Saturday, November 12, 2011

Heathkit Shop P/S board in Drake AC-4

AC-4 Bottom

AC-4 Top View

Installed the 'Heathkit Shop' power supply board today and got it working on the AC-4.  I followed the directions as well as I could but had to put the board on the 'wrong' side of the transformer because that was the way the screws were installed in the transformer.  The board fits but it is closer to the end of the chassis as there is more room on the other side.  Also the wire kit does not really fit when the board is on the opposite side.  It works find and the AC ripple is now lower.

With the AC-4 running the T4XB I show 740 B+ (720 with PTT down but no audio), 278 V DC on the mid supply with about 4V AC and -60 VDC on the bias with .0 VAC .  I don't think my VC-99 Auto ranging meter does well on the AC ripple measurment on the B+  it still jumps from 3 hundred to 4 hundred reading.  Then I tried AC reading while putting more of a load on the supply by closing the PTT line and putting the T4XB in Xmit this gave .6 VAC on the B+, .4VAC on the 250V line and 0VAC on the bias so this is better than what I was showing before.  The B+ reading was not accurate before so I can't comepare really.  The 250 V line was dropping out of regulation and the OA2 was going 'dark' when the PTT was closed.  This is now back to the OA2 just dimming a bit (normal) and the ripple went from about 5VAC to .6VAC so that is the big change.  
In general the kit is well done and makes it easy to re-do these old things.

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