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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Are these EL34's good?

I found 3 of these EL34's in a guitar amp. Wondering if they would work well in a Hifi amplifier?

Printed in gray on the glass it says:


They have black bases with red printing:


They have two getter at the top at 45 degree angles and one on the side. Here are a couple of pictures:



Any info is greatly appreciated.
Thanks Scott. I am thinking about trying them in your design.

I was just wondering if these were just average tubes or possibly something special. I forgot to mention that the guitar tube head I pulled them out of is a fully functional Music Man One Thirty (huge power and output transformers and a pretty healthy chokes). The forth output tube is different than those 3. Narrower diameter envelop and what I can read on the glass says:

6C <something rubbed off> C

It has one getter at the top.

What you have is the American 6CA7. Made differently from the EL34.

6CA7 to EL34 [Archive] - The Gear Page

Check out the link. They talk about the differences. I tried to look up a data sheet but only the "EL34" data comes up. The 6CA7 was one of the last tubes that GE/MPD made before they closed. I dont think its a true pentode; the internal structure looks more like a 6550 than an EL34.
Hope this helps...
Here is a data sheet link for the 6CA7 made by Tung-sol:

From what I've read, the 6CA7 is a beam tetrode with different G3 construction. Both have G3 available as an external connection. The 6550 and the KT88 both have G3 tied internally to the cathode.

I have both the EL34 and the 6CA7 by Electroharmonix. The EL34 is in a slimmer bottle.

Since the tubes can be used interchangeably your 4th tube is probably an EL34.
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Yes, I agree about mislabeling. It happens from time to time. The nearest explanation I have come across is that a 6CA7 is "Similar" to an EL34 but not the other way around. That was from Mullard back in 1972 when I had a problem sourcing EL34s. The screen grid has physical differences as does the cathode. That's all I remember from the conversation.
If a 6CA7 is a beam tetrode it doesn't have a screen grid. The beam tetrode was developed by RCA to avoid paying Philips a patent fee for making pentodes. Also I don't think the EL34 is an "English" design as it was developed by Philips in the Netherlands. It may be that the best EL34s were made by Mullard in their Blackburn factory, but that's a different story.
No. A beam tetrode lacks a suppressor grid. Beam tetrodes have a screen grid - indeed it is the interaction of the screen grid and anode with secondary electrons which makes the pentode or beam tetrode necessary.

The beam tetrode was invented by Marconi-Osram (GEC) in the UK, but then developed further by RCA.
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M-O did produce beam tetrodes such as KT66 and KT88. Later KT77, which is another EL34-alike. I understand they found problems, though; perhaps in making smaller valves? I have noticed that many US RF 'pentodes' are in fact small beam tetrodes, so I think it was reliability and ease of manufacturing which RCA added.

Later, I suspect that European valve makers started using at least partly aligned grids in pentodes to reduce screen current and so improve efficiency in output stages and reduce partition noise in small signal valves.
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Yes they did but, from what I've read, only after their close partner RCA had proved that beam tetrodes could be reliably mass-produced. KT66s were produced before the Second World War (I have a 1937 M-OV catalogue with them in) but I don't think there were any KT88s until after it and the KT77 was the last to be developed, precisely to combat the EL34 which, I think, was first produced by Philips in the early 1950s