I finally found and bought a Fluke 12 meter after watching you. I had been using a cheap Chinese capacitance meter that worked horrible, along with using a regular multimeter, it is nice to have both things combined. Also, I have always found that the best endorsement any tool can have is seeing a professional like yourself using it religiously. And because I watch all your videos, the first thing I did was change that battery out for a fresh one so I don't get erroneous readings. Let's hope my buttons and screen hold out.
I don't know where you are getting your tubes from, but Antique Electronics Supply will replace any tube that is bad within 10 days of purchase. I have done it a couple of times. I buy all of my tubes for my customers and myself, from AES for that reason. They also have the best selection of tubes IMO.
@Teknogod17 Yes, the "gigantic dial" adjusts the line voltage up or down. Mine came from Circuit Specialists and has a digital meter for output voltage. Been using it for a couple of years now with no problems. HTH
@Teknogod17 Well, first off I would not say it regulates the voltage. You must monitor the output voltage yourself. The output will still vary in response to the input voltage. If you set the output at 115VAC and the line voltage goes up or down 5 volts then no problem. Back in the 60s the line voltage was between 110 and 120 VAC so the transformer primary windings were wound to provide the necessary voltages for the tubes requirements based on that voltage. Now days the line voltage can be higher in some areas, ours is 124 to 125 VAC So the secondary transformer winding raises voltage proportionally. When the voltage to the tubes get too high, you can lose tubes. HTH
know tubes sound good when the music sample even sounded amazing through my crappy monitor speakers through display port. this is why i love tubes so much plus fun to have something about glass bulb things that get warm/hot and glow while making sound just feels more.. natural aha.
The tungsol & JJ GZ34s have been known to arc over new from the box if the input caps value exceeds the maximum value given in the RCA receiver tube manual.
This makes the most sense with the evidence presented. It’s too easy to blame it on a defective component out of the box. I had an ole 1960’s Motorola tube transceiver on the bench around 1986’ish. I recall a tube having an arcing problem. As a younger tech, my boss stopped me from changing the tube and insisted on me scrutinizing the supporting components. I recall that it was a defective variable cap. Though, I don’t believe that it was a rectifier, thinking it was in the tx pre-amp section. Can’t say I never had a bad component out of the box. Just don’t let what seems obvious trick you. Let us know what you ultimately sort out.
@@ricknelson947 The problem is current production of these rectifier tubes are not to the same spec as the old stock tubes. Back in the day we had 110 volt mains. Now they are 120 volt, and that by the time the transformer gets done is about an additional 40-50 volts. Couple that with the current tubes, and you get arc over on many. I did the diode mod on this, adding protection from high reverse voltages, and walla, the tube stopped arcing over. The video of the mod in on the channel.
12voltvids I’m pleased to know that you didn’t receive a defective component. Thank you for the explanation. Also reminds me that I have been away from working with tube circuits too long to intelligently throw my 2cents in..... I’m just going to continue watching the current professionals.
@@ricknelson947 I have forgotten more. Tubes were on their at out when I was getting into electronics. Didn't have much to do with tubes for my entire career. Just tinker with them at home with old radios. Use them on my power amp and have a couple kit amps.
The 5AR4 was notorious for this problem mainly because of todays line voltage. Back when this amp was made and this tube was made the line voltage was at least 5-10V lower and this tube in this ST-70 and even the MKIII was driven to nearly its max and now with higher ac feeding it, it is going beyond its threshold and thats why it is arcing and blowing the fuse. Its a smaller design with a cathode that was able to deliver much higher voltages than a 5U4 and does work well under the right conditions. Sadly The new russian tubes designs are even worse being able to handle these amps high AC being fed. I myself have ordered these very russian tubes and ran into the exact same issue you are having! however All is not lost...There is a modification to the circuit to help correct this that involved moving some of the wiring and adding two 1N4007 diodes that will help buffer this tube some against the higher AC this tube has to endure. Look into this.
I Sue know tons about JJ an Gold Lion KT 77’s 2 were bad out of the boxes. The rectifier tubes are the hardest tune to get right for Russia or China . I use vintage old stock RCA rectifier. My one is in use for 15 years
Do not use original nos 6L6G tubes ! ( check original datasheet) EL34 and 6CA7 ( KT77) the latter one is a beam power tube, the first a penthode..pin out of these tubes /screen is not internal connected to the cathode as is custom for other tubes. Best sounding and reliable GZ34 was made by the Philips group...........but expensive.
Dam shame about the rectifier tube :-(, i think the makers don't care because you have very little choice other than buy a new off them again. Sounds like a quad op amp circuit and ref pot to auto adjust the bias would have been a nice option.
I like my little 9 watt class A kit amp I have in the studio. It has auto bias. Doesn't matter what tubes I plug in it works. I run 6L6EH Electroharmonix tubes in it.
I know the store it going to tell him to pound sand, but I would be going back in there and bitching to them, and then telling the shop to stuff it, and get one from an online shop that fully tests the tubes before they sell. If this was mine I would just pit in a pair of HV diodes and make it a solid state rectifier, and leave the dead tube in just for aesthetics.
Sounds like the 9 watt amp has been well thought out. See if the bias system circuit can be adapted for your st70, it's worth looking at the diagram, maybe make a copy of the auto bias?
@@zx8401ztv the kit I built (which was over 1000 btw) is a class a. 1 output tube per channel so the tubes are driven hard as they are at 50% conduction even when no signal. The dynaco is a class b push pull. Totally different design. My amp has a bunch of transistors in it and an IC for the auto bias circuit, but the entire audio path is tube.
There is at least one auto-bias board available for the ST-70: www.erhard-audio.com/ST-70_Install.html or directly from the developer on *Bay. Different versions exist depending upon your driver board. For example the VTA driver board above vs the stock driver board.
Agreed. Will be adding protection on this to see if this tube will work as aparantly tungsol rectifier tubes are more sensitive to over voltage and remember these were current when the grid was 110. Now the grid is 120, and after the step up transformer that equals about 45 volts higher which pushes a tube running close to maximum over the edge.
@@jehosaphatcardona6026 check the bias on the right channel, make sure is set right. If nothing, move the tubes from the left channel to the right channel. If you get sound then it's your tubes. If not the disconnect the Amp and check all the wiring and make sure everything looks good. That's just to get you started.
Yes it can, and if it was mine that is exactly what I would do. I did that on one of my vintage radios. My tube amp, which is basically the same design as this one uses a SS rectifier. Some claim they like the sound offered by a tube rectifier because they tend to sag, or cause the HV to drop slightly on peak power which can make the amp more musical whereas a ss rectifier has faster recovery. Mesa Boogle Bass amps have a switch to select between tube and ss rectifier so the player can get the sound he / she desires.
@@12voltvids Wow! Thank you very much for your detailed explanation, I didn't imagine that a valve rectifier would impact the sound - *for some* - in a positive way.
@@12voltvids Ah my early days with Valves and the same question.. can't I replace that rectifier tube with a simple selenium diode setup? UHH no. UHH why not? Because it will cause the valves filaments to FLARE ie display a FLARE/FLASH of light before the filament illuminates et WHY? Because the sudden surge of power to the filament whilst also to the ANODE at the same time as the response time of the solid state diode setup is FASTER. NOTE the filament voltage is a tapped voltage OFF the transformer NOT via rectifier.. but the surge to the anode can cause that effect to happen and it will dramatically shorten the life of the tubes. Igniting the filament whilst the ANODE is powered causes an increased electron flow hence the surge filament wise. A valve rectifier takes time to warm through thus the correct power to the ANODES is not reached for some seconds allowing the filaments to warm through et You CAN use a solid state rectifier but usually using it a thermal shunt that detects the rise in the temp of the filament and resistance drops allowing the full anode voltage. 🤔👀
Had a similar problem with a Reflector 5AR4 a couple of years ago. Also arching. Why wont they make good tubes anymore? Oh well, money talks! One definately need to protect the new 5AR4's with uN4007 or better!
Tubes are now a specialty market. Very few people use or need them and all the big companies stopped making them long ago. With the cease of major production also ended the production of the components that make up the tube internal. The materials used were trade secrets for many major players. Today they current manufactures can get the specs but not the original raw materials. Some because the elements used on some vintage tubes can not be produced as they contain hazardous chemicals, so substitute ingredients are needed and they may not perform as well. Another thjng is many tubes were tweaked as the were produced and the tube reference books that the modern ones are made form may not have been updated.
I won't buy those Tungsol Russian tubes anymore. I have 6 of the 6L6G tubes that have gone to air in less than a year. 500 volt plate rated and built to GC specs, but they are a POS! I now use the Russian built Gold Lion Genalex made by Electro-Harmonix and have had no problems with them. They don't warranty them, and I won't buy them again, that is how that works.
I'm confused when setting the bias...can i play the amp for one hour then remove the inputs to check bias...? but then again i heard it's not good to run the amp without a load connected...🧐
12voltvids, older circuits use to "Positive bias" the tubes so that the tubes shielding had very high voltage on the shielding of the tube, any reasons why to "positive bias" the tube? Why did they switch over from using AC +6vac to +12vac on the tubes heaters to using a DC voltage on the tubes heaters? If AC ripples percentage AC ripples voltage will increase higher if the tubes would draw more current any reasons why?
Positive bias? You sure about that? The plate is always positive with respect to the cathode. That is how tubes work. The cathode is hot, and electrons "boil" off it. They are attracted to the positive plate. A diode has no grid. and this full current will flow to the plate for half the AC wave cycle, and not on the other cycle. In a triode, the simplest tube, a single control grid is placed between the cathode and plate, and that grid is given a negative bias to regulate the flow of electrons. It is biased just enough to provide a minimum of current flow. Then as the input signal is presented to the grid the slight changes in grid bias will cause more or less electrons to flow. The electrons striking the plate will modulate the plate to follow the same waveform as was presented to the grid, but at a higher ampliture. This is knows as amplification. In other tubes, additional grids are placed between the control grid, and the plate. The The tetrode adds a screen grid between the control grid and plate, and it is usually positively charged. Either connected through resistors to the plate, or to a center tap on the output primary. (Ultra lilnear operation) Pentodes take this 1 step further, by adding yet another grid between the screen and the plate. This is the supressor grid, and it is internally connected to the cathode and is there to prevent electrons from bouncing off the plate and making it back to the control grid. Pentode pretty much replaced tetrodes
@@12voltvids Yes they used "Emitter Tubes" in RF transformers which the vacuum tube were not glass but a dark metal can shielding if you put you hand to grab the metal can tube it had very high voltage. I guess they used them in Transmitting TV signals. The metal can shielding had the high voltage which is a positive bias they call it. I'm not sure more information about these types of metal can tubes. But some technicians say that Biasing is "balancing" the voltage & current Ratio of a vacuum tube, transistor, FET components, is this a true statement that biasing is Balancing only the voltage & current or is biasing doing other factors?
I couldn't find anything on the internet if i'm using a dynaco that has its transformer changed for 230v electric, if the bias setting would differ from what the amp recommends 1.56v on 120 v america...my common sense says it should still be the 1.56v setting as if it were on 120v...because the transformer makes the amp work on 230v and I would think that has nothing to do with the bias setting...❓
Yes as close as possible. The bias is just the idle current.To keep the tubes from going into cutoff as that would introduce cross over distortion. Too high, and it is going to consume excessive power, will shorten the life of the output tubes, and it really excessive, will red plate the output tube and could damage the audio output transformer. Now there is a different bias voltage for different numbers of tubes. Some require more and some less. The .4v drop across the cathode resistor, which is what is being measured is for EL34 and 6L6G tubes.
Wouldn't be able to clear a short in the rectifier tube the way one can a CRT in a older TV that shorts by using the Clen and Balance on a tube tester,..to Knock out the short and then rejuvinate it? I was just wonder ing if that could be done on any kind of tube,.. that may work if it was Possible. have you ever tried that just as an Experiment. Then that ways money not wasted. as thats Alot to lose on a dead tube.
@@12voltvids Ok,.. but if you get ahold of one that does try it out , but do it on an old tube you don't need first, if that should work it would save money and some tubes get a second chance even if for a while. as they are out there, most were used to Rejuvinate old CRT's but i bet they can do other types of tubes too, might be worth looking into.as i seen some that do test and Rejuvinate tubes before.
@@randymoyer5351 I do have a CRT tester / rejuivinator but that is for picture tubes. Have never used it. Was given to me last year. Used to have one at the shop, but I was forbidden to use it. Shop owner did not want any tubes boosted. I almost got fired one time when I did use it. Back when the owners dad had the shop he used to use it. The son took over (which is whom I worked for) and he was more interested in selling a new set. Jolting an old tube and giving it a second life meant he couldn't sell them a new one right there on the spot. One time I had a customer that was sentimental on an old Zenith (one of those curved ones that went in the corner) and the red gun was bad. I jolted it and got it going and the boss was furious with me. Sent me home for the remainder of the week without pay as punishment to disobeying his shop policy. When I returned to work the CRT tester was gone. He got rid of it so I could never do that again. I left the business in 2003 and actually jumped for joy when it went bankrupt in 2012. The owner lost his house, shop and wife at the same time. It was a pretty miserable place to work the last year I was there so to see it shut down was actually quite satisfying.
@@12voltvids - I had a similar experience, work for a guy that got the business from his dad and wanted to do thing his way. I did not stay there long.
@@EngineeringVignettes I did a life sentence there. That was my punishment to getting into the electronics repair business. Just shy of 20 years I got out for good behavior. LOL.
Wonderful amp, love mine. It tended to blow fuses though so I replaced the rectifier with a solid state Weber Copper Cap. Works great as you can see in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-cLIOW28RxXo.html
The one that was defective was a Ruskie. The Chinese original works. Going to add a couple of diodes to kill the reverse phase as that is what is likely causing flashover on the russian tube.
@@EmilioGarcia-fr5po Sorry know nothing about those. Never seen one. Not saying i couldn't fix one if it crossed my bench but unseen i have no knowledge of the circuit, and therefore can not give any advice. I only responded so you are not waiting for a reply.
my sony tape deck was working plug it in tonight all DARK power on transformer but stop going to board no fuse in this deck what is mystery? you know---
