Dynaco st-70 driver board hum troubleshooting

The driver tubes were also relatively new zenith labeled uncarbonized 7199s, of unknown american manufacture. Dynaco st70 6gh8 6gh8a ecf82 driver board pcb pc3 kit dyna. The preamp delivers crisp, clean sound for those looking to boost their audio systems. I opted to supply the tubes myself to defer some of the upfront cost until i got the st 70 built. A custom dynaco st70 kit diy audio electronics from. Trying to troubleshoot the original board with the original parts is generally a waste of. This is very important as if the grid drive is reversed, it will turn your st 70 into a power oscillator damaging not only your amplifier, but your speakers and likely your hearing in the process. Find great deals on ebay for dynaco st70 and dynakit st70. Legendary dynaco st70 has been relaunched the absolute.

The triode electronics kit eliminates the superfluous holes in the chassis and makes use of a cap board inside rather than the tall quad cap, along with a different driver board. I just finished a gutrehab of a st70 which now powers my second system. Dynacodynakit st70 a great performer and affordable tube amp is the st70. Note the location of input and output resistors on the circuit board and unsolder. So do we need to replace a new driver board of some alien designs to get better sound out of a st70, my answer is no if one knows enough the business. We now have 18 inch acrylic driver board covers in stock for both the vta st 70 and vta st 120 amp kits.

Number and unsolder all wires from the driver board. I opted to supply the tubes myself to defer some of the upfront cost until i got the st70 built. Some of this info is general enough to be used with other amplifiers. The original st70 simply had the driver board exposed to the air not good if someone accidently pours liquid onto your amp like at a party. They do not fit older vta driver boards pre 2012 that used 12at7 driver tubes. Replacing 7199 with 6gh8 and comparing thd in a dynaco st70 vacuum. The original st 70 simply had the driver board exposed to the air not good if someone accidently pours liquid onto your amp like at a party. The st 70 represents a very desirable package for the modifier as it lends itself to a large number of modifications from the most simple to the most complex, witness the ar st 70 c3 that graced the pages of the audio amateur about 20 years ago. These amps smoked the dynaco from the beginning of the bandwith to the last and final note. The dynaco stereo 120 power amp was revolutionary when it came out in the mid 1960s. I also upgraded the power transformer with the larger unit from triode as the stock one started humming and. Dynaco mark iii poseidon board vs original dynaco 6ana driver board. Among collectors, the panor dynaco st 70 is not as desirable in comparison to vintage st 70s of the 1960s the earliest st 70s with clothcovered transformer leads are the most soughtafter models among audiophiles and collectors bob latino february 22, 2009. It follows the original wire hole layout, but it was modified to use widely available 6gh8 6gh8a 6kd8 ecf82 tubes instead of the obsolete and hard to find 7199 tubes.

This a drop in replacement for the original dynaco st70 pc3 driver board but with modern epoxy fiberglass pcb. Some people would rather repair their stereo 120 without updating it, maintaining the original design. Bad bias control pots are often the source of output stage noise, try moving the. Adams dynaco stereo 70 troubleshooting tips electronixandmore. I had a pair of dynaco mkiv monoblocks that are basically like an st70 and i had an. Also popular are rebuild kits with newly engineered driver boards that one can use to improve an existing st 70. Threads started on or before 43006 are archived here. All parts needed for a complete upgraded dynaco st70 type kit except for the tubes. Our 6au6 board might sound to some of you like a step backwards, but using 6au6ef94 opens up lots of opportunities for bargain nos tube rolling, as theres at least a dozen pincompatible types with 7bk and 7cm basing that potentially could be used, eg. One of these tubes has been replaced, for reasons which will be discussed further in the section on the driver board. If the dynaco st 70 is great, then the heathkits are world class.

This upgrade to the original st70 was first introduced in 1988. Dynaco st70 6gh8 6gh8a ecf82 driver board pcb pc3 kit. Including our custom made transformers, which are made to original specs right here in the usa. This board is a must for any serious restoration of the dynaco stereo 70 to full stock condition. This board shouldnt be doing to the amp what it is doing.

What are the different models of dynaco amplifiers. In a stock st70 the board replaces lugs 5, 6 and 7 of the 7 lug terminal strip. This guide can used on most dynaco st70, mk4, mk3 and mk2 amplifiers generally, altho some sections assume you have either our board or the original board with new parts. Comparison test of dynaco st70 tube amplifier modifications. Stereo 70 driver board 7199 board replacement modules a. It is a special 32v g2 levelshifting device keeping vg2 potential 32v lower than its plate while operating triode mode. The dynaco driver board is the weakest part of the st70 design, and after 20 or 30 years it is due to be tossed out. I used to crank it when i was a teen into his homebuilt corner horn type speakers but havent heard it since. The mods included upgraded power transformer, extra choke, extra capacitors on the power supply side of things, triode pentode switch and of course their new style vt70 driver board.

Jul 04, 2012 dynaco mark iii poseidon board vs original dynaco 6ana driver board. Dynaco stereo 120 repair information update my dynaco. We hope this web page and the hints it offers could make it easier. The kit uses all new parts stainless steel chassis wow. One of these tubes has been replaced, for reasons which will be discussed further in. Stereo 70 driver board 7199 board replacement modules.

Legendary dynaco st70 has been relaunched the absolute sound. It had some problems, though, mostly related to underbiasing of the output stage. Clearly, these are superb tubes to use in a reference dynaco st70. I just finished a gutrehab of a st 70 which now powers my second system. The dynaco or dynakit stereo 70 also known as the st70 vacuum tube amplifier. The next major difference between the amps was the driver section.

The measured specifications show that the stereo 70 is an amplifier of unequalled performance, and its listening quality is also unrivalled by any regardless of price. If you are in the market for a preamplifier that delivers dynamic sound quality, the dynaco is what you need. Ive done several of the triode electronics mods on a couple of st70s and also a set of mkiiis. As well as our upgraded dynaco st70 heavy duty stainless steel chassis, triode usa dynaco st70 driver board ef86 or 6au6 model, or no driver board, and our triode usa dynaco st70 upgraded capacitor board. Restoration module this is an exact replacement for the original dynaco pc3 board fabricated from milspec materials.

The dynaco or dynakit stereo 70 also known as the st70 vacuum tube amplifier was one of the most popular tube amps of its time. This board is a must for any serious restoration of the dynaco stereo70 to full stock condition. In fact, there are tens of thousands of the original dynaco tube amplifiers still in use around the world. Page 1 this is a very worthwhile investment easily paying for itself considering the cost of premium replacement tubes. Output tube changes the original triode electronics board design manual included modifications to this board and to the amplifier to allow using other output tubes in a st70. Threads started on or before 22806 are archived here. Hum and noise is listed for the st35 at greater than 80db below 17 watts for. This a drop in replacement for the original dynaco st 70 pc3 driver board but with modern epoxy fiberglass pcb. Perhaps the most famous and enduring modification to the dynaco st70 was created by roy mottram of vacuum tube audio vta. This is very important as if the grid drive is reversed, it will turn your st70 into a power oscillator damaging not only your amplifier, but your speakers and likely your hearing in the process. The board replaces the large multi section electrolytic capacitor and the bias supply circuitry in dynaco st70 amplifier. St70 baseline2 dynaco sca35 st35 tube amplifier upgrade.

Our update kit for the dynaco stereo 120 lets you rescue your dynaco from demise in the dumpster and make it better than new. The stereo 70 uses a circuit arrangement based on that of the dynakits. All parts needed for a complete upgraded dynaco st 70 type kit except for the tubes. May 09, 2016 dynaco senior engineer dan fraser explains. Im new to the forum having surfed in during my searches for a set of speakers. The original st 70 used the 7199 tube as the driver. Output tube changes the original triode electronics board design manual included modifications to this board and to the amplifier to allow using other output tubes in a st 70. The result was the crossover distortion that came to be the unpleasant hallmark of transistor sound. I also upgraded the power transformer with the larger unit from triode as the stock one started humming and got very warm. The triode stpc i and mkpc i are intended to be drop in replacements for boards in dynaco st70 and mark ill amplifiers with no modifications necessary just bolt in and solder in wires to the pc board but may also to be used as a platform for numerous easily installed modifications and experimentation. If the dynaco st70 is great, then the heathkits are world class. This guide can used on most dynaco st70, mk4, mk3 and mk2 amplifiers. If the power supply doesnt work, then the amplifier certainly wont work.

Also popular are rebuild kits with newly engineered driver boards that one can use to improve an existing st70. Here are the instructions for changing thr mk4 to triode operation. Pa060s power transformer nearly twice the lamination stack size of the original, a470s output transformers. These were all full mods where not only was the cap board replaced but the driver board as well. I was searching for dynaco amps on audiogon and came across an ad for new dynaco st70 kits. The driver circuit on the original amp with the two 7199 tubes was done to save a tube. I am just finishing up a complete rebuild of my dads old st70. I am just finishing up a complete rebuild of my dads old st 70. The series ii had a nice metal plate covering the driver board.

View and download dynaco stereo 70 owners manual online. As well as our upgraded dynaco st70 heavy duty stainless steel chassis, triode usa dynaco st70 driver board ef86 or 6au6 model, or no driver. All connections to the board are marked with the original number markings on the top and bottom silkscreen layers. Nov, 20 the mods included upgraded power transformer, extra choke, extra capacitors on the power supply side of things, triode pentode switch and of course their new style vt 70 driver board. The original dynaco stereo 70 is a true classic that is still regarded with awe by audio enthusiasts worldwide. They were originally built from 1959 up to the early 90s and according to wikipedia over 300,000 st70s were produced, this is an amazing number of amps, and thanks to this huge volume of these fine amps in the field, an entire industry has sprung up around this amp.

Dynaco stereo 70 manual stereo power amplifier kit hifi. Finally the original dynaco pc driver board is subject to failure not due to limitations of the components although the tube sockets are questionable but rather due to the substrate material of the board itself. I was searching for dynaco amps on audiogon and came across an ad for new dynaco st 70 kits. My final configuration was the tubes4hifi 12au7 driver board wrca clear tops, nos mulled brown base gz34 and a quad of shuguang treasure 6ca7zs. There is a reason they were built as they were, and can sound very nice with a stock circuit. Tiziano di natale heres a pdf copy of the original dynaco st35 manual. For more information please see our dynaco page here is the driver board instructions note that sprague 715p716p orange drop capacitors will not fit this board. Ive done several of the triode electronics mods on a couple of st 70s and also a set of mkiiis. These driver board covers fit only the 12au7 ccs board that we have been using since 2012. They claim this board reduces hum, noise and distortion.

Forty years of technological progress allows us to bring you lower distortion and greater efficiency, along with protection circuits that make your amp nearly bulletproof. Active protection schematic for any amp with multiple output tubes and cathode bias. First is our stereo70 upgrade system on board sob a complete amplifier on pc board. The modded amp runs 6l6gc outputs instead of el34s. Dynaco st70 capacitor board st70 power supply capacitor board this board replaces the large can capacitor in the power supply section of the dynaco st70 ampli. The st70 represents a very desirable package for the modifier as it lends itself to a large number of modifications from the most simple to the most complex, witness the ar st70c3 that graced the pages of the audio amateur about 20 years ago. Schematic for psu for reformed st70 using original 1960 pt if it is. The layout was changed to use the contemporary components and 6gh8a tubes. Find great deals on ebay for dynaco st 70 and dynakit st70. Threads started on or before 123105 are archived here. This dynaco st 70 driver board pc3 has been developed and designed to be a dropin replacement for dynaco 7199 board. Triode usa dynaco st70 tube diy amp kit triode electronics. Hard to find parts including dynakit original dropin replacement components typically ship within 24 hours of ordering. The only thing thats left to be done on the amp is to retube.

The signal from the driver board circuit is sent to each of the. I had a pair of dynaco mkiv monoblocks that are basically like an st70 and i had an intermitent hum and hiss problem in one that would get better. The dynaco or dynakit stereo 70 also known as the st 70 vacuum tube amplifier was one of the most popular tube amps of its time. Forty years of progress later, we can do a lot better. It is being included here to allow the owner to experiment, and. The original st70 used the 7199 tube as the driver. Exact replacements for the original can capacitors are dif. Clearly, these are superb tubes to use in a reference dynaco st 70. This dynaco st70 driver board pc3 has been developed and designed to be a dropin replacement for dynaco 7199 board. Adams dynaco stereo 70 troubleshooting tips by adam vaughn. One or more open sections often will cause a 120hz hum in the speakers. This is unique for dynaco because in the st70 only one driver board was shared by.