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 components. It is based on actual experience in building, rebuilding, using and selling a variety of new and used Dynaco and Dynakit Audio Components.  

Example: To take a "garage sale" tube amp that is 50 years old and expect it to work properly and sound good is simply absurd. I've even seen amps being offered as "tech serviced" with the rectifier tube being the only replaced part. Negative opinions based on units in this condition say more about the person than the amplifier. These opinions should be properly framed before hanging. 

Estimated sale figures for the Dynaco 70 alone go as high as 380,000 units. So, I ask you this; were the magazines in the 60's and 70's filled with negative comments about the Dynaco components? No. Were all of those buyers misguided, duped by slick salesmen and hype? No. There were tens of thousands of satisfied buyers and countless articles published suggesting that many popular and famous audio makers of the day had met their match.

 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 unfortunate few who got caught off-guard by some eBay grifter or retro-audio huckster peddling "serviced" gear. “Caveat Emptor” is good advice. Know what you're getting in to.

 

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. Todays 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 kind.

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, added expense and can add noise into the signal through the AC lines.

Question:  " have these old transformers been abused, have they been operated properly in the past"?

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 question becomes, are these safe, will they last, how will they sound? If needed, replacement parts and associated labor are expensive.

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

Answer: You uninstall them from the amplifier first. You take off 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, locate new hardware that fits and looks right. Sometimes the transformer covers are dented, you can try to repair the dent or buy a new cover.

Question: "is the cloth covered wire better than modern wire"?

Answer:  No. It's antique wire, state of the art for its time, but simply inferior by today's standards. Old wire jacket gets hard, the cloth sheathing cracks, the metal stranding itself can be difficult to get soldered as it is not tinned like modern wire. There is usually corrosion or oxidation present. Very often the wires were cut very short and this makes it difficult to reattach to the terminals.

There's other issues that can come in to 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.

All About New Transformers:

Now, lets 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. These modern version 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.

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 to run into problems when desoldering 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.

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 the incorrect parts, just how well will that work? Same goes for those old capacitors. Even if they are still in a useable value range, they cannot compete with modern, high quality film capacitors. Guitar guys love old capacitors because they inject noise and distortion which can make for a great sound, but this is not a guitar amplifier. If you have good testing vintage caps and like they way they sound, then go ahead and use them. In a side by side audition and analysis, the new amp with all new parts will best 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 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.

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

Answer:  For few bucks and in little time, you can replace the original choke. Old chokes can be used, 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. 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 amplifiers 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 amplifiers transformers and other components. If the amplifier had been used with modern AC voltages in the past then the filter capacitor has been subjected to excessive overvoltage and is more likely to fail, if it even 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.

The old original wiring is very stiff and the PVC sheathing does not hold up so good 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 and inferior 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.

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.

An entire article could also be written about tube selection.....

The video at the bottom of this page includes actual photos of what you can and will encounter when servicing and/or rebuilding vintage gear.

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