Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
Allowable drop in gain of a band amp over an hour
What would be normal and what acceptable for a solid state or valve/tube
stage amp. ? Well you would not want the gain/ output audio to go up over an hour of use with a constant input. Testing a solid state amp that had a problem that certainly affected the FET gain killer protection circuit so (falsely) cutting the output over an hour to close to zero. But checking to see if there was any other gain drop problem but then realised I don't know what the norm is. Amp rated at 200W (music power) which I've taken as 100W (continuous RMS if you could). Running a constant source of 1Kz through amp to give a continuous 1/5, 20W in a dummy load , which with heating itself is not necessarily constant. Result of testing over 40 minutes was a 9 percent drop in V rms into the load so about 20 percent drop in equivalent audio watts. No fans on this amp and the heatsink settled at 68 degrees C after about 30 minutes. The output was still dropping after 30 minutes but very much slower and decided to cancel after 40 minutes -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
Posted to sci.electronics.repair
|
|||
|
|||
Allowable drop in gain of a band amp over an hour
N Cook wrote:
What would be normal and what acceptable for a solid state or valve/tube stage amp. ? Well you would not want the gain/ output audio to go up over an hour of use with a constant input. Testing a solid state amp that had a problem that certainly affected the FET gain killer protection circuit so (falsely) cutting the output over an hour to close to zero. But checking to see if there was any other gain drop problem but then realised I don't know what the norm is. Amp rated at 200W (music power) which I've taken as 100W (continuous RMS if you could). Running a constant source of 1Kz through amp to give a continuous 1/5, 20W in a dummy load , which with heating itself is not necessarily constant. Result of testing over 40 minutes was a 9 percent drop in V rms into the load so about 20 percent drop in equivalent audio watts. No fans on this amp and the heatsink settled at 68 degrees C after about 30 minutes. The output was still dropping after 30 minutes but very much slower and decided to cancel after 40 minutes In an ideal world I wouldn`t want a pro amp to drop any level over any amount of time. You should easily be able to locate just where the signal is dropping with a scope. There may be a temperature sensitive device in contact with the heatsink. A constant sine wave isn't a very good way to test an amplifiers long term performance, I`d use a signal more indicative of real life conditions. IMO Ron(UK) |
#3
Posted to sci.electronics.repair
|
|||
|
|||
Allowable drop in gain of a band amp over an hour
N Cook wrote: Result of testing over 40 minutes was a 9 percent drop in V rms into the load so about 20 percent drop in equivalent audio watts. Are you sure the drop in power isn't simply due to the transformer heating up and the consequent rise in winding resistance ? Graham |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Band Amp jig for protecting tubes/valves during repair | Electronics Repair | |||
Voltage drop an issue with small 12v and low amp stuff? | Electronics Repair | |||
B&Q - Staff member goes mad - helps customer for 3/4's of an hour ! | UK diy | |||
Horizontal Band Saw Guides & Such | Metalworking | |||
meaning of "amp hour" battery rating | Electronics |