Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: birt on March 17, 2012, 09:40:38 am
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i was looking in my tubes box to see what 6SL7's to use in my ampeg B15 clone and came across some NOS Industro 6SL7GT's. i've never heard of this brand and was wondering if i should use them.
The plates look different from the other 6SL7's i have. They are black and made from one piece of metal instead of 2 pieces pressed together on the sides. they are not in one line either.
i'm hesitating to use old tubes in a new build but i don't have any current porduction 6SL7's. Adzam, Sylvania, Tungsol, GE, Haltron and Raytheon (most NOS) is what i have. and these Industro's.
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put one in its socket with no HV and see hows the heaters reacting. If you have a HV fuse, throw the HV ( standby ) switch and if there is a short, the fuse will blow up. If not, check your voltages and if within a reasonable range, the tube is good. That's how I test my tubes.
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i was looking in my tubes box to see what 6SL7's to use in my ampeg B15 clone and came across some NOS Industro 6SL7GT's. i've never heard of this brand and was wondering if i should use them.
I haven't heard of them either. But "Industro" might be the same as a company of the same name, claiming to be in business since 1969, which makes pumps and industrial equipment. In the old days (maybe today too), if you bought enough tubes the manufacturer would put any name on them you wanted.
Can you post a picture?
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i just found out most of them look exactly the same as JAN Sylvania. except for one that has smoked glass and the normal shape of black plates. so i guess they rebranded.
i also found this:
http://frank.pocnet.net/other/Industro/Industro_TubesForIndustry.pdf (http://frank.pocnet.net/other/Industro/Industro_TubesForIndustry.pdf)
so they seem to be made in USA military spec tubes.
this picture is pretty close to what they look like:
http://2.bp.blogspot.com/_FiPeJotjqpw/TA8Hw8GR-qI/AAAAAAAAAWw/431v1KpFzQI/s1600/6SL7+025.JPG (http://2.bp.blogspot.com/_FiPeJotjqpw/TA8Hw8GR-qI/AAAAAAAAAWw/431v1KpFzQI/s1600/6SL7+025.JPG)
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Well, the Heintz & Kaufmann tubes pictured are what they claim to be.
However, that construction style (with round plates) is very often seen in 50's Sylvania tubes. A few other manufacturers also used that style.
Any date codes/numbers on the tube? If you see "312" then it's a Sylvania tube.
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this is one of 3 identical Industro's. print on the glass says 6SL7GT H4. a Sylvania that looks the same and has 8C 966 A on the other side of the base and an Industro with the 'normal flat plates' and dark glass with 6SL7GT CR.
i can't find any other codes or numbers.
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Yeah, those are very likely Sylvania, Tung Sol or RCA; probably one of the first two. It helps that your Sylvania looks exactly the same.
The octagon around the tube designator was used by the three companies I mentioned. Guessing from the date code, "Industro" is probably one of many "tube companies" that sprang up after WWII, which rebranded surplus tubes for sale. Typical receiving types were pretty inexpensive (as your linked price sheets shows).
But imagine buying some of the magnetrons in there!! Some of those weren't far from the price of a car in those days. Then again, if you were operating a radar in those days, you probably had the money to buy them.
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the nicest thing about that price list is that company stamp. they moved one street but are still in business selling tubes here in Brussels.