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 Wanted - audio board for AWA B92 radiogram
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 Return to top of page · Post #: 1 · Written at 9:35:40 PM on 2 February 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

Wanted, an amplifier board for an AWA B92 3-piece radiogram. The amp board is about 5 by 7 cm, has eight AWV transistors, and is marked 726B5 on the copper side. Being stereo, the copper pattern is symmetrical. (Also used in the B95, B89 and B85 models.)


 
 Return to top of page · Post #: 2 · Written at 9:16:19 AM on 3 February 2018.
Flakes's avatar
 Location: Adelaide, SA
 Member since 27 February 2010
 Member #: 630
 Postcount: 392

Hi Sue

Send me a photo. I got a heap of old radiogram Boards delivered to me from a bloke who stripped them out of the chassis. I can look through them and see what I have.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Valve radios, They just don't make them like they used to

 
 Return to top of page · Post #: 3 · Written at 11:56:58 AM on 3 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

Is yours missing (no, you have the number) or does it just need to be fixed?

Yes, it is possible and usually not too difficult. The AWV transistors (if you have a bad one) can be replaced by commonly-available types viz:

AS147 = BC547
AS157 = BC557

etc.

You can run the amp up with the outputs disconnected and it will operate at low power. You can fault-find it this way then safely connect the outputs. A 24v bulb in series with the DC rail helps avoid nasty surprises.


 
 Return to top of page · Post #: 4 · Written at 12:43:58 PM on 3 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

Assuming this is the same as your other post, the boards are missing. Flakes may be your only hope.


 
 Return to top of page · Post #: 5 · Written at 11:22:37 PM on 3 February 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

The amp board is completely missing, and I can't find a photo of this board, which is why I quoted the number from the manual. All I can do at the moment is scan the diagram of the board in the manual, which shows what the copper tracks look like.

(The preamp board isn't a problem now, I can convert my spare board by changing a few components.)


 
 Return to top of page · Post #: 6 · Written at 7:13:11 PM on 4 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

If you are REALLY keen, I could make you a replica.....


 
 Return to top of page · Post #: 7 · Written at 12:03:42 PM on 5 February 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

Flakes, I've sent an image of the missing board to your email address.

Thanks for the offer Ian, I was thinking of trying that myself if Flakes can't help, but I don't have the gear to do it. I'd need to buy a PCB kit and a small drill press. A hand drill would slip, I think.


 
 Return to top of page · Post #: 8 · Written at 12:41:12 PM on 5 February 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 923

Hi Sue, the last time I wanted a one-off board I only had the handbook page layout that showed the component and track positions full size.
I taped a fresh sheet of carbon paper between the page and the copper board and first centre punched the holes by judging the ends of the components. Then I traced the edges of the tracks with a ball point.
With the paper removed I then used a new Dalo ink pen and played at "fill in between the lines". Then with a fresh bag of etchant I etched the bare copper away. I could then wash the Dalo off and had a bit of a wobbly circuit board.
Then dig out any whiskers with a knife and drill out all the holes with a wire size drill in my hand held minidrill. Then open up any larger holes.
Then clean the copper side down with steel wool and quick spray with lacquer and presto....one board ready for assembly.
Go on.....you can do it, we will all cheer from the side lines!!
Fred.


 
 Return to top of page · Post #: 9 · Written at 2:31:20 PM on 5 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

Guys, I used to do that sort of thing 40 or more years back.

These days, it's so easy to generate a PCB in CAD and email the file to a PCB prototype house. There's a local one - LD Electronics - that was recommended to me by another forum member. Prior to that I used a Chinese site. For what it costs it's just not worth my time any more. A week later and your PCBs arrive in the mail.

Plus, if you first draw the schematic, you can netlist and design rule check the layout so there are no mistakes.

Use the original board layout if you have it for floorplanning.

And it looks SO much more professional! You could even make a surface mount version! Don't laugh, provided you stick with 0805 or 1206 resistors and caps, SOT23 transistors and SO ICs (i.e. avoid the fine pitch stuff) it's quicker to assemble by hand than a through-hole board.


 
 Return to top of page · Post #: 10 · Written at 9:02:57 PM on 5 February 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

Trouble is, I'd need to redesign the board from scratch using CAD, which I don't have and have no experience of using. Tracing the manual's diagram is much easier for me. From there it could be copied directly on the board, or ironed on as a toner transfer (more materials expense for that, though).

Forget the drill press, I've tried a 1mm in a hand drill and the point's so sharp it doesn't slip.


 
 Return to top of page · Post #: 11 · Written at 9:41:57 PM on 5 February 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

Forget the drill press, I've tried a 1mm in a hand drill and the point's so sharp it doesn't slip.

I buy 1mm drills 3 at a time. I name them Snap, Crack and Pop.


 
 Return to top of page · Post #: 12 · Written at 9:57:27 PM on 5 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

Sue, that's such a simple board (compared to what I'm used to) I'll happily do it for you.


 
 Return to top of page · Post #: 13 · Written at 10:45:34 PM on 5 February 2018.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

1mm drills self destruct as often they are run too slow. Ideal is often around 10,000 rpm or more. A chuck being the other problem.

The two fastest items I would have is the die grinder .33,000 RPM or an air drill.

Marc


 
 Return to top of page · Post #: 14 · Written at 12:49:44 AM on 6 February 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

A chuck being the other problem.

I have a mini chuck for bits up to about 6mm, but the 1mm drills are very brittle. I just keep a drawer full of them.


 
 Return to top of page · Post #: 15 · Written at 8:32:12 AM on 6 February 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2013

Masochists!!

Confession - I don't have the fine motor control or the patience. So much easier to let the computer do it....


 
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