RCA AR-88 Restoration

[iw5ci]

I got an old and venerable RCA AR-88 receiver.
It was sold as working, but it isn't.
The received signal is very weak , and audio is distorted at all but very low volume.
I would like to start a restoration but the first problem is that many condensers have been already replaced and the new ones are not in the same position of the originals, so i am very doubtful about what and how start working on the radio.. Any suggestions?

[w3jn]

Start by comparing the wiring with the schematic.  Check power supply voltages.  If they're not right, nothing will ever be correct.

Then troubleshoot using a signal generators, starting at the audio output stage and move towards the antenna to find the bad stage(s).

If you dont have a signal generator, compare voltages at each pin of each tube with the manual - that should get you in the area.

[WD5JKO]

I got an old and venerable RCA AR-88 receiver.
It was sold as working, but it isn't.
The received signal is very weak , and audio is distorted at all but very low volume.
I would like to start a restoration but the first problem is that many condensers have been already replaced and the new ones are not in the same position of the originals, so i am very doubtful about what and how start working on the radio.. Any suggestions?

    I think I'd leave the power cord unplugged for a good while as you go through the unit. This radio needs to be looked over pretty good, and might be beyond just a repair job. Do you have the manual with all the pictures showing component locations, and alignment points? Those images are a necessity since the alignment process is pretty long and detailed.

   I have an AR-88 here. It was bought by Ozona Bob (SK), W5PYT about 20 years ago. Bob was suckered (yellow sheet add), and the receiver was sold as working also. It was missing the wiring harness, a couple of IF cans, and two front panel rotary switches. Bob was so disgusted that he gave it to me since I promised I'd try to get it going again. Boy was that a job! I did get it working, and did so before Bob passed away.

Jim
WD5JKO

[iw5ci]

Unfortunately i haven't already found a source of a good schematic , and photo of the components.. bama manual is inusable, has anyone a good link with grayscale scan of the schematic?

[WD5JKO]

Here is the schematic of the CR88. I have the complete manual, about 3 mb in size. Pass along your email address, and I will send it to you. (mine is jcandela AT prodigy DOT net) The schematic is a pretty clear image. I am not sure what the differences are between a CR88 and an AR88, but the schematic seems to be a dead ringer to my AR88 except I do not have the S-Meter.
I might suggest you print this onto a 11 X 17 paper. Going to Kinko's might be worth it.

Jim
WD5JKO

[KM1H]

Is there a Kinkos in Italy?

[WD5JKO]

Is there a Kinkos in Italy?

  Well, you got me there. 

There are many Kinko's abroad, but apparently none in Italy. Perhaps this one would do:

Print & Service Di Santicioli Alda
Piazza Lorenzo Ghiberti, 9-red, 50122 Firenze, Italy
+39 055 248 0076

Jim
WD5JKO

[iw5ci]

thanks so much!!!
my email adress is andreal1967 AT gmail DOT com, if you can send me the manual i can start the restoration.
I will send some photos of the unit...
i will find a print service that can print in big size the schematic you sent me.

Here is the schematic of the CR88. I have the complete manual, about 3 mb in size. Pass along your email address, and I will send it to you. (mine is jcandela AT prodigy DOT net) The schematic is a pretty clear image. I am not sure what the differences are between a CR88 and an AR88, but the schematic seems to be a dead ringer to my AR88 except I do not have the S-Meter.
I might suggest you print this onto a 11 X 17 paper. Going to Kinko's might be worth it.

Jim
WD5JKO

[Pete, WA2CWA]

Is there a Kinkos in Italy?

Kinko's sold the business to FedEx several years ago. Most locations, if they still exist, are now called FedEx Office, http://fedex.com/us/office/

[G3UUR]

Even if C119 between the 6K6 plate and ground measures OK, it's wise to disconnect the grounded end and move it to the HT side of the output transformer. These capacitors have a habit of going S/C at some time or other, and usually take out the speaker transformer. Taking this precaution now can save you some grief later.

There are some spares available in the UK.

Have you got the 'D' or 'LF' model?

Dave.

[iw5ci]

HI Dave. it's a plain model as you can see in the photo in my blog:

http://boatanchors.tumblr.com/

The radio was recapped, probably in the seventies....

http://www.boatanchors.it/public/ar88-1.jpg
http://www.boatanchors.it/public/ar88-2.jpg
http://www.boatanchors.it/public/ar88-3.jpg

as you can see, the smooting filters have been exluded and instead we have 2 small modern capacitors!
i have replaced several capacitors of the seventies because they was leaking (tested with a megger) but unfortunately the radio still does not work.

the audio is still distorted (i use headspeakers) if i go up with the volume, and the sensitivity is really bad (i pick up only strong BC stations).

unfortunately i haven't' the skill for troubleshooting the receiver also because there are some modifications  done by previous owners...

the tubes are ok, maybe the sensitivity fault is in the rf stages but i don't know how how to proceed..

[G3UUR]

You can tell which model of AR-88 you've got from the frequency range it covers. The AR-88D covers 0.535 to 32Mc/s and the AR-88LF from 0.073 to 30.5Mc/s with a gap between 0.55 and 1.48Mc/s.  The AR-88LF has an IF of 735kc/s.

The fact that you've got low sensitivity and distortion at higher settings of the volume control indicate you've got a problem with the DC conditions around the valves (tubes). If you have the handbook for the AR-88, you should find Table 2 on page 14 and that gives all the DC voltages at various points in the receiver. You should first check that all of these are correct before trying anything else.

Why were the LF chokes (L49 and L50) disconnected from the circuit?

Dave.