Resurrection: Old Parts - New Amp.

[MJL21193]

Come now Jacco, I'm sure you have a box full of those somewhere...

They are from a Pioneer, one of the "silver" ones - badly beaten up on the outside, but working just fine. Missing knobs and the plastic lens that covers the magnificent flouro VU meters was cracked but I did manage to save the display. I may use it for this if I can figure out how it wires up. I should have payed more attention when I stripped the amp.

[MJL21193]

Well, I've hit a snag...

The 2SC2291 is common base, not common emitter like the 2SA798. Somehow I completely forgot about this. Suitable for a cascode or current mirror but not the differential input. Curses!

A decision to make: Change the input devices to the C1845/A992 and eliminate the cascode or change the topology.

Luckily I didn't have much of the layout done.

[MJL21193]

After much deliberation I've decided to stick with the symmetrical. This still looks just as good, simulation wise, and saves a few components to fight another day.

New schematic below. The cascodes are no longer needed as the C1845/A992 are 120V devices. Other than that, no changes.

[jaycee]

Cascodes may be beneficial anyway.

You've also reminded me that this kind of topology is one that I havent yet dissected in a simulator. I may have to have a go at it! I did "Simulate" a Leach ages ago, but I didn't really know what I was doing with LTSpice then.

[EWorkshop1708]

Originally posted by MJL21193
After much deliberation I've decided to stick with the symmetrical. This still looks just as good, simulation wise, and saves a few components to fight another day.

New schematic below. The cascodes are no longer needed as the C1845/A992 are 120V devices. Other than that, no changes.

NICE!

I like to see when good old parts get used instead of thrown away!
Nice amp design!

BTW, I just scrapped and disassembled 5 televisions, and now have plenty of power devices, power resistors, assortments of valuable capacitors, coils, and lots more! Lots of good hard to find stuff. Now I'll be searching everywhere for televisions!

After doing the math, savings exceed $100 or more & time invested vs going to parts express & radioshack to buy all those individual components new! Old parts are GREAT! Certain types of parts never go bad anyway.

Keep us posted on the amp. I love those huge older power output transistors you are using!

[jaycee]

CRT monitors are good too, theres often very high quality devices in there as monitors have tighter timings than a TV does. The only thing is, where you would have found good high voltage low Cob devices, you now find an IC.

[EWorkshop1708]

Originally posted by jaycee
CRT monitors are good too, theres often very high quality devices in there as monitors have tighter timings than a TV does. The only thing is, where you would have found good high voltage low Cob devices, you now find an IC.

Very true jaycee. I've stripped a few computer monitors in my day. I have a few bad ones I've got and haven't broke em down yet.

I forgot to mention an awesome find from a big-screen projection TV, the SMPS transformer.....This thing is HUGE! Like almost as big as a 60hz transformer, but meant for typical HF SMPS usage!

That will be the new transformer for my offline SMPS for a new amplifier! Heck with the expensive 60hz toroid now! Planning on over 600W RMS total to run multiple amp channels!

OLD PARTS RULE!

[jaycee]

I've been recycling parts since.. oh since i started electronics as a kid it was the only way i could get any parts at all!

It annoys me how much stuff goes to the bin, usually just because of a simple fault. I was given a Denon microsystem by a guy from Freecycle, it'd stopped working and he'd been told it wasnt worth fixing... he told me "im sure it's something simple but I don't know much about these things". Sure enough, the fault was that a 1A fuse had blown from old age.

[MJL21193]

Originally posted by jaycee
Cascodes may be beneficial anyway.

You've also reminded me that this kind of topology is one that I havent yet dissected in a simulator. I may have to have a go at it! I did "Simulate" a Leach ages ago, but I didn't really know what I was doing with LTSpice then.

Originally posted by EWorkshop1708


NICE!

I like to see when good old parts get used instead of thrown away!
Nice amp design!

BTW, I just scrapped and disassembled 5 televisions, and now have plenty of power devices, power resistors, assortments of valuable capacitors, coils, and lots more! Lots of good hard to find stuff. Now I'll be searching everywhere for televisions!

After doing the math, savings exceed $100 or more & time invested vs going to parts express & radioshack to buy all those individual components new! Old parts are GREAT! Certain types of parts never go bad anyway.

Keep us posted on the amp. I love those huge older power output transistors you are using!

Sorry for the late reply - I've been busier than normal.

Jaycee: Same here. I'm getting better and better with the simulator and my understanding of amp design is growing with it. I'm at the point now where I can sim it, lay it out and build it...and have it work as predicted! A major stride but there is only so many amps that I need, so this was an attempt to "mix it up" or make things less boring (yawn).
Bit of a joke there...

EW: Thanks. Nice to hear from you - your help has been valuable in the past.
I love cracking open an old amp or receiver to find what goodies are waiting inside. I'd like to see more of it in DIY land, too many have the idea the only way to build a great amp is with new parts bought at a premium. I too was guilty of this not long ago.
Savings can be extreme when you have the ability to reassign parts to a new amp, especially the higher cost parts like transformers, heatsinks and outputs.

Anyway, a strong start but I'm stalled. I don't have enough free time to pursue this right now, so I'll put it on hold for a while.

[limono]

Nice post -reminded me of a leftowers of old Mitsubishi amp with Sanken 2SA1216 /2SC2922 and NEC C2275A/A 985A and STK3122m in I asssume pre stage and big 2x30V 2X35V Tamura Power transformer.I wonder if I could build some thing with those. I remember that amp was typically Japanese soundig (bright and etched ) and PT was a little noisy.Than it "fell" from the shelf and I decided to save the guts. Hm , since snow is falling down maybe it's time to start monkey around with those.