alliclaytor Posted July 10, 2008 Share Posted July 10, 2008 So I just got my first tube amp...modified Dynaco ST-70. Itrocks and the price couldn't be beat. I don't hear the muddy bass out of myCornwalls that some speak of, and it takes just a touch off of the high end. Iwouldn't say it was an amazing difference from the Mac 2125...not animprovement per se. It seems to have a more "spacious" sound and forsome reasons it feels more lively. In any case, I know there are lots of mod-sand things you can do to these...I think I will wait a while. Apparently thecaps and power supplies have been upgraded which may account for the moreauthoritative bass. If anybody is looking for a nice intro into tubes I wouldhighly recommend. Also, I feel like a very confuzed 20-something...I have vintage tube and solid state, vinyl, PA amps, a PS3, an XTI 1000, Cornwalls, RF-7's and a cinema sub...here is a view from my perspective Quote Link to comment Share on other sites More sharing options...
oldtimer Posted July 10, 2008 Share Posted July 10, 2008 Well the decor definitely looks 20-something![] Quote Link to comment Share on other sites More sharing options...
alliclaytor Posted July 10, 2008 Author Share Posted July 10, 2008 FYI...tubes rock with Pink Floyd...and thankyou? Quote Link to comment Share on other sites More sharing options...
oldtimer Posted July 10, 2008 Share Posted July 10, 2008 LOL! [H] You're welcome. Quote Link to comment Share on other sites More sharing options...
Deang Posted July 10, 2008 Share Posted July 10, 2008 Another nice score Clay! Quote Link to comment Share on other sites More sharing options...
alliclaytor Posted July 10, 2008 Author Share Posted July 10, 2008 Thanks Dean, you are always free to drop by...maybe a comparison between this and the D45 sometime on Jubs...anybody know anything about this configuration? The previous owner says it gets not just 35 w/channel but 40!!! The one thing that suprises me is that these are dead SILENT, not even a little hiss or hum. Does anybody know how to stop the gate current "pop" when I first turn it on? Quote Link to comment Share on other sites More sharing options...
seti Posted July 10, 2008 Share Posted July 10, 2008 Thanks Dean, you are always free to drop by...maybe a comparison between this and the D45 sometime on Jubs...anybody know anything about this configuration? The previous owner says it gets not just 35 w/channel but 40!!! The one thing that suprises me is that these are dead SILENT, not even a little hiss or hum. Does anybody know how to stop the gate current "pop" when I first turn it on? It is a popular misconception that tube amps are noisey or loud. My favorite tube amps are dead quiet. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 11, 2008 Share Posted July 11, 2008 "Does anybody know how to stop the gate current "pop" when I first turn it on?" What you're most likely hearing is an acrcing switch. I learned a trick from an old Dynaco schematic years ago that really helps, but you have to have a small amount of handiness and the ability to solder two connections. In rush current 'thump' is different from what you're hearing, and your problem can often be solved by adding a small value, high voltage (as in 1k volt) 'snubber' capacitor across the switch. It will absorb that little spark so you don't hear it. If you happen to have an inside shot of the amplifier, I should be able to tell you if that cap is there. If so, and it's the original, it or your power switch (if original) may need to be replaced. Sounds like Dean is closeby (?), and maybe he could help you install that cap. Remember there can be very strong storage charges in those filter caps, so you need to be sure the amp is turned off, unplugged, and drained of all stored voltages before doing anything. Check with the voltmeter to make sure. I have been amazed a few times over the years about the kind of a shock an unplugged and seemingly totally unenergized component can give![:|] a .01uf 1kV would probably do the trick. Congrats on the Dyna! Erik edit: Okay, I noticed that the usual rectifier tube is not present, and that there is an extra switch on the front panel. If you have a couple of SS diodes in place of vacuum tube rectification, that extra switch may be a standby switch (?). It's use will allow the tube to warm before applying the high voltage plate supply. Is that what you have? Quote Link to comment Share on other sites More sharing options...
oldtimer Posted July 11, 2008 Share Posted July 11, 2008 It all sounds like such a great advertisement to own one! Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 11, 2008 Share Posted July 11, 2008 If so, and it's the original, it or your power switch (if original) may need to be replaced. That is definitely not an original power switch. Dynaco used a cheap slide switch that was mounted on the back of the chassis. You also shouldn't have a pop when you turn it on as the output tubes haven't even had the heaters warmed up. That looks like it has been converted to a SS rectifier, replacing the tube. Full inrush current to the EL34s. Hmmmm.Bruce Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted July 11, 2008 Share Posted July 11, 2008 Congrats. Great system! Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 11, 2008 Share Posted July 11, 2008 Bruce: It's not the original switch, and there is also an additional switch. A higher pitched popping or snapping sound when using the switch is probably not related to in rush current, which is more more of a lower frequency 'thump.' Dynacos often used the small capacitor across the switch (PLEASE don't use fancy capacitors here). It absorbs the pop. Cathode stripping due to inadequate heating of cathodes is what the standby switch helps prevent, and sometimes there is a noise more like thumping when the center tap on the power transformer secondary, if that's where the standby switch is located, is grounded in order to apply B+. That's why the extra switch is probably there -- as a standby that can be used to warm the cathodes before applying B+. Some people swear by the use of a standby switch, and others think they aren't necessary. There are also tube rectifiers, such as the 5Y3 that are directly heated, instant turn on types, and know a number of amps that still use them without a standby switch -- with no thumping or popping to speak of. Filters for the kind of inrush current 'thump' that I have heard more often in solid state amps than tube can be more complex than just wiring a snubber cap across the switch. Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 11, 2008 Share Posted July 11, 2008 " You also shouldn't have a pop when you turn it on as the output tubes haven't even had the heaters warmed up" You shouldn't have a pop anytime. Dynaco included those snubber capacitors on brand new components. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 11, 2008 Share Posted July 11, 2008 Let Craig install a high voltage ceramic capacitor across the switch for you. That might help. Quote Link to comment Share on other sites More sharing options...
fini Posted July 11, 2008 Share Posted July 11, 2008 I appreciate your speakers-to-TV-screen size ratio. So many these days are going with ginormous screens and speck-sized speakers. Of course some among us (you know who you are!) have huge everything... Quote Link to comment Share on other sites More sharing options...
jtnfoley Posted July 11, 2008 Share Posted July 11, 2008 *ahem* It's a 74" wide screen with LaScalas beneath for me (tho I'm currently evaluating Cornwalls) [6] Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 11, 2008 Share Posted July 11, 2008 That ST-70 is about as far away from being a stock ST-70 as you could get..... So your comments in reference to the loose bass not being present does not surprise me at all. The amp has been converted to a 4 tube front end most likely all triode. Also the amp has been converted to full SS rectification and the power supply has been grossly upgraded. I bet the turn on issue is in relation to the instant on SS rectification and that huge power supply. I'd advise you to be ready to replace the power transformer sooner or later. It's bound to take a dump under the extra load.... in fact that is most likely what is begging for mercy everytime you turn the amp on. The ST-70 power transformer is reknowned for failing even in stock configuration. Craig Quote Link to comment Share on other sites More sharing options...
alliclaytor Posted July 11, 2008 Author Share Posted July 11, 2008 This is the bottom look of the Dynaco. The "pop" i refer to is a low thud, two actually. One immediatly when I turn on the second swtich, and one immediatly after that. It pushs the woofers to a medium excursion for their use. I let them warm up first for longer and turn all the other items on first, the thud whas significantly less noticiable (less scarry for my corns) and (thanks HarryO) What types of sounds should I listen for to determine if/when the power transformer? What would be a good option for replacement? I figure if I can keep an eye out for one now, it may save money in the future. Overall, I am happy with the sound, and the more I listen the more unique it sounds in reference to solid state. Now I just need to get my turntable working again... Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 11, 2008 Share Posted July 11, 2008 "The "pop" i refer to is a low thud, two actually." A 'thud' is really much different than a snap or pop sound, and so is not the power switch but in-rush current thud. Do you happen to know which of the two switches is standby (tubes will glow, but no high voltage will be present) and which is the high voltage switch? Your power transformer is actually being relieved of one of it's main current draws -- the filament supply that would normally be used for the vacuum tube rectifier. In fact, it may run a little cooler because of that. There can still be noises and stress associated with SS diodes working in conjunction with hefty filter capacitance -- often higher-pitched or sort of oscillation that can be filtered to ground on the AC side of the power transformer secondary (before rectification). Do you know which switch is used for standby? It's important to know which is which and how to use each. The tubes may be getting slammed with high voltage before they even have a chance to warm. There are some robust replacement power transformers available for Dyna ST-70 if you even need one. Welborne Labs is one source. The photo is helpful, but just a little two distant to make out how the standby is wired -- whether it lifts the center tap of the power transformer or is in-line with B+ voltages (those are the high voltages of your amplifier). Good luck Quote Link to comment Share on other sites More sharing options...
mike stehr Posted July 11, 2008 Share Posted July 11, 2008 I wouldn't advise anyone to go through Welborne labs. Unless they really want to get ripped-off.......... Quote Link to comment Share on other sites More sharing options...
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