[ARC5] BC-312 considerations

[JAMES FALLS]

I had an L version for a while in my shack with its sister 314-D. I chased failing bypass caps until I took Dave Stinson’s (AB5S) advice and ran it on reduced B+. 

This may not serve in a halftrack installation unless you hide things, but I completely unhooked the dyno and got the fils their 12V, then ran variable Plate voltage (0-135VDC) in thru the back, tacking it to the lug on the connector board the HV output on the dyno would go to. 

I found that there really wasn’t a dramatic difference in ‘phone audio after 120V. I usually ran it at 90-100. The dyno puts out 250. Another factor is heat and stability. Both rigs had very little drift after 10 minutes warmup: Old resistors are also much happier. 

One thing you will probably have to address are the 3 bypass cap cans mounted sticking up at the rear of the RF deck. Mine were all bad from the get-go, and I replaced them w/modern equivalents along with a couple below deck. 

I lucked out and didn’t have to get into the big RF cans that share the same “shiskabob” shaft. Low B+ didn’t overly stress those old parts. Removing and replacing them isn’t for the faint of heart. Really tight access. 

I got off with a conventional IF/RF alignment. It tracked very well and WWV is a good reference in between the ends of the band sections (I aligned them specifically for the ham bands and the ends weren’t too far off).

I remember the uppermost band was a massive PITA to get right, because the trimmer caps are all standard straight-line capacity, rather that straight line frequency which would’ve been much more easy. Lotsa back and forth unless you have an assistant. The other band sections are not nearly as touchy. 

It worked well receiving SSB with that great, no-backlash reduction drive. 

I’ve done the same to my BC-348-R that is paired with a BC-475-E. 

Jim Falls K6FWT