I recenntly bought two 1980's Maplin 50 watt Hi Fi amplifier modules off ebay.
One was supposed to be working and the other had transistors missing.
The one that was supposed to working was osicllatiing so I fixed that with a capacitor in the VAS across c-b.
The other had obsolete transistors missing so I found modern equivalents just to get it going.
The amplifier just wouldnt work with the new transistors.
I eventuall tracked down a high voltage on Q5 base that shouldnt be there.
I tested the transistor and it DVMed fine. BC and BE low resistance one way and high the other with high resistance from c-e. I checked Q4 too then it struck me they both chekced out fine in teh same phase yet one is NPN and the other is PNP. Q5 was the wrong transistor !
So I changed Q5 for a modern equiv just to try it and the amp burst into life.
Amps can be hard enough tto fault find without people putting in worng components.
I just need to tidy up the pcb now and it will another addition to my collection of old amps.
Here is a picture of the first working one.
http://www.ckp-railways.talktalk.net/m50.jpg
One was supposed to be working and the other had transistors missing.
The one that was supposed to working was osicllatiing so I fixed that with a capacitor in the VAS across c-b.
The other had obsolete transistors missing so I found modern equivalents just to get it going.
The amplifier just wouldnt work with the new transistors.
I eventuall tracked down a high voltage on Q5 base that shouldnt be there.
I tested the transistor and it DVMed fine. BC and BE low resistance one way and high the other with high resistance from c-e. I checked Q4 too then it struck me they both chekced out fine in teh same phase yet one is NPN and the other is PNP. Q5 was the wrong transistor !
So I changed Q5 for a modern equiv just to try it and the amp burst into life.
Amps can be hard enough tto fault find without people putting in worng components.
I just need to tidy up the pcb now and it will another addition to my collection of old amps.
Here is a picture of the first working one.
http://www.ckp-railways.talktalk.net/m50.jpg
Ian,
here's two of the magazine articles. Apparently it was reprinted a few times over the years.
50W HiFi Power Amplifier LW35Q Maplin Kit
50W HiFi Power Amplifier Maplin
here's two of the magazine articles. Apparently it was reprinted a few times over the years.
50W HiFi Power Amplifier LW35Q Maplin Kit
50W HiFi Power Amplifier Maplin
Don't know about their SQ, never heard them.
I'm still using a pair of Crimson Electrik CE1708 modules (from about 1979) that superficially don't look any more sohisticated and they sound rather crispy. I traced the Crimson circuit out once and decided they were like a Quad 303 circuit on steroids. I could be all wrong about that, it was a long time ago when I knew even less than I do now!
I'm still using a pair of Crimson Electrik CE1708 modules (from about 1979) that superficially don't look any more sohisticated and they sound rather crispy. I traced the Crimson circuit out once and decided they were like a Quad 303 circuit on steroids. I could be all wrong about that, it was a long time ago when I knew even less than I do now!
I had forgotten how good these little amps sound.
It seems to have a good range and sounds very clean.
I originally made one in 1980 for use on a disco.
It sounded great but wasnt loud enough for a disco so I bought a Maplin 225WRMS amplifier module.
Yes they still do the thick catalogues.
My local Maplin is less than a mile away and is always handy for the odd component I am short of. They are pretty expensive tho, 16p for a resistor when I buy them from RS for a penny. But in an emergency Maplin are useful.
I have been a customer of Maplin since 1980.
They used to do some good gear. I built their mobile disco with record decks. preamps, amplifiers and sound to light in 1980.
Tracked down some of the obsolete transistors to ebay of all places.
BD711, BD712, BC141 and BC161.
I have uploaded the schematic for the Crimson PCB you seem to have, to:-http://homepage.ntlworld.com/bepowell/schematics/35_01-5.pdf
The output stage was like the Quad 303 but I added the crossover diode after issue 3. See:-http://homepage.ntlworld.com/bepowell/schematics/Crimson%20Power%20Amp%20PCB%20Data%201976%20Onwards.docx
Thanks for sorting out the link Zen Mod.
The other file is on http://homepage.ntlworld.com/bepowell/schematics/35_01-5.pdf
The other file is on http://homepage.ntlworld.com/bepowell/schematics/35_01-5.pdf
Brian,
Thanks for the schematic. It's really good that you are documenting your older designs.
The SQ comment was unfair as that was listening on headphones before I 'refreshed' the whole amp last year.
Apart from replacement of old electros etc, I used your Iss 5 parts list to convert my CE1708's to CE1008 but with 4R load line limit resistors and then ran it all off the lower voltage transformer taps.
My modules are Iss 4; very similar to Iss 5 as you told me by PM last year.
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