PART THREE: Reliving the 1976 sound of Dynaco PAT-5 preamplifier and SWTPC power amplifier!

Gentle reader,

This is the third but not the final post on my gathering the components that made up my first stereo that I built from kits in 1976. Here are the previous installments:

Reliving the 1976 sound of Dynaco PAT-5 preamplifier and SWTPC power amplifier!  

AND
PART TWO: Reliving the 1976 sound of Dynaco PAT-5 preamplifier and SWTPC power amplifier!

Here is a link to a post that lists every article I have written and illustrated regarding stereo equipment:UPDATED Every Vintage Stereo Equipment and Speakers Blog post I have done! UPDATED.

Part one includes a link to the original article I wrote when the idea came to me. I moved to Richmond, Virginia in 1975 and soon met a neighbor my age, one of four brothers and a little sister. He too was into cars and it turns out, stereos. 

At the time I had a plastic "suitcase" stereo. It had a carry handle on top and looked like a suitcase. Yet, flip the latch and the center portion folds down revealing the record player and amp, all in one unit. The portion of the case still upright were the speakers. Sounded great to me. But I soon found out how wrong I was.

My new friend had a 60 watts-per-channel Pioneer integrated amp, a turntable and huge Revox reel-to-reel tape deck. Plus, he'd built these enormous speakers with 18" woofers! First thing he played was Pure Prairie League's LP Two Lane Highway. Not only was it incredibly LOUD, but it sounded so GOOD! When I got back home and saw that plastic "stereo" I whimpered and vowed to build a real stereo.

If you read the earlier posts, there is more information and photos of the components that I'd bought and built to create that stereo. 

I have written about just about every component you see here. If you have a sharp eye, you might see that the speakers in the middle of each totem-stack are a little different. More on that later. This is how everything looks as of this date, September 6, 2017.

This is how it looked today when I first played the middle speakers that arrived yesterday. They are 1970's vintage Dynaco A25 speakers. The left one is a standard A25VW. The V stood for vinyl veneer, I have no idea what the W stood for. The one on the right is a Dynaco A25XL. No, it doesn't stand for Extra Large. More like extra loud. The XL models are 3dB more efficient than the A25. They also reach higher into the treble range and the woofer moves out and in farther too for better bass response and reproduction. The crossover is at 1200 Hertz verses the standard's 1500 Hertz.

Here is what I found when I opened the box. Speakers, despite having no padding, look undamaged as does the box. Good, or so I thought.

Here they are without the grilles. Yes, the left one is dirty and in fact looks like water dripped on the woofer. It is OK. I picked it up and placed it atop the right Klipsch KG4 (big speaker on the bottom). When I picked up the right speaker, I heard, "thunk" inside. That could not signify anything remotely good at all. 

I remembered a guy who bought some speakers from me insisting that I remove the tweeters and wrap them separately. He told me of magnets falling off tweeters during shipping. "Sigh." So, I unscrewed the tweeter. lifted it out and no magnet! Any Dynaco "XL" model speaker is very rare. When I saw these on eBay I bid the opening $100 and to my utter delight, I won! I couldn't believe no one else bid on them. 

So, I contacted the seller. We talked by phone and he was more than willing to refund some money to cover the cost of a replacement tweeter. Which he did: $50. After considerable web searching, I found the part number for the SEAS tweeter for the A25XL: H086. To my utter disbelief, there was one on eBay! In Poland. Yep. $42 plus shipping. So, I jumped and bought it.

Prior to all this, I'd found a single A25 on eBay which is the VW model. Neither seller knew anything about speakers and both stated theirs sounded great. The A25VW arrived very well packed. I tested it with the old preamp and power amp and it sounded fine, but quieter than the Klipsch GK4s. 

Now, this all began when I won an old Luxman turntable. I did not know where to put it but found that cool folding wooden shelf that was more than large enough to hold it. At first I'd mounted it on the wall to the right. Then realized that was a poor choice. So I moved it to the present location and had to remove the two steel TV shelves that previously held many smaller speakers, but originally the BOSE 301 speakers my wife had bought for me. Plus, I had to move the shelf upward so that the cover could open far enough.

If you look at the "Before" photo, (second from the top of the article) you'll see the Dynaco PAT-5 silver preamp and SWTPC small power amp on top of it with both on top of the subwoofer. It's never a good idea to have components on top of any speaker. I have these resilient rubber feet that I added to each component thinking that would acoustically isolate them from the subwoofer's potential vibration. 

As you can see, the Southwest Technical Products 215A stereo power amplifier uses 1/4" microphone terminals for speakers. That is what commercial amplifiers used until the advent of XLR balanced terminals. So, I had to buy speaker cables with those plugs on one end and double-banana plugs on the other. I chose 12 gauge Seismic Audio cables in 10 foot lengths.

I wired the "B" speakers through the high level inputs and outputs ans I have done many times before. The subwoofer's internal amp divides the bass from the rest of the music which it sends on to the small speakers.

The PAT-5 is probably the only preamp with speaker terminals and a speaker selector switch, which you can see wired here. The double-banana terminals are the input terminals.

I was using some old 18" video cables made by Liberty Cable in their Z-500 series. Once I shoved the whole stack back and connected the turntable, I realized this was just not going to be practical. I put casters on my stereo shelf/table for a reason: Easier access to the back.

Thus, I settled upon this arrangement. Having two separate stereos on the same structure driving two pairs of speakers, each. Plus the larger (black) kit also drives two more pairs in THIS room which are my Cerwin-Vega LS-12s and the aforementioned BOSE 301s.

Here's the A25XLs as they appeared when I opened the box and below without their grilles. The grill cloth is supposed to be off-white. But someone in the past replaced it with black. Since I don't use the grilles, it doesn't matter.

Above is the left "totem-stack" with the right one below. The tiny speakers were once Radio Shack's Minimus 7W models. The "W" referring to walnut. All other Minimus speakers have diecast aluminum cabinets. I always wanted some of the W models. I completely replaced every component and wrote about them in a series of previous articles.

Above is the A25VW. One can easily see the differences in the veneers. This one is in remarkable condition. Below is the A25XL. Note the smaller tweeter.

In my early testing of the silver Dynaco PAT-5 preamp, I discovered (well, I knew it, but it's been years since I had one) that the input and output RCA terminals are very close together compared to modern equipment. I'm told there were "premium" RCA interconnect cables and speaker cables in the 1970's but I was not aware of them then. So, I realized that I'd need to buy "cheap" cables. The kind I had in 1976. Plus, since CDs did not exist then, I would not hook one to the "1976" stereo. The cheap cables arrived today which is why I began this task today. That and it's raining outside. Started just as I plunged a shovel in to start planting the plants my wife bought Monday. Darn.

If you compare the thickness of the modern quality cables and their male RCA terminals in the lower photos with these cheap cables you can quite a difference.

It has two outputs, so I plugged a cable in for the subwoofer too. Below, you will note that the double banana plugs are no longer in the input speaker terminals on the PAT-5 preamp.

I had previously cut a short piece off each cable that has the 1/4" plugs on one end. As I have written before, it's easier to shorten a wire than it is to lengthen it. I came up with the solution (below) of plugging one end of the Monster Cable Z-Series cables that once connected from the black Dynaco power amp to the high-level inputs on the subwoofer, into the female ends of the double banana plugs. I wire-tied them and covered the now unused male ends with electrical tape to prevent any possibility of them touching metal.

Above and below: "Cheap" RCA cables plugged into the inputs of the SWTPC power amp.

Because the aforementioned Z-Series cables are too long, I had to loop them. Note the size difference between the white standard AC cord of the SWTPC amp and the blue/black aftermarket Pangea brand power cable for the much newer and four times as powerful 1990's Dynaco Stereo 200 power amp. You can also see the Proton 1100 preamplifier has been wired back up minus the cassette deck. Note the size difference between the "audiophile" RCA cables and the "Cheap" ones below them plugged into the PAT-5 preamplifier.

The power switch quit working on the PAT-5 (Geez, you buy a forty year old amp and the switch stops working?) so I decided to use a power strip to turn everything off and on. I have a really nice power strip/2100 joules surge protector coming which will replace this cheap strip. NOTE: The really thick black cables with no woven covering are Radio Shack ones. Too long.

Above shows the back of the Denon turntable and the aftermarket RCA terminals I installed in it to enable me to use said thick cables. I once had exclusively Liberty Cables in the system. But then started trying other brands as can be seen below:

The grey (or is it: gray?) ones are Monster Cable ones and too long, thus the looping. I believe they are plugged into an equalizer. I stopped using them. 

These darker blue ones are also too long and Monster Cable brand. I eventually sold all the Liberty Cable brand cables and have a hodgepodge of mostly Monster Cable and the sole remaining 1/2 meter Liberty Cable units hooking the black preamp and power amp together. I noted below one of the photos higher up some thick Radio Shack cables. I once had a bunch of them:

As you can see, they are very nice. This particular pair was 20 feet long and I used it to connect the subwoofer to a preamp when the room was configured differently.

NOW, the conclusion. How does the "new" 1976 stereo sound and how does it compare to the much newer all black components? 
WELL, if you must know. In a word......FANTASTIC! Firstly, I was shocked at how good the cheap RCA cables sounded and not a whit of interference hum (60Hz) from any AC wire or cable. It really knocked me for a loop! I'm just glad I never bought any "audiophile" cables new nor spent anywhere near three figures for any of them. 
Even cassettes, granted, my JVC deck is a top-line 3-head unit which of course sounds better than most decks. Yet, the cassettes sound amazing. And the two I played are from the late 1970's. 
I CAN'T truly compare the two systems. I can switch cables to the Dynaco A25 speakers and listen to the same album and compare them that way. In a few words, even though the two A25 speakers are different models, I put it in mono, closed my eyes and kept adjusting the balance control on the silver preamp until the music seemed equidistant from each speaker, then set it back to stereo mode. 
THE DYNACO PAT-5 preamp was substituted in place of the PROTON black preamp and played through the Klipsch speakers. But I couldn't do a direct comparison. I have not yet tried the Dynaco speakers with the all-black system, yet. But I will.
SUFFICE it to say, I have reached this conclusion: The new "1976" stereo sounds fantastic! Since the Dynaco speakers are not nearly as efficient as the Klipsch speakers so the little gold SWTPC power amp has to work harder when playing loud. What I built and used for years were this amp's bigger brother. Two units the same size, but each put out 60 watts verses this little one's humble stereo 25 watts per channel. Below is a pair that showed up on eBay and were snatched up ($150 for the pair) before I could get them.

 Above is the factory sheet for my humble power amp. They use the same circuitry but the little one uses smaller less powerful power transistors and transformer which allowed them to fit it all in one case.

Here's the back of the two 60 watt mono amps. Since the heatsink (two of them back to back) is inside these, there is plenty of room for all these goodies on the back panel.

SO, am I glad I took on this challenge? Yep! Since CDs did not exist, I did not hook one to the 1976 system. Only what was available then. Lastly, I drew the line at speaker cables, I was not going to buy "zip-cord" as lamp wire was called and hook bare wires to the amp and speakers. In that respect and since it is a different turntable AND I didn't own a cassette deck then, frankly, they may not have existed in 1976 either. No matter, I'm VERY HAPPY!

Thanks for looking,

Scott