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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Jan 2021, 9:48 am   #1
DMcMahon
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Default What is a P.A.C. Unit ?

First attachment is a section from a Roberts 1725 Reel to Reel tape recorder schematic. This shows 4 capacitors and 2 resistors within a dotted line box identified as "35-09 P.A.C. Unit". This looks to be part of the Bias Oscillator circuitry. The second attachment is a close up of the dotted box area.

I saw this when comparing the 1725 schematic to the Akai 1700 schematic, the Roberts 1725 recorder being derived from the Akai 1700 recorder. The Akai 1700 schematic shows very similar components/connections but not within a dotted line box/not identified as P.A.C. Unit.

So have been racking my brains trying to work out what P.A.C. could be an abbreviation for, any ideas please ?

David
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Old 14th Jan 2021, 10:17 am   #2
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Default Re: What is a P.A.C. Unit ?

Looks like an encapsulated unit, often these were encapsulated in "cement" I had a radio receiver (Hammarlund) that used them for RC stage coupling.

Lawrence.
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Old 14th Jan 2021, 10:22 am   #3
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Default Re: What is a P.A.C. Unit ?

So maybe Potted A..... Circuit?
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Old 14th Jan 2021, 10:27 am   #4
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Default Re: What is a P.A.C. Unit ?

Potted Audio Circuit??
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Old 14th Jan 2021, 10:30 am   #5
dazzlevision
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Default Re: What is a P.A.C. Unit ?

I think these were made by Erie Resistor (of Great Yarmouth), to the customer's specification.

Murphy Radio used a shorter one on the video/sync PCB in their Astra TV chassis (V600 & V700 series).

I should have an ERIE data sheet on these, which will explain what P A C stands for.
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Old 14th Jan 2021, 10:35 am   #6
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Default Re: What is a P.A.C. Unit ?

A common name for the integrated RC coupling units was "couplate"

Lawrence.
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Old 14th Jan 2021, 10:37 am   #7
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Default Re: What is a P.A.C. Unit ?

Quote:
Originally Posted by dazzlevision View Post
I think these were made by Erie Resistor (of Great Yarmouth), to the customer's specification.
Well done, Dave.

That led me to: https://worldradiohistory.com/hd2/ID...-Page-0085.pdf

So it's Pre-Assembled Components
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Old 14th Jan 2021, 11:01 am   #8
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Default Re: What is a P.A.C. Unit ?

Well done, I would never have guessed Pre-Assembled Components.

This Roberts is Roberts Electronics of California part of the Rheem Group, I do not know if Roberts Radio is/was part of the Rheem Group.

Erie of course is an American company so maybe USA Erie supplied the PACs.

David
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Old 14th Jan 2021, 12:52 pm   #9
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Default Re: What is a P.A.C. Unit ?

PAC units were quite common in American jukebox amplifiers of the late 50’s and into the 60’s. Sometimes wondered why they were used as discrete components were cheap enough and in most cases only saved 1 or 2 solder joints. When a resistor overheated an cooked the PAC you had to replace the whole unit instead of just one resistor.
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Old 14th Jan 2021, 6:55 pm   #10
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Default Re: What is a P.A.C. Unit ?

With the general size of discretes in 1961, given a small space, vertical components was the only way to go.
Here is one I prepared earlier (LHS of the pcb). The pre-assembled board used eleven of the Erie "plug-in" components.
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Old 14th Jan 2021, 7:58 pm   #11
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Default Re: What is a P.A.C. Unit ?

Erie data sheet - F Y I
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Old 15th Jan 2021, 9:07 am   #12
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Default Re: What is a P.A.C. Unit ?

Quote:
Originally Posted by vidjoman View Post
When a resistor overheated an cooked the PAC you had to replace the whole unit instead of just one resistor.

Perhaps that was the point, sales of spare parts, you had to go to the manufacturers rather than use generic parts.

Peter
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Old 15th Jan 2021, 9:35 am   #13
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Default Re: What is a P.A.C. Unit ?

These are an example of the style as used by Wurlitzer in a 1956 valve Jukebox amplifier as a switched treble tone control. They refer to them as PEC and are thinner than the example Data Sheet. These are more like a thick film unit. These amps contained 2 units, this one purely passive, but the other included an anode load which usually burnt.
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Old 15th Jan 2021, 9:43 am   #14
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Default Re: What is a P.A.C. Unit ?

When the components are just soldered to this intermediate pcb I don't think it was beyond any competent Tech to make a replacement.

The Regentone BT17T for example https://www.radiomuseum.org/r/regent...tor_bt_17.html

However in some cases they were encapsulated

Then it would have been a bit messy

Cheers

Mike T
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Old 15th Jan 2021, 10:50 am   #15
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Default Re: What is a P.A.C. Unit ?

Those look like the rod resistors with silvered ends that had brass pushed on tags for inserting into a PCB but used here directly soldered to a PCB. I believe Thorn industries used the lead-less resistors on some products directly soldered to a pcb.
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Old 15th Jan 2021, 11:43 am   #16
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Default Re: What is a P.A.C. Unit ?

A bit like the pitch-encapsulated blocks found in pre-War HMVs and Marconiphone sets, I suppose.
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Old 15th Jan 2021, 1:38 pm   #17
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Default Re: What is a P.A.C. Unit ?

I've seen these go under a few names.

- Packaged Assembly Circuit
- Pre Assembled Components
- Couplates
- PEC - Packaged Electronic Circuits
- Thick Film Circuits

They usually only contain capacitors and resistors, typically ranging from 4 to over 20 components. As you can see from the attached photo of my Lowrey Heritage organ, Lowrey seemed to like them (a lot !). I guess they saved a lot of assembly time but they're not much fun when they fail and need to be replaced!

Jerry
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Old 15th Jan 2021, 11:07 pm   #18
DMcMahon
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Default Re: What is a P.A.C. Unit ?

I am surprised and very pleased that so much information was forthcoming, many thanks to all.

David
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