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3B4 (DL98, 3B4WA) to replace the RES164

See also: "ATP4 to replace the RES164 (B443S, L416D) "
and "ATP4 directly relocated to replace the RES164"

Another interesting replacement tube for the RES164 is the 3B4. Like the ATP4, it is a transmitter tube for portable radio devices that operate on batteries. There seem to be a lot of them in stock and it's available cheaply.

The data found by the 3B4 mainly relate to class C operation as an HF amplifier:

Socket B7G miniature 7-pin

Beam Power end tube for HF application

directly heated, 2.5 V, 165 mA,

Operating values ​​in class C operation:

Ua_ = 150 V

Ug2 = 135 V

Ug1 = -38 V

Ia = 25 mA

Ig2 = 6.2 mA

S = 1.7 mA / V

Ri = 70 kΩ

µG2 / G1 = 3.7


Pav = 3 W (anode power loss)

Ua-max = 200 V

Ug2-max = 150 V

Ia-max = 25 mA

These data show that there are only a few possible applications for this tube - but, very desirable, the replacement for directly heated end tubes around ± 1930, especially of course for the RES164 used in the VE301.

The 3B4 can be adapted without compromise to the operating values ​​of the RES164 as they occur in the VE301, while maintaining the full power and controllability like the original with the RES164, in case of doubt even better.

Because of the miniature 7-pin base of the 3B4, an intermediate adapter is required in order to be able to insert the 3B4 into the B5 European socket. Components for adaptation can then easily be accommodated in this intermediate adapter.


Adjustment of the heating:
The smallest problem is the different heating voltage. The 2.5 V of the 3B4 can be easily adapted to the 4 V of the RES164 via series resistors, which are accommodated in the intermediate adapter base.
In order to avoid the development of hum, the series resistor is divided as symmetrically as possible over both ends of the filament.
By selecting the resistors R1 and R2, the 3B4 can be optimally adapted to the heating voltage that is actually present during operation. For the ¼ W resistors R1 and R2, depending on the heating voltage available, you can choose:

4.3 + 4.3 Ω at 3.92 V.
4.3 + 4.7 Ω at 3.99 V.
4.7 + 4.7 Ω at 4.05 V.
4.7 + 5.1 Ω at 4.12 V.
5.1 + 5.1 Ω at 4.18 V.

The small asymmetries such as 4.3 + 4.7 Ω are barely noticeable and can be compensated with the "Entbrummer".

Adjustment of the operating values ​​(anode + screen grid)

The maximum anode power loss of 3 W, which corresponds exactly to the RES164, is pleasing.

The anode voltages 150 V operation and 200 V maximum should not be viewed as critical, especially since they are intended for class C operation. As long as the tube has a good vacuum, there is no risk of a breakdown if it is operated at 200 ... 220 V. It is much more important that the anode power loss of 3 W is adhered to, i.e. the product of the anode voltage * anode current!

When looking through various VE documents, operating voltages in the range 210 ... 230 V DC, anode voltages (on the RES164) in the range 190 ... 220 V, anode currents in the range 11.5 ... 14 mA were found.

The 3B4 must now be operated in such a way that it works properly under the conditions of the VE. Attempts should be made to maintain the negative grid bias voltage of -10 ... 11 V, which is generated with the 700 Ω resistor, and the 100 kΩ screen grid series resistor should also remain unchanged.

Initially, the 3B7 was only operated with the heating series resistors in the adapter base, without changing the other wiring. This resulted in an anode current of approx. 16 mA, which of course was too high.
Since the anode current is determined by the screen grid voltage, an anode current that is too high can be reduced by reducing the screen grid voltage. This was easy to implement with a resistor R3 of 100 kΩ, ¼ W, parallel to the screen grid, which reduces the anode current to 13 ... 13.5 mA, which corresponds to the operating values ​​in the VE. As a reference point, R3 lies on the center of the filament, which solves the problem of symmetry.

Other applications than in the VE301:
The very simple adaptation to the RES164 shown here with the 100 kΩ resistor parallel to the screen grid is only possible if the screen grid in the device is also fed via 100 kΩ from an anode voltage of approx. 220 V. In other devices in which the screen grid of the RES164 is fed in a different way, a different adaptation is also required.

Use as an end triode:
Since the 3B4 has a very low µG2 / G1 of only 3.7, it is also well suited as an end triode by connecting G2 to the anode.
This would make it suitable as a replacement for some RE-end triode types, such as. B. RE134 and RE144. However, due to the limit value of the screen grid, the operating voltage may not exceed 135 V, in the extreme case 150 V. On the other hand, the 3B4 as an end triode could even be operated with a total anode power loss of approx. 4 W, since the screen grid power loss is added here.
From a purely electrical point of view, it would therefore be the ideal output tube for ancient receivers that were operated with anode batteries of a maximum of 120 V, if the optics did not speak against it. However, because of their small size, one might consider installing them in the bulb of a hollowed out older tube.

Comment on the article "Replacement of the RES164 tube"
(with the 3B4) - idea by Arthur Bauer

First to Completing my investigations into the suitability of the 3B4 as a replacement for the RES164, which resulted in the above post, I discovered this post by Arthur Bauer, which was posted by our colleague Thomas Lebeth. All the thoughts and backgrounds that led to my above article arose from complete ignorance of the article by Mr. Arthur Bauer, who unfortunately is no longer with us.

After I discovered this text, it quickly became clear to me that this solution of adapting the 3B4 to the RES164 makes little sense. Arthur Bauer obviously did not understand the nature and characteristics of pentodes!

Pentodes work like constant current sources. The anode current is essentially determined by the voltages on grid 1 and grid 2, - changes in the anode voltage have only very little influence on the anode current. It is therefore the least suitable method to change the "operating point" of a pentode by changing the anode voltage, in this case via the capacitor-bridged 3.9 kΩ resistor.

The only effect that is achieved by this resistor is the reduced anode voltage, whereby the anode power loss of the tube is correspondingly reduced - however, this is reduced Output power, however, to less than half !

This resistor does not particularly protect the tube, as the anode power loss of 3 W is maintained even without it, but the full original power is available without restriction, just like with the RES164!

This supposed method of adapting the 3B4 to the RES164 is not recommended, but the mechanical structure of the intermediate adapter and its description is exemplary and highly recommended for imitation.

Comparison of ATP4 - 3B4

the ATP4 and the 3B4 are both originally transmitter tubes for portable radio devices for battery operation. Both are directly heated, which is a particular advantage as a RES164 replacement tube. When the device is switched on, they immediately draw current, just as the RGN354 rectifier tube, which is also directly heated, supplies voltage.

However, if indirect heated replacement tubes are used for the RES164, such as B. the PL95 or even triodes of the PC series, high overvoltages occur due to the delayed heating, which can be dangerous for the capacitors.

The ATP4 is in the classic architectural style with a pinch-foot construction, which is why it optically fits well between the rectifier tube RGN354 and the Audion tube REN904 or AF7 in the people's receivers.

As a miniature tube with the Pico-7 socket B7G, the 3B4 is several generations more modern than the tubes of the VE and is therefore less optically compatible with them. However, it is still available cheaply in larger quantities and is therefore suitable for everyday use “without regrets”. It is definitely better than the PL95 and the like.