New vs. Vintage

Let me start by making clear that I am not at all against vintage audio gear. This information is provided simply to help you decide whether to buy new or invest in vintage Dynakit components. It is based on years of personal experience in building, rebuilding, using and selling hundreds of new and used Dynaco and Dynakit Audio Components.  

To take a "garage sale bargain" tube amp that is 50 years old and expect it to work properly and sound good is simply absurd. Negative statements or opinions based on units in this condition tell us more about the person than the amplifier. These statements should be properly framed before hanging. One must surely have the experience of listening to an all new amp and the vintage amp, side by side, to draw a factual conclusion. I have that experience, the new units outperform the old ones, in every way.

Estimated sales figures for the Dynaco 70 alone go as high as 380,000 units. More sold than any other amplifier, ever. So, I ask you this; were the magazines in the 60's and 70's filled with negative comments about the Dynaco components? No they were not. Were all of those buyers misguided, duped by slick salesmen and hype? Nope. There were however, legions of satisfied buyers and countless articles published suggesting that many popular and famous audio makers of the day had met their match. The Dynaco earned its place by virtue of its performance.

This incredible sales data tells a simple truth, it does not support or indicate a sub-grade product. It in fact, defends the Dynaco brand against claims made by the unfortunates who got caught off-guard by some eBay grifter or retro-audio huckster peddling  gear as a side hustle. “Caveat Emptor” is good advice. Know what you're getting into.

Used or New?

• Question:  "should I buy and rebuild a used Dynaco or get a new one"?

Answer:  I started out buying used units and rebuilding them to sell. I had good and bad experiences. I can flatly say that there has always been more satisfaction in the end with the all new units. This includes their sound, reliable operation and their appearance. Although I did some really nice refurbs, they just simply cannot compare to the all new unit. The one exception is regarding those who are motivated by the desire of having a true vintage unit. I get that.

• Question: "Were the old transformers really that good"?

Answer: Yes, they were and still are. There are inherent problems to consider however. The main issue is the old transformers were made to operate from 117 volts. This was a common voltage of days gone past. Today's voltages are typically 120 and up to 125 and occasionally a bit more. This may appear as a small and trivial difference but this voltage will be increased exponentially down the line. The increased voltages will exceed the ratings of the relative components resulting in problems of all kinds.

To properly operate a vintage transformer you need a way to reduce the voltage back to the 117 volt range. A variac is often used, you can buy or build "bucking transformers". Either way or whatever way, it's another piece of gear, more wires, added expense and can add noise into the signal through the AC lines.

• Question:  "how do I know if these old transformers have been abused or operated improproperly"?

Answer: Nobody can expect a reliable, defining or truly accurate answer to this. You take your chances. Obviously if the transformer or relative components show signs of excessive heat or visible signs of arcing or scorching, burnt wiring, patched or repaired wiring, you can be sure there has been a problem. The questions to ask yourself; are these safe, will they last, how will they sound? If needed, replacements and associated labor are expensive.

• Question: What do I have to do to make them look nice again?

Answer:  CAUTION: removing the bolts and covers from transformers creates a risk of allowing the laminations to become loose and misaligned. Some transformers are dipped in tar or varnish to seal out moisture and eliminate vibration. Disturbing this coating can have negative consequences. If you choose to proceed, it's risky.  Uninstall them from the amplifier first. You carefully remove the covers and strip, sand and paint them. They might turn out nice, they might look worse, depending on your skills. It can be frustrating. Then, to complete the look, recondition or locate new fastening hardware so that when completed and installed everything looks good again. Sometimes the transformer covers are dented, you can try to repair the dent or buy a new cover. Address any wiring issues on the transformer at this time.

• Question: "is the cloth covered wire "magic"? Is it better than modern wire"?

Answer:  No. It's antique wire, state of the art for its time, but simply and totally inferior, by today's standards. Old wire jackets/wrapping/insulation will get hard and brittle, the cloth sheathing can be cracked or frayed, exposing live (hot) wires. The metal stranding itself can be difficult to get solder to adhere as it is typically not tinned like modern wire. There is usually corrosion or oxidation present, compounding the difficulty. Often the wires were cut too short, this makes it very difficult to reattach them to the terminals.

There's other issues that can come into play but I think you get the picture here. Be ready to invest time, work and have a high threshold for risk if you decide to go the vintage route.

About new Transformers

Now, let's consider the New "made in USA" Dynakit PA-060 power transformer, which is wound and designed for 120 volt operation, an important factor to consider. The modern Dynakit transformers do not require a step down transformer, they are designed to operate on higher voltages, they run cooler, produce less distortion and easily outperform vintage transformers in every category.

The new Dynakit transformers were reverse engineered from the original designs using modern technologies and superior insulations. The increased lamination stack allows them to run cooler and provide better regulation. These are super high quality transformers that meet and exceed every aspect of the originals. In any comparison, these new transformers are better than those old originals. Modern advancements in materials, combined with traditional methods and better technologies used in their production has resulted in absolutely superb transformers that produce improved sonics and provide cleaner power. Again, they operate quieter and run cooler than the originals, they provide less distortion and increased reliability, they're just better. The power transformer is mounted on isolation bushings to stop mechanical vibrations from reaching the chassis.

 The new A470 output transformers are also greatly improved, like the power transformer they are also made in the USA. These current production output transformers are interleaved/layer-wound and incorporate the high quality M-6 grain oriented laminations like the original design, because that is a good design. These use better quality wire with better insulation, the primary is wound the same as the original A470 using the same number of turns on the same number of sections. These are made using the same patented Dynaco winding method, and made on the same core size and material type as the originals. These transformers are exceptional.

Circuit Boards and Components

• Question: "should I or can I reuse the original circuit board and components"?

 Answer: If you decide to service, rebuild and reuse a vintage circuit board, please consider the following. The older the board, the more likely it will be you will run into problems when desoldering and removing the old resistors and capacitors.  The board itself was never designed to be in service for so many years. The substrate will often be deteriorating and warped from heat and age. The solder traces are thin and delicate and can even be broken or cracked, leading to more problems down the road. I just won't take a chance, it doesn't make sense, especially considering the amount of work involved. If you're simply going for that total vintage build that's understood, but there is no magic in those old circuit boards. Only seasoned "pros" should attempt this soldering challenge in my opinion. Get a nice new genuine Dynakit driver board!

The old resistors will usually have drifted off value and out of an acceptable range. Reusing out of spec parts is comparable to building a new board, but using all incorrect parts, just how well will that work? Same goes for those old capacitors. Even if they are still in a usable value range, they cannot compete with the performance of modern, high quality film capacitors. Guitar guys love old capacitors because they inject noise and distortion which can make for a great vintage repop sound, but this is not a guitar amplifier we're talking about here. If you have good testing vintage caps and like the way they sound, then go ahead and use them, if they don't impress then replace them. In a side by side audition and analysis, the new amp with all new parts (like I build them)  will beat the vintage amp every time.

The original ST-70 circuit board required two 7199 tubes. This tube went out of production completely back in 2007. The price for 7199's went sky high and they have become increasingly difficult (and expensive) to find. Dynaco released an updated driver circuit which uses the 6GH8A or 6U8A tube. There are also adapters available that allow the use of the 6GH8A tube on those older version boards requiring the 7199 tube. The audio circuit remains intact aside from the rerouting of some solder traces to accommodate the different pinout of the 6GH8A tube. I've listened to both PCB variants and cannot distinguish any difference. I use the 6GH8A boards exclusively in the ST-70 due to the difficulty and cost in sourcing 7199 tubes.

I have always found the stock circuit to be the best, they didn't sell over 350,000 ST-70's because they sounded mediocre. Consider this, if you will. If any of the past or previous modified or alternative circuits were really better, wouldn't those have, back then, or currently dominate the market? I prefer the real deal, why try to fix what isn't broken? Imitation is the highest form of flattery, but when you install a VTA (tubes 4 hifi), Curcio Audio,  Triode Electronics or any other driver circuit, the amplifier is no longer a Dynaco. So, if your ST-70 doesn't sound good, there's simply something wrong with it, or within your system, somewhere.

• Question: "what about other components like the choke and filter capacitor"?

Answer:  For a few bucks and in little time, you can replace the original choke. Old chokes can be reused, if they still test within an acceptable value range. Old chokes will often have a nasty gooey & waxy substance oozing from them. This is an indication of high temperature and age. It does not necessarily mean the choke is faulty. (The new chokes from Dynakit are sealed, encased in a metal housing)

If you plan to keep the original choke, it should be tested before installing it. To check the value of its Henries, you will measure by using a frequency generator and an oscilloscope or an LCM multimeter. It can also be calculated through a voltage-current slope measuring the change in the electrical current passing through the coil. This is not a feasible test for the average hobbyist, obviously.

The filter capacitor (multi-section) or can capacitor is critical to the amplifier's operation and performance. These capacitors suffer greatly from long term storage often associated with vintage gear. Long periods of non use will allow the cap to dry out, drift out of spec and become noisy or even dangerous to the transformers and other components. If the vintage amplifier had been used with modern AC voltages in the past then the filter capacitor has been subjected to excessive overvoltage and is even more likely to fail, if it works at all. The most common symptom of a bad filter cap is hum in the output signal. Again, it is just better to replace the filter cap with a new one. Warning! This can be a dangerous task for the untrained hobbyist as there are high voltages present, stored up in the capacitor, making contact with it could result in injury or even death. The capacitor must be fully and properly discharged before making any attempt to service the amplifier in any way.

• Question: "can I make an old rusted, corroded or pitted chassis look good again"?

Answer: Maybe, but it will never look like a new polished stainless steel chassis like the new amplifiers have. Restoration will be difficult as it requires the complete disassembly of the amplifier to gain access to the nooks and crannies which will give the best results. When I was doing rebuilds I removed every single screw and part from the chassis. Then I hand polished the metal to restore the shine and finish to its best possible state. This process cannot remove pitting and cannot completely restore rusted areas, it can only improve the appearance commensurate with the level of deterioration. They cannot be highly polished to the degree you see in the new chassis. The old chassis were plated steel and plating is subject to subsurface rust and imperfections which cannot be repaired and will keep worsening over time. The new chassis are mirror polished stainless steel, not subject to the problems aforementioned. Polishing the chassis without damaging or destroying the printing/lettering is one of the most difficult parts of the restoration process. Once it's gone, it's gone for good.

• Question: "what about these old tube sockets and old wiring"?

Answer: Old sockets can be a real bummer. Corrosion of the pins themselves can be improved by using chemicals like Deoxit. The pin receptacles will usually be stretched out from tubes being inserted and removed over the years. It is a tedious task to reform all 8 of these in all 5 sockets to ensure solid and reliable contact. Many of the old sockets are made from Bakelite and will have become brittle from age and heat. All of the solder connections to each terminal should be reflowed to repair bad or broken contact. A cracked tube socket contact is always a possibility and is very difficult to diagnose and locate.

The old original wiring is very stiff and the PVC sheathing does not hold up so well during soldering/desoldering/re-soldering. The wiring itself is usually a mess, even in the factory wired units. I have actually found several wiring mistakes on so called factory wired units, likely caused by someone else's handiwork in the past. Neatness doesn't make for improved sound, but it represents carefulness and pride and certainly is preferred over a rats nest job. Modern high quality stranded or solid core wiring is best. Rewiring an entire unit takes time and work but has its rewards.

• Question: "what about the bias supply and original bias pots"?

Answer: Again, long term storage, over voltage, age, corrosion and inferior workmanship and antique grade components should be addressed. It's a tedious job to rebuild the bias supply but quite necessary if you expect the amp to live long and perform at its best. I use a modern setup with all new parts, every time. Why take a chance?

The bias pots should be checked for values and thoroughly cleaned if found acceptable and can be reused. I use new pots and install safety resistors that will help minimize damage should a pot fail.

The vintage selenium rectifier should be replaced with a diode. This has no effect on audio quality but improves reliability immensely.

Spend a few extra dollars and install good quality brand resistors, electrolytic capacitors and film capacitors in the bias supply when rebuilding it for a quiet, safe and reliable amplifier.

Summary:

Although not an exhaustive reference to the problems you may encounter, the information above only briefly reveals what you can expect with vintage audio gear. There are still many smaller factors which come into play and require attention. The condition of the cover, the power cord, the fuse assembly, the feet, the power switch, the input and output jacks will all need inspection and usually require some attention.