Gates m-5168 remote preamplifier

[Johnblue]

Hi, I have had this little gates remote preamp forever and I’ve never powered it up because it rinds on a strange battery lineup that I’m not sure how to reproduce.

Gates Twinsistor remote preamplifier
M-5168

Lots of old germanium in here.

Anyone have a schematic? Also I think this piece I have is heavily modified by the radio station that had it, it had a large project box underneath to hold bigger batteries for sure, and the notes are pictured below.

They say it wants

-22.5  : gray wire
+22.5 & - 1.5 white wire
+ 1.5 red wire

So if I’m going to try something should I get
A 24v battery set up and a 1.5v battery and just run it easy peazy?

The most information I could find was gates sold a battery pack thing to use with it, it would be nice to build a little power supply for her, I have a bunch of 48v POE switchers... but that’s a lot of math and this thing is so small, maybe batteries are the way to go.

 

[PRR]

.

 

[mjrippe]

I think that what PRR is (not) saying is that the unit runs off of -24VDC.  Meaning 24V with positive connected to ground.

 

[emrr]

I bet that's one nasty 2% at +14dBm.

I wonder what the 1.5V is for.  Was anyone using bias batteries in early SS?    If you did an outboard switcher supply, you could probably derive both voltages from it with the right dividers. 

 

[mjrippe]

I bet that's one nasty 2% at +14dBm.

I wonder what the 1.5V is for.  Was anyone using bias batteries in early SS?    If you did an outboard switcher supply, you could probably derive both voltages from it with the right dividers.

I think the 1.5V is simply there to make 24V total.  22.5V batteries were available, or you could use (3) 7.5V and (1) 1.5V, etc.  For today's use you might get away with three 9V in series but they probably won't last long.

 

[emrr]

I think the 1.5V is simply there to make 24V total.  22.5V batteries were available, or you could use (3) 7.5V and (1) 1.5V, etc.  For today's use you might get away with three 9V in series but they probably won't last long.

I dunno.  Other things run on 22.5 from that era, and the two battery types would have different draws.  Maybe. 

 

[mjrippe]

I dunno.  Other things run on 22.5 from that era, and the two battery types would have different draws.  Maybe.

Good point.  And where does that White wire go?  That might answer the question.

 

[Johnblue]

I’ve dug a little deeper, removed the added battery/project box.

The wires switch color inside the main box, but still three legs of power as described above.

There’s two different input transformers. One mic and one line.

Green wire = +1.5 vdc hits a 110r resistor then the mic input secondary CT

Grey wire =  -22.5 vdc hits both input transformer primaries.  On the line transformer it hits the primary CT . This trace on the Circuit board also starts to travel out hitting a cap and a transistor.

Notable is the mic transformer has CT sec and the line transformer has CT primary.

Red wire = +22.5 & - 1.5 vdc hits ground wires for both transformers and ground to the chassis.

There is an added mod, an entire second circuit board that looks interesting.  It’s hitting the line input primary. 2 more rca 2n1307 transformers.

For now, I just got a 22.5 vdc Wal wart shipped  in and I have a battery. Let’s see what she’s got.

I recapped the big electros, left a bunch of PIO couplers.

—- okay, hum city . As soon as I started power, the meter was pinning. All the way at the end, at first I didn’t notice because it was facing the other way, but it was a strange sound coming from the meter area, o thought it might be a cap about to blow sounded like boiling... then I saw the meter going crazy. Even with the 22v unplugged it was pinning, just from the 1.5v battery?

I’m going to start removing superfluous stuff, like all the battery and spare battery and pseudo power switch headphone jacks...  Gotta clean this thing up if I’m going to figure anything out.