300B Mk1 Single Ended Triode

Mono Block Amplifier

The Mission Schematic Parts List

Tube Pinout Construction 1 Construction 2

Layout Drawings World Builders 300b Mk2

The Schematic So then, it is as simple as this!

All in all, a total of just 16 components .

Add a tube rectified Power Supply .....

And another 8 components for the P.S.U.

So, all you have to do is to ask yourself if you can connect together sixteen parts in a compedent manner. Then do that again - and then have a go at the PSU. So you see, if you look at it in individual parts of a greater picture then it is not so ...err...daunting a proposition.

This schematic is from Angela Instruments and is otherwise known as the J.E. Labs 300B.

WARNING.......The usual warning must be acknowledged - that herein this circuit contains letal voltage that can KILL.... We are talking serious damage !!! Do Not Mess with it unless you are familiar with good electrical safty practices.

Parts List

Quantities are for dual mono construction

1.....2 req - Angela Universal Power Transformer - 380-0-380V / 200mA

2.....2 req - Hammond 1627SE Output Transformer - 2k5/160mA/25W/4,8,16R

3.....2 req - Hammond 193J Enclosed Choke - 10H/200mA/82R

4.....2 req - Angela Oil Cap 15uF/600VDC

5.....2 req - Angela Oil Cap30uF/600VDC

6.....2 req - Angela Oil Cap50uF/518VDC

7.....2 req - Angela 0.22uF/630V Paper in oil, Copper Foil

8.....2 req - Black Gate 100uF/100VDC bypass cap

9.....2 req - Black Gate 47uF/160VDC bypass cap

10....2 req - 220K /2W

11....2 req - 68K /2W

12....4 req - 24K / 2W

13....4 req - 1K /2W

14....2 req - 470ohm/2W

15....2 req - Angela 880ohm non-inductive 25W Cath Res

16....2 req - Dale 50K / 25W power supply bleed res

17....2 req - 3k3 /5W metal-oxide power supply res

18....2 req - Clarostat 75ohm/2W wirewound pot

19....2 req - 5U4GB ( or Mullard GZ37/GZ34) rectifier tube

20....2 req - 6SN7GTB

21....2 req - 300B Tubes

22....2 req - Ceramic silver 300B Socket

23....4 req - Octal Ceramic Socket for GZ37 and 6SN7WGTA tubes

24....2 req - Power supply cables

25....2 req - Speaker Binding posts

26....2 req - 100K log Pots - Bourns

Capacitors

Angela Capacitors are manufactured in Denmark by Jensen, as indeed AudioNote are and weather they are marked Audionote, Angela or Jensen they are identical except for the label thereon. They are an paper in oil, aluminium foil type, but I have used the paper in oil,copper foil one for the siganl bypass section.

ASC Capacitors - For the power supply section I have used Angela Polypropylene and oil which is manufacturered for Angela by the same company - ASC - that supplies the like of Conrad-Johnson and are highly regarded in the Japaneese audiophile ranks. I love these so much that in the Mk3 ALL the caps are these very same ASC oil types, even used them in the cathode bypass position. Sure that they take up a lot of real estate, but if you can spare the space - there is just no other to use throughout ... you will be then the few owners of an amplifier with NO electrolytics in it.

Jensen Tobias Jensen Ltd. was established in 1917,... thats 84 years ago, in the same year the Great October Revolution laid the foundation of the Soviet Union. Today the USS don't exist anymore, but Jensen are still manufacturing electronic capacitors, which have been developed through the decades of the electronic age. Over the years, good quality, high reliability and long life expectancy have become the central part of the company philosophy. Many years of experience, a staff of qualified experts, an advanced production equipment supported by an extensive control system (ISO 9001) guarantee a high level of quality.

Black Gate Heart of Music as they say and though everyone has their preferences , most will agree that these are amoungst the finest electrolytic capacitors available. Superior construction and the use of fine grained particles give them a lower ESR ( by about 10%), lower noise floor lower distortion,greater bandwidth and a lifelike musical reproduction..no wonder that Audio Note use them by the truckload.

Resistors

Riken Ohm Resistors are a Japaneese audiophile grade resistors, that have a huge following with tube fans in their home country, with gold plated leads that have a 1% tolerance ( produced by depositing a thin film of carbon on a ceramic former) and has the sound combination of an Allen Bradley and a good metal film type, together with very low noise floor and will not suffer from temperature drift. These would be the resistor of choice - However for this initial project, I have used carbon film 2W that were more readily available.

DaleThese ceramic wirewound resistorswith aluminium heatsink, from one of Vishays subsideries, are a popular choice for power suppies... users include, Pass Laborities

CTS Clarostat are a N.O.S. 2W military specification wirewound pot with a locking shaft for the hum balance of the power tube filament supply

Ironware

Mains Transformer Perfect for this amplifier is Angela Instruments Universal Mains transformer which is a 380-0-380v 200mA enclosed type, with additional 6.3V at 3.5A for the power and input tubes as well as 5V at 3A for the rectifier filament. They reckon that it's so good that they carry a 5 Year guarantee

Choke choice here has been for the Hammond type for no other reason other than it is availabe from Angela also and has the necessary qualities required, being of the same heritage as the output transformers and it is nice to maintain the continuity where possible. It is an enclosed type though it has a lower ohmic value than what was specified in the original circuit and a higher load value too.

Output Transformer Oh dear.....there was a lot of thought into this one. There are so many opinions out there that it can be a minefield to the inexperienced. I spent so long debating it that it held me up for months as my initial feeling was to go for one of the more expensive, more upmarket makers, assuming that they real good ones are more expensive. But it just kept me from ordering and it was getting silly , so instead I opted for a sensible choice in the form of the Hammond 1627SE, which has air gapped laminations and weights 11lbs. The use of interleaved windings helps to maximise the high frequency responce and have an excellent bass responce.

Hammond traces its roots back to 1917 - some 84 years ago, co-incidentially the same as Jensen above - and was incorporated as Hammond manufacturing in 1927 and currently has a turnover of $166million and employs 1,200 people. In the 1930's, Hammonds previous years experience was to put them in the forefront of the manufacture of magnetic components during World War II for communication transmitters and very specialized transformers and the beginning of the Cold War in the 50's thrust upon the Company significant volumes of military transformers, especially as a result of the construction of extensive early warning radar systems across Alaska, Canada and Greenland.

Their ratings are for full power at the rated plate current and their specs are +/ -1dB rolloff points - 20-20KHz , again at full power, as well as having a tested HV rating of 2000VAC. These models use a "distributed air gap" to eliminate core saturation and high quality M6 grain oriented silicon steel laminations.The multiple interleaved secondaries allow 4, 8 or 16 ohm load impedances .

BUT - if you want something REALLY special, there is the Plitron (Amplimo) PAT 3025SE which raises everything up to another level. See more about this on the Mk2. This output transformer is so special that it required me to develop the Mk2.

Tubes

Power Tube The 300B....First developed by Western Electric as an audio device in 1935 is still one of the most linear audio tube ever made - need I say more. For the first 6 mths I used the JJ Tesla but have replaced it with Western Electric...beyond belief and worth every penny..... er... well, that was until I got the KR300bXLS. This tube has left me speechless , it is everything that the WE300B is, but

with better, deeper bass and a more extended and sweeter top. In other words more of everything at the top and bottom. But, the really scarey thing is that these are the only 300B that Have used that does not suffer from some form of microphonics. The equates to superb tonal definition and micro-detail and ambience. The bass timbre is reproduced with sublime realism. This is one deadly quiet valve. And before you say it, no! ... it was not just luck that I got a quiet tube, I have since bought many many pairs of these and every pair, from different productions are all equal. There is a new King of the Triodes in town with the KR300BXLS.

RCA Red Base 5692.....a sweet alternative to the 6SN7GB and one that some will say is the very best of its type. Absolutely superb and my best recomendation for this amp. Though very expensive, it has a wonderful midrange and better bass tonal definition.

Rectifier I have used the 5U4GB General Electric tube for this amp but have also tried a Mullard GZ34 and GZ37 and found that there are some benifits brought with it in terms of bass definition and an increase in the top end - I finally setttled on the GZ37 for better sonics and slow ramp up time (which the 5u4g/gb does not have). The GZ34 will produce slightly higher B+ voltages but you can use any mentioned here with no changes.

TUBE PINOUT and CONNECTIONS Just in case you didnt know!

300B

Directly Heated Triode

Filament...5V/1.2A

Pin f/k - Filament/Cathode

Pin A...Anode

Pin G...Grid

Pin f/k...filament/Cathode

5U4GB

Directly heated, full wave rectifier tube

Filament...5V/3A

Pin 2...Filament

Pin 4...Plate No. 1

Pin 6...Plate No. 2

Pin 8...Filament

6SN7GB

Indirectly Heated Dual Triode

Filament...6.3V/0.6A

Pin 1...Grid -section 1

Pin 2...Plate - section 1

Pin 3...Cathode - section 1

Pin 4...Grid - section 2

Pin 5...Plate - section 2

Pin 6...Cathode - section 2

Pin 7...Filament

Pin 8...Filament

Angela PTX Schematic

Red...Rectifier...Pin 4

Orange...n/a

Red/Yellow...Ground...Central ground point

Purple...n/a

Orange...n/a

Red...Rectifier...Pin 6

Yellow...Rectifier heater...Pin 2

Yellow....Rectifier heater...Pin 8

Green...6sn7 Heater...Pin 7

Green/White...Ground 6sn7 heater...central ground point

Green...6sn7 Heater...Pin 8

Blue...300B heater...Pin f/k

Blue/white...n/a

Blue...300B heater...Pin f/k

Ground Buss Layout

The ground buss consists of a single continous length of 12 AWG (2.5sq.mm) formed so as to make an eyelet for the earth screw to connect it to the main chassis top plate. This point being as close as possible to the input socket. It must also be kept as close as is possible to the actual surface of the top plate in order to aid in reducing hum. This screw I also used as the incoming mains power earth fixing point.

The Construction Process

The 4mm aluminium top plate, showing the cut-outs. To this are fixed the front and back which are of 40mm L section aluminium. The multiple holes are for additional ventilation and are hidden underneath the transformers, which are themselves raised by the isolating mounts by 2mm - so lots of airflow - and it will also keep the ironware cool as an added benifit. The actual size of the top panel is 12" x 15"

The bottom is similar to the top but this time the 40mm x 40mm x 4mm L sections are fixed to the sides. So why didnt I fix everything to the top.....well less visible screws - OK? And additionally I believe that it aids the location and integrity of the two sections

Ok,here is the juicy bit - the part that we all want to see........component layout and the grounding techniques.

The spiral wrapped cables are the mains power cables. Keep all cables as short as possible and as close to the chassis as possible at all times and this will aid in hum reduction. Keep all AC lines together and away from the input signal and you will notice that all power lines are on right hand side of the chassis and only the signal and HV on the other. Not much else for me to say as the picture tells a thousand words! Go figure!

Maybe you can see something else of interest from here.... the triangular shaped aluminium bracket in the center back position , is to retain the power caps in place as I did not use the usual clumsy clamps. The hole for the caps must be exact and then the rim of the cap will not pass through it and this way only three screws keep them all in place as opposed to twice that in the usual manner. Usually amps are riddled with screws everywhere - something that I hate! A little thought can aid in the final appearance. And remember that it should look as good inside as it does outside....well thats my ethos anyway!

....or for those of you who prefer.....here's the idiots guide !

The ground buss is nothing more than 12 AWG solid core copper, whilst the input to volume pot is Audioquestsolid core, apart from these two, there is no internal wiring other than the component leadout wires themselves.

The Construction Process

Layout enabled me to have the hum pot and the power resistor soldered directly together. The large gold capacitor is the copper foil/paper in oil coupling cap and the others are the Black Gates. In fact, all components were wired together using only the component lead-out wires and the only additional wire is from the input socket to the volume control and from the volume pot to the tube socket and of course the ground buss. Solder is of the silver loaded type and is a must when one is soldering to gold as there can be corrosive effects with nornal type after some years..and lets face it this amp will outlast you!

Just some of the detail of ther back section. This RCA socket is not actually being used, but is there for future possible use. The top panel and bottom panels are secured together by means of two dome nuts and a threaded rod. Kills two birds with the one stone, maintains good mechanical integrity of the cabinet and also provided suitable feet

Looks like the volume control......how right you are! But you get a good view of the corner joint where all the aluminium pieces come together. All the metal work was hand done using nothing more than a couple of files and a hand held Black and Decker drill....so it just goes to show that you can get a perfect finish with due care and attention. All screws should be countersunk if you dont want a Heath-Robinson look....then again maybe you do!

Looks good from here too! Yeah, but what trouble I had with the painting of the T/Xs....the laminations were sanded down with an orbital sander without the endbells in place but the laminations were however secured with their through-screws, just to make sure that the laminations were not disturbed. Now, on this point, it would be said by a transformer maker not to disturb it at all because of the fear of upsetting the intergity of the unit. When I refitted the endbells - the screws were tightened with a torque wrench to the same Ft.Lb. I hope I didnt do any harm here and I was extreemly careful in the overall handling while all operations were carried out but despite this or maybe because of this, I still managed to drop one of the transformers which then managed to sever a couple of the cables before finally coming to rest outside the back door!

One should also remember to keep the two endbells isolated from each other if you are changing the screws because if the bolt is allowed to connect to the endbells, it can act like a shorted winding due to the changing flux on the core. Hence the reason for the fibre/nylon washer seen on the covers

And finally.........

First one finished....now all I have to do is make the other one in reverse, but if you do likewise be careful not to get caught out by some components that may be oriented differently when reversed in the layout. Happened to me with the tube sockets and it means that the pin layout is different and

Some useful drawings

dimensions and wiring

These drawing may be of help and will answer many common questions. Put this together in your mind with what you have already seen here and it all begins to make sence and fall into place.

The layout and especially the grounding has proved for me to be absolutely foolproof in the couple of amps that I have made. As I said before, you will get the hum levels below 5mv at least like this - however that also depends upon the input tube that you use. I have also spent literally tens and tens of hours trying to come up with a better layout and everytime I come back to this.

Having said that - it would be much better if the PTX and the choke were reversed, which would give even better and more direct wiring. Note that it is common practise to orientate the choke at right angles to the PTX, but asthetically I didnt like this and I tried it both ways and found no difference anyway. Like wise reversing the PTX and choke would have given an unbalanced aspect visually to the amp

The dimensions are only, only for the Angela and Hammond ironware. If this chassis was made just a fraction larger then you could fit the Plitron OTX. It didnt in my case and that was one reason for making the Mk 2 version....oh well....any excuse!

Dimensions

Tube socket wiring

P.S.U. layout

Walton Audio Mk2 300BThe Plitron Deluxe version

Having been totally satisifed with my last 300b I decided that some improvements could be made - namely using a better OTX and a better PSU filter. The Plitron 3035SE toriodal output transformer has amazing specifications, with a flat frequency range from 16hz to 65khz, a -3dB range from 3hz to 90khz and can be configured for 4ohm or 8ohm load. It is encapsulated in a beautiful texured finish, so what better option than to also use Plitron chokes, given their wonderful quality of build and specs. A 20H and a 10H are the basis of a double Pi filter together with A.S.C. oil caps.

This is basically the same as myy previous amp but with better PSU and not the JElabs delux version which uses 26 as the input tube.....cost has got to stop somewhere and I also went for the ease of availibility of tubes. However the PSU is that from the JEL Delux - check it out there, I will put it up here in due course. For details of the amplifier schematic see my previous 300b.

The benifits brought about by the use of the Plitron components cannot be stressed enough as well as the improved PSU.

The Plitron 3035SE OTX has a thunderous bass and what seems like an additional octave compared to the Hammond, a refined top end that defies belief and a mid range that you never thought was possible....ever! The Hammond suffered a slight ringing in the uppper octaves, giving a certain edgeiness to sibliants and the Plitron addresses all the shortcoming of

the Hammond but at a price - a price that is worth the admission fee for sure and the fact that they are encapsulated and finished justifies the price.

This TX which was developed over a three year period by Plitron and Menno VanderVeen, has been designed specifically and optomised for the 300B triode with a plate resistance of 700 ohms and primary capacitance optimized for a very wide bandwidth. Primary inductance is kept constant, independant of quiscient current through the power tubes and are designed to withstand DC current and impedance mismatchs using larger diameter wire and special winding techniques.

The Plitron 20H is just so amazingly good at its job - that had I known just how good it is I would not have bought the 10H - I really didnt need it with the 20H. In fact, the 10H on its own would have been a huge improvement. I substituted it in my original amp in place of the Hammond 10H and the noise floor, residual hum just dropped outa sight and the dymanics improved by a noticable amount - so Yes choke brand does matter - it is clearly audible.

The use of a double Pi PSU allows me to have seperate B+ for the input and driver sections, with the benifits that that brings in terms of additional headroom and super dymanics. This is now so good that the first time I fired it up and played a CD the initial transient was so dymanic and powerful that I honestly thought that something had blown up, so frightening was it. We are talking scary and awesome in the true meaning of the word

Tubes

*My choice of tubes remains as before despite having tried many many different input tubes - out of the dozens that I have I just love the RCA 5692 red base. A second choice, though quite different is the KenRad VT231 and then RCA6sn7GTB

*The Western Electric 300B has now replaced the JJTesla and yes, it is a silly price but believe me I would now find it very hard if not inpossible to live without it. Their customer service and 5 year warranty are beyond reproach and I have had to avail of the warranty and they were most helpful with my problem. This is a major factor when spending the sort of money that these tubes command. By contrast to that, if I had never heard it I would have forever been happy with myJJTesla.

*Rectifier - choice of three here 5u4 family, GZ34 or GZ37. All three quite different and I prefer to like the GZ37. It has the advantage of being an indirectly heated tube and the slow ramp-up of the B+. However, using the GZ34 will raise the B+ some 30v or more but can be used into a first cap of up to 60uf, whilst using the GZ37 requires the input cap to be 4uf, though I have to admit to using 7uf. knowing that many people out there are using this tube into much greater values. Even some commercial design that I have also do do, so I reckon that 7uf is safe enough and I have been using it like this for the last 9mths. The 5U4G can be used into a first cap of up to 40uf but as a directly heated rectifier means that there is no slow turn on of the B+. You make your own choice on this one.!

Parts

All the capacitors, cathode and psu resistors and ceramic tube bases were sourced from Angela Instruments again but upgraded the Black Gate ones a stage higher for this amp. For a parts list - see the original amp as everything is basically the same

The Schematic

All resistors I used were 2w carbon and the hum balance pot is a ten-turn type. The cathode by-pass capacitors are BlackGate FK type for the 300b tube and VK for the driver. FK being the highest grade and VK the next down. In the mk1 I used the Std type. The coupling cap is the Angela copper foil,paper and oil. Internal wire is 99.99% pure fine silver. Alps Blue Velvet pot completes the line up.

The voltages shown are only a guide and will vary with different tube line up and also mains supply variations, which makes these impossible to be exact about.

The Power Supply Unit

The value of the first cap can always be dependant upon the type of rectifier tube one uses and the required B+. I chose to install on the chassis, two 15uF caps and three 50uF caps. Depending on how the pair of 15uF are connected I therefore have the choice of 7.5uf / 15uF / 30uF.

In the case of using a GZ37 which according to Mullard Data sheet states that the max input cap value should not exceed 4uF, I am choosing to use 7.5uf, well lets call that 7uF, yes I know it is inexcess but when I see what value others use in this position - up to 50uF - I think I am being conservative! In using two 15uF caps in series to get 7uF one must use a voltage divider ( two resistors of equal value) to give equal voltage across each capacitor.

Using just a single 15uF, as I did in the original amp with say, a 5U4G/GB is also fine with only a couple of extra B+ volts (due to the increase in capacitance) as the GZ37 and the 5U4 have similar voltage drops.

Using a GZ34 however hikes up the B+ considerable as this typically drops 17v as against 45-50 for the 5U4 - but the GZ34 can be loaded with up to 60uF, which will also raise the B+. Using two caps in parallel to attain a value will result in a faster time constant, though in this case it is probably just an acedemic exercise! One could substitute two Angela 30uF caps in place of the Angela 15uf in order to get 60uF, as they are the same diameter cans - only higher.

So you can see with the options here we can have a choice of tube, with a suitable cap value and variety of B+ all built in. If one of the 15uF are not being used then we can put that in one of the other sections in the filter..so there are no redundant caps however we connect them. Everything is there future-proof and flexible so to speak.

The resistors in the rectifier plate circuit are to provide the correct load for the tube, a matter that is rarely ever mentioned or addressed. In the case of the GZ37 , it requires a plate load of 75ohm min and a GZ34 this should be 150ohm. Using the Sowter transformers, they have a low reflected secondary impedance of about 24ohm, hence the inclusion of the additional resistors. They are also current limiters at switch-on.

The 50K bleed resistor is placed after the second choke where it draws a standing current through the chokes and aids regulation.

The Plitron OTX and chokes are available in Europe directly from the designer, Menno van der Veen, in the Netherlands at Amplimo, or in Canada from Plitron. Eitherway you get the very same product. Power and heater transformers are available to your specifications from Sowter - an alternative to this would be the Angela Universal PTX which incorporates both heater and HV windings in one.

Links

**AMPLIMO

**VANDERVEEN

**PLITRON

**SOWTER

**ANGELA INSTRUMENTS

FAQ

Hum levels...

Using AC on the heaters and with a multi-turn hum pot and attention to detail the residual hum is approx 1 - 2 mv. This is only audible on my 98dB Lowthers with my head a few inches away. Any speaker with lower sensitivity , well its just not audible at all. Input tubes also effect the results here.

Will it work with low sensitivity speakers...well, see how it performed at the 2003 Dublin Hi-Fi Show *HERE*

Currently I am using it to drive Spendor BC1, which is 84dB, but then it is not in a large room.

How much did it cost...

How long is a piece of string or how deep are your pockets? - impossible to answer, so I can only answer for myself especially as I am not USA based but live in Ireland and get stung by duties, taxes and freight. More money than sense? No - I sold everything that I wasnt using to pay for this over a year period - I just wanted to make that very best that Icould, once and for all . - Ha!....I will do better the next time......I will refine this amp further later this year but will require a new chassis

However, in round figures:

2 Plitron OTX = $450 4 Plitron chokes = $900 4 Sowter PTX = $650 10 Angela Cap = $170 2 Angela coppercaps = $50 4 BG FK = $80 2 Alps pots = $60 Western Electric 300B = $850 2 RCA 5692 redbase =$160

2 Mullard GZ37 = $100 Metalwork = $200 Sundries = $200

Total approx $3870 .....not including taxes, duty and freight.....but dont tell my wife that - I want to live to build another amp!

Where did I get the chassis...

The chassis is made by myself from nothing more than 4mm aluminium sheet and channel extrusions that I got from a metal supplier. All the cutting, drilling was done with nothing more than a couple of hand files and a hand drill....just takes care and patience and can be finished with watchmakers accuracy despite what might be seen as rather crude tools. See also JELabs for a similar and more detailed description of this method.

If you have any questions please ask