This board allows you to lay out a professional quality, three-valve, passive EQ phono stage, in a very small space. The small size is acheived by judicious choice of components; only using power-resistors where absoultely necessary, and avoiding unecessarily oversized 'audiophile' capacitors -this is very much an 'engineer's amplifier'.
The circuit topology is predefined but the design is flexible enough for you to experiment with various circuit details. You can either devlop your own design from scratch using information from my book, where a very similar circuit is presented, or you can use the component flow chart link at the bottom of this webpage. The flow chart allows you to build up a full set of component values to suit your choice of valves, cookbook style, with no brain power required!
Overview: The basic circuit topology is classic, consisting of three valves: input stage, second gain stage, and DC-coupled cathode follower. The cathode follower is essential to ensure a low output impedance for driving cables. The valves must be dual triodes of the popular pin-compatible type, e. Pin-9 of each valve socket has its own test pad so it can be left floating or be connected to ground, depending on the valve type chosen -see the component flow chart. The RIAA equalisation can be set up for all-in-one-go upper diagram or split lower diagram passive equalisation type-I, see section Drilling the chassis is a breeze: There are six holes for mounting the board to the chassis using standoffs.
Just place the board on the metalwork before you start, then poke a pen through the holes to mark their positions on the chassis. There is also a hole in the centre of each valve socket site so you can mark the positions of the valves. Now get drilling!
You could also use these holes to mount 3mm LEDs for a cool up-lighter effect The image below shows the full schematic for one channel with all the available component sites, not all of which will be used in a single design.
The components in the other channel have a 2 in front, e. You can find a full schematic, PCB layout and other design information in the user manual. You can find the issue.
User Examples. The Valve Wizard Parts for valve amplifiers! Menu Home Back to Shop.He has been active in electronics since the age of five watching his dad build a Heathkit Williamson. Prior to starting Ram Tube Works and Music Reference inhe opened a high-end retail store where he met and later worked for Harold Beveridge.
His other interests are music theory, piano, singing, building musical instruments, solar energy, architecture, and understanding how things work.
This article attempts to correct a few misconceptions about some of the popular dual triodes used in audio amplification. I have developed circuits for both home audio and musical instruments. I keep a little collection of these classics to test whether my equipment works with both old and new tubes. Remember that the solo player can use distortion to enhance that instrument.
Yet the same distortion, added again, destroys the reproduction of such a recording. Preamplification Once upon a time there was only the 12AX7. This is not entirely true.
Textronics and others used them in oscilloscopes and other high performance test equipment. I used 12 of them for my first commerical design effort with Harold Beveridge, Inc.
The RM-1 preamp that resulted had, and still has, the quietest phono stage extant with tube input. Its design led me to investigate the physics behind a low-noise tube. I also found that the 6DJ8 had better linearity lower distortionwider bandwidth, and better ability to drive the output jack with a strong low-impedance signal, which is preferable when you use a long or high-capacitance cable.
But a triode with high gm is not necessarily a high voltage-gain triode; the 6DJ8 has almost 10x the gm of the 12AX7, but one-third the mu voltage gain. Transconductance in triodes and pentodes increases quite dramatically with plate current, which is a source of distortion because it increases as the signal swings negative and decreases as it swings positive at the plate.
This is the basic distortion mechanism in all active devices, vacuum and solid state. Two Other Factors In typical triode circuits mu becomes the controlling amplification factor or gain and is easy to spot in the data books since it has not units. Mu will vary with these, but not much or so hope those of us who desire low-distortion, nonfeedback amplifiers. Instantaneous voltage gain mu must be constant to achieve low distortion.Latest Projects Education.
Constant Current for Tube Heaters. Extend the Life of Your Amplifier’s Vacuum Tubes
Thread starter Girish Bodhale Start date Jun 14, Search Forums New Posts. Dear Forum, Its my first post on heaters, also am working for the first time on heaters. I have 12 No's, v w single phase heater. Now please do guide me to find out how much current will be delivered by each phase R, Y, B when heaters are powered on. Please see the attachment for the heater connections. Scroll to continue with content. Girish Bodhale said:. BR Joined Sep 22, 4, It appears the voltage across the heaters is close to the heater rated voltage, so I would assume the current draw will be close to total power rating and should plan for that occurrence.
It won't be that high because the voltage isn't quite up to snuff for the power rating. My beliefs include the idea that there are volts RMS at the ends of each 2 resistor load. By estimating the resistance of the loads, I can find the current and power in each load. The instant you try to add them, you hit the phase relationship problem. I have never worked in that area, so I'm stuck.
I could look it up and educate myself, but so can the Thread starter. You can calculate further, and get a closer number, but it won't be correct either. The voltage on 3 phase is never balanced.
I wouldn't waste the time. Turn the switch on, measure the current, adjust thermal overloads on starter relay.Log in or Sign up. Steve Hoffman Music Forums. Location: eastern us. It's getting time to replace the tubes in my Music Reference RM I'm thinking about going with something NOS but don't want to spend an arm and leg ie no Telefunkens or Mullards. Also, I've been using Svetlana EL34s and have gotten good use out of them, but is there any better 'current production' EL34 brand I could go with?
Not sure I want to go NOS on these as 8 of them would be rather costly. Highway StarAug 17, Location: Gortshire, England.Microphone Tube Test - Amperex/RCA, Mullard/Dumont - 6299 E88CC
I am afraid it's years since I let go of my amp with EL34s in and I used the valves tubes that you aren't considering I could pick them up for much the same price as the New production stuff. Location: Sagamore Beach, Ma. You can still get Sylvania ECC88's at thetubestore.
SckottAug 18, Thanks for the information Andrew and Sckott. I'm going to give the EH brand a try. Highway StarAug 19, Location: Germany. No, I don't see anything etched in the glass. They must pre-datesince that's when I purchased the amp. Highway StarAug 20, Location: Somewhere in the middle. I found this on different ECC88 types at the www.
The Heater voltage is 7V. Mostly these tubes have goldpins. Sometimes these tubes come with pinched waists, the glass has been clamped at the place of the top-mica. They work at a little more heater current 0. This tubes sounds very well, and is very well made.
Delta-connected heater current calculation
This tube beats the crap out of modern Russian tubes! All the best - Andrew. Indy mike, check this out for vintage EC, I am certain that these tubes were made in Heerlen, Netherlands, and I am almost certain that your Amperex were the same tubes made in the same factory. I e-mailed the people at The TubeStore about the Electro-Harmonix big bottle 6CA7 versions and was told that EH screwed-up the internal wiring on the tubes and they were all recalled.
I'd like to give a set of these a try especially in my Wright P but I don't know how long it will be before the corrected tubes get to the suppliers. Saw a set on Ebay from Hong Kong but? Highway StarAug 21, Posted: Sat Nov 24, pm. Posted: Sun Dec 02, pm. Congratulations Bruce! For sure it sounds amazing. All that is left at this point is a tube eq! Posted: Tue Dec 11, am. I've been looking for a project for ECC88 for quite a while, and now my dream comes true However, my knowledge of electronic is almost none if not sub-zero.
Thanks for sharing this!!! Posted: Fri Dec 14, pm. Hi, Pretty much all the parts are standard ones they are listed on the schematic and can be obtained from several sources. The three transformers all come from the same place Edcor - on the web. There is no particular way to build the project. I just used a PCB I had from another project.
There are no "premium" parts in the project. Good listening Bruce. Posted: Sat Dec 29, am. Thank you, Bruce. Your advice is appreciated. I used to own Earmax SE for a period of time, and impressed with the footprint. Any idea? Thanks again for sharing. Posted: Sat Dec 29, pm. Hi, Related to your question There are a couple of ways to connect the output of an amp to the speaker or in this case headphones.
There are advantages and disadvantages to each. The three main ones are transformer, capacitor and direct. In a transformer coupled one the primary limitation is the quality of the transformer. The advantages are that it can more efficiently transfer power to the load impedance matching. In capacitor coupled there are two main limitations, low efficiency and the limitations of the capacitor itself response, linearity mostly. In direct coupled the limitations are again low efficiency and also complexity of the circuitry, primarily in the power supply.
I chose the transformer as I could get cheap wide band transformers that could be used push pull. Push pull has the advantage of cancellation of some harmonic distortion and inherent good sensitivity to rejecting power supply noise and hum. I wanted a very simple design that would be easy and cheap to duplicate.
In capacitive coupled designs there is usually a need for multiple parallel tubes. Parallel tubes do not have the advantages of distortion and noise cancellation and thus make it necessary to have a cleaner power power supply think more current and added cost and complexity.
Additionally, they need to have large quality output capacitors. The capacitors are likely to cost more than the transformers I used.This page lists all of the 6DJ8 tubes I currently have in stock, including all industrial and European versions. It is a long page, use your scroll button and scroll down the page to see it all.
This list is organized now by each vintage tube manufacturer. Be sure to scroll to the bottom of the page to see every brand we have. These are extremely high demand vintage tubes, so I have these listed on their own page, as my stock changes rapidly.
If you need a quantity of these tubes, or have specific needs such as matching, special construction, etc. Stock levels with actual quantity on hand shown are being phased out as we update inventory.
The only exception to this will be very scarce tubes where we typically will only have a small stock on hand. Of course, any time you need a large quantity of tubes of any type, is is a good idea to email us for a stock check first. We can match most small signal preamp tubes on a Tektronix curve tracer. Scroll down to watch a video on this below. This runs the tube at full rated plate voltage, and plots the curves at 10 different grid bias levels.
The most accurate method to test tubes, the curve plots can actually be compared to the printed examples for each tube type that appear in the manufacturer technical data sheets and books. Prices listed below for "matched pair" tubes are Gm matching only, and there is no additional charge for Gm matched pairs. For most uses, Gm matching is fine. Curve tracer matching would be recommended if the tubes are to be used in a phase inverter circuit, phono or microphone preamp, or other critical or demanding circuit.
Curve tracer matching is an additional special request item and is charged in addition to the listed price of the single or matched pair tubes on this page. Get two full years of warranty coverage for these tubes!. Can't find a particular tube? Please Read. Return to the Audiophile tube page. Return to the Main tube page.
Return to the Home page.This is a project that has roots to back about 2 years ago. I wanted a quality headphone amplifier to be an addition to my Hi-Fi stereo system. It was to be something to use when I didn't want to disturb everyone else in the house. I tried several different tube types in the amplifier design process.
Generally all worked, but none seemed to have either the needed output level or didn't match well likely to the choice of transformers and sounded on the dull side.
They had the combination of sufficient current flow, modest voltages on the anodes important for the matching transformers and enough gain to make the amplifier sing. Almost as good, but they are getting a bit scarce and the new production JJ E88CC are now quite common and reasonably priced.
I am sure other triodes could be used and there is no reason why a high impedance on the primary side small push-pull output transformer would not work.
I doubt that you can find one much cheaper than the matching transformers I used. Certainly not with similar response and distortion characteristics.
This low power tube headphone amplifier is designed along the lines of the Oddwatt power amplifiersexcept that this headamp does not require a driver stage. All the circuit gain is in the single output stage. Once again I used a constant current source CCS IC in the cathodes but since only low power levels were needed there is no provision for balancing the load between the two triode sections.
None was needed either as the output is quite symmetrical to levels way above anything you could use with headphones.
I wanted simplicity in the circuit. It has neither coupling capacitors nor any feedback loop. In fact there are a total of only 7 components including the tube in each channel. The power supply, alas, has many more components. This is common in many of my designs. I find that a very clean power supply is essential to achieve high quality audio performance.