer looks at home in the AT-1. 
 
Back to the rebuild. I did have a feeling of which wires were what in the trans. Only problem was the confusion between the 5.0 VAC line for the 5U4 and the 6.3VAC line for the rest of the tubes. Which one was it? Not having a handy dandy VOM, VTVM, or DVM, I had to do some slight experimentation. I had two bayonet light sockets on hand and two spare round #47 style bulbs. I clipped in the sockets to both filament leads and plugged in the transformer to the wall via a "cheater" cord. The brighter of the two bulbs confirmed which winding was which. I also swapped the bulbs to confirm brightness. Not only that, the 6.3VAC line was just long enough to solder into the correct sockets while the 5.0 VAC line was long enough for the 5U4 socket. Case closed!
 
After the p.s. wiring was complete, I continued on another hour on the 6AG7 circuit. I decided to cathode key this stage as opposed to having it "free run". The manual gave the use the option of doing this. My intent was to not have to listen to the free running osc while in standby mode. Yes, I know all I have to do is disable the tone by putting the xmtr on stby but I wanted to hear my keying. So, with the cathode keying in place, I also wanted to ensure that should I have any "chirpy" crystals, I could adjust out the "chirp". WA6VVL did this by replacing the 15pf cap with a 3-30 pf item and keyed the AT-1 on 40m (the band which his AT-1 was susceptible to chirp) and adjusting the trimmer for minimal chirp. Since I didn't have the trimmer, I left that step unchecked. What is left to wire up is the 6L6 final stage and the tank circuit. That will probably wait until this weekend.
 
Other items: I separated the support bracket and clips from the tank coils. I cleaned and repainted the bracket using that same copper paint I used to refinish the AT-1's chassis. I also cleaned off all of the clips using some fairly acrid degreaser. Cleaned off a lot of the old junk! Also (thanks to a kind reader), I received an original replacement knob for the meter switch! Thanks! I will be writing on article on modulating the AT-1 for a future ER. I'll mention your name there too. I think I have the xtal socket waiting at home so I'll find out 
 
O.k. That's it. I'm enjoying the heck out of rebuilding this radio as I listened to vintage jazz music! 
 
73 de Cal, N6KYR. 


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