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Old 2nd Aug 2023, 9:42 am   #1
GregVK5LG
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Default AR88 wiring loom query

Hi,
I have got my AR88 re-capped and going quite well, except for the manual RF gain control being inoperative as it does not have any minus volts on the end of the pot.
Circuit wise I can see quite clearly the minus volts are supposed to come [electrically] from the centre-tap of the transformer, but for some reason it is not reaching the RF gain pot. Short of making a mess by dismantling the stiff old harness, does anyone know physically the wiring route from the centre tap to the RF gain control? I have continuity to the 8 pin plug on the chassis rear but can't find continuity to the RF control.
An expedient would be to just run an additional wire, however I would like to find the open circuit if possible.

Thanks in advance Greg
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Old 2nd Aug 2023, 9:56 am   #2
Station X
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Default Re: AR88 wiring loom query

Could this be or have been an R1156?

See post #3 in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=50017
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Old 2nd Aug 2023, 4:52 pm   #3
thoyer454
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Default Re: AR88 wiring loom query

Quote:
Originally Posted by GregVK5LG View Post
Hi,
I have continuity to the 8 pin plug on the chassis rear but can't find continuity to the RF control.
I hope you mean pin 6??

Tom
W3TA
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Old 2nd Aug 2023, 5:40 pm   #4
Alan Bain
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Default Re: AR88 wiring loom query

It may be worth drawing your attention to the wiring loom diagram in the CR88 manual. This was indispensible in fixing mine which had been "got at" and had unconnected wires beneath the chassis.

I'd really like to find an original of this as the only scans I can find are poor. There has been a US seller on ebay but they only sold reprints and postage was excessive. Pages from poor scans attached.

Looks like top of RF gain is net 69 Red-Yellow (if your wires are like mine the colours are virtually indistinguishable) and this goes to pin 4 on the HT cap block (correction to previous post).

Worth also confirming that the chain from top of R43 (on paxolin board) to chassis is intact but clearly it is if your set mostly works. I tweaked R55 to allow the RF gain voltage to get high enough to make the set meet its sensitivity spec. The EMER 773 suggests it should be possible of get V1/2/5 grid as positive as -1.2V with gain at max so I tweaked it until this was true!
Attached Files
File Type: pdf CR88-route.pdf (2.17 MB, 75 views)
File Type: pdf CR88-RF-route.pdf (456.0 KB, 35 views)
File Type: pdf CR88-top.pdf (225.3 KB, 51 views)

Last edited by Alan Bain; 2nd Aug 2023 at 5:50 pm. Reason: Chain to chassis cannot be broken for a mostly working set. Sorry!
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Old 2nd Aug 2023, 6:45 pm   #5
ms660
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Default Re: AR88 wiring loom query

So far as I can make out from the CR-88 layout the Red-Yellow wire from the RF Gain control goes to the common connection of C96 and C97 then to Pin 6 on the octal socket then to the secondary winding center tap on T1 then to R43.

Lawrence.
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Old 2nd Aug 2023, 7:20 pm   #6
thoyer454
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Default Re: AR88 wiring loom query

Quote:
Originally Posted by thoyer454 View Post
Quote:
Originally Posted by GregVK5LG View Post
Hi,
I have continuity to the 8 pin plug on the chassis rear but can't find continuity to the RF control.
I hope you mean pin 6??

Tom
W3TA
Ignore my reply please. I read your post as pin 8 on the octal not the 8 pin octal as you wrote.

My lack of reading comprehension kicking in

Tom
W3TA
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Old 3rd Aug 2023, 12:42 am   #7
GregVK5LG
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Default Re: AR88 wiring loom query

Thanks very much to all who replied. As you guys know, most of these receivers have been "got at" by previous owners, some with not much expertise. I will let you know what I discover in due course, and thanks to all for the helpful information.
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Old 3rd Aug 2023, 8:40 am   #8
GregVK5LG
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Default Re: AR88 wiring loom query

Quote:
Originally Posted by thoyer454 View Post
Quote:
Originally Posted by GregVK5LG View Post
Hi,
I have continuity to the 8 pin plug on the chassis rear but can't find continuity to the RF control.
I hope you mean pin 6??

Tom
W3TA
Hi Tom, thanks for the correction ,...yes can't count
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Old 3rd Aug 2023, 9:02 am   #9
GregVK5LG
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Default Re: AR88 wiring loom query

Quote:
Originally Posted by Alan Bain View Post
It may be worth drawing your attention to the wiring loom diagram in the CR88 manual. This was indispensible in fixing mine which had been "got at" and had unconnected wires beneath the chassis.

I'd really like to find an original of this as the only scans I can find are poor. There has been a US seller on ebay but they only sold reprints and postage was excessive. Pages from poor scans attached.

Looks like top of RF gain is net 69 Red-Yellow (if your wires are like mine the colours are virtually indistinguishable) and this goes to pin 4 on the HT cap block (correction to previous post).

Worth also confirming that the chain from top of R43 (on paxolin board) to chassis is intact but clearly it is if your set mostly works. I tweaked R55 to allow the RF gain voltage to get high enough to make the set meet its sensitivity spec. The EMER 773 suggests it should be possible of get V1/2/5 grid as positive as -1.2V with gain at max so I tweaked it until this was true!
Thanks Alan.

In fact you have solved the mystery. In replacing the HT cap block with electrolytics a wire to the RF control was overlooked! ... by me. Also I will adopt your tweaking of R55. At the moment am -3.5 volts at best with no signal, -1.2 sounds better! Thanks again for your great suggestion.

Regards, Greg.
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Old 18th Nov 2023, 9:39 pm   #10
Martin G7MRV
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Default Re: AR88 wiring loom query

Quote:
Originally Posted by Alan Bain View Post
It may be worth drawing your attention to the wiring loom diagram in the CR88 manual.

Thanks for these scans! I've been trying all afternoon to identify the capacitor connected to T10 and it's been driving me mad trying to decide between two possibilities - thanks to these diagrams I know what value to change it to!
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Old 20th Nov 2023, 7:42 pm   #11
Alan Bain
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Default Re: AR88 wiring loom query

Have you seen the good quality version of the scan which I have attached here in a zip to stop the software compressing it to be illegible again.

Story is a bit embarassing. I kept asking on forums if anyone had a more legible copy of the wiring diagram. Then one day the cat knocked down an old envelope folder at home. In it I found an original copy which I scanned.
Attached Files
File Type: zip CR88-wiring.zip (808.7 KB, 31 views)
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