Stephe, I used DHTRob's schematic with the 6C45Pi, I had a power transformer 506VCT and fullwave tube rectifier 6D22C. Instead of a plate choke I use a 15W/230V bulb and for the cathode resistor (6C33C) also a bulb, 75W/230V.

Running One filament /cathode will prevent ypu a lot off problems ! One of these is runawsay and redplating ........( always a risk with shared cathode bias ) Also avoiding heat problems essentially on the socket ........ DHT Rob ( Durch) made great amplifier designs at that time and used always quality components...also shared good advice and his personal experience . For the fun and history ...........When a soviet pilot defected to the west and landed his MIG25 in Japan , the CIA examined the latest soviet secret weapon and they were asthonihed that this modern plane still used the ( old) tube techology .....Baby on board , NO but the 6C33 tube etc on board !....some started laughing because the USAF used already SS and computers on their fighter planes...............until someone made a the following comment... " In case of a nuclear exchange all tour own planes will fall out of the sky but NOT the Russians !" EMP would benefit from the protection inheren from the technology of tube techology to withstand and survive an EMP ........... That's good news for us with our tube ampliers also ..........We will still be able to listen to our favourid and beloved music........... Kind regards

I used to read my dad's Radio electronics back from the late 40s after ww11 they had articles about to use them RF tubes from the JAN. Anyway I remember a single ended amp using a 826 similar tube for audio. The old books had some good ideas. Anyway. Keep safe Amps have lethal voltages🤬🌹❤️

This amp will be a beast. That is a lot of iron!

I got excited and went to PSUDII because I've been using it to optimise the power supply on my tube amp. You could pick the 6H 159R 200ma 150ohm choke, which is the same size and weight as the 4H 159S. Then you can choose cap values of 33uf for C1 and 230uf for C2 to get a 250V B+ supply. There is an audible downside from picking a large first cap - it slows down the power supply. I am enjoying a noticeable difference in clarity shifting from C1/C2 cap values of 108uf/108uf to 58uf/216uf.

This is _the best_ tube audio channel!

I was thinking to fine tune the B+, instead of using a big and costly choke for that you could add a simple R C section. Tuning the voltage drop with a simple resistor. Much more inexpensive and easy to tune to get your desired B+. An RC section also helps in filtering the ripple, just not as much as with a choke. So basically if you need less ripple , add another choke, if you need to drop voltage add a resistor.

Fixed bias ...versus autobias ( cathode bias )..... As designed by some maufacturers ( Luxman and others ).............You can build as hybrid bias , this ia partly a cathode bias and fine tuning the current with a fixed bias .....this works realy well and sounds good as well as give some kind of protection to the tube..

Very good brain work

Moin, There's a reason for the two cathodes.... If you only using one for having easier circuitry you end up with a overheating cathode, which will dramatically drop service hours of your tube. But you using the tube all 'illegal' anyway.... There's a quote in the datasheet which says: if you running onr cathode only or 200 volts you need to derate the tube... Also it needs a rather low impedance driveing stage, any decoupling cap in series with the driver causes instability of it.. And make the output tube goes into oscillation. Either do a direct coupling or a cathode follower as a driver to have a real, low driver output impedance. Trust me, I built a real monster amp using six (that's 6) 6c33c tubes in pushpull at 200volts and both cathodes lathodes. Delivering around 350watts clean (0.5% THD at maximum output 30hz up to 18khz) sind an Ei 130 magnetic core size output tranny (around 15kg/30lbs of core weight alone) Driver section is 6sn7 followed by a phase splitter 6sn7 and another 6sn7 with both sections in parallel - one for the high driver and another one for the low side of the pp configuration. In order to prevent RF ringing at maximum output. Because the 6c33c has a rather high control grid capacity which need a fair amount of current at large swings even if the tube itself is still in class A. If you try real A2 mode (with positive control grid voltage) the control grid needs several milliAmps of driving current... And if your driver can't handle it, it will go ringing, because the control grid isn't fully controlled by the driver section and go into oscillation due to the large anode/grid capacity all by itself. Good luck.

Stephe: I'm excited to follow along with this new monoblock amp design process. One suggestion...how about mounting that ugly cathode bias resistor inside the chassis, but with vents in the top of the chassis? The vent holes or a vent grill of some type could be more aestheticly pleasing than an ugly ceramic resistor on top of the chassis IMHO, but still dissipate the heat.

@garagepunkfan 0 seconds ago I still maintain that Dave Gillespie's EFB biasing scheme is ideal for this tube. It's the pathway to more output wattage and less THD, using less power, than cathode bias, without the instability that this tube displays running fixed bias. The tube always stays in it's optimum operating condition, with the bias voltage always tracking a perfectly inverse relationship to B+ voltage as it rises and falls with sag. All this is done with $10.00 worth of parts

If you are using half of 6s33s you can use 6s41s tube because its half of 6s33s

Lotsa iron phew! Looks a bit cramped but as long as it sounds good! A big ole SE amp I'm betting it will! Lotsa sweet even harmonics. Not so many odd harmonics!😊

24:00 Chassis is looking pretty "busy" with all that iron. It also has me wondering what the weight is going to be. Definitely curious about the cost. Looking good so far!

As pentode you could use an EL86 / 6CW5 ? Those are used to drive some power tubes

Have you considered the Hammond 1626SEA audio output transformer for this project? Or is it too expensive comparted to the Edcor?

Hi Stephe! If you need to shave off B+ but don’t really need more filtering what are the benefits of using chokes over large resistors or even a voltage divider? Thanks! Looking forward to this build series!

Name it "Big Iron."

wow the chassis is small looks nice

Just came across this, read the DHRob article, it’s not in there - can anyone tell me what its output is?

hi will you add more videos on this build?

Hi Stephe. I’ve seen some awesome metal “tube rings” on your builds where the tubes extend out of your chassis. Are those custom machined? If not, where can I buy some? Thanks in advance!

Can't you mount the choke on the vertical side of the chassis you have?

please, could you be so kind and give us, the people in europe with 220/230 volts on electric grid, some ideas on power transformer. thank you in advance

I build this amp and sound good but nothing special in SE.