Dynaco st-70 driver board hum troubleshooting

This a drop in replacement for the original dynaco st 70 pc3 driver board but with modern epoxy fiberglass pcb. I just finished a gutrehab of a st 70 which now powers my second system. If the power supply doesnt work, then the amplifier certainly wont work. Hard to find parts including dynakit original dropin replacement components typically ship within 24 hours of ordering. 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. If the driver board in your st70 is damaged, new driver boards using the stock circuit sometimes modified for 6gh8s or somesuch, since 7199s are getting hard to find are. Bad bias control pots are often the source of output stage noise, try moving the. This board is a must for any serious restoration of the dynaco stereo70 to full stock condition. If you are in the market for a preamplifier that delivers dynamic sound quality, the dynaco is what you need. I used to crank it when i was a teen into his homebuilt corner horn type speakers but havent heard it since. The modded amp runs 6l6gc outputs instead of el34s. It is being included here to allow the owner to experiment, and.

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. The original st 70 used the 7199 tube as the driver. Some people would rather repair their stereo 120 without updating it, maintaining the original design. 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. These were all full mods where not only was the cap board replaced but the driver board as well. Adams dynaco stereo 70 troubleshooting tips by adam vaughn.

First is our stereo70 upgrade system on board sob a complete amplifier on pc board. The kit uses all new parts stainless steel chassis wow. Dynaco st70 6gh8 6gh8a ecf82 driver board pcb pc3 kit. There is a reason they were built as they were, and can sound very nice with a stock circuit. Hum and noise is listed for the st35 at greater than 80db below 17 watts for. With parts means all board parts, you solder on board yourself. Dynacodynakit st70 a great performer and affordable tube amp is the st70. The stereo 70 uses a circuit arrangement based on that of the dynakits. I had a pair of dynaco mkiv monoblocks that are basically like an st70 and i had an.

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. 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. 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. 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. Tiziano di natale heres a pdf copy of the original dynaco st35 manual. Here at dynakit you will find the right parts to restore, repair or upgrade your original dynaco vacuum tube amplifier. The preamp delivers crisp, clean sound for those looking to boost their audio systems. One or more open sections often will cause a 120hz hum in the speakers. This board shouldnt be doing to the amp what it is doing. We now have 18 inch acrylic driver board covers in stock for both the vta st70 and vta st120 amp kits.

All parts needed for a complete upgraded dynaco st70 type kit except for the tubes. Comparison test of dynaco st70 tube amplifier modifications. I opted to supply the tubes myself to defer some of the upfront cost until i got the st70 built. 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. May 09, 2016 dynaco senior engineer dan fraser explains. Jun 28, 2016 perhaps the most famous and enduring modification to the dynaco st70 was created by roy mottram of vacuum tube audio vta.

Find great deals on ebay for dynaco st70 and dynakit st70. This board is a must for any serious restoration of the dynaco stereo 70 to full stock condition. In a stock st70 the board replaces lugs 5, 6 and 7 of the 7 lug terminal strip. St70 baseline2 dynaco sca35 st35 tube amplifier upgrade. 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. The layout was changed to use the contemporary components and 6gh8a tubes. 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. One of these tubes has been replaced, for reasons which will be discussed further in. Stereo 70 driver board 7199 board replacement modules a. I also upgraded the power transformer with the larger unit from triode as the stock one started humming and got very warm. 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. Triode usa dynaco st70 tube diy amp kit triode electronics.

A custom dynaco st70 kit diy audio electronics from. 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. 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. Note the location of input and output resistors on the circuit board and unsolder. The signal from the driver board circuit is sent to each of the. I am just finishing up a complete rebuild of my dads old st 70. Perhaps the most famous and enduring modification to the dynaco st70 was created by roy mottram of vacuum tube audio vta. They do not fit older vta driver boards pre 2012 that used 12at7 driver tubes. Restoration module this is an exact replacement for the original dynaco pc3 board fabricated from milspec materials. 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. 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. Stereo 70 driver board 7199 board replacement modules. They claim this board reduces hum, noise and distortion. This dynaco st 70 driver board pc3 has been developed and designed to be a dropin replacement for dynaco 7199 board.

Dynaco stereo 120 repair information update my dynaco. Im new to the forum having surfed in during my searches for a set of speakers. Threads started on or before 22806 are archived here. I opted to supply the tubes myself to defer some of the upfront cost until i got the st 70 built. 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. Find great deals on ebay for dynaco st 70 and dynakit st70. In fact, there are tens of thousands of the original dynaco tube amplifiers still in use around the world.

Schematic for psu for reformed st70 using original 1960 pt if it is. Dynaco mark iii poseidon board vs original dynaco 6ana driver board. Adams dynaco stereo 70 troubleshooting tips electronixandmore. The next major difference between the amps was the driver section. Also popular are rebuild kits with newly engineered driver boards that one can use to improve an existing st70. The result was the crossover distortion that came to be the unpleasant hallmark of transistor sound. Dynaco stereo 70 manual stereo power amplifier kit hifi. It had some problems, though, mostly related to underbiasing of the output stage. Exact replacements for the original can capacitors are dif. 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. Active protection schematic for any amp with multiple output tubes and cathode bias.

I just finished a gutrehab of a st70 which now powers my second system. I was searching for dynaco amps on audiogon and came across an ad for new dynaco st70 kits. The board replaces the large multi section electrolytic capacitor and the bias supply circuitry in dynaco st70 amplifier. Also popular are rebuild kits with newly engineered driver boards that one can use to improve an existing st 70. Our update kit for the dynaco stereo 120 lets you rescue your dynaco from demise in the dumpster and make it better than new. I was searching for dynaco amps on audiogon and came across an ad for new dynaco st 70 kits. Ive done several of the triode electronics mods on a couple of st70s and also a set of mkiiis. The original st70 used the 7199 tube as the driver. The dynaco stereo 120 power amp was revolutionary when it came out in the mid 1960s. Including our custom made transformers, which are made to original specs right here in the usa. 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. I also upgraded the power transformer with the larger unit from triode as the stock one started humming and. Clearly, these are superb tubes to use in a reference dynaco st 70.

Forty years of progress later, we can do a lot better. The original dynaco stereo 70 is a true classic that is still regarded with awe by audio enthusiasts worldwide. 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. If the dynaco st 70 is great, then the heathkits are world class. Legendary dynaco st70 has been relaunched the absolute sound. All connections to the board are marked with the original number markings on the top and bottom silkscreen layers. 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. The dynaco or dynakit stereo 70 also known as the st70 vacuum tube amplifier. 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. Legendary dynaco st70 has been relaunched the absolute. This guide can used on most dynaco st70, mk4, mk3 and mk2 amplifiers. Replacing 7199 with 6gh8 and comparing thd in a dynaco st70 vacuum.

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. I then had the urge to try this schematic on a pair of heathkit w7s. Threads started on or before 43006 are archived here. Page 1 this is a very worthwhile investment easily paying for itself considering the cost of premium replacement tubes. This upgrade to the original st70 was first introduced in 1988. Pa060s power transformer nearly twice the lamination stack size of the original, a470s output transformers. We hope this web page and the hints it offers could make it easier. 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. One of these tubes has been replaced, for reasons which will be discussed further in the section on the driver board. Some of this info is general enough to be used with other amplifiers. Threads started on or before 123105 are archived here.

I am just finishing up a complete rebuild of my dads old st70. This is unique for dynaco because in the st70 only one driver board was shared by. We now have 18 inch acrylic driver board covers in stock for both the vta st 70 and vta st 120 amp kits. Trying to troubleshoot the original board with the original parts is generally a waste of. This a drop in replacement for the original dynaco st70 pc3 driver board but with modern epoxy fiberglass pcb. All parts needed for a complete upgraded dynaco st 70 type kit except for the tubes.

Dynaco st70 6gh8 6gh8a ecf82 driver board pcb pc3 kit dyna. Ive done several of the triode electronics mods on a couple of st 70s 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. If the dynaco st70 is great, then the heathkits are world class. 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. Clearly, these are superb tubes to use in a reference dynaco st70.

Here are the instructions for changing thr mk4 to triode operation. This dynaco st70 driver board pc3 has been developed and designed to be a dropin replacement for dynaco 7199 board. 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. It is a special 32v g2 levelshifting device keeping vg2 potential 32v lower than its plate while operating triode mode.

The only thing thats left to be done on the amp is to retube. The series ii had a nice metal plate covering the driver board. 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. 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 driver tubes were also relatively new zenith labeled uncarbonized 7199s, of unknown american manufacture. These amps smoked the dynaco from the beginning of the bandwith to the last and final note.