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Old 24th May 2004, 12:37 AM   #1
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Default Rodek output stage rebuild.

Well, this was an interesting project. I don't do much with car audio at all.

A friend gave me a dead Rodek RA 280 amplifier. I looked at it and the construction and parts seemed to be somewhat nice for a small car amplifier. There was something about it I liked. Also, the fact that it is discreet SS, not full of ic's.

I found by testing it that one of the eight output transistors had a CE short. They were sets of TIP35C and TIP36C and four per channel.

I was thinking of what I would like to use in there for transistors and remembered that I had a box of onsemi MJL21193 and MJL21194 transistors, just the right amount to do this amp.

I checked to make sure they'd fit, since they are larger than the TIP transistors, and they just fit perfectly. So I put them all in there and powered it up. Boy, I must say, this thing sounds nice for a car amp. The transistors I put in there are a lot nicer than the ones I took out, but I wasn't completely sure of how it would sound once it was done. Needless to say, I'm pleased very much with this amplifier.

Has anyone else had experience with this model? It is an older one. Seems early 90's. I figure that such a transistor upgrade could make a good difference in a lot of cases.
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Old 7th June 2004, 06:20 AM   #2
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No one has any comments on my work with this amp...
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Old 10th June 2004, 05:49 AM   #3
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Duo wrote:

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No one has any comments on my work with this amp...
Hey Duo, those Rodeks are great amps. Congratulations on reviving one! Early 90's is a correct guess.

IIRC, the 280 is 80WPC into 4 ohms, 160WPC into 2 ohms, rated at a flat 12 Volts. Few car amps surpass it in build quality or sound quality.

The TIP35/36 were used in quite a few nice car amps in that period. Aren't they TO-218 case Darlington's? I'm not familiar with the MJL21193/4's you used, but I think I still have an amp around here that uses the TIP35/36's. What kind of improvement would you expect from such an upgrade?

Hold on to that amp. It is good enough to demonstrate weaknesses in the rest of your car stereo. It's 'clean' enough and powerful enough to be an excellent mid/high, fullrange, or subwoofer amp. With real 2 ohm stability, it will also easily run 4 fullrange speakers plus subwoofers with proper passive crossovers.

Tim
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Old 10th June 2004, 07:09 AM   #4
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Hi there, thanks for your reply.

Yes, I agree with you about this amplifier. It is very nice. I am planning on using it for a full range system in the car. I tried it in the house so far and its quality is quite observable.

The original transistors were not darlington, just ordinary output type transistors.

The new MJ series, which are motorola (on semi) transistors, are very nice. They have a much higher power rating than that of the original transistors, better bandwidth product, and generally a larger SOAR. They are specifically designed for high power audio, and they definitely serve the purpose well.

The amplifier is very stable with these transistors in it and has good over-current protection. I really like it.
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