DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

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Thursday, December 7, 2017

845 Mono Amplifiers - Part 2


In part 1 about these single ended mono blocks with the 845 tube, I showed some first photos mainly of the chassis materials. In this part I will show the assembly steps.

The interstage transformer, decoupling choke of the driver stage and most important capacitor in the driver stage are mounted directly under the top plate.

This enables short signal path wiring.

The high power resistors are mounted on a separate aluminium rail close to where they are needed.  Here a detail of the mounting technique:

The output transformer, decoupling choke of the output stage B+ and final choke of the LCL filament supply are on the next level right below the top plate:

The most important capacitor of the output stage, in this case a NOS paper in oil type, is close to the output transformer to have a short signal loop. On the next level below there are the main capacitor banks for smoothing of the high voltage:

The cutout is there to leave room for another choke which will be mounted on the next tier below.

Another set of capacitors and the choke mentioned above:

Again a cutout, this time for the main power transformer which will be on the bottom tier.

The power transformers (separate for filament and high voltage) and the first LC section of the filament supply:

The filament transformer is not mounted yet, it will reside in the upper left corner. Next we see a photo of the finished amp without chassis which shows how all these modules are stacked together:

As you can see almost no space inside is left unused. Right side view:

I wanted to keep the height of the amp to my standard chassis size of 40cm (without tubes and feet), 30*30cm floorspace. So each layer had to be carefully planned to fit everything in. Left side view:

Testing of the amp is complete and assembly of the second mono block is underway. Stay tuned for an update with the finished units.

Best regards


Thursday, November 30, 2017

Winter Sale!


Some Lundahl transformers and chokes of which I have too many in stock. Your chance to get them at a bargain price!

The list prices per piece are given for each item. This is the net list price for export outside the EU. Inside the EU 19% sales tax is added. For a purchase of one pair subtract 20%. 25% discount when buying 2 pairs at once, 30% for 4 pairs and 40% for 6 pairs or more. A mix of any of the listed types can be ordered to apply for the discounts. Multiple pairs of each type and variant are available. The offer is valid only while supplies last. Send an email for a quote including shipping. Payments can be received by bank transfer or PayPal.

LL2753 large interstage transformer 1:1 (list price 120,- Euros per piece)

available with different air gaps for these currents:
25, 30, 35, 40 mA

LL1638 low DCR choke (list price 85,- Euros per piece)

available with different inductance and current ratings:
6Hy/250mA, 4Hy/400mA, 3Hy/500mA

LL1694 high current/filament choke (list price 64,- Euros per piece)

available for these currents:
1.0, 0.75, 0.5 A

Best regards


Sunday, November 26, 2017

Preamplifier Production


Here a quick overview of some recently finished phono and line preamplifiers.

These photos show some of the color schemes and variants I am offering.

In this photo there are 2 D3a phono stages and 3 10Y line preamplifiers.

Here we have a differential D3a phono in smoked eucalyptus and with gold anodised metal plates:

Next a single ended D3a phono in black chassis and with silver plates:

A 10Y line stage in smoked eucalyptus with transformer covers and capacitors in black:

The same in Walnut and maroon red metallic transformer covers and capacitors:

And lastly another 10Y line stage in birch tree and with graphite grey metallic covers and caps:

Some of these will stay here as demo units while the others are ready to be shipped to their new owners.

Best regards


Wednesday, November 22, 2017

Tube of the Month : The 17AX4


This month it is TV Damper tube time again! Let's have a look at the 17AX4.

As the name implies, the 17AX4 is a variant of the 6AX4 with different heater voltage. All other parameters are identical to the of the 6AX4. I already showed another heater variant of these, the 25AX4.

It also shares the same pinout. The 17AX4 was designed for series heating which was commonly done in TV sets. Several tubes with the same heater current would be hooked up in series. The nominal heater voltage of the 17AX4 is specified at 16.8V and it draws 0.45A. Since tubes with odd heater voltages are not very popular nowadays such tubes can be picked up at very low cost. If the exact heater voltage is not available a higher AC voltage can be simply reduced with a suitable dropping resistor. These will perform just as well as other TV Damper tubes. Since I have plenty 6.3V heater TV  dampers, I only stocked up a few of these, made by General Electric and Sylvania. But they have been made by many other manufacturers as well. Let's start with the Sylvania 17AX4:

Among this small heap of tubes there are several different variants. Here a closer look:

The top:

Another one:

These all came in the typical yellow boxes:

The tubes and boxes have dual markings 17AX4 and 17DM4:

It was common practice to stamp tubes with several designations of variants with the same characteristics.

Next a 'coin base' type:

General Electric 17AX4:

Here a 6AX4 and 17AX4 side by side.

Now let's open this one up to see the internal construction:

Glas removed:

Close up to the plate:

The connections at the bottom:

The top:

The heater removed from the cathode:

The spiral around the heater provides the necessary distance and isolation to the cathode.

The spiral removed from the heater wire:

The cathode:

Cathode, heater and insulation spiral:

The plate:

Here we see the plate opened up:

And finally some photos of a tube with the heater lit up.

Close ups to the top and bottom:

That's all for the 17AX4.

Best regards