Morning I have a practically virgin cadet all intact started her up on Sunday and have virtually no output where do I start looking , have swopped valves , cleaned all contacts , tested different inputs , all the same , this unit was inherited and was very seldom used before I got it in 1997 .
any ideas of where to start looking and testing , I have a scope and lots of Fluke testers .
Regards
any ideas of where to start looking and testing , I have a scope and lots of Fluke testers .
Regards
We should be able to help.
Here is a start.
If you do a search this amp has been discussed here before.
dave
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messing withunit
No its been sleeping on top of the cupboard , all the valves are new replaced in 97 all are nice and black , what im getting is distortion on the output sounds like a badly tuned radio , im an electrical hydraulics and pneumatics technician by trade , but am a bit scared of valves , no previous experience ,
was hoping for a person with experience to say ,,, (Dont worry its only the ....... , do this and it will be fine ) I dont want to rip the unit to pieces and its a bum output .
No its been sleeping on top of the cupboard , all the valves are new replaced in 97 all are nice and black , what im getting is distortion on the output sounds like a badly tuned radio , im an electrical hydraulics and pneumatics technician by trade , but am a bit scared of valves , no previous experience ,
was hoping for a person with experience to say ,,, (Dont worry its only the ....... , do this and it will be fine ) I dont want to rip the unit to pieces and its a bum output .
You should plan on replacing the voltage doubler caps (marked 100uF/275V) as shown in the schematic to start - if either of these is bad your B+ will be very low and the symptoms you describe would be the result. When looking for replacements for these two 100uF caps consider ones have a voltage rating of 300V or better, and the highest ripple current rating that will fit in the available space.
At > 40yrs old all of the electrolytics are suspect and I would recommend replacing coupling capacitors as well.
Odd value caps like the 24uF/450V types can be replaced with commonly available 33uF/450V types, although in most cases 22uF/450V types will prove adequate if space for the slightly larger 33uF is not available.
40uF/16V can be replaced with a 47uF/16V type. (Use a good one here, silmic or equivalent as it is in the audio path - radial would be ok since it is unlikely any good audio electrolytics are available in an axial package these days.)
The 100nF/400V coupling caps should be checked and probably replaced. These are also known as 0.1uF/400V and there are many choices.
Finally you may need to go through the pre-amplifier circuitry as well.
I'm assuming resistors are mostly ok, that may not entirely be the case so I would measure ones where the values can be determined unambiguously in circuit, if malfunctions are evident after your first round of work you might need to do some more involved trouble shooting.
Hopefully you can solder, and I recommend before doing anything you read the safety threads.
At > 40yrs old all of the electrolytics are suspect and I would recommend replacing coupling capacitors as well.
Odd value caps like the 24uF/450V types can be replaced with commonly available 33uF/450V types, although in most cases 22uF/450V types will prove adequate if space for the slightly larger 33uF is not available.
40uF/16V can be replaced with a 47uF/16V type. (Use a good one here, silmic or equivalent as it is in the audio path - radial would be ok since it is unlikely any good audio electrolytics are available in an axial package these days.)
The 100nF/400V coupling caps should be checked and probably replaced. These are also known as 0.1uF/400V and there are many choices.
Finally you may need to go through the pre-amplifier circuitry as well.
I'm assuming resistors are mostly ok, that may not entirely be the case so I would measure ones where the values can be determined unambiguously in circuit, if malfunctions are evident after your first round of work you might need to do some more involved trouble shooting.
Hopefully you can solder, and I recommend before doing anything you read the safety threads.
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thanks
I have found one suspect cap so far ( soldering and schematics are no problem -its part of my trade )I used to work for a high end audio dealer and spent a lot of time fixing most of the early Musical Fidelity amps 1992 circa ,
lots of dry joints and psu problems , and virtually all A100 and A 100x amps had issues with the output transistors and wire wound resistors ,I hated the MF products after 3 months on a boat to get here all the big monoblocks had fallen apart ,the valve cd players I used to modify the wiring harness as it used to get stuck in the cd mechanism , the transformers were 220 volt we run on 230volt , lots of fun and games , I think the caps are going to be the first components changed , its really a very basic system but i will need values on the output transformers .
Regards
I have found one suspect cap so far ( soldering and schematics are no problem -its part of my trade )I used to work for a high end audio dealer and spent a lot of time fixing most of the early Musical Fidelity amps 1992 circa ,
lots of dry joints and psu problems , and virtually all A100 and A 100x amps had issues with the output transistors and wire wound resistors ,I hated the MF products after 3 months on a boat to get here all the big monoblocks had fallen apart ,the valve cd players I used to modify the wiring harness as it used to get stuck in the cd mechanism , the transformers were 220 volt we run on 230volt , lots of fun and games , I think the caps are going to be the first components changed , its really a very basic system but i will need values on the output transformers .
Regards
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