I happened upon this link while assisting a fellow AKer (no affiliation). Interesting reading for DIYers...
http://www.ramlabs-musicreference.com/bio.html
http://www.ramlabs-musicreference.com/bio.html
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Good advice from Roger Modjeski
- Thread starter eiraved
- Start date
Ray Gianelli
Super Member
From the linked article:
I repaired an average of 10 pieces a day
I was averaging a unit an hour, start to finish, including writing the ticket.
I had to raise an eyebrow at this.
I did like what he had to say about component derating.
I repaired an average of 10 pieces a day
I was averaging a unit an hour, start to finish, including writing the ticket.
I had to raise an eyebrow at this.
I did like what he had to say about component derating.
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I find it hard to believe. Time to open the unit and close back up takes time, it's like 15mins already unless you know the unit by heart. For simple tube power amp, it might be a little faster. For SS with pcb, taking out and put back the pcb takes a lot of time. Even for tube amps, if it is an integrated amp or with radio, there is a lot more stuffs to go through.
then come the troubleshoot part. Try having 2 blown transistors, one blown diode and one blow resistor like what I just had two days ago!!! I designed the stupid circuit, who know the circuit better than me? I spent over 3 hours just on pcb time, no assembly and disassembly of the unit. I almost panic!!! Maybe I suck in troubleshooting, but it's not going to be fast even for experts.
I worked in field service of Norelco micro cassette dictating recorders in the late 70s, there was a chief guy on the bench in the office. We only service 5 or 6 models, we knew the machines by heart. For very smooth day, you can do 10 a day......BUT there were always a few that made your hair turn grey. That say 10% of the bad ones took like 90% of the time. There were always one or two that sat on top of the bench for months not able to fit. We had to give out loaners and take the time to fix it.
How about you have to spend part of the day talking to customers, listening to their complains and write it down. Time to order parts. Then explain to customer what is wrong.
No, 10 a day AVERAGE, that sounds like......you know what I'm going to say.
then come the troubleshoot part. Try having 2 blown transistors, one blown diode and one blow resistor like what I just had two days ago!!! I designed the stupid circuit, who know the circuit better than me? I spent over 3 hours just on pcb time, no assembly and disassembly of the unit. I almost panic!!! Maybe I suck in troubleshooting, but it's not going to be fast even for experts.
I worked in field service of Norelco micro cassette dictating recorders in the late 70s, there was a chief guy on the bench in the office. We only service 5 or 6 models, we knew the machines by heart. For very smooth day, you can do 10 a day......BUT there were always a few that made your hair turn grey. That say 10% of the bad ones took like 90% of the time. There were always one or two that sat on top of the bench for months not able to fit. We had to give out loaners and take the time to fix it.
How about you have to spend part of the day talking to customers, listening to their complains and write it down. Time to order parts. Then explain to customer what is wrong.
No, 10 a day AVERAGE, that sounds like......you know what I'm going to say.
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I don't agree with his assertion tube instruments are more reliable. I think he is comparing tubes to SS stuffs from the early 70s. transistors and IC gone through a quantum leap to say the least. I remember before you cannot heat the transistors too much, now you have IC that you actually solder by heating the top or using hot air gun. This is because wire bonding to the die improved tremendously. It used to the bonding melt under high temp, not anymore. I just finished soldering a cap over the matched pair of BC546, I rap the two transistors together, then fill solder on top and squeeze from all sides to make the cap fit tight over the two transistors. The process is like 5minutes. The transistors still alive and kicking. I did this on all my matching pairs, never have any issue. SS comes a long long way in reliability. There is no comparison on reliability between SS and tubes, SS win hands down by a mile. Not to mention with all the high voltages in the tube amps, those cap get old and they blow. I don't think big caps in SS amp blow that often.
Regarding to noise of resistor. This is very well researched and documented. Noise of resistor is categorized into 3 types, flicker noise, thermal noise and shot noise. thermal noise depends ONLY on resistance, shot noise is current noise when current flowing through the resistor. Both are ABSOLUTELY independent to what resistors material, expensive or cheap. Just only depend on temperature and current going through. The only noise is flicker noise that is resistor material dependent. This is called 1/f noise that is inverse proportional to frequency. Carbon resistor has 1/f noise, metal film resistor don't.This flicker noise ( also called pop corn noise). Flicker noise is the main thing you should look out when choosing resistors on noise. Of cause voltage coef of resistor and capacitor is important for low distortion circuits.
I scan through the rest quickly, he's just bragging. I kind of feel he is looking at everything in the point of view of audio amps only.
Regarding to noise of resistor. This is very well researched and documented. Noise of resistor is categorized into 3 types, flicker noise, thermal noise and shot noise. thermal noise depends ONLY on resistance, shot noise is current noise when current flowing through the resistor. Both are ABSOLUTELY independent to what resistors material, expensive or cheap. Just only depend on temperature and current going through. The only noise is flicker noise that is resistor material dependent. This is called 1/f noise that is inverse proportional to frequency. Carbon resistor has 1/f noise, metal film resistor don't.This flicker noise ( also called pop corn noise). Flicker noise is the main thing you should look out when choosing resistors on noise. Of cause voltage coef of resistor and capacitor is important for low distortion circuits.
I scan through the rest quickly, he's just bragging. I kind of feel he is looking at everything in the point of view of audio amps only.
