EL34

The EL34 was intended for audio output. It is a pentode, with a maximum anode dissipation of 25W. It was introduced by Philips/Mullard in 1953. It was intended for hi-fi and public address systems, but was also made popular for guitar amplifiers by Marshall. As a true pentode, it is easy to drive. However some US-produced versions, which may be labelled 6CA7, are beam tetrodes and so will tend to have higher grid current.

There is a fascinating account of the story of the EL34 on a German website. See also some information from the Mullard description of the EL34. It is still in production in Russia, China and eastern Europe.

RFT EL34

Photo of RFT EL34, side view
RFT EL34, side view

A now-popular version of the EL34 was produced in East Germany by RFT. At the time this was looked down on by people who preferred branded Western goods. What they did not realise was that some of their Western brands were simply labels attached to Eastern products. This effect can be seen today: a Brimar-branded RFT EL34 will sell on ebay for more than an identical valve labelled, say, Zaerix. For a while even some 'Mullard' EL34 were actually RFT, and they still sell for silly prices to those not in the know. Now that some modern EL34 are not so good, the RFT is appreciated and regarded as a good NOS buy.

Photo of RFT EL34, top view
RFT EL34, top view

There are some features of the RFT EL34 which make it fairly easy to recognise, especially if you have seen one in the flesh. They are:

Glass
The glass envelope of an RFT EL34 is straight and narrow, with a fairly flat top. There is no change in diameter as the glass enters the black base. In the middle of the top there is a dimple (a small depression in the glass).
Anode
The anode is grey and boxy (i.e. not round). There are two distinct slots in the outer face. The flanges have four staples each, and the staple prongs are left sticking out rather than being flattened against the flange.
Grid cooler
There are two grey grid coolers, attached to the g1 support rods. (The single halo getter is attached to one of the g3 support rods.)
Mica
The mica spacers are quite characteristic of RFT valves. The points of the stars are quite pronounced. The mica is fairly thick, and so not as transparent as some Western valves.

I have described here the most commonly seen RFT EL34. There are variants, but they are quite rare (in the UK at least). The Saratov plant in Russia produced a very similar EL34, using RFT-sourced tooling, but I understand that this does not have the dimple in the glass and may have a patchy anode coating.

Brands

Photo of eight RFT EL34, different brands
One valve, seven brands

As mentioned above, the RFT version was branded by many different companies. It is sometimes colloquially known as the 'Siemens' EL34, as many appeared with this branding. I have shown eight examples here, as these show a brand name. I have unbranded valves too. From left to right, top row then bottom row, these are:

  1. Pinnacle (UK)
  2. Bentley Acoustic Corporation (UK)
  3. Trigon (UK)
  4. Zaerix (brand name of Z&I Aero Services), also marked 6CA7
  5. Another Zaerix, marked 'Made in G.D.R.' - the only one admitting its origin!
  6. Colomor (UK - still trading as a shop)
  7. ITT Lorenz (German)
  8. Siemens (German)

The same valves appear below with their boxes. Another pair of RFT EL34 are shown in their Marshall box. At first sight these ones appeared to be unmarked, but on closer examination I found that they have a partially removed Trigon label - an example of double rebranding?

A row of 8 EL34, with their boxes Marshall EL34 in box
A row of eight RFT EL34, with their boxes; a Marshall box

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updated 18 July 2008: more on Russian lookalike