On Jul 4, 1:10 pm, Engineer wrote:
On Jul 4, 11:20 am, wrote:

Note to all:

(snip)



************** I'm using a matching transformer from 300 ohms (LO) to
8 ohm speaker. I plan to install a proper OPT to match the 6K6 to 8
ohms but leaving the original there for posterity.

The trick is that the 6K6GT isn't biased the way it would be to
deliver a couple of watts as a speaker driver. Sure it will work, but
it will be running flat out.

**************** I'll check that and, if needed, rewire it. I
noticed the screen voltage exceeded the plate voltage by quite a bit.
A 6K6 o/p stage is dead easy to brew up.

(snip)]



The problem with that is the dynamotor, if not running, will present a
near-short circuit to the power supply. And the 24 volt heater line is
connected to the dynamotor input, so it will be shorted too.

************** No, it is now totally disconnected

By simply removing the dynamotor assembly and putting in a dummy
chassis so the loose wires don't short, you can retain the rx wiring
and run from an external supply. Then if you ever want to drop in the
dynamotor and run from 24 volts, you can do that too.

************* B+ P/S is a separate Heathkit reg. unit and I don't want
to lose the dynamotor over the next 50 years! So. I'll just leave it
in the chassis for the next collector...

(snip)

Cheers,
Roger

PS
Heaters now powered by a 24 volt HVAC control transformer - connected
between chassis and pin 2 of the 1st IF tube, VT-86/ 6K7 (bypasses
resistor "76-A".) BTW, these 24 volt HVAC control transformers are
easy to find as scrap units (look in old house demolition bins.) I had
two in my junk box - one 12 VA (not enough) and one 40 VA (too big but
OK, so I used it.) You need 17 VA minimum.
B+ remains from a separate vintage Heathkit regulated tube supply -
one of 3 such items here, so I can dedicate one to the BC348. My big
28 VDC supply is now surplus!
Next things to do:
1. Install a terminal block and a 4 conductor power cord to the
external P/S's (DC and AC)
2. Check all those old paper caps I was warned about...
3. Check the alignment, tweak as needed (the manuals have full
instructions for all those 1940's radio techs - RIP, most of them!)
Support the military! (Who is watching "Dogfight" on Discovery
channel?)
Cheers,
Roger