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Old 13th February 2007, 01:59 PM   #1
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Default TO-3 Bipolar Output Transistors

I have an older 125W amplifier design that I would like to update with newer devices. The original design used parallel TO-3 packages for the outputs.

The drivers were TO-220.

I know that 2SA1943/2SC5200 pairs are popular. Are there similar parts available in TO-3?

The original drivers were TIP41C & TIP42C. I thought I migt replace these with MJE15030/MJE15031. Other thoughts?

Thanks
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Old 13th February 2007, 02:07 PM   #2
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Default some input

what's the problem with the original devices? do you have it in your mind that that is where the hinge of fidelity lies? don't forget the amp is probably loaded with junk parts and might be better suited for a good recapping. just a thought.
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Old 13th February 2007, 02:17 PM   #3
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This amplifier was considered very good in its day. I have other updates planned including caps.

One of the attributes of this amplifier is that it had very good heatsinks. They were hard coat anodized so that insulators weren't needed under the transistors. This improved thermal conductivity. I don't want to mess with the transistor mounting
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Old 13th February 2007, 02:19 PM   #4
anatech is offline anatech  Canada
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Hi danville,
I really have to agree with RetroAudio here. Update the components where they matter. If you don't know what matters, don't do anything until you understand what you are doing.

Also, many amplifiers will oscillate with newer / faster output devices. you can't just stick parts in without understanding what is going on.

Now, what is the make and model of this poor old thing? There are newer devices made in TO-3 style. You may be further ahead to use matched pairs (matching the transistors in gain where it matters).

-Chris
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Old 13th February 2007, 03:02 PM   #5
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I understand your concern. I designed power amplifiers and preamplifiers in my youth. I have a patent (expired) of a phono preamplifier.

The company was Van Alstine Audio Systems (VA Systems). This was a company that was founded by Frank Van Alstine, myself and two others in 1976. Frank Van Alstine left the company in 1978. I was one of the two electrical engineers in the company.

The amplifier is a VA Model 3. I know this amplifier quite well. I believe that I could design a respectable amplifier today.

I certainly understand that I may need to make adjustments if I change transistors. I can deal with this. At the moment, I am playing. Isn't this what DIYAudio is about?
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Old 13th February 2007, 03:30 PM   #6
DRC is offline DRC  United Kingdom
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MJ15003 & MJ15004 ?

not nearly so good but i don't think there is much choice, in TO-3

please post if you find something better
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Old 13th February 2007, 03:51 PM   #7
MikeB is offline MikeB  Germany
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MJ15024/15025, MJ21194/21193 ?
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Old 13th February 2007, 04:20 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
since you mentioned 1943/5200 I take it that "modern" =hFE>2MHz.

ONsemi only do MJL (To264 plastic package) faster than 4MHz.
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Old 13th February 2007, 05:47 PM   #9
anatech is offline anatech  Canada
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Hi danville,
Quote:
The amplifier is a VA Model 3. I know this amplifier quite well. I believe that I could design a respectable amplifier today.
That throws a whole new light on things, now doesn't it? Not knowing your experience, we would err on the safe side.
Quote:
At the moment, I am playing. Isn't this what DIYAudio is about?
Heck YES! Just safely, that's all.

With regard to output transistors I'd have to recommend MJW1302A and MJW3281A, data sheet here. I tried the lower powered devices (MJW0302A and MJW0281A datasheet ) and was blown away by the performance. N and P matching was very close. Gain variations were lower than any other device to date from anyone (US manufacture). Those are both the plastic cases.

I have tried MJ21195 and MJ21196. They are also very good, but NPN to PNP gain varied 2:1. At tleast that's better than new samples of MJ15003 and MJ15004 at 3:1. The parameters are much tighter than I've seen in the past. This means that it's almost like buying preselected parts. Of course, these in a TO-3 case.

-Chris
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Old 13th February 2007, 06:11 PM   #10
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Quote:
Originally posted by danville
The amplifier is a VA Model 3. I know this amplifier quite well. I believe that I could design a respectable amplifier today.
People may give you more valuable help if you:

1) Specify max +/- rail voltage supply

2) The value of main smoothing capacitors. Type of circuit protectors if present.

3) The signature of old power devices

4) How many pairs per channel are actually employed.

5) a general description of the topology of the whole amplifier, in order to evalutate maximum gain, compensation and safety margins.

Hi
Piercarlo
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