The Integrated 300B Amplifier - Part 1

Hi!

I repeatedly get asked about the possibility to offer an integrated amplifier and also headphone amplifier based on the 300B and preferably in a single chassis.

So I decided do develop one and see if there really is demand. I mocked up a test circuit using a new Lundahl output transformer with a new high bandwidth winding technique and which has optimum values to be used with Elrog ER300B.

Above the bread boarded test circuit, one channel completed. To fit all into a single chassis no interstage transformer and no transformer volume control. Volume control is done via a DACT stepped resistive attenuator (not seen in the pic above yet)

I selected the 6DN7 as driver tube. The two systems offer the right amplification factors and plate resistances for this job.

Initial measurements and listening tests with a bunch of lab supplies gave very good results. So time to bread board a power supply as well.

Some older metal plates got recycled for the test. The result is very pleasing. A headphone version of this will be offered as well with selectable impedances for 32/150/600 Ohm. Now everything will be fitted into a single box and the metal plates for that have to be designed.

Drop me a mail if you are interested to become one of the first owners of a 300B integrated amplifier or headphone amplifier. Other tubes will also be possible.

Best regards

Thomas

The New D3a Phono Stage - Part 3

 Hi!

In part 2 about the new D3a phono stage I promised to show a few more photos from the inside.

In the meantime some missing chassis parts arrived and the phono section is complete. Next step will be to build the external power supply in the same style.

In the last post I showed this stage of the assembly:

A subassembly with the tubes, LCR modules and some transformers will be placed into the empty space.

The inside completely assembled, wired and tested:

Top side:

The bottom with preliminary feet. Some suitable metal feet are being manufactured.

The tubes can be easily accessed via the lid at the top:

A minimalistic design was chosen on purpose for a discreet look.

Stay tuned for part 4 for an update about the assembly of the power supply

Best regards

Thomas

Tube of the Month : The PL519

Hi!

Smart amplifier builders always looked beyond the mainstream tubes and searched especially among tubes developed for TV applications. In the last post I showed an amplifier with such a tube, the 6CB5A. Today I'd like to present a european TV tube, the PL519.

The PL519 is a European type which was developed as output tube for the line deflection circuit in TV sets.

It is a pentode on a 9 pin Magnoval base and the plate is connected to a top cap. The pinout is shown on the left. The first letter 'P' indicates a 300mA series heated tube. This means that it was intended to be heated in series with other 300mA heater tubes. If heated in this way 40V will be present across the heater. There is also a 6.3V version for parallel heating, called the EL519. It has the same electrical specifications as the PL519 except for the heater requirement. The cathode of this tube can deliver insane peak currents like other deflection output tubes. In this case 1.5A. It has a maximum plate dissipation rating of 45W. Connected in triode such beast can easily deliver more than 10W in single ended mode. Such TV tubes are extremely rugged and don't mind to be run at their limit. I recently visited a customer who has a 6CB5A amp built by me and which is in use since 2010. I checked the output tubes and they showed no signs of wear. I'm confident a PL519 would hold up just as long. As always lets have a look at the triode connected curves of this beauty:

A great alternative to 300B and the like if on a budget. And it leaves more funds to be spend on the output transformer and other parts of the amp. 

Lets have a look at some PL519 samples from different manufacturers starting with Philips.

The top cap:

The Magnoval base:

Some close ups:

The next one is labelled 'Karo'. Never heard of them probably rebranded from one of the main manufacturers.

Industria labelled PL519:

The box:

A whopping 6 months warranty. Back in those times 90 days warranty was the norm.

Valvo:

And lastly a Telefunken PL519:

Niclas from Sweden, again borrowed these to me, so no dissection. But some tube glow:

Best regards

Thomas