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On Sunday, March 11, 2012 2:03:01 PM UTC-4, John Byrns wrote:
In article ,
Roger Jones wrote:

On Mar 11, 3:03*am, wrote:
On Saturday, March 10, 2012 4:00:05 PM UTC-5, Roger Jones wrote:
Hi, Vacuumlanders,
This is a long shot... I'm refurbishing an EICO HF12 integrated
amplifier (it is working.)
*Part of the pre-amp contains a wax-
covered, so-called "printed circuit" component with 7 pins, about one
inch square. EICO Stock No. 29751. *Name: PC1
It has the treble and bass controls connected to it.
It's looks a bit like those multi-pinned wax components in some AA5
radios at the detector/AVC/audio stage (I invariably replace these
with the generic circuit at the back of the RCA tube manual.)
Does anyone have the internal schematic of this thing in the EICO?
I've replaced all the wax caps. As a wax item, I'd replace it, too,
with new discrete parts if I knew what they were.
Thanks and cheers,
Roger

* *That is what it is : the actual OEM is Centralab PC-191. Pins :
*1-2=100K . 2-3=4700pF . 3-4=120k + 330pF . 4-5=1k + 330pF .. 3-6=4700pF .
6-7=100K . It is a small project .

Many thanks. I'll sketch it out to see what the overall TC schematic
is before doing any replacement with discrete components. At this
time the TC's work correctly, so I have to presume this thing is OK.
Thanks again for the sleuthing. I googled a few things could not find
anything!
Cheers,
Roger
PS. For general interest, here's what I've done so far on the EICO
HF12:
Tested all tubes: 12AX7's all at least "good", but not "good+"... left
them all in.
Replaced both EL84's, aka 6BQ5's, now semi-matched for current
(before, one was dead... it had +1.2 VDC on g1 from leaky coupling
cap. Other had about +10 mVDC on g1, OK.) Did not add a current
balancing pot as close enough for now.
Replaced coupling caps to all tube g1's (they were wax and paper
types.) Both 6BQ5 g1's now at about +5 mVDC, OK.
Replaced 6BQ5 single 165 ohm cathode bias resistor with two matched
330 ohm WW's, each bypassed by 100 uF. I left the hum pot slider on
one of them (gives about +11 VDC on all heaters to reduce hum.)
Moved both 6BQ5 screen supplies from EZ81 cathode (highest B+, was
more than the plates after OPT secondary DC voltage loss) to one
filter section down on the B+ filter after the original 10K resistor.
Replaced this 10K with 4.7K WW to get most of the voltage back.
Added extra 20 uF (to hand) after this 4.7K to get better B+ filtering
with the now lower series R value. Other B+ filter caps left "as is"
- they seem OK now reformed.
Replaced all wax and paper capacitors with modern caps (on subsequent
test all paper caps were above stated capacity, some by a large
amount.)
Replaced first B+ filter cap with new 20 uF, 450 volts (precautionary
only, but ESR of original not known and I can't test it!)
Added 100 ohm WW to cathode of EZ81 before new first filter cap to cut
ripple current and slightly improve filtering. B+ now about 10 VDC
low from original value and final pre-amp B+ about 2 VDC low (with 117
VAC in.)
Cleaned all pots and switches with Deoxit D5 (VC was very noisy, now
OK.)
Hope this helps...

Here is another take on what is inside the PC-191 that I eviscerated from the
schematic of another EICO amp.

http://fmamradios.com/stuff/PC-191.gif

Note that the connection to pin 5 is different than the one described in the
previous response. I suspect that wiring it as in the previous description will
cause the tone controls to function in an aberrant way!

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Absolutely. A picture is worth a 1000 words ! In general,that is...