Jump to content

Settings for testing 5998 tubes in a tube tester?


Recommended Posts

Raffy is looking for a pair of TS 5998's for his SP and I have a pair that are supposed to be NOS. I would be happy to help him out but I don't know how to test these on my tube tester. I have a B&K 747B. I tried testing them with the 6as7 settings but they both test low this way. Since they are not equivalent to the 6as7's, I am not so surprised (I think this has happened with every pair of 5998's I have tested this way). So can anyone help me/us out? Pretty please.

Link to post
Share on other sites

Shelly,

Here's a piece of the 747 tube setup sheet, at least according to the Boat Anchor Archive, which is usually pretty correct. I've highlighted the 5998 settings, but since I've never used a 747 tester I can't really tell if they make sense.

5998

n_maher-albums-random-stuff-picture2592-5998.jpg

Here's the 6AS7 info, which maybe you can match to your manual and see if they are the same. That might serve as a good check that the 5998 data is correct.

n_maher-albums-random-stuff-picture2593-6as7.jpg

Link to post
Share on other sites

Thanks Nate. The 6AS7 data is the same as in my manual. I will try those settings for the 5998. The only difference seems to be the sensitivity setting. Since it should be set lower on the 5998, doesn't this means that the tubes should actually test lower than they would on the 6AS7 settings or am I oversimplifying or inverting things? In any case, I will try it out.

Link to post
Share on other sites

When you say the 5998s test "low" on the 6AS7 settings do you mean they test bad or just lower than 6AS7s? And honestly, I'm not sure how much difference that slight an adjustment on the sensitivity dial on your 747 will make and in which direction.

Also, if you want the full tube setup file that I plucked that info from just let me know. It's a pretty small file and I could email it to you.

Link to post
Share on other sites

They test in the bad region which really surprises me. I haven't tried a pair of 6AS7 in the tester recently. So maybe I should try that (if I have a pair... pretty sure I at least have some 6080's). I also have another pair of 5998's that I could try.

The whole file would be great. I will send you my email by PM.

Link to post
Share on other sites

The 747 is a farily reliable tester, and one that I use regularly. However, it's got some issues. First, there are almost certainly some inaccuracies in the setup manual (endemic to all testers). Second, the tester needs to be calibrated. Instructions are in the manual, but it's a pain in the butt to do it. If your tester is stable for long periods of time, it need not be done often. I keep a set of known tubes just to test periodically. As long as I get the same readings at different times, I'm fairly confident that calibration hasn't drifted. If you do get consistent drift over time, then an overhaul of the tester is probably in order. Finally, there were changes in tube production over the years. Some tube types changed radically. I've had NOS tubes test near 100 for some vintages, and the same type from a different brand/year test at 10%. I also use a Heathkit TT-1A, which can often get accurate readings on tubes that the B&K has trouble with.

Finally, a low reading on the tester does not necessarily mean that a tube is not NOS. Some tubes simply read lower than others. Many will never get near 100 on the 747's scale. If you believe that a tube is NOS, try doing a life-test. The life-test reduces filament voltage by 10%, but also provides a compensating signal boost. A tube is considered "good" if the actual drop in signal is less than 25%. However, NOS tubes can be insensitive to the small drop in voltage (tubes become more sensitive to this with wear). What you might see then is an actual increase in gm when you do the lift test. If you see this increase in gm, or at least no drop, when you perform the life test, the tube is probably near NOS at least, regardless of the actual gm.

You can do this with a larger voltage drop by reducing the filament voltage manually. If you test a 6v tube at 5v, and the results are still fairly consistent (only a minor drop at worst), the tube is likely very strong, again regardless of actual gm.

Edited by hirsch
Link to post
Share on other sites

hirsch: Thanks, this is very useful information. I bought the B&K from Brent Jesse less than a year ago. It was calibrated at that time. I sent the tester back in August because I was getting some low readings on NOS 6sn7 tubes and the meter was bouncing around a but. Brent looked over it and changed the regulator lamp which was causing the meter to bounce. It was also the case that the manual had the wrong settings for the 6sn7 in it (has something in the 60's for sensitivity I think where Brent said it should be 80). Now it is working well with the 6sn7's. I wonder if the manual has the wrong settings for the 6AS7 or 5998. I'll do some more tests tonight. It is useful to know about the life test; I hadn't been paying much attention to it. I wonder how many good tubes I have thrown out in the past because they tested "bad/low" on the B&K. :(

Nate: I may take you up on your kind offer if I cannot get things sorted out locally. Many thanks again.

Link to post
Share on other sites

As mentioned before, it's a good idea to check a tube with another tester before throwing it out. You can confirm your readings with a respected tube seller's results when you buy from them.

Also, make sure you let the tube warm up for some time in the tester. Some old tubes seem to need more time to get up to speed.

I was impatient a few times and didn't wait long enough, less than a minute, and the tubes tested weak. I retested again, letting them warm up in the tester and after using the tubes in the amp. They tested OK.

Link to post
Share on other sites
  • 10 years later...

Hey guy, read the fuckin' manual for the 747 whatever that is?  Assuming it's a B&K unit in which case, just Google. If not...

Also, how the hell do you know the tube is near NOS? Did you buy it back in the 50s? Otherwise welcome to the wonderful world of tubes that can and will fail whenever they want regardless off whether or not they've ever been used. 

  • Like 3
Link to post
Share on other sites
On 10/8/2020 at 10:22 AM, n_maher said:

Hey guy, read the fuckin' manual for the 747 whatever that is?  Assuming it's a B&K unit in which case, just Google. If not...

Also, how the hell do you know the tube is near NOS? Did you buy it back in the 50s? Otherwise welcome to the wonderful world of tubes that can and will fail whenever they want regardless off whether or not they've ever been used. 

Manual read and tube gifted from a friend who's tested this tube as near NOS, strong, good, all of the above. 

Link to post
Share on other sites

The manual ironically has carbon copy same settings for both 6as7g and 5998. That can't be right, 5998 has a much higher gain than the 6as7g. Regardless there seems to be a pattern here with some tubes that the B&K 747 cannot test accurately, or can it? I think an updated manual would be appropriate. Only this company doesn't exist anymore. There is a solution. And I found it last night. PM me for details. Some immature folks here would not understand.

Link to post
Share on other sites
24 minutes ago, Craig Sawyers said:

They are different tubes. The only thing they have in common is the pin out and the fact they are both double triodes.

Buy an AVO. The manual is quite clear about the different settings for the two tubes.

Thanks, the transcunductance is higher on the 5998, so not sure why B&K has the same settings for both but glad I figured it out. 

Link to post
Share on other sites

My experience - the settings on most tube testers for the 5998 and 6AS7 are the same. And bear in mind, the only thing really worth looking at on a tester are shorts and if you're comparing sections or tubes, the relative readings. I've had tubes that tested "bad" that worked for years and tubes that tested "NOS" die the next day.  

  • Like 1
Link to post
Share on other sites
4 hours ago, n_maher said:

My experience - the settings on most tube testers for the 5998 and 6AS7 are the same. And bear in mind, the only thing really worth looking at on a tester are shorts and if you're comparing sections or tubes, the relative readings. I've had tubes that tested "bad" that worked for years and tubes that tested "NOS" die the next day.  

I concur, and thanks for the comment. I truly believe it's an inherited problem with B&K 747 units. It's said it can test ANY tube out there and I believe it can...if you know or have the right settings. I have low tested tubes that sound amazing... I know what your saying here..I laughed out loud when I read it. I shouldn't overthink it as you suggested or buy a Jackson, Hickok, or TV-7? So I figured out how to test these domino plated tubes... hint in photos. 

 

2020-10-11 21.20.51.jpg

2020-10-11 21.25.16.jpg

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...