Cathode Bias Red Plating

I just built my first cathode biased amp. When the tube sounded good briefly, the bias needed to be quite a bit colder than the Shuguang. • Improved overall operation of the amp due to the reduction in the danger of a tube red plating • The AB-D ensures that bias is kept at the pre-set value (see Initial Setup) even as the tubes age • The AB-D comes with a soft start feature, which slowly brings up bias to each output tube Quick Overview:. Again two slightly different models - the top was made by Sylvania itself at Erlangen, the lower one was made by Narva at Brand-Erbisdorf. making the tubes red. +1 on that. I was playing it many years ago and the tube started red plating. I'm going to have to have to put a large value pot in to find the sweet spot, because this took me too long to do by switching resistors all day. Like 50 mfd, instead of OEM 25 mfd. 5 watts with these tubes and 454 volts on the plates, Ohm's Law says the cathode current should be 39 mA. I'd swap the tubes around and whatever tube I put in that socket would start red-plating. Even a small area of red plating will sooner or later cause damage way beyond the cost of replacing (both of them or all four. Crazy paint job on the bomb Phil! Did you get your EC-80 A units working for the "Eruption" dive?. Now consider two LEDs connected back to back across an external voltage supply source, such that anode of one LED is connected to the cathode of another LED or vice versa. Some have trim pots for each tube and some are cathode biased. How does it sound now with the better matched tubes. Class AB amps have a separate bias supply to apply a negative voltage to the output tube control grids, usually but not always adjustable. Excluding the specialty and continuous-strip plating industries, more copper is plated than any other decorative metal except for nickel. Kwkened, you have a B1270 circuit PR. What makes a Valve ( Tube ) fail ? By Peter Stewart Gebbie This blog is the first in a series talking about the components in you high- end valve hi-fi amp or guitar amp. Part 4: Preamp Tubes. Step 5: With the amp fully warmed up, turn out all lights and observe the plates of both tubes for any signs of red plating. The first step in electroplating is to negatively charge the object (to be coated) by connecting it to an electric circuit and applying a bias voltage. Questions: Would the slight variances in the resistors above be extreme enough to red plate my third set of 7868's in a year?. I can thus set output tube bias using either the cathodes or the plates. Incredible prices & fast delivery!. I think it is the one farthest to the right, while looking at the front of the amp,. The two groups are preamplifier valves such as ECC83 (12AX7) and power output valves (such as 6L6, EL34 etc. Simply plug your tubes into the adapters and then plug the included 8-pin octal-based adapters into your amp. I had the unit on for a couple of hours, all was going just fine, then I glanced over and noted that 1 of the tubes was having some serious red plating (it got hot enough to melt the paint off the tube). - another set of valves or at the very least replace the red plating valve and see what happens (cathode biased power valves will allow you to just throw in a new one with out much drama) - borrow or buy a set of vintage (60s or 70s) 6BQ5 valves, even some partially used ones. Very soon the tube will die. All it does is isolate the suppressor grid and have it float on whatever level it will get. They lasted 92 days before red plating. After years of research and technological innovation, ZY-1313 multi-arc ion magnetron sputtering coating machine integrates planar cathode arc ion plating technology, DC magnetron sputtering technology, mid-frequency magnetron sputtering technology and pulsed bias technology, and uses high power mid-frequency sputtering power supply as well as mid-frequency magnetron cylindrical targets to. Can someone please help me figure out what and how to bias this with only having pin access. Don't forget that changing the cathode resistor changes the current flowing through the valves, therefore the Plate voltage will change. However, I let them play continuously for over a week and bias remained stable, and there was no red-plating. I have 135 Ohms on each pair at the moment, and although there is no red-plating, i know i could still run the EL84's a little cooler. I am figuring you might see it with possible red plating on the tube(s). The fault with the amp was an internally shorted 5881, causing the bias to be way off, it is cathode biased, and thus the working 5881 was red-plating. They were just horribly mis-matched so I popped in one that was close. Since the cathode resistor of the cathode follower (V2A) has to be changed from 100K to 82K, should the plate resistor (R16) of the tone stack recovery amplifier (V2B) also be changed from 100K to 82K?. I had a bad 12ax7 and a bad power tube, after I changed them everything worked normally again. 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. Twist the two red leads together and position them around socket VI. Drew, you posted that the anode-to-cathode ratio is to be in the range of 3:1. The tube that's red plating is a 6BQ5 from the Magnavox amp. You might consider rewiring the power tube pin 1 to neg bias mod, so the grid suppressors can keep the current more stable at higher volumes to prevent red-plating and other related disasters that have plague EL34-type amps. Mine=WAS the same but i went to 450R after one tube was slightly red plating. This time, it is both; best I could tell at the same time. As long as you aren't red-plating the 6V6GT. Front panel: On/off power wafer switch. However, there is also some DC drop across the resistor due to the load current flowing in it, so there is a compromise between smoothing and voltage drop. - Improved overall operation of the amp due to the reduction in the danger of a tube red plating - The auto bias modules ensure that bias is kept at the pre-set value even as the tubes age - The auto bias modules come with a soft start feature, which slowly brings up the bias to each output tube. Connect one green lead to pin #2 of socket V 2 and the other green lead to pin #7 of V 2. Tried an Nos GE 6V6 and the red plating was less but still present. Everyday Low Prices Kenzomen S Embroidered Logo Sweater in a wide variety of styles. Red plating is not often caused by a faulty valve alone, so changing the valve probably won't help cure your red plating. I also read 355v on the anode. I usually go from pin 3 on power tubes to the red center tap on my old Fenders. The other power tube bias was adjustable, but soon quickly climbed high, red-plating the tube. When too much current is drawn through the tube than can be dissipated, the metal parts get very hot. 99% of the time red plating is a bias problem. The process of applying an additional layer of metal is called metal plating. 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. The manufacturer claims the Tung Sol tubes are the best thing for VOX AC30 amps and I have to agree. As well as connecting lines. My amp eats lesser tubes from Russia and many NOS offerings, but the Tungsol EL84 tubes hung in. Class AB amps have a separate bias supply to apply a negative voltage to the output tube control grids, usually but not always adjustable. I really don't understand why everyone is trying to reinvent the wheel on biasing these amps. hello, regarding the 200 ohm bias,i just think your concentrating more on boosting your B+ rather than actual biasing of the el84's. If there was no negative bias applied to the tube, it would go into full conduction, the plate would glow red hot, fireworks will happen and that would. No dry joints. Applying a given bias voltage to a tube is OK, if it's adjusted the tube will idle properly (and work properly). The subject of output tube biasing has many otherwise rational men arguing amongst themselves like little school children. When the current through the device is reversed, the electrodes switch functions, so anode becomes cathode, while cathode becomes anode, as long as the reversed current is applied, with the exception of diodes where electrode naming is always based on the forward current direction. The tube will reach a stable point of equilibrium and stay there. You need to go through the diode, caps, and resistors. The first step in electroplating is to negatively charge the object (to be coated) by connecting it to an electric circuit and applying a bias voltage. But if your amp blows a fuse, it's most likely a symptom of power-tube issues, and you should know that fuses will likely continue to blow until you replace the bad tubes. I think the B+ is too high, especially given today's higher mains voltages. Feeling like I was going to be happy for the rest of my life with the Genelex Tubes, I went back to the amp to check the bias again and found the left channel WAY high, like at about 150ma or more. Okay probably not a good idea, but on mine I just lightly tapped the tube with the back of my finger nail and you could hear my taping almost like it was microphonic. The cathode current multiplied by plate voltage will (roughly) be the wattage that the tube is pulling. Filament heater artificial center tap consists of two 100 ohm 1/2 watt resistors connected between either one of the power tube socket's pins 2 and 7 (heater wires) and pin 8 (cathode). No separate bias circuit, like in the push-pull Fender amps (fixed bias). Dynaco Repair, Restoration, & Modification Center. It has more compressed tone (perhaps a bit too compressed), and it has much better response to guitar setup (like pickup selection), than 15w. I replaced the fuse, and while it warmed up again without noise or red plating, the bias is way off on both sides now. The tubes won't last long. Initially I though maybe some excess dust burning on the tubes but I quickly looked in the back and saw a single tube red plating. OTS 50 - bias problem/question and the one drawing 70 mA may have been red plating and on its way out. How to Cure Red plating. In addition, I wanted to see if there was any improvement in the sound. read the whole thing here. I want to go a little bigger so size do matter. I realize the pic is pretty low rez, but I see some big grey resistors that appear to be tied to pin 8 of each output tube socket. The fault with the amp was an internally shorted 5881, causing the bias to be way off, it is cathode biased, and thus the working 5881 was red-plating. If there is the slightest sign of a dull red glow on the spine of the anodes get it to a tech. There's no red-plating at all, & the amp sounds great, but something is amiss here. The grid voltage should be independant of tube operation unless you have a bad tube. In this mode. I didn't want to go any higher til I talked to someone about it. Groove Tubes got around this with their number rating. (Class A push-pull preceded Class B and Class AB amp development. Replaced the open resistor, along with the other 6. ) Pin 7 to ground is not 323 volts DC. Put the red meter lead on the cathode pin of the tube socket and place the black meter to the chassis star ground tag. I had the unit on for a couple of hours, all was going just fine, then I glanced over and noted that 1 of the tubes was having some serious red plating (it got hot enough to melt the paint off the tube). Speaking if which, one tube did start red-plating. Put the red meter lead on the cathode pin of the tube socket and place the black meter to the chassis star ground tag. However, as soon as the bias was set on both, they both climbed quickly high red-plating both. If the new tube red plates, it's the amp. It has plenty of mids, treble, gain, and volume, but there is not enough/barely any low end. 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. Quick links. And also, the value of that grid-to-ground 220k-ohm resistor hanging off the 6V6GT's grid. 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). ) Pin 9 to ground is now 304 volts DC 6. ) 312 Volts DC voltage measured between plate and cathode. The three-dimensional structure increases the specific surface area relative to the planar Cu, reducing the local current density. Power is being dissipated by by the tube that cannot be measured when setting the bias. You need to go through the diode, caps, and resistors. Red plating is usually loss of bias. Black Cat Combo. VTX is cathode bias there is no adjustment to change. A vacuum tube "bias probe" to individually measure Plate, Screen and Cathode current in power output tubes of audio amplifier circuits. I like about 65% based on my ears personally. ) 2 tubes (EL84) 2. You should see normal cathode bias voltage, normal B+ voltage to the output stage, and there should be no red plating after any length of operation. This time, it is both; best I could tell at the same time. Part 4: Preamp Tubes. baron55 wrote:Keep in mind JJ tubes have smaller than standard pin diameters, it is possible the tube sockets are not making good contact and pin 5 is not getting a good negative bias supply. Not really tho' you can, esp if discolored. Forward bias: When the voltage across the diode is positive the diode is "on" and current can run through. Setting the Bias. NOTE: If this is the 1st startup, watch the plates of the tubes to be sure no red-plating occurs. They should be replaced at least annually. You should be safe regardless (from red-plating), because as your input voltage rises from 110 to 120 so does your bias tap, and since your bias tap is rectified to negative it goes more negative and causes your tubes to conduct less. They were just horribly mis-matched so I popped in one that was close. Your Champ has a cathode-biased output tube - single-ended. If we set the bias too high, too much current flows from anode to cathode and one or more valves will start to red plate. The main factors influencing substrate temperature such as ion bombardment, heat radiation, and heat conductivity are analyzed for Pulsed-Bias Arc Ion Plating (PBAIP). OK, redplating occurs when the bias is off and too much current flows through the tube causing the plate to glow red. Finally, another type of tube glow that needs mention is red-plating or “cherry” plate glow. A few modifications can/should be integrated as well. I am thinking that 63VV's redplate is happening in the fixed biased mode and that the bias. It is still prudent to keep an eye on them to make sure they are not red plating. 24: Need a little help with a red plating 6CA7 tube and/or amplifier (6. The bias voltage can fall within a range where it is acceptable. When the current through the device is reversed, the electrodes switch functions, so anode becomes cathode, while cathode becomes anode, as long as the reversed current is applied, with the exception of diodes where electrode naming is always based on the forward current direction. Part 4: Preamp Tubes. hello, regarding the 200 ohm bias,i just think your concentrating more on boosting your B+ rather than actual biasing of the el84's. INSTALLATION AND USER MANUAL FOR THE AB-Q-ST70-ST120 AUTO BIAS MODULE. If the fuses are ok, and none of the tubes are arcing or red plating the output tubes are OK. All caps were replaced. FWIW, I think Peavey is being cheap by not provide a way to adjust the fixed bias set-point. Question for Dave and those who own a Pink Taco. Is it one of those 2 things that would make mine 10-15 watts and the BC and chieftain 30 and 40 respectively?. If you got a pair of power tubes and they are working ok at home and you don´t check how much they draw cranking the amp at the gig could bring them to red plating and your gig is blown, amp maybe as well. Recalculate plate dissipation. 5 watts in a push/pull amp. I have one odd-ball tube red plating. 24: Need a little help with a red plating 6CA7 tube and/or amplifier (6. 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. I talked to the dealer who suggested that I increase the resistance in the bias circuit and I did, multiple increases, and could never get the current to come down. An orange glow from the filament or cathode in the middle of the tube is normal and can vary from very bright to very dim depending on how it is covered from view by the surrounding structures. so I thought I knew what I was doing yesterday when I changed the tube but overnight I started second guessing myself and now I've convinced myself that I'm 100% wrong. Left/right/stereo/reverse mode wafer switch. Now, both showed bias current. We love ’em, don’t we? But to help them really love us back—and I mean with big, juicy, bear-hug love—we need to know a little bit about what makes them tick, how they vary, and what they do for our precious guitar tone. In general, a 250 ohm cathode resistor is going to run them out of spec regardless of whether they're red plating or not. The Cause and Cure of Red Plating Valves in Guitar Amplifiers. The amp was biasing at 44ma and red-plating with tubes that were not old stock USA verities (even … read more. Setting the bias higher on your KT88 isn't the reason that the tube red plated. Does anyone know what the causes of Red Plating Tubes are other than improper bias? Had problems with Tubes Red Plating after performing the Dual Voltage Mod, however was able to solve it by using new tubes and getting bias correct. If it wasn't the same two valves, it was probably only one each of the red-plating pairs. Questions: Would the slight variances in the resistors above be extreme enough to red plate my third set of 7868's in a year?. I replaced the fuse, and while it warmed up again without noise or red plating, the bias is way off on both sides now. Gunther (1); Siemens AG, Corporate Research and Development, Erlangen/F. Under biased will sound weak and have a nasty distortion to them. IMHO, seeing any kind of red-plating is undesirable, especially if you plan to use expensive OEM Mullards. The upper jacks are 6V6 #2 cathode, cathode ground, and 6V6 #1 cathode. The fault with the amp was an internally shorted 5881, causing the bias to be way off, it is cathode biased, and thus the working 5881 was red-plating. I have one odd-ball tube red plating. Whenever I re-tube an amp I let the new tubes burn in for a few hours while I check them for red-plating in the dark. Suitable for tube model EL34,KT88,6L6,6V6,5881,6550,KT66,KT100,KT120,7027 etc. The hum was no better, and the valves, though a bit less angry, were still running too hot, one much more than the other. Gec Kt66 in Dual red-plating. Is it one of those 2 things that would make mine 10-15 watts and the BC and chieftain 30 and 40 respectively?. If the amp is designed to get the most out of the tubes you probably will get red plating. Homemade EL34 / 6CA7 PP Stereo Tube Amplifier from Cathode to Fixed bias. 6 AndyJ 4 years ago. Hello all, Is it possible for a power tube such as an el84 to red plate if the pins were not seated in the socket correctly? I recently put in a brand new matched set into my amp, a mesa f30. The process of applying an additional layer of metal is called metal plating. Cold bias isn't better either. The normal is 200 to 250 ohm. I have a marshall style build that i recenty changed to cathode bias. making the tubes red. Since the cathode resistor of the cathode follower (V2A) has to be changed from 100K to 82K, should the plate resistor (R16) of the tone stack recovery amplifier (V2B) also be changed from 100K to 82K?. 78mA isn't enough to cause the plate to glow. Most of this circuit sits on a separate breadboard, under the power lamp. Replaced the open resistor, along with the other 6. You are close enough. Operating class is independent of biasing method. Before, I had trouble with one tube red-plating since all had to be very well matched to share a common bias point and that wasn't working out. No bypass caps So in short the big diff here is the cathode resistors and the caps that mine doesn't have. I biased up slowly again and then listened to one record side, which sounded amazing. A copy of the AC80/100 "Impact" was the brand name of a range of amps marketed by Pan Musical Instruments Ltd, a small British company founded by Don Mackrill in 1963. First, I could be wrong about everything I just said. Weber Bias Calculator 1. If there was no negative bias applied to the tube, it would go into full conduction, the plate would glow red hot, fireworks will happen and that would. The red plating I thought had initially disappeared so I was happy. If the fuses are ok, and none of the tubes are arcing or red plating the output tubes are OK. @ 110volts. This resistor also helps set the idle bias, as well as the cathode tied 470-ohm resistor. One of your valves could be faulty but does not explain why both sets of readings are well away from what you want. ) If cathode bias the actual plate. The two groups are preamplifier valves such as ECC83 (12AX7) and power output valves (such as 6L6, EL34 etc. FAQ; Logout; Register; Home Forums At the Workbench 18watt Technical Discussion; Donations. I have what's left of it (mainly the beads) and I believe they're a chrome red plating since they aren't totally chrome red (inside is a white-ish plastic). In electroplating, the usual basis is voltage drop. The amp itself should be fine but better safe than. 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. The voltage should be greater than the forward voltage (V F) in order for the current to be anything significant. New Posts Hot Thread (New) Hot Thread (No New) No New Posts Contains Posts by You Closed Thread. They were just horribly mis-matched so I popped in one that was close. Eddie, I am curious to read what others think about this. 8, 2013 Title 29 Labor Part 1910 (§ 1910. Germany Received on March 6, 1987 - Accepted by the Editorial Committee Summary: Physical vapour phase deposition processes have sucessfully expanded into the field of coa- tings against wear and friction. ) Pin 9 to ground is now 304 volts DC 6. The machine integrates cathode arc ion coating technology, intermediate frequency magnetron sputtering technology, pulsed bias technology and other advanced technologies. The bias is set by the operational parameters of the tube. Pro jnr red plating. The guts are metal: plate (anode), grid, and cathode. Don't put the tubes back in until the bias circuit is fixed. Just look at the tubes while the amp is running. The more simple auto-bias as this site inform also tune or control the bias tube all the time, in my humble opinion. The cathode biased 2 x 15 watt amplifier is made into a 2 x 33 watt fixed bias amplifier. Fixed bias tends to sound cleaner and punchier, especially the lows and it develops more power than cathode bias. First: I do have to subract the shown cathode current from the shown plate voltage and then use that figure for the actual plate voltage when calculating the plate dissipation, right?. You can run the amp in standard fixed bias mode or flip the switch to a more 5E5 Pro vibe with a more 'tubey', round, warm and compressed tone due to it's fluctuating cathode bias. The Impact 100 amplifier. ) If cathode bias the actual plate. When it comes to bias there is no right answer. The 47k resistor is slightly off at 43k. In addition, I wanted to see if there was any improvement in the sound. Freller and K. Let me know exactly how are you biasing the amp (IE: what method you are using) as based on what you are describing it appear that you may be reading the negative voltage at the bias splitters verses monitoring the current through the power tubes cathode or plate. 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. Wholesale Black Gold Plating ☆ Find 1,201 black gold plating products from 421 manufacturers & suppliers at EC21. VTX is cathode bias there is no adjustment to change. Optimally, should be within 5% of that value. Classic, Custom, and Dual. This will tell you the cathode current of the tube. 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. In fact, if it is visible in normal room lighting, it's pretty bad. 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. The Fender 5F6A Bassman and most Marshall amps are fixed bias Class AB amps. Copper goes into solution at the anode as it is plated at the cathode. This is how Fender amps tend to be biased from the factory, and it's safe but not ideal. The amp plays fine for a while then buzzes and red plates the first power valve briefly then goes back to Being ok again then cycles this pattern. The tube will reach a stable point of equilibrium and stay there. That does not sound like a very good circuit design for cathode biasing, it's more typical to see a common cathode resistor and capacitor combo for each pair of tubes rather then a quartet of tubes. 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. Does anyone know what the causes of Red Plating Tubes are other than improper bias? Had problems with Tubes Red Plating after performing the Dual Voltage Mod, however was able to solve it by using new tubes and getting bias correct. One tube was receiving a -19V bias, whereas the other was receiving only a -10V bias I assume that would allow much more current flow through tube number 2, causing the red plating. It is voltage not current that causes this and CCS couldn't stop this phenomenon at the voltage level. The amp is cathode biased, therefore the tubes will *usually* drop in and operate without worry. In this video, we'll find out how to spot red plating 6L6GC output tubes in a modified 1966 Fender Blackface AA165 Bassman Head. The biggest piece of Kenzomen S Embroidered Logo Sweater furnishings you will own, cost match guarantee, and number of other available features you're certain to be satisfied with our service and products. Willing to bet the bias is high on the bad tube. I just tried out a set of Genalex Gold Lion 6v6s and I see a mild orange glow up the centerline of the tube, on both tubesmakes me sad. Making of a 211 amplifier, Part 3: Listening Hi! Regular cathode bias allows the tubes to settle themselves. Paradoxically, when a tube amp loses bias it will often. This means too much power is flowing through the tube and is a bad sign. Since nothing is smoking, red plating, popping, or just doing weird things, you're okay to use it now. For this reason, the bias should always be checked, even with cathode-biased amplifiers. I have a cathode biased amp. For W cathodes, N’s with cathode bias, a biatomic ion collision with the cathode retain about 40% of the total incidental energy. Class Va Vg2 Vg1 Ia Ig2 Zout Pout THD Notes. What I did not know (I was blind today) is the bias pot is at the rear of the chassis not on the board. I talked to the dealer who suggested that I increase the resistance in the bias circuit and I did, multiple increases, and could never get the current to come down. This is just a thought and, even though I don't expect it is the case, it is worth checking before you go hunting for a bad coupling cap. making the tubes red. Adjust it so both tubes pull the same current --> 1. @ 110volts. Now keep in mind, many old amps ran the piss out of their tubes so I wouldn't be surprised if you're amp is running hot. 1 thought on “ Tube Guitar Amp #1 (2012) ” Mike December 13, 2013 at 12:02 am. I removed the 12AX7 from the bias circuit and installed a separate 12VAC filament transformer for the input tube. 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. 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. i used the bias circuit found at 18watt. You will never hear the difference. The common cathode bias uses an 82ohm 10w resistor. Orange Ad200B Technical questions Discussion in 'Amps Blown tubes (red plating) and maybe blown OT. If the grid voltage is closer to zero or positive, replace the coupling capacitors, usually 0. If you insist on DC heaters there are going to be a lot of TO-3's in the regs. Not sure about the new production sovtek 5881 but so long as the tubes aren't red plating (plates glowing red, overheating from excessive current) you should be good. I usually end up about 60% in fixed bias, havent owned a cathode bias amp in years. Plating has been done for hundreds of years; it is also critical for modern technology. After a short introduction on the basic principles of the galvanic process, this work will focus on the aspects that feature in a good quality galvanic plate: respecting the characteristics of the plating bath parameters, of the chemistry of the electrolyte solution and the preparatory phases of the electro-plating process. The Cathode bias resistor had a small bite out of it (presumbly from the arcing) and the screen. Subjective at this point. Classic Deluxe Head February 14, 2019. I also read 355v on the anode. As soon as I turn it on it doesn´t red plate or even if I play moderately at home. Plating is a surface covering in which a metal is deposited on a conductive surface. 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. Like the grid driven configuration, B+ is applied to the plate and B- to the cathode. com for the. so I thought I knew what I was doing yesterday when I changed the tube but overnight I started second guessing myself and now I've convinced myself that I'm 100% wrong. I know cathode biased amps are biased hot to avoid crossover distortion because the bias voltage is not stable and will increase as you turn up the amp on a cathode biased amp. The upper jacks are 6V6 #2 cathode, cathode ground, and 6V6 #1 cathode. The voltage should be greater than the forward voltage (V F) in order for the current to be anything significant. Interesting in that article on the link you provided about Fender changing the tremolo design from the bias modulation of the brownface era to the blackface era opto coupler method due to the amount of complaints Fender were receiving about the drop in tremolo intensity or the power tubes red-plating when the bias was incorrectly set. Are the tubes red-plating? If it sounds good and isn't red-plating, play it. FAQ; Logout; Register; Home Forums At the Workbench 18watt Technical Discussion; Donations. 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. 5 watts with these tubes and 454 volts on the plates, Ohm's Law says the cathode current should be 39 mA. It's not like theres an exact correct amount. (80's Sunn 120 watt Enforcer with 60/120 watt switch). Just as well I did as one of the EL84 power valves is starting to red-plate which is never a good sign. 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!. The object is then dipped into a solution containing a metal salt. They are cathode biased so you may pop in fresh tubes at will. However, some alloys can be electrodeposited, notably brass and solder. I have a Weber Bias Rite that reads the plate voltage and the cathode current and I have a couple questions about biasing. Cathode bias by its nature has the bias voltage vary as the signal cycles (through the 360 degrees) If you are simply suffing tubes in any amp (fixed bias or cathode biased) without monitoring the current (and plate voltage) you are asking for trouble. That much heat reduces the tube's lifespan significantly. I guess I could go up to a 180 ohm but any other fix? Could I bias one tube with a 300 ohm and the red plating one with 340 ohm?. The amp is cathode biased so there is no bias to check like you would with a fixed biased amp. measure the cathode voltage (which is the gate voltage) with a voltmeter from cathode to ground. This is a good time to stop, and increase the bias voltage slightly. Speaking if which, one tube did start red-plating. I haven't measured the voltage across the 82ohm but I'm about to. A pity this site not mention the Manual Bias of cathode. A red or orange glow on the surface of the plate is bad and is referred to as "red-plating. (Actual Plate Voltage) 5. I just tried out a set of Genalex Gold Lion 6v6s and I see a mild orange glow up the centerline of the tube, on both tubesmakes me sad. A quick and easy tube change can make the most dramatic. WARNING: A tube amplifier chassis contains lethal high voltage--sometimes over 700 volts AC and 500 volts DC. No bypass caps So in short the big diff here is the cathode resistors and the caps that mine doesn't have. Normally when a tube red plates, you would check these components, but in this case, there is nothing to do. Download the PDF version. This is the method that is best for hobby techs and do-it-yourselfers. But if you CHANGE your tube or tubes, how do you know they'll bias properly without adjusting the bias? The new tube might be different in bias requirement.