I have an offset rv7 and RV8 at the back of a Rogers a75-s2 amplifier that needs to be adjusted. I don't know how many millivolts the resistance at both ends of its emitter e is. Please help me have a look. The manual of the machine is attached. Thank you,
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Yes, I am also looking for the schematic diagram. Please help me find it if necessary. Thank you,
Why do you think they (actually six trims) need to be trimmed? Is it running hot? Distorted? Have you replaced major parts?
This has driver transistors which makes it early-mid 1960s (or same technology a few years later). These were not precision designs or parts. The trims get the parts to a "working" point, not an "optimum".
The total current of this machine is 1a, and the resistance at both ends of the e pole is 1r=1 ohm. When the machine came back, it checked that the DC voltage of the four e pole resistors behind were uneven, some were 36mv 40mv Therefore, I want to make the DC offset of this machine better adjusted and in a better working state, rather than trying to adjust it casually. As time goes by, the numerical offset of the machine can not be avoided. We can not avoid adjusting it to make it glow with the power of that time. Thank you,
who can help me ?thank you ,
The circuit is similar to that of the Rogers Ravensbourne amplifier.
In that amp, the four presets associated with the four output transistors should be adjusted until the voltage across each of the 1.0 ohm emitter resistors is 25 mV.
You need to fiddle about because, at the same time, you want the DC voltage across the speaker terminals (with speakers connected) to be less than 20 mV.
In that amp, the four presets associated with the four output transistors should be adjusted until the voltage across each of the 1.0 ohm emitter resistors is 25 mV.
You need to fiddle about because, at the same time, you want the DC voltage across the speaker terminals (with speakers connected) to be less than 20 mV.
So it has a transformer coupled output stage, that explains a lot. All the 1 ohm resistors should have the right values.
Then when the bias voltages are set to the usual 26mV, the output DC will be close, and just need a little tweaking
after warming up.
Then when the bias voltages are set to the usual 26mV, the output DC will be close, and just need a little tweaking
after warming up.
The power of this machine is larger than ravensbourne amplifier. The power is 8 ohms 45w+45w. Are the parameters the same? Just a little skeptical,
Hi jacky-bb,
Here is the service manual for the Rogers A75 Series 2 amplifier. This will give you all the information you need. About the mains input voltage (240-245V) specified at steps (g) and (h) on page 8, this is for amplifiers sold in the U.K. Your amplifier’s input voltage is set accordingly to where you bought it. Thus you simply use your mains input voltage as the specified value for these steps.
Do not hesitate to ask me if something is not clear on the attached file. I will do my best to answer your questions.
Have a nice day.
I hope my English is not too bad. It is not my first language.