Setting the Bias. Yes and no. Most all tube Hi-fi amps need to be biased properly. I have an old Harmony amp from the early 60's that runs a single 6V6 cathode bias. Raise the other 10K by the same amount. 5V on g1 on all valves including V6. which indicates that each output tube has reached the preset bias level and all is good. I had a similar problem with a different brand amp running EL84s, and a reputable tech told me that any red-plating like that is bad news. To be sure, all the valve holders were cleaned and retensioned to ensure there was no intermittent contact. ★ Discount Leather Sofas ★ Barnstormer Leather Standard Sofa by Red Barrel Studio Browse Through Our Wide Selection Of Sofas, Mattresses, Beds, Center Tables, TV Units, Dining Table Sets, Recliners And More. 2v To 200V Regulator PDF Details: zener diode serves as a reference voltage. Check the cathode resistor and bypass cap. I still had a red plating problem on one of the four valves so I returned the valves to Hot Rox for re-testing. A properly operating power tube will not have plates that glow. 156: Inmate Central, RE: Some countries aren't so forgiving (0. I recently picked up a decent condition project Invader amp minus speakers and tubes for $80. On several of these 6050MH heads i've seen they are bias well in to the 90% range. In a fixed-bias amp, the tube can go into "runaway" where it loses bias, draws more current, heats up, loses more bias, and ultimately destroys the tube. Optimally, should be within 5% of that value. The dc bias was applied continuously during each impedance measurement and the bias was increased in steps. Use steel wool to clean the copper metal anode and the nickel plated steel or brass cathode. This particular unit came in for extreme hum and red plating issues. 05/05/17 Received a replacement set of EL84’s PC 38. I waited a bit and fired her back up to see and the same tube almost immediately red plated again. Oxygen potentials in Ni + Ni O and Ni + Cr2O3 + Ni Cr2O4 systems. 1mv on pin8 measuring 24v resistor checks at 583ohm pin3 364v on 2nd 6v6 pin 8 measures 28v resistor checks at 743ohms pin3 364v Looking at that I know I need to change the cathode resistors as they are out of 5%spec. chopped fresh cilantro 1/8 tsp. The Peavey JSX Head signature Joe Satriani offers a lot ouf sound possibilities to play Joe’s entire musical repertoire. There's a problem with the bias. Any additional help would be appreciated. This will tell you the cathode current of the tube. Making of a 211 amplifier, Part 3: Listening Hi! Regular cathode bias allows the tubes to settle themselves. Your tubes should not red plate period. Probably from the mid-2000s. 58) Thanks for all of your information. The photodetector includes at least one trench formed in the first main surface and a first anode/cathode region having a first conductivity formed proximate the first main surface and sidewalls of the at least one trench. Home | | View Cart | Shop | Contact Us. I looked and saw that someone had changed the screen grid resistors to 150 ohm, instead of 1k o. Set your volt meter to the 1V, 2V or 5V scale in DC volts. the carrier reduces the plating rate by increasing the effective thickness of the diffusion layer. Tube Amp Maintenance Question (Carvin XV-212) I have an old Carvin XV-212 (originally bought in 1989), which I have not used much at all for 5+ years. Normally when a tube red plates, you would check these components, but in this case, there is nothing to do. Regards, Ted Mooney, P. Red plating is not often caused by a faulty valve alone, so changing the valve probably won’t help cure your red plating. It cannot possibly serve as the definition of cathode, because the cathode is well-defined for all sorts of devices that don’t have any mobile cations, e. By Rob Robinette. Connect one green lead to pin #2 of socket V 2 and the other green lead to pin #7 of V 2. I have rose gold here which has copper. EDIT: I know 70% is the usual base line, I meant I dont know if it is common to run fixed bias EL84s on the hot side. For a more consistent reliable cathode draw or bias current a 10 ohm 1/4-1/2W MOX should be used at the 7591 power valve cathode pins to ground, remove the original jumper and replace. Our friend Eddie Haddad sits with Mojotone Amp Category and Product Manager and talks about the Mojotone GA-5 Style Amp Kit. Q3: What is bias exactly? A: Good question. of cathode is required. Unlike the grid driven amplifier, however, both the grid and cathode are at DC ground potential (which also means that the B- terminal of the supply is attached to ground). Im doing a test at self bias my current power tubes, before I install my NOS'sAnyways, I just noticed that I can bias full HOT, and they still dont red plate? I have my amp at 6 (certainly loud enough for stage) Im in a dark room, I can tell im turning the bias thing the right way, as the hum is getting slightly louder and louder. The tubes were red plating so I shut it down. These tend to be lower in wattage and are sometimes operating in Class A—another kettle of fish entirely! Cathode biased amps include the Vox AC30, Bad Cat Black Cat 30, Cornford Roadhouse 30 (but not 50), Matchless DC-30, and many more. @ 110volts. Remember to make sure your output tubes plates are not glowing a nice cherry-red, or that you have exceeded maximum plate dissipation. At this point the tubes weren't red plating anymore. Contrary to popular belief, it's just a fixed bias amp. Or is the 1 ohm just in series with the cathode bias. Intermittent red-plating issues often indicate a bad tube. They should be replaced at least annually. 1 thought on “ Tube Guitar Amp #1 (2012) ” Mike December 13, 2013 at 12:02 am. I still had a red plating problem on one of the four valves so I returned the valves to Hot Rox for re-testing. So I measured the plate voltage with the TAD 6L6 tubes and got 462 volts. C) I know the Gemini 1 is Cathode biased. As soon as I turn it on it doesn´t red plate or even if I play moderately at home. The cathode biased 2 x 15 watt amplifier is made into a 2 x 33 watt fixed bias amplifier. A hot cathode is a cathode that is heated by a filament to produce electrons by thermionic emission. If it is, the cathode resistor and bypass cap needs to be replaced and possibly have the resistor increased in value. In electronics, cathode bias (also known as self-bias, or automatic bias) is a technique used with vacuum tubes to make the direct current (dc) cathode voltage positive in relation to the negative side of the plate voltage supply by an amount equal to the magnitude of the desired grid bias voltage. Principles of Power A Practical Guide to Tube Power Amplifier Design By Kevin O'Connor Offers a simplified method for designing tube power amps for audio. The bias on a bank of 4 KT88 is running away and causing red plating or worse-blown KT88's. Mesa amps are fixed bias and generally they are very cold. 79) Posted by smitlar on 2007-05-11, 18:06:30 (71. Con nect the other red lead to pin #6 of Twist the two green power transformer leads together and position them to socket V'2. Any additional help would be appreciated. IDENTIFY THE ANODE/CATHODE of LED's While referring to any schematic involving led's we sometimes get confused with the identification of the terminals. Tried a 2nd TS 6V6 and no change. It’s like setting the tick-over rate on the car. If an amp is run with reduced B+ and closer to or in Class A, and especially in Self/Cathode biased operation, the likelihood of ever red plating is vastly reduced yet the amp will have "that sound" of being signal pushed as opposed to supply pushed, in short, smooth saturation. There is a pretty good chance that when the tube shorted, it burned out the screen grid resistor, or the cause of the tube failure was not actually a short, but an interruption of its bias supply (this is generally preceded by a hum which gets progressively louder, the tube's plate structure glowing bright red and then the fuse (hopefully. Most all tube Hi-fi amps need to be biased properly. The rest are Motorola EL84. Vacuum Tube Amp Bias Current Probe Tester 8Pin Socket for 6L6 6V6 EL34 KT88 6550. So for a pair of EL84 tubes, that would equate to anything from 120-160 ohms. It has more compressed tone (perhaps a bit too compressed), and it has much better response to guitar setup (like pickup selection), than 15w. First, I could be wrong about everything I just said. Request PDF on ResearchGate | Growth of hydrogen-free diamond-like carbon films by a particle-free hollow-cathode arc ion plating system | A hollow cathode arc (HCA) ion plating system was. The EL34's are what concerns me and maybe its correct but could somebody explain Red Plating and how I tell if my tubes are funky. How to Cure Red plating. Recalculate plate dissipation. For 6L6 amps, 76mV should be on target. 5 watts in a push/pull amp. The Japanese Blind Hams Club I N Japan today there are more than 200. we have manuals for McIntosh, Harmon-Kardon, Heathkit, EICO, and many more, plus thousands of PDF manuals for tube projects including hundreds of amplifiers, preamplifiers, and more!. C-3PO? – We believe this is C-3PO but we can’t quite tell with that red arm and all. Red glow in a tube on the plates, is not good. As it turned out the dissipation set in these amps with the samples sent were at about 115 watts per tube which is considerably above what they are rated for. Water-plating line. Vladimir Zhitomirsky. Structure and morphology. The amp was biasing at 44ma and red-plating with tubes that were not old stock USA verities (even … read more. I would suspect that your one 6v6 redplating would be due to it being biased too hot. NOTE: If this is the 1st startup, watch the plates of the tubes to be sure no red-plating occurs. K-3PO – This Echo Base droid carries the grim of working in a frozen, Tauntaun infested secret base. Another EL34 was barely conducting. The tubes only red plate after 30 min of hard work. Or you can check plate and currect and change the cathode resistor to fix your bias to the tubes you have. 000 blind people. I fire it back up again (this time line level rather than phono) and I’m about 20 minutes in again and now NO tube is red-plating. The tubes won't last long. OK, redplating occurs when the bias is off and too much current flows through the tube causing the plate to glow red. Most people don't do that. The red plating didn’t start right away but took minutes to start appearing, the amp was listenable even with the red plating but I noticed the associated channel has distortion as the red plating started. 112) I have a Audio Note kits EL34 push-pull pentode connected amplifier with individual cathode bias of the output tubes. Are there any common problems with the TSL. A "choke" is the common name given to an inductor that is used as a power supply filter element. (80's Sunn 120 watt Enforcer with 60/120 watt switch). Or you can check plate and currect and change the cathode resistor to fix your bias to the tubes you have. You should check the valves for "red plating". If it's the bias circuit itself, you're new tube is going to red plate exactly as the old one. July 16, 2001 CODE OF FEDERAL REGULATIONS 40 Parts 50 to 51 Revised as of July 1, 2001 Protection of Environment Containing a codification of documents of general applicability and future effect As of July 1, 2001 With Ancillaries. One of your valves could be faulty but does not explain why both sets of readings are well away from what you want. RED test lead to cathode and BLACK to anode (Reverse Bias) and note the reading and measurement displayed by multimeter. Talked to the tech today and he thinks I just need to replace the worn out Power tubes. Regardless of whether the amp is fixed or cathode biased. If its red-plating, that is usually a sign of too small of a bias voltage or too high of a screen voltage. Tried an Nos GE 6V6 and the red plating was less but still present. Every time you have to change the Tubes you need a Technician to Bias this Amplifier for you. A cold bias does not sound as warm, is not as loud or dynamic, but the benefit to a cold bias is prolonged tube life. They are cathode biased so you may pop in fresh tubes at will. I've got a guitar with red-plating issues on the output tubes. No red-plating; I'm inclined to leave it alone but wondering if anyone willing to comment on the cathode. Why? It has been explained to me that this only means that the tube is ok. Anyone try this on a 2?. This reading might be a little higher to start with and will get close to or exactly to the preset bias voltage as the output tubes warm up. com and damaged in shipping, so. plating of fenders, grills, and toasters) to protect them against corrosion and passivation, by using an electric current. The amp is cathode biased, therefore the tubes will *usually* drop in and operate without worry. It could be that the tubes have been compromised in this situation or they were the problem in the first place. If the tubes are biased too hot, the plates can glow red (at the extreme, and this is called "red-plating"). All seemed fine but the clean channel started sounding bad. It also affects the tube next to it, which will also start red plating a bit. You could use a Spice model and a tube curver tracer like the Tek 570 or Dennis's tester along with a 576 or 577 to investigate your circuit mod. Can sulfuric acid be used to remove nickel plating from aluminum? 2005. This will cause excessive current flow through the tube and get red hot. I'd swap the tubes around and whatever tube I put in that socket would start red-plating. EL34 Tube Amplifier. Cathode spots are usually highly unstaionary and jump across the cathode surface. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. Testing in my own cathode biased amp confirmed their statements. IEEE Transactions on Plasma Science, 2000. That is, the spots are moving randomly over the cathode surface without an imposed magnetic field [9,29-40], and contantly splitting or combining with each other [41,42]. Set your volt meter to the 1V, 2V or 5V scale in DC volts. i used the bias circuit found at 18watt. Ended up replacing both the power tubes and preamp tubes (they were due to replacing anyway). of anode, 3 sq. I tried and all of my brand new Sovtek EL84M tubes still red plated. - Regis From Randy Aikens site: A general rule of thumb is that class AB amplifiers are usually operated at no more than 70% of the maximum plate dissipation of the tube (to account for the higher dissipation that occurs under signal conditions), while true class A. (1V-12V) 3) All three Plating Pens operate at the same time. A cold bias does not sound as warm, is not as loud or dynamic, but the benefit to a cold bias is prolonged tube life. This does not mean that idling them cooler is "against the rules"; in fact, it is a good. Class A power amps may be single ended (e. The MP15 is a "fixed bias" type, as opposed to the "cathode biased" type, and it has a potentiometer on its circuit board for adjusting the output tubes' bias voltage, and thus the anode (plate) current. Check the cathode resistor and capacitor values. At this bias setting there was no sign or red plating and the tubes have been working perfectly after a good solid 100 hours or more. I am figuring you might see it with possible red plating on the tube(s). 5 volt across it at idle I work that out to be 50 miliamp x 252 volts on v1 = 12. After all, I'm not running horn tweeters in a multi-amp system, but a pair of full-range speakers that can take whatever I can dish out. ) If cathode bias the actual plate. First, I could be wrong about everything I just said. Adjusting the bias sets this current not too high and not too low. The supplier said it was red gold and had a copper additive. com FREE DELIVERY possible on eligible purchases. Almost has a 'gypsy jazz' quality to it. Fender Harvard or Champ) or push-pull ( Vox AC30). Since two tubes are red plating I'm guessing one of those resistors is open. I should add that the 75k boot-strap resistors on the cathode driver transistors do provide a degree of self-regulation without making the tube circuit self-biased in the classic sense. Part 4: Preamp Tubes. Eddie, I am curious to read what others think about this. I took out the stainless steel plates I was originally using to make HHO gas and replaced the cathode with a copper (I know not the same color as the original plates, just testing with it) plate and the anode with a broken zinc backplate. I hear you man. 2015 Editor's Note: In our last article , Calla Gold , a Santa Barbara jeweler specializing in custom jewelry design and jewelry repair, described gold plating and its best practices. Since the electrons are attracted to the positive nuclei of the metal atoms, they normally stay inside the metal and require energy to leave it; this is called the work function of the metal. One was much worse than the other, no reasonable amount of bias adjustment or B+ lowering via variac reduced it. If they are more positive than -15, you probably have a leaky coupling cap. Optimally, should be within 5% of that value. Cathode bias is different than fixed bias in the fact that you can 1 order mesa spec'd tubes , they will bias correctly. Re: Used Vibrolux Reverb: Tube biasing question If my memory serves me correct, which it rarely does, the bias resisitor is on one of the smaller boards, not the main board. If a fuse is blown or your output tubes are arcing or red plating or your rectifier is arcing, replace output tubes, rectifier, and fuse with equivalent replacements and repeat part 3 of troubleshooting procedure. Testing in my own cathode biased amp confirmed their statements. Yes but the bias on a cathode biased stage can be set. Cold, lifeless tone ---> over-biased. And also, the value of that grid-to-ground 220k-ohm resistor hanging off the 6V6GT's grid. Cathode bias is different than fixed bias in the fact that you can 1 order mesa spec'd tubes , they will bias correctly. What do you have?. Basically, it runs ok now, but only when I let the amp warm up for a while on standby beforehand. By chance I happened to check out the valves on my Laney LC30 MkII as it had been sitting sobbing in the living room unloved for a couple of months. i used the bias circuit found at 18watt. You replaced the output transformer. vs Red (+)] — plating bath will be. You must know whether your amp is cathode biased, in which case the grid contact must be at zero volts, not positive at all. (10) He didn't have the meters of thick ablative hull plating that warships carried. I've chucked the worse one. If we look at a battery connected to a load, like a bulb for example, the electricity flows from the positive terminal to the negtive terminal. Now, in a cathode biased amp you typically bias the tube at 100% or so because when you apply signal to a cathode biased power tube, the dissipation goes down. When chamber is fully vented and the chamber door seal is broken, close the chamber vent valve. However, I find it fascinating! Because what is this blueish glow, really? To me it sounds like secondary emission of either the anode or the. I have this question out at several amp sitesand it seems running a 6SN7 as a cathode biased single ended power tube is a rare enough phenomenon that it has the experts scratching their collective heads. ) If cathode bias the actual plate. Tube FAQ High Voltage! Valve amps work with voltages that in places far exceed the "normal" mains voltage. Marshall specify 32. You must know whether your amp is cathode biased, in which case the grid contact must be at zero volts, not positive at all. The two high-quality analog milliamp meters measure the tubeʼs cathode current. This is what you DON'T wanna see in the back of your amp - red plating power tubes! In this example I turn up the bias up way too hot on a worn-out set of EL34's I had laying around, to show you. In the bias circuit the adjustment pots are in between two 10k resistors. Bad bias pot, perhaps?. 99% of the time red plating is a bias problem. Write the voltage down. When the PV was 315VDC it was at 39mA's. Like 50 mfd, instead of OEM 25 mfd. It's varying from 90mv to 215mv with no stability. If the new tube red plates, it's the amp. This should give a nice bias. Q: Does the "70%" bias rule apply to cathode-biased amps? A: No, that is a guideline used for biasing class-AB tube amps. It has more compressed tone (perhaps a bit too compressed), and it has much better response to guitar setup (like pickup selection), than 15w. 6GW8 pentode PP common 130Ω 10W cathode biased output stage, with all screens taken to screen supply. They’re perfect for use in outdoor settings, industrial environments, or anywhere else where water, chemicals, grime or dirt is present. Tube FAQ High Voltage! Valve amps work with voltages that in places far exceed the "normal" mains voltage. Episode twelve of the Fretboard Journal's all-new podcast series on all things guitar amplification, including repair tips on Fender, Ampeg and Gibson amps. With cathode biasing a resistor (and a capacitor for filtering) is used in the cathode circuit so that when current flows from cathode to anode, via this resistor, the cathode become slightly positive with respect to ground. Checked the bias and the one side running away right up to 26 amps. This happens when a tube is incorrectly biased, causing the plate to overheat and literally get red-hot. 7 from Hot Rox. Category 5e 350mhz Cat5e Cross Over Patch Cables Without Boots Yellow 32ftX-Over Patch Cables For voice data video distribution this cable will handle bandw. If you have any questions, send them in now, and I'll try to address them in part 2. The Fender 5F1 Champ is a Class A cathode biased amp. So for identification , led’s comes with a unique way to identify its terminals as Anode or Cathode. Tube Amplifier Debugging Page Popping sounds Unintentional and ugly distortion even when set for clean operation Low power or volume, or volume drops off Smoke or burning smell Intermittent operation Electrical shocks Reverb problems Vibrato problems Scratchy Controls. It’s like setting the tick-over rate on the car. 6K swamp resistors on V6 and V7 with a new pair just to make sure and afterwards measured everything again and didn't get any red plating. You need a scope and signal generator to do this kind of stuff. He says these EL84´s gets slammed by the amp high current bias. I biased up slowly again and then listened to one record side, which sounded amazing. They were just horribly mis-matched so I popped in one that was close. The two groups are preamplifier valves such as ECC83 (12AX7) and power output valves (such as 6L6, EL34 etc. I don’t know the answer personal. If you have not been trained to work with high voltage then have an amp technician adjust the amp's bias. I found that the cathode current was 72 mA with the bias trimmer set to minimum resistance. At this bias setting there was no sign or red plating and the tubes have been working perfectly after a good solid 100 hours or more. In a fixed-bias amp, the tube can go into "runaway" where it loses bias, draws more current, heats up, loses more bias, and ultimately destroys the tube. For 6L6 amps, 76mV should be on target. I have been playing my new TT for some time now, and noticed that I like 7w setting much more. Each tube is running at about 33ma cathode current. There is no compensation for the loss of high frequency as the volume is cranked down. Yes but the bias on a cathode biased stage can be set. If they are more positive than -15, you probably have a leaky coupling cap. If the tubes need a lower bias voltage, then they'll run too hot and risk premature death (mildly costly) or "red plating", melting down which can take your power transformer with them. Red glow in a tube on the plates, is not good. A common "fix" for VOX AC30s is to change the 4 power tubes' cathode resistor from 50 ohms to anything from 60-80 ohms. I recently picked up a decent condition project Invader amp minus speakers and tubes for $80. Play one side of music and then check bias again--bringing it up to 100% for that tube type. If the JJ and the RCA red plate --- you have an issue with either the cathode tied 470-ohm resistor and/or its 25mfd/25VDC bypass cap. 7 from Hot Rox. 9v's across the cathode resistor There's no red plating with strong Sylvania 6V6GT's but I know that seems high, 13. The supplier said it was red gold and had a copper additive. If your voltages going into the power tube are good and your cathode bias resistors are both measuring good, then you will be OK. Red plating tubes. I'm also kinda curious as to why my one current tube would be red plating regards if I put in the V3 or V4 sockets? I know very little about tubes so I don't know if its the cathode resistor or grid resistor (if either of those two things exist in a tube) that crapped out or if it might be something else in the tube. Recently, when JJ reissued the 6CA7, I swapped out the wimpy EL34s I'd been forced to use (after 6CA7s were discontinued in the late '70s). salt Method. Tubes are biased too hot; you're right the tubes are overdissipated. 3 Voltage measured across cathode resistor 3. vs Red (+)] — plating bath will be. Cathode bias is different than fixed bias in the fact that you can 1 order mesa spec'd tubes , they will bias correctly. Questions: Would the slight variances in the resistors above be extreme enough to red plate my third set of 7868's in a year?. Warm and dry, cuts nice. The amp was shut down and the tube replaced but to no avail. This time, it is both; best I could tell at the same time. the carrier reduces the plating rate by increasing the effective thickness of the diffusion layer. SEE PICTORIAL. Find many great new & used options and get the best deals for VTL Deluxe 225 Monoblock Tube power Amplifiers (Pair) at the best online prices at eBay! Free shipping for many products!. ★ Discount Leather Sofas ★ Barnstormer Leather Standard Sofa by Red Barrel Studio Browse Through Our Wide Selection Of Sofas, Mattresses, Beds, Center Tables, TV Units, Dining Table Sets, Recliners And More. Replace those caps, and you shouldn't see that blush any more. I usually end up about 60% in fixed bias, havent owned a cathode bias amp in years. In fact, even when biased at class B, or zero idle current, these tubes will exceed their dissipation by almost 8W at some points in their operation. Look for ‘Red Plating’ Burn marks or ‘hot spots’ inside the glass is a sign of ‘red plating’ which is when the tubes glow a constant red even when the amps on standby. I would caution anyone using attenuators to very closely monitor there power tubes for red plating, as once this starts it can lead to catastrophic failure up to and including blown output transformers. Place all ingredients in a medium sized pot. Worst red-plating I’ve ever seen. A tube with unstable bias or drift problems usually tests good on a tube tester unless it was damaged by the red plating. ) If cathode bias the actual plate. If I rush into turning standby off (after a cold start), the power tubes will glow red. One reader wanted to see how the Broskie auto-bias circuit could be used with power output tubes; above is a more fleshed-out version of the Broskie auto-bias circuit that would work well with a set of power tubes like the 6L6, EL34, KT88 or 2A3—or even a single output tube. Part 4: Preamp Tubes. Look at Weber's bias calculator and see for your self. They sounded almost identical to JJ6L6's though. The should each read about the same. com FREE DELIVERY possible on eligible purchases. My second experience with an Orange amp and a red-plating EL34 Or in this case an EL34B I turned the amp on yesterday and crackle crackle - funny noise - and looked inside to see one of the output valves red-plating and turned the amp off immediately I didnt notice this before so I think it could be a new issue. Upon looking at the tubes, I don't know how long this had been occurring as one of the JJ's red paint was cooked brown. Try replacing the fuse (get extra for back up, no we don’t sell fuses) and rebiasing the amp. You can use. ) When I started to set the bias, I couldn't get them to go much below 60ma and I was shooting for 40-45. It is far and away the safest of the two methods, and can be successfully done with medium- and even low-quality test equipment. Power indicator. This happens when a tube is incorrectly biased, causing the plate to overheat and literally get red-hot. First, I could be wrong about everything I just said. I have no experience with the Swart AST Pro, but I do run an STR Tremolo and had an issue with power tubes. Who knew cucumbers could be so much fun!? They’re actually quite the versatile veggie, making snacks and appetizers more appealing even for the little ones. Some tubes aren't balanced either, so if the bias is set pretty hot, but the one tube just performs under the red-plating area, then the other could be red-plating. In cathode biased amps it's the voltage ACROSS the tube (Vplate - Vcathode) that matters, not just Vplate. In fact, even when biased at class B, or zero idle current, these tubes will exceed their dissipation by almost 8W at some points in their operation. After about a minute or so, they developed a small spot of red-plating along the seams of one of the power tubes. 38D: Corrosion-resistant plating (TIN) — "Tin roof! Rusted!" Merry Christmas to all relevant parties. You will see a yellow orange glow usually at the top or the bottom of the tube. Tube FAQ High Voltage! Valve amps work with voltages that in places far exceed the "normal" mains voltage. Check your bias reading and adjust with a small flat blade screwdriver in the adjustment potentiometer on the back panel next to the tip jack. So for identification , led’s comes with a unique way to identify its terminals as Anode or Cathode. I'm paraphrasing here but, OP claims that 70% lets the amp run cooler and could be beneficial to the longevity of the DT. In standard ASTM salt spray tests the coating has resisted white rust for up to 360 hours and red rust for up to 1000 hours. Class-A or B, cathode, fixed bias, and push-pull and single-ended designs are covered, as are many front-end circuits. I haven't reached anything close to red-plating. Now, in a cathode biased amp you typically bias the tube at 100% or so because when you apply signal to a cathode biased power tube, the dissipation goes down. The cathode biased 2 x 15 watt amplifier is made into a 2 x 33 watt fixed bias amplifier. Since the electrons are attracted to the positive nuclei of the metal atoms, they normally stay inside the metal and require energy to leave it; this is called the work function of the metal. It's an important thing particularly in the case of plate coupling caps in the final stage of an amp, where a smallish amount of leakage-measurable in microamps-can shift the bias point of the tube enough to cause it to be seriously overworked-red plating is also part of the mix. Dynaco Repair, Restoration, & Modification Center. Note the measurement and reading. If you have any questions, send them in now, and I'll try to address them in part 2. Put in the new tubes turn on amp and then slowly bring the bias up on each tube to about 85% of the normal bias for that tube type. For push-pull, quad cathode-biased --- around 250-ohms. However, just as different tubes from different manufacturers will draw varying amounts of current in a fixed-bias amplifier, the same is true of a cathode-biased amplifier. My recommended bias measurement method is the " Output Transformer Resistance Method. Bias is adjustable. It's not like theres an exact correct amount. I still had a red plating problem on one of the four valves so I returned the valves to Hot Rox for re-testing. edu is a platform for academics to share research papers. Cathode-biased amps are usually designed for maximum power in that mode, so the tubes idle at their full dissipation rating. The grid voltage intercepts occur at -3V and -9. making the tubes red. The cathode resistor is usually set to a reasonable value by the manufacturer so that there is a good tolerance either way for the bias, so in practice you don't have to change anything. 31) Posted by vbenonisen on 2018-08-18, 15:57:37 (46.