Genuine 1970s Tesla EL34 vacuum tubes NOS, matched quads and octets available For Sale

Please read general information before purchase.
Vacuum tube type: EL34
Manufacturer: Tesla Referral
Made in: CzechoslovakiaFactory date code: WL (all tubes the same date, two batches marked 128 & 312)Manufacturing date: April 1978Plant: Tesla Referral RoznovCondition: NOS
Box condition: no boxesMeasured: yes
Important notice: price is for 1 tube. If you need quad => you buy 4 units.
Genuine 1970s Tesla Referral EL34s. Manufactured on Philips machines in Tesla Referral-Roznov plant. Highly sought after and valued for their unique sonic qualities. Extremely durable tubes, renowned for their longevity. An investment that will last for years. They are becoming increasingly difficult to obtain in larger quantities from a single series, so that matched pairs and quads can be comfortably chosen. Quite rare in such pristine condition, unfortunately they come from a bulk box, so they have no individual boxes.
In this listing I offer 16 never used NOS tubes and 2 slightly used by mysef. It is not even visible that this pair have been used (no base discoloration nor dark stains on glass or any other signs), nevermind the measurments (they measure perfect, as you see) but I want to be honest with you. I took that pair out from the 18 NOS tubes and used for few months in my private amp. I list them for slightly lower price than other 16 tubes that are virgin NOS.
All tubes were carefully measured on L3-3 tube analyzer. Pre-heating time 5 minuts for each tube. Electrode insulation and gas test done with buil-in nanoamperometer. Faulty currents not measurable (all tubes passed). Operating point: Ua = 250 V, Ug2 = 250 V, Ia = 100 mA. -Ug1, Sa and Ig2 were measured. Reference values below. Most important factor for power tube matching is transconductance (also known as mutual conductance - Gm). It is parameter that tells how well matched are tubes for AC signals and also a good indicator of tube vitality (as a parameter that falls quickly when tube wears out). Negative grid voltage shows how well tubes are matched for DC currents. More negative value = stronger emission. Minor variations are however of less importance, since it will be balanced out, either via manual bias or via automatic bias (with cathode resistors). Measuring tubes at constant anode current is the professional method, although many emission testers rely simply on measuring tube current at constant grid voltage. Remember that in manufacturer datasheet, transconductance is always stated for a certain operating point (for EL34 it is Ia = 100 mA).NoDate codeBatchProduction date decodedConditionShorts testGas testUg1 [V]
measured at Ua = 250 V Ug2 = 250 V Ia = 100 mAIg2 [mA]
measured at Ua = 250 V Ug2 = 250 V Ia = 100 mASa [mA/V]
measured at Ua = 250 V Ug2 = 250 V Ia = 100 mA% nominal SaNotesB1WL128Apr read comment in the photo shows four subsequent tubes to clearly show the details. These fours are not matched quads, in any way, they are just consecutive numbers. When you place an order, please let me know which tubes you want to get. I can also help you with technical advice on selecting the most optimal match, if you wish.
General Information:I\'ve been a collector of vacuum tubes for many years. Vintage electronics, radio engineering, and amplifier design have been my passions. Over the years, I\'ve collected thousands of vintage parts, mostly from the tube era and originating from Eastern Europe. Since I started designing tube amplifiers professionally, I no longer feel like soldering in my free time because I do it at work. I\'ve decided to sell my long-standing collection. I\'m not a dealer, nor am I trying to make a fortune. I want to honestly sell items I\'ve accumulated over the years, primarily of collector\'s value to enthusiasts like myself.
Most of the tubes I sell are NOS (new old stock), often also NIB (new in box). Some tubes are used, but fully tested and functional, and this fact is always stated in the sale. This applies primarily to more valuable types, such as the EL34. I don\'t sell used tubes of less valuable types in individual listings. Although I do have some, listing and processing the transaction would take more time than it\'s worth. I\'ll probably do group sales with a mix of used tubes later.
I don\'t sell used tubes as NOS, although after browsing current items, I see that this is common practice. Having been involved in this industry for so many years, I can easily tell from a distance whether a tube has been used. When you buy from me, you\'ll be told honestly whether it\'s used, new from old stock (NOS), or new in box (NIB). Less valuable tubes sold in NOS or NIB condition are usually not measured – this takes a lot of time. By purchasing unmeasured tubes, you acknowledge that I offer no warranty – this is only for tubes I have measured.
When I sell NOS tubes, but without individual boxes (not NIB), that means that I got them either directly from bulk boxes or from spare parts for scientific instruments. I shall repeat: I do not sell used tubes as NOS, so don\'t be afraid tubes without boxes. Also, they are generally listed cheaper than NIB tubes.