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Thursday, June 28, 2018

Tube of the Month : The 1H4


I just found some small directly heated triodes in my tube stash which deserve their spot in the Tube of the Month series. Meet the 1H4:

The 1H4 is electrically equivalent to the 30 which was already covered in this series. It is basically the same tube with an Octal base instead of UX4.

The pinout is shown on the left. Since it only has 4 connections half of the pins on the base are unused. As mentioned, the 1H4 is absolutely identical to the 30 except for the base. It was also intended as detector or amplifier tube in portable receivers. Hence the classification as battery tube. It has the same ultra low filament consumption as the 30. Only 2V and a minuscule 60mA of filament current which is only enough for a very dull glow. It was designed to operate at rather low plate voltages. The RCA data sheet gives sample operating points at 90V, 135V and specifies a maximum plate voltage of 180V. The amplification factor is 9.3 at a plate resistance of a little over 10kOhms. These values are very close to those of the indirectly heated 37. As always let's compare the plate curves from the data sheet with those taken from a tube sample with the tracer:

As linear as can be expected from directly heated tubes!

The 1H4 was made with both shoulder type and straight sided glass. The shoulder type was named 1H4-G and the straight sided ones 1H4-GT. As mentioned above I only have a few 1H4 and only of the shoulder type. Above we see a 1H4G made by RCA.

The tube from different sides:

Some details of the tube:

Shiny, uncoated nickel plate.

The base:

The tube designation on the glass:

This tube came in military packaging.

A bunch of 1H4G tubes made by Sylvania:

Some close ups:

Nice getter flash which almost completely covers one side of the tube:

Some more details:

The top:

Here we get a nice view of the grid and the filament which is an inverted V shape:

Let's see the internals:

Now we get a better view to the top.

Close up to the suspension of the filament:

In different light:

The bottom part showing the extremely thin filament welded to the connection wire:

More views of the plate:

Grid and filament removed:

Here we see the two holders through which the filament was threaded:

The grid without filament:

This is the first time I have seen such supports for the filament midway between the top and bottom.

Probably to reduce the risk of the very thin filament touching the grid when used in portable equipment.

The extremely fine filament is even thinner than a human hair:

What a great little tube!

Best regards


Friday, June 15, 2018

The 46 drives 46 Amplifiers - Part 3


As mentioned in part 2 about the 46/46 mono blocks, I built a second pair since the first set got delivered to it's new owner.

Here some photos of the second set and some further thoughts about the 46.

This set was finished in April already and used for demo at the High End show in Munich.

Shown here with globe 46 tubes.

The 46 continues to amaze me and especially in this 46 drives 46 configuration.

Here with ST shape 46.

The 46 trumps the 45 in terms of midrange magic and tone. With the right speakers it delivers a full spectrum and is capable to reproduce large scale orchestra without any trace of break up. It can deliver solid and powerful bass. Only in terms of high frequency resolution thoriated tungsten triodes like the Elrog ER300B or 801A have a slight advantage.

These 1250 Milliwatts tend to sound like much more power. When pushed to the limit they clip gently. Like hitting a cushion. They are perfect proof that the first Watt is the most important. So better just have one Watt, but the best possible one, instead of high power output. Of course speakers in the 3 digit sensitivity range are necessary to experience the magic of the 46.

Although the 46 seems to get hard to find I could source quite a few more. This box just arrived:

And there is another layer of tubes below. Some more are on the way to me and together with the tubes I already have in stock, ensure that many more 46 amps can be built and replacement tubes are available for many years.

Best regards