The Parallel Single Ended 6CB5A Amplifiers

Hi!

The owner of a single ended 6CB5A amplifier approached me with the wish for more power with the same sound. Since he was not interested in the big transmitting triodes like 211 and 845, I proposed a pair of monoblocks with 2 6CB5A in parallel on each.

In  order to have room for the needed parts, a hefty power transformer and big output transformer as well as all the necessary chokes, capacitors and interstage transformer, I built them in the tower chassis like the last pair of SE 6CB5A monos.

The driver tube can be a 6N7 as in the SE 6CB5A amps but the 6J5 is useable as well and recommended due to it's lower plate resistance for driving two of the output tubes.

The power supply is using a full wave bridge with 4 6AX4 tubes into a choke loaded filter like most of my designs.

Expected output power is a solid 15W per channel.

A few impressions from the assembly phase:

The top plate with the sockets mounted and wired up.

The interstage transformer also sits directly under the top plate for short signal wiring.

Adding two platforms which will hold the most critical capacitors close to their connection points.

Capacitors in place:

On the next level below the top plate is a subassembly with a big Tango output transformer ans B+ smoothing capacitors. And at the bottom the power supply.

Output transformer module mounted.

Fully assembled amps only missing the wooden enclosure.

Initial testing is done with the amps 'naked'.

Measurements show that the target output power was easily reached.

The Tango transformers have taps for 4, 6, 8 and 16 Ohm.

A great alternative to 211 and 845 avoiding costly tubes and high voltage power supplies but still providing two digit power numbers.

Need 20+ Watts? I can build these also with 3 6CB5As per channel.

Want your own 6CB5A amps? Drop me an email and we can discuss the ideal amplifier for your system.

Best regards

Thomas

The New 6CB5A Amplifiers

 Hi!

Last month I showed the initial construction steps of the new 6CB5A amps. In the meantime they are finished.

The amplifiers are constructed in tower style with dark wooden enclosures.

The amps are laid out as mirror images of each other.

The tube complement consists of a 6N7 driving a single ended 6CB5A wired in triode and a full ave bridge of 4 6AX4 diodes.

This yields 8W of glorious single ended power. Output taps are available for 4, 8 and 16 Ohm speakers.

Here a photo of the naked amp without the enclosures showing the vertical assembly technique:

The amps will now test run for a few days before they are shipped to their new owner.

Best regards

Thomas

Making of 6CB5A Mono Amplifiers - Part 1

 Hi!

I just started assembly of 2 single ended 6CB5A amplifiers and will share the construction process.

Readers of my blog will know that I have a long history with the 6CB5A tube and always proposed it as an interesting alternative to the more mainstream tubes.

I have built numerous versions of this amplifier which uses a 6N7 as driver and a rectifier bridge with 6AX4 TV Dampers.

This time it is a fully fleshed out pair of mono blocks built in the floor standing tower style chassis, as used in recent amplifiers like the last Stereo 300B amp I built.

Once the bare metal plates arrive the assembly can begin. Here we see the 2 top plates which are mirrored to each other this time, and all the bits and pieces needed for the internals:

Mounting the tube sockets and some initial wiring:

The top plate with all parts mounted and wired:

The next level below the top plate carries the interstage and output transformers and some capacitors:

Below that another capacitor bank and filter chokes:

And on the bottom the mains power transformer and another 2 chokes:

All the sub assemblies of one channel:

Completion of the amps will continue when some missing parts arrive. Stay tuned for part 2 which will show the final steps of assembly and finished amplifiers.

Best regards

Thomas

The Single Ended 6CB5A Amplifier

Hi!

I have built quite a few 6CB5A amps over the years. Just finished a new one. Here some photos of the finished amp and the assembly process showing the latest construction style.

The amp is a stereo unit with internal power supply, so all in one chassis.

Power supply section on the left and the amplifier section on the right.

The 'naked' top plate:

The back side of the top plate and the support plate for the chokes and signal transformers,
the small pate are for holding the capacitors in place.

Sockets and switches mounted:

Some of the resistors mounted to the underside:

Wiring up the power supply section:

Capacitors mounted and some more wiring done:

First level complete:

The subassembly with all chokes, interstage and output transformers:

The subassembly mounted to the main plate and wired up:

The amp gets tested before it is inserted into the wooden frame:

Done:

Best regards


Thomas