![]() I might just install exactly 68-Ohm resistors to start instead of 74 and 75 ones that drifted over the years. Still waiting for resistors from digikey - hopefully tomorrow. The ground scheme on this amp chassis is crazy - every stacked cap connection was used as a ground point, plus they were interconnected between them. I installed all new electrolytic capacitors in power supply, in amp and preamp when I started. Non-feedback amplifiers can achieve only about 1 distortion for audio-frequency signals. It is a full blown restoration, literally nothing has worked when I initially got this jukebox, power supply, amplifier, record changer, coin mechanism - you name it - it didn't work. Regarding if I had this hum before or not - I do not know. I have access to one side of the emitter resistors, since they are connected to the flat connector, but it is quite difficult to access the side of resistor where it is connected directly to the back of TO-3 transistor socket. So it is stupid difficult to do any measurements - all I see is a foil side of the boards. Then amplifier boards (one for each channel) are inserted into long flat connectors, and cover that are almost entirely. Output transistors along with emitter resistors and several other parts sit on or under heatsink. It's a complicated amp in terms of construction. Would this be a good idea, or should I leave the amp alone? ![]() ![]() I was thinking about installing 60 or 62 Ohm resistors (exact value) instead to check if I can kill these oscillations. Right now, if measured in-circuit, the resistors are 74 and 75 Ohms, so they're quite a bit off, given the application. ![]() What do experts think about adjust bias current trying to get rid of this initial oscillation? Resistor R66 (68 Ohms) after triple diode in each channel (attached schematic) is pretty much the one that determines the current value. Think of input bias current as being due to current sinks at the input. 2) The problem with bias current is that the resistance of the DC path attached to either input must be low enough to source this current, without developing excessive voltage drop. The resistors used in this amp are crap, so I replaced quite a few already. That way, only 1x the input offset voltage gets onto the output, rather than gain times. When I just turn it on, I hear oscillation for about half a second. I pushed them further up to 30V output (didn't touch the preamp, as volume control is between amp and preamp), and no distortion at 1KHz signal. I am almost done restoring a stereo amplifier from Rowe AMI jukebox, but would like to inquire about one remaining thing.įirst, I pushed the amp boards at rated 0.9V input with 14V output with no distortion. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |