Home  Resources  References  Tubes  Forums  Links  Support  Sale  Search 

   < Previous Message Index Next Message >   

Antique Radio Technical Forum
Paco C-25 manual

Posted by Edd on 04/02/2009 21:56

I have referencing to the units schematic, but NOT the owners manual.. . . .for that you would have to pay the piper, but with a read, possibly you can fathom its operation. ( HOPEFULLY !)

Initially, what are the chances that the unit powers up OK and that you confirm that its linear scale eye tube is bright enough
with its produced display.

Many were ye olden tymes radio men that treated that unit akin to the oscilloscope of times to come, wherein they left the unit
turned on and “on display” for all to see, it being within view of “awed” passerbys.

(Thereby depleting the phosphors, with diminishing brightness with time, along with ion burns (dimming) a portion of the

(Certainly you have seen that on older computer terminal displays, whereupon the unit was turned off but the display was still
“on”. )

The referenced EICO 955 is merely a bit akin in the respect of having an eye tube (round) and using a balanced bridge detection mode, with
null indication then being provided by the tuning eye.

The decided DIFFERENCE on this PACO unit is the fact that it is using not the typical low frequency audio for its comparator
bridge AC supply source, but instead, its using an oscillator that is creating a 40 MC RF source for the bridge reference supply.

That is being created at the grid -cathode circuitry of its 6C4 tube and amplified and coupled via its plate to its load resistor
and then with only the resultant variable component affecting the 60~ AC that is used as its plate supply voltage with it being
then direct coupled in its feed up to the 1st grid of the eye tube, being amplified and where that variance is then being displayed as a change in the display width.

These people were doing then, what is now- a- days being done in our ESR capacitor testing test instrumentation, however,
now, only a 100-250 Khz reference signal is being used and placed across the tested capacitor.

They taunt the “In circuit testing” aspect, at times, I am somewhat skeptical, that being in accordance to WHAT is possibly
being in a circuit loop with that tested capacitor and also shunting the measurement.

If confronted with a squirrely reading, I will then lift l one cap lead out of circuit in case there might be some question.

The units test modes switch positions are simplified to:

All capacitor testing of:



A Balancing bridge mode testing of :

2------40 ufd Electrolytic cap testing

40---400 ufd Electrolytic cap testing

Not exactly your instrument for testing lower value capacitors , EXCEPTING their short or open circuit condition.

The unit being at a loss in the fine differentiation of say a 100 uufd---.001---.01----.1 ufd capacitor value.

NOW, Considering that you might / seem to have an operational unit:

Should you want to quasi evaluate the unit now, get a couple of electrolytics or fixed paper units falling about mid range of
both the high and low electrolytic capacitance ranges and experiment with the unit.

GO to the “short” test mode, hook up a capacitor and note the eye tubes display and then short across the leads to get the
“short” response of the eye tube.

GO to the “open” test mode, and hook up a capacitor and note the eye tubes display and then lift a test lead to see the
“open” response of the eye tube.

Switch to the low capacitance range, hook a capacitance of ~ that mid range value and then rotate the center pot thru its
range and confirm the “null” response being in the range of the known value capacitor.

Switch to the high capacitance range and perform the same procedure.

If all works , then it looks that you might have yourself a valid test for capacitors within those ranges, which MOST all
commonly used radio filter capacitors fall within.

73's de Edd

PACO_Model 25. . . . . . REFERENCING :

Paco C-25 manual 
Bob Masse 04/02/2009 10:46 
Radiodoc 04/02/2009 17:20 
Ken W 04/02/2009 18:48 
Edd 04/02/2009 21:56 
Bob Masse 04/03/2009 21:30 
Bob Masse 04/03/2009 21:30 
Andy Rolfe 04/08/2009 16:54 
Bob Masse 04/08/2009 20:58 

   < Previous Message Index Next Message >   

© 1996-2004 Nostalgia Air