Maplin JLH 50 watt amplifier article.

[nigelwright7557]

Here is all the info on the Maplin 50 watt JLH amplifier.

50W HiFi Power Amplifier LW35Q Maplin Kit

 

[homemodder]

Thanks. Do you have the article of the switchmode power supply, Id like to get my hands on that too. This is the stuff I messed about 20 years ago.

 

[nigelwright7557]

Sorry I dont have details of the SMPS.

I built one around 1980. It was built for a disco but wasnt loud enough, in the end I went with the Maplin 225WRMS amplifier.

 

[sreten]

Hi, AFAIK it was not designed by the esteemed JLH, rgds, sreten.

 

[madtecchy]

Hi Nigel .
By any chance do you have the details for the 1.2 Kwatt maplin amplifier kit

Regards Ian

 

[nigelwright7557]

Hi Nigel .
By any chance do you have the details for the 1.2 Kwatt maplin amplifier kit

Regards Ian

Sorry I dont.

 

[blu_glo]

hi still looking for the smpsu circuit for the 50W maplin amp? I may have it if still required! will have to scan it in!

 

[blu_glo]

cant help but think the original design suffered increased THD for having output fuse - I would scrap it and instead have 2 off same in each AC winding of the transformer before bridge rectifier.....

 

[blu_glo]

I would like to get my mitts on a couple of these maplin 50W pcbs - in any working order- but must be complete with the r/a heatsink brackets!

 

[jaycee]

I wouldn't imagine the SMPS is worth having by modern standards, except for possibly details on winding of the transformer. Nowadays you could build a simpler, more efficient SMPS using a controller like the TL494 or SG3525. The hard part is winding a transformer!

 

[AndrewT]

It's not like any JLH that I have seen.
I do see text credit to Dennis Butcher and John Mosely.

For a 1993 publication, it does show rather old transistor models.

 

[Itsmee]

Dennis Butcher and John Mosely only revamped the article, they didn't have anything to do with the design.

 

[blu_glo]

😕 I never saw any reference to it being a JLH design. I remember that amp being described in particular detail in Maplins old catalogues which were back then (1980s) still a mine of information....

 

[blu_glo]

BTW: the SMPSU as I remember was to convert the kit to work off 12V car battery, ie turn it into a car amplifier. The design could still be followed successfully today and did feature a SMPSU chip either 494 or similar...

 

[Itsmee]

If I remember correctly, the amp was taken from an RCA data sheet from the late 70's.

 

[blu_glo]

RCA datasheet?

Hi out of interest, would you be able to identify the original part number/data sheet this appeared in?

BR,

Si.

 

[Itsmee]

No, sorry, it was an old design when I joined the company, the application data book has long gone, and I left Maplin's over 15 years ago.
I have tried Googling for it without result.

 

[blu_glo]

I now am proud owner of two populated boards and brackets. A few dry joints have developed so I'm going to carefully strip and repopulate them.
Someone also had a field-day with the heat-sink compound....

I also read the article posed on earlier post and noticed one of their power supply suggestions could feed it up to +/-39V which clearly exceeds the 60V Vce rating of Q4 and Q5
(at maximum voltage swings on their collectors).

Its probably alright if you don't drive it hard, but all the other transistors are 80V ones it seems silly to leave such a chink in the amp's armour so to speak....
I'll plumb for 2N5679/81 which are still available.

 

[blu_glo]

Maplin High Quality Power supply PCB (Not the switch mode one - the one with the TO-220 rectifiers and radial caps mounted lying down) - Does anyone have any data or original stock code or articles thereof? I did have the maplins magazines but cant seem to find them since moving house.