BeoGram 1000: alternative RIAA PreAmp ?

33 replies
DI
Offline
Dillen
BronzeModeratorFounder
Posted August 19, 2022 at 09:17 GMT
#1648427
Different transistors and diodes were used in production.
Indeed OA81 are found in some versions.

Mexking, I still have your RIAA here, remember.
- And it actually has OA81 fitted.

Martin
KolfMAKER
Offline
KolfMAKER
Bronze
Posted August 19, 2022 at 11:01 GMT
Edited August 19, 2022 at 04:00 GMT
#1648428
Component search I have done a quick check for components. There's two challenges that I see:
  1. Some components have values that are not very common any more, e.g.: capacitor 10uF/6.4v, 80uF/25v, 100uF/6.4v, etc.
  2. I have to make sure that the sizes of the components chosen are the same, to make it fit on the original board remake.
Questions (a) Can anyone recommend an online source where components with these 'vintage' values can be found? (b) Are the diode types AO70 & AO81 interchangeable? Or does it depend on the version of the board which one to choose?

Location: The Netherlands

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beosound.png Beosound.png
Beosound-9000.png Beosound-9000.png
Beolab-18.png Beolab-18.png
mexking
Offline
mexking
Bronze
Posted August 19, 2022 at 17:08 GMT
Edited August 19, 2022 at 17:08 GMT
#1648449
here

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
mexking
Offline
mexking
Bronze
Posted August 19, 2022 at 17:49 GMT
#1648453
Try Mouser Electronics, but you will have to go for radial leaded caps in some cases, looking at the PCB you should be able to fit them. start looking for 80/25 if not there, look for 82/25 and so on just keep it inside the 20%. If you dont find it check with Martin, I know he has some of them if not all. I will go check in my stock I have 80 and 100 axial in stock but dont remember which V

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
mexking
Offline
mexking
Bronze
Posted August 19, 2022 at 17:56 GMT
#1648454
Component list

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
RaMaBo
Offline
RaMaBo
Gold
Posted August 20, 2022 at 11:46 GMT
#1648467
Hi,

 

the components that make headache are not so critical:

80µF / 25 V  could be replaced with 100µF /25 V

33µF / 64V could be replaced with 47µF / 63V

1,6µF /25V could be replaced with 2,2µF / 25V or to be as near with a 4,7µ / 25V in series with a 2,2µF /25 V resulting in 1,5 µF /25V but not really necessary.

125µF / 16V could be replaced with 100µF /16 V or to be as close as possible get a 100µF /16V with a parallel 22µF /16V

The 80µF and 33µF are used to 'clean' the supply and bias voltages.
The 1,6 µF is for removing the DC offset from the input and output so i would use just a simple 2,2µF. It has no influence to the frequency response of the RIAA preamp.
Also every capacitor for 64V could be replaced with a 63V type

I hope this helps :)

Location: Near Munich

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beosound.png Beosound.png
Beosound-9000.png Beosound-9000.png
Beosound-5.png Beosound-5.png
Beoplay-P2.png Beoplay-P2.png
Beoplay-M3.png Beoplay-M3.png
Beoplay-Earset.png Beoplay-Earset.png
Beogram-400x.png Beogram-400x.png
KolfMAKER
Offline
KolfMAKER
Bronze
Posted August 20, 2022 at 14:34 GMT
#1648471
Thnx @Mexking & @ RaMaBo ! Interesting that there are some differences in the values of certain components; between the info I posted in the start of this Thread and the info in the schematics & parts list of Mexking. E.g.
  • Capacitor #22 and 23 = 200uF/25v vs. 80uF/25v
  • Capacitor #49 and 51 = 80uF/25v vs 1.6uF/25v
Is this correct?  

Location: The Netherlands

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beosound.png Beosound.png
Beosound-9000.png Beosound-9000.png
Beolab-18.png Beolab-18.png
mexking
Offline
mexking
Bronze
Posted August 20, 2022 at 17:46 GMT
#1648476
There are apparently at least 2 different versions, one with OA81 and one with OA70 fitted. The OA81 has the smaller caps and different transistors fitted, yours and my pic of the PCB are identical, whereas your trace with components pic is different. So you will have to decide which one you want to copy.

@ Martin, I remember the RIAA, the BG 1000 is still going strong playing with my son in CPH together with the BM 1900 you also restored connected now to some Sonos equipment, but let the young ones play around. I would here put a big smiley if I could

Location: Mexico city

Retired
Printing machine technician
Restored various 1960-70 items
Rock and Roll music
Collecting Vinyl
Restored Jukebox Wurlitzer 1050
KolfMAKER
Offline
KolfMAKER
Bronze
Posted August 22, 2022 at 11:21 GMT
#1648500
I think you guys are right, about the two versions.

I also think the 2nd version is 'easier' to rebuild as the values of the capacitors are closer to components available.

Location: The Netherlands

My B&O Icons:

Beoremote-Beo4.png Beoremote-Beo4.png
Beovox.png Beovox.png
Beosound.png Beosound.png
Beosound-9000.png Beosound-9000.png
Beolab-18.png Beolab-18.png
DI
Offline
Dillen
BronzeModeratorFounder
Posted August 22, 2022 at 13:18 GMT
Edited August 22, 2022 at 13:19 GMT
#1648507
There are several, slightly different, versions.
Three of the ones shown here have different transistors, and the last one is an entirely different (earlier) version, mainly seen in 41FV and 42FV.

Martin
or
BeoWorld Gold Membership card
Join BeoWorld

Register to access the forums, reference material, and exclusive member benefits — including our monthly prize draw.

Become a Member

December 2026 Prize Draw

Gold Members Only

As a Gold member you're automatically entered into our exclusive prize draw — your chance to win iconic Bang & Olufsen products. A unique benefit of BeoWorld Gold membership, every draw brings a new opportunity to win something special.

View Prize Go For Gold