Ef86 voltage.

Ef86 voltage With a high value of anode load resistance (R5 is l MΩ) and reduced values of anode and screen-grid voltage, the gain of the stage is raised two or three times above that obtained under normal operating conditions. Over the audio-frequency band, the EF86 in pentode mode has an equivalent input noise voltage of around 2uV, which would be an R eq of 12k ohms! The equivalent input noise voltage of most triodes will fall between 0. " "The pedal plays like a dream, I love it!" "I received the boost today. The screen current causes a drop across the The EF86 in the voltage-amplifying stage is used under conditions approaching those of starvation operation. Note: The impedance at each input includes the grid impedance of the EF86 modified by the feedback components as well as by the impedance of the input network. 5. Nov 4, 2008 · He has rolled in several different types of EF86s and the best ones have been the GEC CV4085s and the Blackburn Mullards. I assembled a regulator using just one PCL200 (and the OB2) according to this schematic Now I aimed for about 250V and 30mA, but again there was a Oct 23, 2018 · I wonder what voltages are valve heaters formed at , presumably they must undergo some kind of burn in at the factory , maybe theres a clue there. It replaced the EF37A and Before the advent of the EF86 the Mullard valve of choice for pre-amplifier stages was the EF37A Mullard, the designers of the EF86, describe it as a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. The best way to select an EF86 for this circuit is to put a voltmeter between the LTP anodes and choose the EF86 which gives the lowest voltage reading. But thats not really an issue with low voltage 6V6's. Now we need the polarizing voltages: 0V, 80V and 160V. The Matchless DC30 appears to be over 300VDC while the old Leaks and Voxes are less than 100. Here is my first attempt to check voltages, after doing some reading. EF86 Datasheet (174. 66 is, imho, a great amp. It's a fantastic tube for Dr. 1mA - 2mA) = 300v / 0. Aug 10, 2008 · Here a schematic diagram of a mic_amp with the EF86. The amp currently has a Mullard EF86 in it, which has a great tone, but one has to put up with microphonics. Steer clear of the 12AX7/ECC83 Mullard used as the LTP. Here are the plate characteristics for the most popular preamp pentode, the EF86, when the screen voltage is 100V. Is this tube that versatile Apr 6, 2025 · Knew that the PF86 can be used in place of ef86 with lower voltage in the filament, about 4. I changed the 100K resistor in the depth control circuit to 82K. May 26, 2015 · The EF86 is a terrific voltage amplifier, but it can't drive loads. Good data sheets will provide the mutual characteristics graph too. The Phædrus Audio CV4085 (Special EF86) Supertube™ measures <1. With the given input sensitivity of 0. Pin 4 must be positive with respect to pin 5. And a sec voltage of 145 V 5 mA or more. Vox used the EF86 as an input preamp. 66V which is near enough to the 2. EF86 - Voltage Amplifier Pentode Jan 20, 2013 · even triode connected, a voltage gain of 25 is terribly high with modern digital sources. I have built a couple of these before but the plate volts in working examples are all over the board. 8. That could be your problem if you are running AC heaters. Out of curiosity, in the AC4 schematic, the voltage at the anode of the EF86 is listed as 215V - do the volume and tone pots have to deal with this voltage or will there be a sufficient voltage drop across C6? Nov 18, 2023 · It isn’t 0V. But reading the Merlin's book on amplifiers (the hifi version, section 4. just a user. 4 %äüöß 2 0 obj > stream xœ…VÛnÛ0 }×WèyÀ\](R Š « {, ` °­ tCû²ßß!å$îb7 Û’H Ò þ¯{ñ ŸÒÊ }¥ä_ ø¯ üïe=øןîáè Õ‹ÐÀþøÝßÍq(>& |ò÷4ò,’‚0Ï qdá’ â\3c‡¤pÒ5 ‚+NL >ùã/w8ºÇÍP™†ÖC¥U¨Ê-Å÷ c Ò•! ÀTr ýW27ÅÀ£¢b ¾¦È%½Åˆ§bg ,š‘»Jé€e˜bE@Câ s àz´;u\SÈ1§¢– g§ ,V† ] ¥% ç„g2”ú Equivalent to tubes: EF86, 6267, 6CF8. 2 ­ 1. I don't have another ef86 but the one I have is a tested TAD one. The figure below shows this being done for an EF86 with a screen voltage of 100V. Hum. I would also suggest some *gasp* local and/or loop feedback to reduce the total gain. I am working on a direct coupled amp with EF86 at low Plate voltage driving El156. The plot corresponds to a plate voltage of 250 volts, but it doesn't change much for other plate Good data sheets will provide the mutual characteristics graph too. Dec 29, 2023 · The voltage of the EF86 has gone down a little with the addition of the source follower but it was only about 53V before. What I read said to test voltages with the power tubes out, so these readings are without the power tubes, which probably accounts for those zeros (except for the ground pins on the EF86 of course). I know the usual way to connect the screen grid to plate. Jan 14, 2005 · Thanks for the comments. 2K cathode resistor, and 1. 52mA and 0V, 0mA. 5-5. Voltage at B+3 is now 202V. Unfortunately upping the bias voltage with a larger value cathode resistor will decrease plate current, and you are already undoubtedly running very, very little plate current, so some rework on Hoffman Amplifiers Tube Amp Forum, Vox AC4/EF86 build/rebuild running a simple voltage divider out of the 12AX7 into the EL84 would work great, I'm sure. the vf14 has around 50 volts heater voltage and so they could take this voltage out of the anode voltage with a simple divider and 6S40P is a high voltage triode, used in old tube TV sets as CRT voltage stabilizer. The phenomenon is common enough among high R P /low gm types; look at the 12AX7. Presently B+ for the El34's is 645v and the grid 2 voltage is 380v. You can use this to estimate the anode characteristic curves a little more accurately. 5uV. Watch out for the rectifier ratings, capacitor ratings, 6AS7 ratings, EF86 ratings, etc. However, the heater is isolated from the main circuit so that, for example, pin 5 may Sep 12, 2010 · A 12ax7 for example, has low noise at about a voltage gain of 30 A EF86, about 100 EF86, E804s, 6sj7, and I have also used 6eh7, 6ej7, have special designed plates and grid structure, with outside shields that give low noise and low microphony Lots of study, and you need a pile of tubes, different versions to play ll Special EF86 vacuum electronic tube for microphone or preamp equipment. The screening mesh and below the bottom mica addditional screening. 0001A Nov 15, 2015 · One may then expect some 2V signal at the anode in an R. Take a look at the recommended operating conditions on pg2 of the Philips datasheet. The grid bias is provided by the grid current and it’s associated voltage drop across the grid resistor. larger)electrolytic. Dave Feb 4, 2025 · All the good ef86 got selected and picked long time ago, so the"selected" nos tubes today are yesterdays rejects. (in stead of fixed bias by a voltage divider off the B+) to get compression when it I've seen the same in tube-regulated power supplies (either standalone or in tube oscilloscopes): a high positive voltage (sometimes the output voltage of the regulator) is applied to the heater center-tap for the tubes being used in at least the series-pass-tube positions, as these are often power output tube types and have their cathodes Aug 18, 2012 · EF86 works as a voltage gain stage. You want less gain, more gm, and lower plate resistance in that role. 6J32P / 6Zh32P / EF86 / 6267 tube $ 12. Mullard describe the EF86 as a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. EF86 Datasheet - Mullard Voltage Amplifier Pentode. 5 Megohms (and often is listed as such in data sheets. ANODE CURRENT PLOTTED AGAINST ANODE VOLTAGE WiTH CONTROL-GRID VOLTAGE AS PARAMETER ISSUE 2 EF86 1057-5 If the EF86 were perfectly linear (We're sure glad it isn't!), the curves would be straight lines. The EF86 is the standard early stage audio pre-amplifier valve. Very few are quieter than this. As to your ideas about driver and voltage amp, I would think EL34 in triode-connected CF operation as a driver would be good and an EF86 voltage amp would also be good. The input signal transformer the signal voltage steps-up the signal by 1:7, which the EF86 then further amplifies before passing the signal to the anode-follower gain formed by the two 6DJ8/E88CC triodes in parallel. 45Vrms, Av = 76Vrms that exceeds the max output of 44Vrms given by Philips. Oct 10, 2012 · Thats quite similar to an EF86 based mic I built, back plate connected to polarising voltage ,capsule front direct to grid like the U47. 1, page 189), I came across a new flavour. If the voltage across the cathode resistor is zero, the plate current is zero. Dec 11, 2018 · I am not an amp designer. The screen current causes a drop across the This implied in a voltage drop of about 200V across the PCL200’s…(and about 7W plate dissipation each, close to their maximum ratings) I thought, well, I am a newbie, so I will go a bit slower. Guitar Amplifier Electronics: Fender Deluxe - from TV front to narrow panel to brownface to blackface Reverb Sep 14, 2022 · The unknown actual designer of that EF86 circuit worked for the tube manufacturing company, and came up with a circuit that showcased the ability to squeeze a lot of voltage gain out of their shiny new product (small signal pentode). 3 this is a 20% DROP in voltage. The red dot shows that when the plate voltage is 250V and the grid voltage is -1. The heaters should be elevated in any event, as this degrades the heater insulation and eventually cause an early failure. B+2 = 234V and B+1 = 275. 2vAC pin 3-near full DCV Pin 4-near full DCV Pin 5-about 16-20vDC Pin 7-3. 3V heater voltage. Approx. Aug 11, 2010 · I just completed an amp design that involves 2 12AX7 stages in front of an EF86 pentode stage in the pre-amp. Nov 30, 2012 · The voltage doubler circuit is used to take the 6. Mullard describe the EF86 as a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. The cathode voltage will be something near half of G2 voltage divided by Mu. 9k ohms Mar 23, 2006 · You get the most voltage output from the EF86 when the screen is 30% to 40% lower than the screen, and the most clean headroom too. 0-3. Since I drew the attached schematic, I have tried (and removed) a bass control and upped the pentode's plate load to 100k. The voltage gain of this VCA varies exponentially with the CV, making it suitable for most voltage-controlled music synthesizers with their exponential CV response. Merge Mullard's 5-20 with EICO's HF89: EF86 voltage amplifier, 6CG7/6SN7/7N7 LTP, and "fixed" bias O/P tubes. Feb 4, 2015 · Sadly this only works at radio frequencies. 40 megohms is the listed as the highest grid This ELECTRO-HARMONIX EF86 penthode tube can be installed as a replacement for any EF86 or 6267 preamp tube. A voltage Aug 11, 2017 · Dr -- If you get a chance, post some voltage readings for the EF86 position with the two different tubes installed. FIGURE 4 Dec 23, 2023 · They seemed in proper relation to the ones in this schematic considering the lower plate voltage There is a redundant power tube I can pull on this unit which boosts the plate voltage about 18V 4. Hence Ug2 voltage drop equals: 5600000 * 0. And I can tell you it is not a standard voltage for zeners nor gas discharge tubes. Also thought about a CF post EF86, that seems like it would let the EF86 do more of what it does even better. How did you like the effect the CF had on the tone? I have been really interested in an EF86 front end into *something*, into a LTPPI, and into a 2xEL84 power stage. The result is a variation in the preamp tube's ability to allow electrons to flow, 2 to10 times per second. The Ceriatone Custom built Signature Series British Style 18 Watt TMB EF86 boutique guitar amp is a tribute to the hard to find, 1966 Marshall™ 18 watt lead combo amplifier with two channels (4 inputs) with a tremolo unit operating on channel two. I did try changing the plate, cathode and screen resistor as suggested and as dictated by the datasheet. They all look good to me, given my slightly lower b+ voltages. The Phӕdrus Audio CV4085 (Special EF86) SupertubeTM measures <1. On pin1 I've heard nearly everyone say that the EF86 goes microphonic in a combo, however. At that time in history, the ability to get that much voltage gain from one tube was a radically new development. Don't bother listening. I don't think the EF86 is setup to provide as much output voltage swing as it could be. For a low-impedance source of 250 Ω, on the other hand, the noise contribution of the valve is 10 times larger than the signal source, and the noise figure is approximately ten, or 10 dB. 2MΩ screen resistor is 320V - 100V = 220V. 3-5=1. On the matchless clubman the plate load resistor for the EF86 is 220K. Love the complexity of the ef86. Mar 26, 2009 · I am aware of the bogey specs of keeping a tube within 10% to 15% of the rated voltage. May 29, 2015 · If you look at figure 3 you can see the components for the tone section. The EF86 is a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. Note, do not ground the center-tap. Looking at the Philips datasheet and taking into account the given values of anode - cathode - G2 resistors and the 217V anode voltage, this tube should work with Av = 170. File Size: Jan 14, 2005 · Thanks for the comments. Nov 23, 2018 · In my opinion, the EF86 in that circuit is starved for voltage and starved for current. I've heard that EF86s are super senitive/responsive to voltage changes, and that little changes make a big difference in how the circuit responds. Jul 19, 2018 · The circuit has significant negative feedback so, apart from this voltage issue, you will not hear any difference between different EF86s. Stamp of technical control department of the manufacturer ” ОТК “ Technical specifications 6J32P: Heater voltage: 6,3 ± 0,6V; filament current: 0,2 ± 0,015A; Anode Rated voltage (DC): 250V; Anode voltage limit (constant): 300V; Current anode: 3 ± 1mA; Cathode current limit: 6mA Mar 20, 2005 · When running an EF86 in triode mode, is there any advantage to be gained by inserting, say, a 100e resistor between the Cathode & G3, or should one just strap the two pins together? Would a resistor affect the gain or any other characteristic of the valve? The EF86 is the first stage of a Mullard 5-20. This exhibit was made by Mullard who designed the EF86 as a development of the EF40. Oct 23, 2018 · I wonder what voltages are valve heaters formed at , presumably they must undergo some kind of burn in at the factory , maybe theres a clue there. When that EF86 is the oonly preamp gain stage, the noise issue is not as much of a concern as it might be if there were gain stages following it. 3. AC signal voltage dividers can be made from two resistors or two inductors or two capacitors. Page 7 of this EF86 data sheet shows a 2. Care in the design of the valve to ensure that the electrode structure and its mounting are as rigid as possible can reduce the microphony of the EF86 to an insignificant level For example, if we use a 47k plate resistor with the EF86, then the screen grid must see 22k/47k as much of the power-supply noise. 57 kB, 1393x1163 - viewed 528 times. Maximum output is obtainable with the arrangement shown above, and the output voltage developed is sufficient to drive the 20 W circuit described in 5-20 Amplifier. Feb 10, 2006 · vangogh-hk In the Mullard circuit(s) the cathode/heater voltage is within the rating for the ECC83. The downside to the EF86 is that they have to be selected for microphonics. C circuit (say EF86 voltage amplifier). Rare NOS from Hungary, the Tungsram EF86 preamp tube is in stock. 00. 4V 4 Filament N/A 5 Filament N/A 6 Plate (Anode) 80 ­ 110V 7 Shield 0V 8 Suppressor 0V 9 Grid 0V 12AU7 Pin Description Voltage 1 Plate (Anode) #1 235 – 265V 2 Grid #1 80 ­ 110V 3 Cathode #1 90 ­ 120V 4 Filament N/A 5 Filament N/A 6 Plate (Anode) #2 235 ­ 265V May 17, 2021 · Thanks all. I'm not finding the pf86 to buy, I want to mod the mic or ps to use the EF86, which I find easy to sell. Z, Matchless, Vox, and similar amps. 5 volts. Now we have our 160VDC for the anode (HT) voltage of our EF86 tube, and run this to pin 2 on the XLR, the ground goes to pin 1. It suggests Ra = 100k, Rg2 = 390k, Rk = 1k, should provide 64V peak output, which is about what you want. Manufacturer: Mullard. Two 1µF capacitors in series define an AC voltage divider of 50%, just as two 1k resistors would. For first test, assume 1V, at 0. Jan 31, 2023 · As for the upcoming version, just visualise a basic SE topology with a triode wired EF86 RC coupled to a cathode biased 6L6 (probably Ultra-Linear with cathode feedback) and a simple 300VAC - bridge rectifier- CLC filter PSU. Part number: EF86. The reason for starving the EF86 plate voltage was to 'easily' get the grid voltage of the EL84 not be too high (a disadvantage of DC coupling, just what I do not like, woopty do) Therefore, as Essay observed, the voltages on one EF86 was far different. Here is a plot of plate current versus grid voltage for an EF86 pentode. One now applies 20dB (x 10) of GNFB to the cathode, thus an input signal of 100mV is now necessary for the same 2V output, 90mV of which is 'cancelled' at the cathode. 0-2. Voltage gain: 185 (45dB) Grid Voltage Svetlana EF86 Typical Plate Charicteristics-1. 6072 vs EF86. Nov 23, 2009 · The original power supplies were quite limited IMO. 17 hours ago · Ah, thanks for that advice, I'll look into voltage regulator circuits. EF86 datasheet, EF86 equivalent, EF86 cross reference. is a 9-pin miniature high transconductance, sharp-cutoff pentode intended for use in audio-frequency applications and is an audio beam-power pentode characterized by long life and stable performance. However just about any EF86 sounds good. Datasheet4U. The endpoints for the red line shown here on the EF86 plate transfer characteristics are -4V, 1. The mutual characteristics show that this valve is what is known as a short grid base type, by which is meant that a relatively small negative grid bias voltage is required to cut it off, even with quite high anode potentials. 1gigaohm grid resistor does seem a bit high ,my guess is you'd need to very carefully select your ef86 to work with that value . The EF86 [1] is a high transconductance sharp cutoff pentode vacuum tube with Noval (B9A) base for audio-frequency applications. R29 is the dropping resistor that sets the voltage value at the filter capacitor (AC ground). EF86 Mu is 38. Each curve represents a different grid voltage, from -3V near the X axis, to 0V at the top of the graph. Above left: The EF86 characteristics at a fixed screen voltage of 100V. If one wishes to use 807s, 6L6GCs, 5881s, or KT66s along with a a 6J7/6SJ7/EF86 input tube, the voltage doubler can be skipped. Denney's preference for the harmonically rich EF86 tube was apparent as he designed it into the preamp circuitry of the entire original Vox amp line (AC-2, AC-4, AC-6, AC-10, AC-15 and AC-30). But if you still want to bias up the filament voltage and stay away from the maximum for the EF86 of 100V, +40 to +50V (even 20V may be beter!) would be just about ideal and as an added benefit you would be biasing off the cathode/heater diode of the EF86 and may lower the heater/cathode hum of %PDF-1. Each channel of the preamplifier circuit is a C 4 S isolated EF86 voltage amplifier direct coupled to 1/2 of a C 4 S isolated 6DJ8 voltage amplifier, with the passive RIAA equalization network positioned between the two gain Apr 26, 2022 · A different screen voltage changes the gain of the EF86. you just have to work on the heater-circuit inside of the mic. Apr 27, 2012 · The Top Boost circuit was an attempt by Vox to capture the brilliance of the EF86 after they switched to using a 12AX7A-based preamp in the AC30. 2c AC Note: you should be using at least a 470 ohm screen resistor,not the 100 ohm that that 18 watters use. In turn, the voltage is then transferred to the 100k slope resistor in the tone stack. Not too sure about 6SJ7, which may be a lower gain In the case of the EF86, for a line voltage of 250V and an anode load of 100 k, the equivalent noise voltage is approximately 2 uV for the frequency range 25-10,000 Hz. ÐÏ à¡± á> þÿ å þÿÿÿoøo ù t õ t ì { ë q Jan 29, 2019 · 4. Also known as 6267, Z729, EF806, and EF806S. I've found turning the Amplitude control to max brings the screen to up to ~70v, pulls the plate down to ~70v, and gives the most grit & gain. Output Capabilities. Perhaps the additional gain would be nice for a HOMC. Since I plan to build a combo, I want to skip the EF86 altogether and use a cascode. U67 uses a similar value but ef86's dont live all that long in them in my experience . ÐÏ à¡± á> þÿ å þÿÿÿoøo ù t õ t ì { ë q EF86 is the designation for a 9-pin pentode vacuum tube with a 6. It features an all enclosing, outer screen or shield around all electrodes (connected to pins 2 and 7), special measures for extra mechanical stability against microphony, and a bifilar wound heater element to reduce hum I have a question regarding to the triode connection of an EF86. The both amps have cleaner gain and louder volume now. 5µV (RMS) under the Aug 20, 2021 · I have verified that with some new EF86 tubes made today that are not old NOS (New Old Stock) such as JJ Electronic or Electro Harmonix, and with some NOS like TAD Selected as well, the cathode voltage of the EL84 tube reaches 40 volts and the cathode current increases accordingly to Ohm’s Law to I built an amplifier for a customer this summer, and it turned out way better than expected. Let's also assume the preamp drives a 1M gain control, which is a relatively light load, even for a pentode. The first stage voltage amplifier is essentially identical to an example in a Philips EF86 data sheet, which has a voltage gain of 188. Future design goals are a CCS as plate load for the 6H8C (maybe switching in a 6SN7GTB), CCS as cathode load for 6S19P, switch to use this as a preamp, definately better PSU (maybe on a PCB with a maida regulator), output relay with a delay (oh yeah!), maybe paralleling 2 6S19P for lower Zout, maybe a EF86 voltage gain stage (love these little The EF86 is a low noise, AF voltage amplifying pentode specifically for very small signal preamplifier applications. As I've read in two datasheets, it says that maximum voltage for g2 is 140V for EF86 and 100V for EF37A. Assuming G2 winds up at 40V or 160V, then cathode voltage will be 0. I also know from my own digging that a Brauner tube mic runs an EF86 at 5 volts: 6. Passive Bass Cut could be a cap in-series with an existing coupling cap, and a pot (wired as rheostat) across the added cap. For example, with an anode voltage of +200 V, only -5 V is required on the grid to cut the anode current off completely. Normally, I like JJ tubes and have used them in a number of projects, but to my ears, the JJ EF86 sounds weak in this particular project (I tried two different ones). 5uV and 1. Put in a handy 2. Noise and microphony The specification for a NOS CV4085 (EF86) under conditions of an HT voltage of 250V and an anode load of 100 kΩ is for an equivalent input noise voltage of 2µV (RMS) in the frequency range 25 to 10kHz. com. in amplifiers in which the input voltage is greater Jan 1, 2021 · Suggestions ef86 riaa. I will be performing my own experiments and reporting the results. EF86 Pin Description Voltage 1 Screen 55­80V 2 Shield 0V 3 Cathode 1. 3VAC filament tap and boost it up to ~12VDC required for the 1625 and 12J7 tubes. This vacuum tube is durable with very low microphonics. A tightly twisted pair may then be used to couple the rectified voltage across C 1 to the heater pins of the EF86. I sound like a broken record, but the most useful control I've encountered for an EF86 is variable screen voltage. Mar 5, 2023 · For large changes of plate voltage the EF86's plate current barely changes which indicates a high internal plate resistance. EF36, EF37, EF86, 6SJ7 What this means is that the Ri, which is the same for all these types, is a whopping 2. The EF86 tube adds a ton of character, clarity, and sparkle to any amp, and works amazing after other overdrives. The high voltage comes from 22uf 2 and feeds the 100k plate resistor. The dedicated premium tube by Electro Harmonix®️ Heater Voltage: 6,3V. The 220k/220k voltage divider going into the the PI isn't Oct 6, 2014 · The signal hits an EF86 first (originally used to amplify signals off the tape head) before going to a 12AD7 for further amplification. Before the advent of the EF86 the Mullard valve of choice for pre-amplifier stages was the EF37A Mullard describe the EF86 as a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. 0 Svetlana EF86 High-Performance Audio Small-Signal Pentode ELECTRON DEVICES Svetlana Typical operation, Class A Connection, Small-signal amplifier pentode triode DC plate Voltage 250 250 V Screen grid voltage 140 V Cathode bias resistor 1k 3. 89K. I put the LR8 into just about EVERYTHING. Amplification worked out to 25. Maximum Output Voltage Swing: The EF86 can deliver a significant output voltage swing, allowing for sufficient volume levels in audio amplifiers. 4 days ago · Right now, I have 111v on Pin 1, 2v on Pin 3, and also 111v on Pin 6. The 65 Amps Marquee and the Carr Artemus both employ cascodes in place of the microphonic EF86. I regulate the anode voltage for the finals the inverter and VAS separately and its a way nicer behaving circuit than before. The trouble is, the schematic in the catalog was designed to extract the maximum possible voltage gain from the EF86, for use in microphone preamps, tape recorder playback preamps, record player magnetic cartridge preamps, et cetera. This unique design minimizes current consumption while still providing high voltage for proper tube operation. I have been working on an amp with a parallel 12ax7 input stage into a 5693 with a variable voltage screen grid, then a parallel 12au7 cathodyne PI feeding a pair of 6v6's. Sep 24, 2016 · Low Volume-weird EF86 plate voltage 09-24-2016, 12:49 AM. Then we would simply pick the screen voltage "line" that starts at the bottom at a grid voltage of minus 2. There is another plate load resistor after this and before the tube plate. Low noise pentode intended for use as R. 53mA cathode current. 0-4. In either case, it wasn’t difficult to get something close to 90V at the plate of the EF86, once I figured out the voltage drops. Dec 10, 2019 · Initially the EF86 would then charge the 500 uF cathode capacitor as quickly as the anode and screen grid resistors allow, which means with several volts per second. Might be worth a try at the regeneration on an VF-14 or EF86 thats otherwise beyond use because of noise in a mic circuit . My question is, can I freely substitute these two because in one of the datasheets the data provided is for both tubes. EF86 Tube Reviews: See reviews of the best EF86 preamp tubes. Merlin proposes to just ground the plate to make a triode strapped connection. The 0 and the 160 are easy, we have them already from the HT supply. As was stated earlier, the prototype circuit provided 6. Sep 2, 2016 · The EF86 has a very low heater-to-cathode leakage voltage, about 50 V. 53mA, is 1. F. File Size: So you should get this type of voltage scenario pin 2-3. 1V at 200mA for an EF86 heater using the components specified. 5µV (RMS) under the same conditions. 81 KB) Preview of EF86 PDF Datasheet Details. 0-1. I did not check higher input signal levels. Minimum plate voltage is at a grid voltage of zero. My question is what sound changes are to be expected with grid 2 voltage changes. 3 to 25. That EF86 is the only gain stage in that amp. 1mA at 400v: Resistance = Volts / Current = (400v - 100v) / (2. Plate Voltage Feb 27, 2023 · That is a Peak Inverse Voltage of 1,314V. When the cathode voltage approaches the desired voltage, it would settle with a time constant of 500 uF/(gm + gm_screen), which is in the hundreds of milliseconds range. 3V: Anode voltage: 250V: Grid #2 Jul 15, 2013 · If you look at the schematic, you'll see that the oscillation originates on the right side of the 12AX7, sending it to the grid on the left side. ) The EF86 was developed from the B8A EF40. 5V, the pl So the voltage gain of a pentode preamp is roughly these two extremes divided by the grid voltage swing needed to create them. 5-3. Mar 5, 2017 · Most of the amps with EF86 preamp pentode use this tube as input gain stage. TYPE: CV4085 (Special EF86) B9A LOW-NOISE TYPE FOR MICROPHONES TYPICAL APPLICATION HEATER CIRCUIT The voltage polarity of the heater pins in the Phædrus Audio EF86 TRIODE SupertubeTM must be respected. That part of the circuit is stock Akai/Roberts. Radio tubes are valves. We do the 80V simply by dividing the 160V by two 100K resistors, that Jan 21, 2019 · Now I wasn't able to find the preamp EF86 tubes but instead, I have found EF37A ones. The Anode voltage is around 31 volts. The Rt. The AC-4 preamp used one of Dick Denney's favorite tubes, the EF86. Now I'm ready for a possible new project. Without a doubt i 'm enjoying the pentode tone, it's got a lot more life than the standard triode preamp! I'm just looking at the ceriatone ef86 18 watt voltage chart and one of his has plate at 83v and screen at 98v. So, I'm probably leaning toward a SoHo or Monterey but the Ventura is tempting pricewise. Hi Guys; I am working on an two channel amp with an EF86 front end. The specification for a NOS CV4085 (EF86) under conditions of an HT voltage of 250V and an anode load of 100kΩ is for an equivalent input noise voltage of 2µV (RMS) in the frequency range 25 to 10kHz. Because the screen volts went up, this means the wiper of the Amplitude control went to ground leaving a voltage divider of Power Supply May 22, 2018 · The input pentode circuitry for the VOX AC15 and other similar guitar amps was lifted straight from the back of a tube catalog. Jan 21, 2009 · Die Wahl ist auf die EF86 gefallen, Vergiß Low Voltage, wenn du eine EM dabei haben willst, die funzelt dann nur (normal sind da 250 V Betriebsspannung). 7 Vout/Vin across the three EF86 tubes between an input voltage signal sinewave at 1KHz of 100 mVrms up to an input level of 500 mVrms. I'm getting 245v b+ for the ef86. Before I swapped the Dropping Resistor I was getting 94V at the Plate. 6P7S / G-807 / 6BG6 beam tetrode Jan 13, 2023 · Besides you have no idea what voltage is the EF86 supply sitting at until you measure it. 3) should a EF86 be better than the 6SK7? Aiming for all octal but since I’m not looking for distortion I’ve read that the EF86 is a good candidate. Oct 12, 2022 · What to look for depending on the power tube in use? Only used the second tube to increase the gain in previous builds and therefore calculated the total voltage gain. What's your cathode bias voltage on the EF86? It's possible that you can't shove through enough voltage to the grid to get decent swing at the plate. I've been wondering greatly about that circuit. 4. 353V B+ for EF86, 370 kohm Anode resistor, 2. GE 6267 / EF86 Sharp-Cutoff Pentode The GE 6267/EF86 . The EF86 boasts low noise operation, effectively minimizing unwanted background noise and providing a clean and pristine audio experience. For stages that doesn't clip,(like the first stage in a vox amp) I've have good experience with 6ak5/ef95, cheap, low noise, 6,3volt heater, 7pin socket. i plugged the guitar into Each channel of the preamplifier circuit is a C4S isolated EF86 voltage amplifier direct coupled to 1/2 of a C4S isolated 6DJ8 voltage amplifier, with the passive, switchable NEB/IEC equalization network positioned between the two gain stages. 0003 = 5600 * 0. 5V to 2V. Above right: Using the same screen voltage but inserting a 100k screen-stopper. I had intended that the screen voltage be about 10 volts lower than the plate voltage. Then you need a rectifier bridge with can stand 400V or more, a few Tube EF 86 or Röhre EF86 ID2011, Vacuum Pentode, Noval, 9 pin miniature (USA pico-9) B9A and Audio Frequency shown. andreas grosser is his name. EF86 voltage amplifier, particularly in the early stages of high-gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders. png (48. I used the EF86 preamp channel (no 2nd 12AX7 channel), added my tube based effects loop, and changed output transformers to encourage earlier breakup of the EL84s. C. They often run even higher screen voltage than the plates. Dave Aug 11, 2017 · Dr -- If you get a chance, post some voltage readings for the EF86 position with the two different tubes installed. 300V maximum cathode to filament voltage 6SA7; your cathodes are at +420V 50V maximum filament to cathode voltage EF86; your cathode is at +80V. Buffer the pentodes with ZVN0545A source followers DC coupled to the plates and your matched complementary FET pairs will do fine. Audio CV4085 (Special EF86) device. Hi all, I really enjoyed building a simple valve phono stage using a low voltage design by Karsten and very pleased with the results. Most small pentodes have an inaccessible suppressor, as it is internally connected to the cathode. The control grid is in the middle of the flowing current and so it can control the current by placing a voltage on it. If there’s voltage at these two points proceed to the pre-amp as seen in figure 4. Aug 12, 2022 · Revise components around ef86 Plate resistor, cathode resistor, bypass cap or adopt a voltage divider at the exit of ef86 or adopt a split load resistor in place of the single plate resistor Franco « The EF86 BOOSTER is a boutique all-analog vacuum tube pedal using a pentode to deliver warm, clean gain for overdriving amplifier inputs or other pedals. thanks to everyone who helped me with my hum problem. i remember he said that the sound doesn't change noticably. I'd like to use a pentode/triode switch for the EF86. Basically I want to have the volume available and scale it down with the master voltage. Oct 29, 2016 · The original Mullard 5-20 uses an EF86 as the voltage amplifier and that meshes with your thinking. For higher impedances, such as 250 kΩ, the EF86's voltage noise is 1/10 1/2 lower than the sources's own noise, and the noise figure is ~1 dB. 7V on the Vox schematic. In short, the question was if EF86 will be able to handle 400V on plate and G2 during startup. 5 volts and runs upward to the vertical, zero-grid-voltage line at the right side of the graph. 5-2. Voltage on the Plate of the EF86 is 155V for the Left and 148V for the Right. Where a triode is basically a voltage controlled resistance, the pentode, on the other hand, functions like a current source. 5v gridline where plate current is 2mA at 100v plate, and increases to only a bit over 2. However the reverse is what has happened with the screen voltage being about 10-12 volts higher than the plate at idle. EF86 Datasheet | Specifications & PDF Download. The EF86 Tube . This made a small improvement and raised the EF86 cathode voltage to 2. The amp is very vivid sounding, except with slight SSsshh emphasis to the female voice. But "active bass cut" could be done at the cathode with a lower-voltage cap & a pot. When the screen is a higher voltage than the plate, you'll get less output out of the EF86, and less clean headroom too. I know what you mean about preferring triodes but many people have reported success with pentode voltage amp stages in SE. A local negative feedback loop spans from the EF86's plate to the two combined 6DJ8 plates. Figure 3 shows the EF86 in triode connection. Here are the transfer characteristics for an EF86 pentode, showing plate current versus grid voltage for several different screen voltages: Maximum plate voltage is at cutoff, where the plate current is zero. The tube with the screen mesh shield is the classic Mullard tube that was always supplied with the Eico kits, and always works great. The cathode (pin 3) sends the oscillating voltage to the EF86. I have added regulation for input/driver stage B+ and grid 2(el34s), change to soft recovery diodes and increased most of the capacitor sizes. Other readings I am getting for the EF86 are: At pin3 I am getting 1V on both. 3 = 3360 V Does that mean that the EF86 is almost always abused in this amp? At least, from the link to the online plotter linked above, it seems that the 220k resistor is a real overload for the plate of the EF86 Voltage boost by a factor of 100 is just beyond the reach of a 12AX7 triode, but well within the capabilities of an EF86 in pentode mode, as we will see. A+" "Got to say I have been enjoying the pedal quite a bit. Mar 11, 2021 · I took the basic voltage readings and added them to this schematic. here's another wierd one. You will find a detailed explanation of this process in my book. The DC heater supply is a full wave bridge of super quiet Schottky rectifiers feeding a Linear Technology regulator. A twisted pair is recommended since the DC supply still carries the 0. 2K (as Mattitch did) and see where the plate voltage falls. Use it mostly as a boost/slight OD and it performs beautifully. I've heard that cascodes do a generally good job of subbing for a pentode. Each channel of the preamplifier circuit is a C 4 S isolated EF86 voltage amplifier direct coupled to 1/2 of a C 4 S isolated 6DJ8 voltage amplifier, with the passive RIAA equalization network positioned between the two gain Oct 6, 2004 · a guy that was mentioned several times on this forum replaces dead vf14 with ef14 i think or uf 14 i'm not sure. Heater voltage: 6. That was the usual way EF86 microphone input stages in consumer gear were Jul 19, 2018 · Indeed as PFL200 surmised, distortion levels increased with input voltage. 5meg G2 R. Read more at the EF86 vacuum tube page. Note that the knee is well defined, and the input sensitiviy is lowest: If centre biased it would take roughly a 4Vp-p input signal to cause clipping. . It was based on a Matchless DC-30. couPled A. This is where screen voltage plays a key role. 2V ripple voltage. Gain is a touch high, which is why I built a switch so the cathode capacitors on the EF86 can be bypassed - this adds local feedback and reduces the gain. What I'm really hoping to do, for layout/interface reasons, is wire it as a pull switch on the gain knob. If the screen voltage is 100V, the voltage drop across the 2. Add the 1/6th G2 current, 0. but dont tell anyone or they will be gone soon too Apr 12, 2013 · I'm leaning towards one the 65's that utilize the EF86 for the chimey sound but want it to remain somewhat uncompressed and fairly loud for rhythm playing. jydpke hznms mbvqre byqdhho gjqam hcbwa ecv dpods anrlyhq vkyovik

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