https://www.diyaudio.com/community/threads/jlh-10-watt-class-a-amplifier.3075/post-7716150
You were very lucky to have anyone in your life to support your electronics interest. I was in high school, about the same time (~1969), and had very little money to spend, most of which I spend on magazines like those that advertised SWTP.
I found my "Lil Tiger", or what became of it in the basement. It probably still works but I just keep it for sentimental reasons. It drove a sub-woofer and is built into a box with the XO. Not a lot of power but it sounded fine. No one I knew had ever heard of using a sub in those days, so it impressed a lot of people.
You were very lucky to have anyone in your life to support your electronics interest. I was in high school, about the same time (~1969), and had very little money to spend, most of which I spend on magazines like those that advertised SWTP.
I found my "Lil Tiger", or what became of it in the basement. It probably still works but I just keep it for sentimental reasons. It drove a sub-woofer and is built into a box with the XO. Not a lot of power but it sounded fine. No one I knew had ever heard of using a sub in those days, so it impressed a lot of people.
You were ahead of your time with that, nice!
The kit of parts with circuit board was $10 and I told my parents it was all that I wanted for Christmas.
They were very supportive of anything having to do with electronics, science or books.
My brother (5 years older) built one also, and helped to find power supply parts.
I saved for a long time to buy those parts.
I still have mine also for sentimental reasons but it doesn't work having blown up so many times.
They didn't like 4 ohm loads!
The kit of parts with circuit board was $10 and I told my parents it was all that I wanted for Christmas.
They were very supportive of anything having to do with electronics, science or books.
My brother (5 years older) built one also, and helped to find power supply parts.
I saved for a long time to buy those parts.
I still have mine also for sentimental reasons but it doesn't work having blown up so many times.
They didn't like 4 ohm loads!
You'll notice I didn't show the insides. It's a mess and includes lots of technical sins like using the chassis for ground connections. But somehow, I got away with it. Many of the parts were scrap salvage. There was no Radio Shack etc in my hometown in Alberta, Canada. I ordered parts from Allied Electronics by snail-mail, a long way from Northern Canada and subject to import duties. I did not extend the OP to EF3 but the outputs are larger with emitter resistors and mounted on a heat sink on the back. There is no isolated mounting on the PNP, ie collector is "ground". You may also notice that the ~chassis and ~box are home made.
PS: There was a supplier somewhere in Ontario that I bought cheap "Radio Speakers of Canada" 12" and 15" speakers. They had paper suspension and ~1" voice coils. That was later when I had a construction job and a bit of money.
PS: There was a supplier somewhere in Ontario that I bought cheap "Radio Speakers of Canada" 12" and 15" speakers. They had paper suspension and ~1" voice coils. That was later when I had a construction job and a bit of money.
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A lot of people here don’t seem to remember the good ol days where this is what “DIY audio” was. No one could accumulate the masses of money needed to buy a decent stereo. Or even do a DIY build as we know them today. You salvaged parts. You re-wound transformers. You used the chassis for ground (and only used a 2 prong plug). There WAS no LM3886, and the LM377 sounded like @$$. You didnt own an oscilloscope, distortion analyzer, or variac. But somehow managed to make amplifiers that worked - using only the few dollars (or cents) that were left over after spending everything else on responsibilities.
When I only had one amp, I finished it on a scrap piece of pine wood, no box, also mounted the
power supply on it and the 2N404 Ge preamp that was also from Popular Electronics. The Pre with
PNP transistors ran on a negative supply that I had to use batteries for. I guess I never figured out
that I could have just tapped off the transformer with one more diode to make a negative supply.
Built many Dynaco kits around that time, then a few years later we discovered an electronics surplus
place in our home town - amazing. They had some strange chassis with everything to make a
stereo 50W/ch amp. PSU with huge caps and diodes, heat sinks and PNP Si power transistors, even
more than one dual input transistor, all for $5. Turned it into an almost clone of the Citation 12.
power supply on it and the 2N404 Ge preamp that was also from Popular Electronics. The Pre with
PNP transistors ran on a negative supply that I had to use batteries for. I guess I never figured out
that I could have just tapped off the transformer with one more diode to make a negative supply.
Built many Dynaco kits around that time, then a few years later we discovered an electronics surplus
place in our home town - amazing. They had some strange chassis with everything to make a
stereo 50W/ch amp. PSU with huge caps and diodes, heat sinks and PNP Si power transistors, even
more than one dual input transistor, all for $5. Turned it into an almost clone of the Citation 12.
I built a sorta Leach clone with the components I could scam in the wilds of Ithaca, NY circa 1977-78. Poly Paks had a say in the deal, and I bought the output devices used from a guy in town who repaired stereos for a living. The chassis was a remnant from an old barcode reader from the company where I worked at the time. That amp served me faithfully through the 80's into the early 90's. It was ugly, but functional. I pieced the PCBs together using rub-on resist pads, with rub-a-dub marker to connect the pads together. As long a you used 1 oz copper, you could get away with etching the boards without a lot of pinholes in the tracks. Having said that, the ferric chloride I used to etch the boards was a PITA to deal with (especially the staining), and it gave me contact dermatitis on more than one occasion.
I never had a chance to build SWTP stuff specifically, because I always had to custom design around what I could get. There was one which stood out - a challenge to build the BEST possible amp using only what could be sourced from Radio Shack. It ended up being 10 watts per channel, powered by their 25.2VCT/2A transformer. Matched diff pair with a current source tail, current mirror, current source loaded VAS, CFP (unity gain version) outputs using TIP41/2. The 2N3055 version did not do as well at 4 or 2 ohm due to beta droop. It burnt the 2N3904/6 drivers out in testing, the TIPs didn’t. It did sound very good - dare I say “blameless”….. I would like to have had nice TO-39 drivers, but what in the world would one use for a PNP? I wasn’t paying ECG prices, and the idea was “all” RS parts.
The diff pair came from a grab bag of 40 transistors they used to sell for like $2. Yeah, you could find two identical without buying out the store. No idea what they WERE as most were unmarked, an the rest house numbered.
At one time, the Shack was selling some nice complementary TO-3’s (in addition to the 3055/2955) the only catch was they were 40V/15A devices. They were long discontinued by the time the “challenge” had been issued. Hell, the 36 volt power supply was the real limit anyway - TO-3s wouldn’t really have helped much in the real world.
The diff pair came from a grab bag of 40 transistors they used to sell for like $2. Yeah, you could find two identical without buying out the store. No idea what they WERE as most were unmarked, an the rest house numbered.
At one time, the Shack was selling some nice complementary TO-3’s (in addition to the 3055/2955) the only catch was they were 40V/15A devices. They were long discontinued by the time the “challenge” had been issued. Hell, the 36 volt power supply was the real limit anyway - TO-3s wouldn’t really have helped much in the real world.
Original Lil Tiger LtSpice Sim:
https://www.diyaudio.com/community/threads/swtpc-lil-tiger-amp-18w-spice-simulation.414282/
https://www.diyaudio.com/community/threads/swtpc-lil-tiger-amp-18w-spice-simulation.414282/
I did my diy exploration before SWTC started advertising. I had been repairing the 1954 TV with new tubes from the corner store since age 8. I had tried to repair my Mother's RCA stereo from Top Value Stamps (Kroger). A new needle did not stop it from ripping the highs off of records. Then in disassembly I found it had a 2" driver in each 10"x14"x3" "speaker". The '59 Ford Ranch Wagon handed down by my Dad had a better speaker, a 6"x9" in a 4 cuft dash.
By 1968 I had $3400 saved up for college. 8 years of mowing lawns, raking leaves, cleaning gutters, and working in a wire mesh factory summers of '66, '67, '68 added up. I was impressed by the sound of the dynaco SCA35 + gerrard turntable in the college library listening rooms. Before college every morning I was driving school busses for my alma matter. No loans, free room & board at my parents, I paid cash for my college education. So when a used dynakit PAS2 + ST70 + AR turntable with Audio Dynamics cartridge showed up in the shopper paper for $150, I was loaded & dangerous. With the criticism and help of the MacIntosh salesman at Home Entertainment amp clinic, I managed to replace some capacitors and the rectifier tube to achieve > 25 watts/ch of <1% HD sound. With a new stylus the AD mag phono cartridge did not damage the beautiful LP's I was buying. My ears were perfect before ROTC camp summer of '69.
I used some diy speakers for a couple of years, 6"x9" Quams in cardboard boxes with a 1" square vent in the back. Getting the '59 ford to stop burning a quart of oil every 25 miles took priority to better speakers. By 1973 I tried my first SWTC project, a sea sounds box to play at night to cover the hoots, phone call klaxons, vent blasts and general chaos of the Marathon oil refinery 2 blocks from my rent house. Peaceful sleep for a few months until the SWTC box started making huge bangs through the ST70 at random times. I never was tempted to dive into SWTC again.
By 1968 I had $3400 saved up for college. 8 years of mowing lawns, raking leaves, cleaning gutters, and working in a wire mesh factory summers of '66, '67, '68 added up. I was impressed by the sound of the dynaco SCA35 + gerrard turntable in the college library listening rooms. Before college every morning I was driving school busses for my alma matter. No loans, free room & board at my parents, I paid cash for my college education. So when a used dynakit PAS2 + ST70 + AR turntable with Audio Dynamics cartridge showed up in the shopper paper for $150, I was loaded & dangerous. With the criticism and help of the MacIntosh salesman at Home Entertainment amp clinic, I managed to replace some capacitors and the rectifier tube to achieve > 25 watts/ch of <1% HD sound. With a new stylus the AD mag phono cartridge did not damage the beautiful LP's I was buying. My ears were perfect before ROTC camp summer of '69.
I used some diy speakers for a couple of years, 6"x9" Quams in cardboard boxes with a 1" square vent in the back. Getting the '59 ford to stop burning a quart of oil every 25 miles took priority to better speakers. By 1973 I tried my first SWTC project, a sea sounds box to play at night to cover the hoots, phone call klaxons, vent blasts and general chaos of the Marathon oil refinery 2 blocks from my rent house. Peaceful sleep for a few months until the SWTC box started making huge bangs through the ST70 at random times. I never was tempted to dive into SWTC again.
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