Tesla EL34 identification

[cyberpunk409]

Hello everyone, I just purchased a pair of Tesla EL34's on eBay for $167 (tax and postage included).




They have brown bases and double O getters.

I know they're from the Czechoslovakian plant in Zavod Trinec.

No idea how to decipher year of manufacture or whether these are the good Tesla's or less desirable ones??

Any info would be greatly appreciated, thanks! Was this a good, decent or horrible price to pay?

 

[cyberpunk409]

I have the following information about these tubes:

 

[PelliX]

No idea how to decipher year of manufacture or whether these are the good Tesla's or less desirable ones??

Someone with a little more knowledge may chip in concerning the date of manufacture, but the real test is to see how they perform in *your* given amp.

I will add that the sellers' description is a little disappointing. "The tubes all test within or near the NOS range". There is no 'NOS range'. There are tolerances in performance and these either fall within those or not. Additionally, even mentioning "NOS" when selling valves where the base is so obviously discolored from prolongued use and thermal strain is questionable...

The price is a matter of opinion; what's it worth to the buyer? I wouldn't spend that much money on a single set of EL34's that have probably already had a rough life behind them. They might however, like any vacuum tube, go on for another few decades. They might also pop tomorrow.

One thing that I'm a little puzzled by - and perhaps someone with sufficient expertise on the construction can add to this - is the waviness of the glass. I wouldn't be surprised if these had some quite distinct blue glow.

 

[StingRay85]

I don't think Tesla tubes had date codes

 

[cyberpunk409]

Well the way postage from US to Australia is operating at the moment, I should have these tubes in hand by December!! I hope they'll sound good, blue glow is not what I want

 

[StingRay85]

They are clearly used tubes though.

 

[PelliX]

Well the way postage from US to Australia is operating at the moment, I should have these tubes in hand by December!!

Ugh, good to know the demise of the postal services is not a localized thing...

I hope they'll sound good, blue glow is not what I want

The blue glow some valves have is nothing to worry about at all. In fact, the presence of the blue glow typically indicates very low amounts of gas, which is desirable of course. The glow itself is caused by stray electrons hitting imperfections in the glass envelope.

 

[cyberpunk409]

They are clearly used tubes though.

How can you tell?

 

[PelliX]

How can you tell?

The base was originally a single colour. Now it fades from the ocker/brown to "crusty fried brown with a tint of black". That's the effect of serious heat over a prolongued period of time.

 

[cyberpunk409]

I don't think Tesla tubes had date codes

Are you sure

The base was originally a single colour. Now it fades from the ocker/brown to "crusty fried brown with a tint of black". That's the effect of serious heat over a prolongued period of time.

Wouldn't the glass have signs of that too? Just trying to learn as much as I can.

 

[cyberpunk409]

Just reading all of the above... Sounds like I got a dud set?

 

[Pete Farrington]

One thing that I'm a little puzzled by - and perhaps someone with sufficient expertise on the construction can add to this - is the waviness of the glass

One cause can be severe overheating. An area of the glass eg closest to a hot spot on the anode gets so hot that it softens and the vacuum draws it in a little.
I've seen Mullard EL34 whereas that's happened to such an extent that the glass has been drawn back to be touching the anode, stretching so much the vacuum mercifully failed.

I wish I'd taken a photo

 

[cyberpunk409]

They

One cause can be severe overheating. An area of the glass eg closest to a hot spot on the anode gets so hot that it softens and the vacuum draws it in a little.
I've seen Mullard EL34 whereas that's happened to such an extent that the glass has been drawn back to be touching the anode, stretching so much the vacuum mercifully failed.

I wish I'd taken a photo

That sounds super extreme!!! I don't think me matched pair is anywhere near that close to failure?

 

[PelliX]

Wouldn't the glass have signs of that too? Just trying to learn as much as I can.

Well, according to Pete's account (and I've seen similar online which I might take a little less seriously), yes it could. I'd have thought it would take at least 1000C to get glass to soften, but I'm not an expert on that.

Just reading all of the above... Sounds like I got a dud set?

Unlikely that they're "dud" as in stuffed. They might be at the end of their useful life (aka "knackered"), they might not. You certainly paid a serious price for a pair of abused old valves.

 

[Pete Farrington]

They

That sounds super extreme!!! I don't think me matched pair is anywhere near that close to failure?

No, just that they may have been worked hard, perhaps just for a limited time.
I wouldn't be too concerned about their condition, because the getter flashing looks fine.
Usually the flashing of output valves that have worked hard for a long time develop rainbow edging / becomes transparently thin around the edge.
My experience of those Teslas is that they sound great and last well, so hopefully you'll get a lot of use out of them.
Enjoy!
Hopefully, on tgp, valve experts Jeff West or Timbre Wolf might chip in with info regarding the codes.

 

[cyberpunk409]

Well this is my matched pair brown base....



Going up against a quad priced at $495 right now..




I don't really see much difference?!?

And a pair going for $274

 

[cyberpunk409]

I do appreciate all the replies, but I was wondering if anyone could decipher the date codes and tell me when these were made?

 

[PelliX]

I don't really see much difference?!?

Agree.

Once upon a time the bases looked more like this (note the uniform colour):

And a pair going for $274

Yes. Some people will pay those prices and thus others will ask those amounts. There's a grain or two of truth about older valves being more reliable or having better construction, but now you see old pulls (i.e. valves pulled from gear after long use) advertised as the best thing since sliced bread merely *because* of their age.

 

[cyberpunk409]

Thanks, any ideas about the year of manufacture based on the codes provided?

 

[PelliX]

Thanks, any ideas about the year of manufacture based on the codes provided?

@StingRay85 suggested that there are no date codes on those. I believe 37 is the factory ID (front). The 507 B6 designation *might* be a date code, which puts them post 1984 judging by this chart:

https://tubes-store.com/article_info.php?articles_id=5