Нашёл схемы усилителя под данную лампу и описание процесса на английском языке:
Sometimes I simply have to go on, make new stuff, try out new things. This time the victim was the Kapittel I SV811-10 amp. I liked it really, the sound was very nice, but had the idea it could be better, especially with the new sources I have now. Of course again the amp has to deliver low power, but perfect power, this is the only aim I go for. This means as less as possible paper/oils, much coils, as less components as possible, good iron, and of course no feedback.
The AV302B-SL as power tube was very easy choosen. The good name this tube has together with the 300B hype and the fact that I was distributor for AVVT for the Benelux at that time add up to a logical choice. I could use a more heavy type made by AVVT, but the 8 watts I can get out of the AV302B-SL will be more than enough to drive my 104 dB Lowthers in the range above 150 Hz, 2nd order crossed. I choose to bias of this tube to be 400 Volts/100 mA (-90V), simply because of the fact I still have the 2*500V/1A torroidal transformer, coil coupled this transformer will give about this voltage with more than enough power. I only had to remove the first capacitor out of the old power supply of the Kapittel I.
The driver was a more complex choice, I wanted it to be a directly heated triode, and preferable only wanted to use one tube. This means I was looking for a DHT with quite some power, lineairity and high amplification, to keep the amp at least a bit sensitive. Possible candidates were the KC1 (too less current to drive the slew current of the AV302B-SL), the 220P, 45 or 10Y (too low amplification) and the S6 made by electro mecano. The last seemed to be very suitable for this application, having an amplification of 25, 15 watts, 5k plate impedance and DHT. With the 330 Volt transformers I could get 350 volts, and bias the S6 at 17 mA (-5V). The S6 is loaded with a 40H signal coil. This gives an easy very lineair 100 volts output with enough slew current with only 4 volt input sensitivity. To prevent the S6 of amplifying also the low frequencies and the high output belonging to them, I choose to add an extra filter capacitor at the start of the amp. The amp filters now at 150 Hz, 2nd order, this also keeps out extra low frequencies out of the Lowthers, since they are not backloaded they are very sensitive for high cone excursions.
The iron I got from a new discovered brand in the Netherlands. The owner makes very good stuff. I choose to coil load the S6 instead of an interstage load, because making a good 10k interstage with good bandwidth is a very hard thing (if not impossible) to do. I have enough bandwidth at the low side with 40H, simply because I use the amp from 150 Hz. I wanted to have something real special so I used the van den Hul MCS-200 high purity matched crystal silver cable on it. Especially in the low amplitudes of the prestage I think this is a very big improvement. The output transformer uses normal copper cable, the amplitudes are much higher there and thus less cable sensitive. I used double-C permalloy cores, because permalloy is so very beautifull sounding and double-C simply has some very good technical advantages. The bandwidth of the signal coil and the output transformer is 40Hz-80kHz!
All wires internal are silver (including the powersupply), resistors Allan-Bradley and Kiwame, capacitors in the signal are CDE silver-mica and Jensen paper/oil, powersupply capacitors GE paper/oils (8*20 uF/370Vac) in the prestage and SCR MKP's (4*100uF/630V) in the power stage. There are no solidstate and very few electrolytics in the complete amp except for the heather supplies. Negative bias voltage supply, pre-stage supply and powersupply are all separate and tube rectified.
And well, the most important, the sound.... Only two words, real love, from the start... Even when the still had to break in, voices were so very impressive you simply are drawn into the music. Also this amps really knows how to seperate the different instruments and has tremendous depth and detail. Listening to especially vinyl has become trippin'. Enough said now, have to listen again, it is quite addictive....
Powerstage of the amplifier:
The power supply was choosen 425 volts, this is the output of the coil coupled supply with the 500 V torroidal transformer I had already build in. The bias current was choosen 100 mA, just below the maximum rating of the tube, to prolong its live. The negative bias voltage need to be -90 V with this bias point.
The output transformer primairy impedance was choosen 4k, giving a very lineair 8 watt output.
The 10 Ohms resistors at the kathodes will be connected to my "on panel" voltage meters (range 0-1.5 volts). This way I can easy check the current through the the tubes, and correct them if necessary. Also they protect the outputtubes, when the current gets too high, they will simply burn out, and stop all current. So use 250 mW types!
The other complex network of resistors is the humbalance. I needed all the resistors to be able to use the very beautifull Allan-Bradley potentiometers.
Driverstage of the amplifier:
I wanted to use just one stage before the end-stage. This asks for a driver tube capable of handling high lineair voltage swing with sufficiant amplification. Also I wanted to use a directly heated triode, the final choice was the S6 made by Electro Mecano from Denmark. This is a very lineair, very well build very good looking 15 watt DHT. The sound is very great, in my eyes the ideal driver!
The S6 gets a DC heathing voltage, solidstate rectified (yes, there is some of that new stuff used!), resistor decoupled and stabilised to get it as clean as possible. When using AC or non-stabilised DC, the hum just became too much, it keeps very hard to get a lownoise feedback free amplifier playing at 104 dB speakers....
The S6 is choke loaded. I used a 40H signal choke (interstage without secundairies) permalloy Double-C core, with silver wire. This is to be sure the very low level signal is handled best, to get an as good as possible final result. For full range the value of the choke has to be somewhat bigger, I can use 20 Hz, because I use the amps only above 150 Hz.
To make the amp full range, one has to chance the coupling capacitors as pointed out.
High voltage (B++) powersupply:
This powersupply is build partly on a seperate enclosure, not only to save space on the amplifiers, but also because I have but one (and didn't want to buy another!) highvoltage transformer. It's a 1200 VA ILP torroidal transformer, 2*500 volts, about 1 Ampere. It is choke loaded, to have an as smooth as possible sound.
On board of the seperate powersupply there are also the tube rectifiers (5R4WGT), two filter coils (Sowther, 10 H/250 mA/50 ohms) and capacitors (ChateauRoux, 100 uF/630 V, MKP). When coming on board of the amplifier enclosures, there's another 20 H coil and ChateauRoux 100 uF/630 V MKP capacitor.
The power gets switched on and off by relais driven by the negative bias voltage of the monoblocks. If this voltage drops for one reason the powersupply will also be switched off, so the powertubes will not get harmed. Also it prevents the high voltage powersupply from being on without an amplifier connected, which could be a potential dangerous situation.
First stage (B+) powersupply:
My first thought was to get this powersupply from the B++ supply. Because I needed a seperate transformer for the negative bias voltage anyway, I decided to make it seperate also. It's tube rectified with a 5Y4GT, an octal double diode (5Y3GT with different pinout). With all the coils and the capacitors it the voltage is very clean and hum-less.
Negative bias (V-) voltage:
To be real consequent I also made the negative biasvoltage powersupply tube rectified and stabilised. I use a 5W4 double diode as rectifier and a OA2, 150 volts stabiliser to get the voltages I want. It's decoupled with an GE 20 uF paper/oil capacitor to be sure that no garbage gets through it to the amplifier stages.
Heather supply:
This high current supply I rather had on a seperate chassis. This supply is quite heavy and coil decoupled. There are some big cooling blocks on them to get rid of the surplus voltage. The 4.7 mH/1 Ohm aircoil with the 30000 uF (13 Hz) will filter the garbage out of the voltage, and prevent the high capacitance from drawing to high currents out of the transformers. Big advantage is the slowness of this supply, it will only come up slowly, preventing the tubes from drawing big inrush currents.
This supply also contains the stabilised DC supply for the driver tubes. Even before the LM317T stabilisation chip it is made very clean, just to be sure no Hf-noise (made by the switching of the solid state rectifiers) gets into the system anyway.
Photo Gallery:
Powertube heather supply (2*6.3 V/4 A, 10 mV ripple).
High voltage supply (2*600 V/200 mA).
Technical data:
Supplies : 425 V @ 100 mA, 350 V @ 20 mA, -125 .. -65 V bias (tube stabilised).
Tubes : S6 Electro Mecano, AV302B-SL AVVT, 5R4WGTB Chatham, 5Y4GT RCA,
OA2 Philips, 5W4GT National Union.
Iron : 40H Signal coil custom made Agro double-C permalloy with van den Hul MCS-200
silverwire. 4k-5 Ohm Output transformer custom made Agro double-C permalloy.
Measurements : Monoblocks 335 x 455 x 230 mm, power supply 440 x 220 x 30, heather supply 200 x 250 x 100.
Weight : About 20 kg each side, power supply about 20 kilos, heather supply about 10 kilos.
