Saturday, January 05, 2008

New Project

Soon, I'll be starting a new project. This project involved the use of the old almost forgotten electronics parts and it is almost extinct. However, due the characteristic and the reliability if used in a well designed circuit, some is still being re-produced and some is even reviving the old abandoned factory. What the heck am I talking about??? well, I left the hi-fi audio hobby many years ago. Most of that time, I am restoring, designing and repairing audio amplifiers used in hi-fi system. I restore mostly vacuum tubes power amplifiers and preamplifier. My first tube amp is a diy and using EL34 tubes which commonly used in guitar amplifiers. But some well known manufacturers is also using them in the home hi-fi system. That time, my housemate gave me a pair of output transformer made by TDK Japan ( those days, TDK makes OPT too, not only table fans). My amplifier is a SE (single ended) type. Then, I made another one using KT88. This one is in a push-pull configuration and gives much higher output power.

After playing and learning about vacuum tubes, I started repairing and restoring old amplifiers. My first restoring job is with QUAD II. This amplifiers is very old and it was produced in a mono block design. They don't use pcb and most tube amplifiers don't use pcb those days. It's all hard-wired!! I still remember that the valve socket is made by McMurdo. One of the QUAD II output transformer is faulty. I have to remove all the wax before I can take it out from the pot and send it for rewinding. NOT everybody can re-wind audio output transformer!!!

I then build another single-ended power amplifier. This one was good. The output power is only 8W r.m.s max. Paired with a high sensitivity speaker, it sings loud! 300B tubes is what I am talking about. The plate voltage was only 350Vdc...oops.... don't get electrocuted by dc voltages! it's more dangerous than ac voltages.

2A3 is also another tubes that is loved by the purist! Although it's max output power is low (2-3W rms).

211 is a much larger tubes. But this one require high plate voltage. It needs about 750-1000Vdc. That's 1kV! You want an amplifier in your room running at 1kV??? I don't mind but making and testing the amplifier is not something that I'll enjoy if it is talking about 1kV.

For now, my new project is based on 6EW7 tubes. This tubes is a twin triode tubes and it is used in vertical deflection circuit in early age TV. Now, where is this tubes will come from for my project? My friend, Ew is going to send me the amplifiers. At this moment, the amplifier is ready assembled by Ew since he is the one winding the opt and designed the amplifier. My job now is to make a speaker box for the speaker. Easy??? not really! I am using a full range driver! That's mean without any crossover circuit and only one driver for each channel. Why? because the amplifier only gives 2W rms max before clipping and full range drivers has high sensitivity! Mine has 89dB/W/m. That's enough for me now. When I have enough money, I'll get the one with 94dB/W/m. Those one can sing loud! but I am not into loud music (SP)..... hi-fi is not about playing loud! It's all about the sound quality (SQ). Hear the highs, the mids, the mid lows, the lows.... hear the details.. the staging etc...SQ!!

Will talk more later when this project starts. For now, I stick to machining some alloys for whatever I can think of.....

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