information about adastra a50 mixer amp

[byronboy]

Hi,guys. Has anyone any info on adastra public address amp model 952.934uk or A50-50w mixer amp.It is designed for mains or 12v battery use.I have two of these neat looking amps both appear to have the same symptoms,that is, no sound.The output stages appear to be ok.You can hear a slight hum when the speaker is connected.Voltages on the output stage transistors seem about right.No signs of overheating or cracks in the print It uses a 4558 ic and some other small transistors near by with tone controls and 3 input stages making up the main amp pcb.The only added complication is another pcb mounted above with an ne555 timer ic and mc14046bcp chip.It may be being muted but without a circuit diagram it,s a bit tricky.Power supply is very simple,4 bridge rectifiers and smoothing caps and a 11v regulator device.Any help with a circuit would be a great help.
Kind regards, Peter.l

[J M Fahey]

Write Adastra Adastra : Contact trying to sound like a Service Shop owner/tech (as in: "a School we service sent two AdastraXXXX , serial nš:yyyy ", please Email Schematic), and post it here.

[byronboy]

adastra info

Write Adastra Adastra : Contact trying to sound like a Service Shop owner/tech (as in: "a School we service sent two AdastraXXXX , serial nš:yyyy ", please Email Schematic), and post it here.

Cheers, Juan. I will try that and let you know how I get on.Peter.

[Jazz P Bass]

I don't have a clue what they are doing with the mc14046bcp IC.
Check pin 5.
It is the INH input.
A high level will inhibit the output.
http://www.stanford.edu/class/ee133/...MC14046BCP.pdf

[byronboy]

Hi, guys. I contacted adastra as Juan suggested and they emailed the circuit to me.The circuit is for the A50 but the A25 has a similar if less powerful output stage.The no sound problem was due to a faulty thermistor [ tip 31] shape number juc-20f 95degree temp rating.A 47ohm 1/4watt is fitted instead on the A25 model.Thanks to everyone who replied.This is what this forum is all about.I have a complete circuit for a Carlsbro marlin 150 aswell as the adastra circuit in pdf but I,m not sure how to attach them to this reply. Can anybody help?
Cheers, Peter. [byronboy]

[J M Fahey]

Hi brionboy, good you could solve it.
The tip about writing the manufacturer's is Enzo's actually.
Whenever somebody asks for a schematic here, his first response is "DID you write the manufacturers?"
As of those PDFs: when you write, click below in the "advanced" box and a new, more complete window opens.
There you'll find the "manage attachments" option, which accepts
Valid file extensions: aac bmp doc flv gif jpe jpeg jpg m4a mid midi mp3 pdf png psd txt xls xps zip
If too big, write one separate answer for each file.

[byronboy]

Hi guys.
Please find attached circuits for the Adastra A50 mixer amp and complete circuit for the Carlsbro Marlin 150 watt PA amp,which I have managed to source.Hope they will be of use to someone.
Cheers, Peter. {BYRONBOY]