[JTbbb]

interesting, I'd have to check into this one.Looks almost carbon copy like the Chatham 5998.

You did comment on these which I posted here early 2021.

 

[Electron Mitigator]

I should add that tubes weren't branded at the time of manufacture. They were stored on shelves in very large lots and branded when branded stock ran low. A specific tube, say 6L6GC, wasn't built daily. It might have gotten built once a year or less depending on the tube, the demand and what decade. Branded lots were done in large amounts too, as you wouldn't want to be changing silk screens, etc. after every tube. In the 50's and 60's those dates could be close. In the 70's and 80's there are tubes branded several years after they were built. In the 70's and 80's you can even find close sub's branded as something else that a company needed at the time. On the far side of that you can find tubes built in the 70's branded in the 80's and 90's as STR (Special Tube Reserves). Not all STR tubes are of this ilk, however. In more recent times companies have been using the STR moniker (Special Tube Request) on more recently built tubes. This is a really good place to mention one more thing. Over the last 30 years I have kept every faulty or unusable tube I have encountered. Probably close to 300 tubes. In that box only about 20 tubes are pre 1980 built. With those stats a 60 year old tube has a 15 times greater chance of still being good today compared to a 15 year old tube. Go figure.

Just wanted to make a correction to my stats that is more exact. Out of 282 dead tubes 45 are pre 1980 built and most of those are rectifier and power tubes.

 

[JKDJedi]

Hello there all,

Just what do I have here? Clear top, bottom D Getters and rectangular top mica supports. The rectangular supports I associate with earlier tubes?
I have seen identical tubes like this marked as ‘Chatham Electronics 5998’ ‘Western Electric 5998/421A’ and ‘Western Electric 421A’ and the internals are the same. And now ‘Chatham Electronics 2399’ with the code No 3002399, which I’m thinking should have the date code in it? Then there is also the number 743, which I take as week 43, 1957?

I am guessing we will never fully understand the why’s and wherefore’s of what manufacturer‘s got up to with markings back then. But any ideas on the pedigree of this tube? Thanks

That there could literally be the Mother of ALL 5998/421a/6520 tubes The 2399 is an identical precursor to the Tung Sol 5998?

 

[Cazmok]

Hi all,

Can I ask a question here about testing 5988 tubes? Or, is there a thread specific to this topic?

Thanks!

 

[JKDJedi]

Hi all,

Can I ask a question here about testing 5988 tubes? Or, is there a thread specific to this topic?

Thanks!

Ask away man, think you meant 5998. I'm not all the way sure on this, but not all testers can really test the 5998 accurately. @bcowen could explain this one a lot better than I could, and maybe help you out with your question.

 

[Cazmok]

Ok, cool. Yes, I meant 5998. The Hickok 539C chart has a Gm test for this tube, but has a different test setup to only test emissions on the similar 7236 and 6250. Does Gm really matter much with the 5998 if emissions, shorts, and leakage tests are good? Is the Hickok 539C chart setup maybe not ideal for this tube?

I found some Chatham 5998s, and, of course they test good for emissions, but Gm is a little iffy (not very strong).

Also, I don't currently have an amp to try them in. I am interested in building something around them someday though.

Thanks!

 

[JKDJedi]

Ok, cool. Yes, I meant 5998. The Hickok 539C chart has a Gm test for this tube, but has a different test setup to only test emissions on the similar 7236 and 6250. Does Gm really matter much with the 5998 if emissions, shorts, and leakage tests are good? Is the Hickok 539C chart setup maybe not ideal for this tube?

I found some Chatham 5998s, and, of course they test good for emissions, but Gm is a little iffy (not very strong).

Also, I don't currently have an amp to try them in. I am interested in building something around them someday though.

Thanks!

Well hoping @bcowen can respond but my opinion is that the Gm does count even if everything else checks out. Having said that a low Gm doesn't mean you can't enjoy them in an amp. Just means the life cycle won't be as long as say one with a higher Gm. I say this with the idea that Gm means the overall strength of the tube. It's been awhile since I've talked tube testing and would probably have to read the manual on how to use my tube tester again here soon. I have a few tubes that test at 30% of their strength that sound really good. Just keep them until they retire. Again hopefully Bcowen can confirm or correct what I'm saying here.

 

[Cazmok]

Ok, thanks for your feedback! I think I'd like to try a OTL DIY with these someday.

 

[JTbbb]

Hi all,

Can I ask a question here about testing 5988 tubes? Or, is there a thread specific to this topic?

Thanks!

The testing of tubes is a dark art! So many variables between testers and what they measure, and of course is the tester calibrated. I am able to give you some help with your query as I have sent my 5998/421a to a professional for testing, and he gave me an explanation regarding the results, which I quote below. Also a pic of one of my tubes which is pretty much reading nos, new old stock.

PC Plate Conductance, TC Transconductance. Measured on an AVO VCM 163.

“The PC/TC figures are pretty much a standard that people use to buy / sell valves to give an idea of their ‘goodness’, but in reality the 421A / 5998s are very high power triodes used mainly in Military applications back in the day, so to be honest for the purposes of matching the valves for your preamp, the PC score is really irrelevant, whether a valve can drive 90mA or 40mA is of no consequence when it is in circuit driving 5/6mA, they will pretty much all work until they become noisy or completely exhausted. A more useful parameter to match against is the TC (transconductance, loosely described as the gain of the valve), so use that as a basis for matching, but again don’t worry unduly, because I think you would be hard pushed to hear the difference between a valve with a TC of 9 or 14, but always good practice to get as close as possible. The main criteria with your amp I would suggest is how noisy they are, as that directly affects the listening experience, old valves can become noisy and microphonic, as you know.”

 

[Cazmok]

Interesting, JKDJedi and JTbbb. This makes sense. I think I'll try some other low testing tubes in an amp now. Maybe they'll sound just fine.

 

[leftside]

Transconductance and gm:
https://www.edaboard.com/threads/why-is-transconductance-called-gm.338520/#:~:text=The%20symbol%20'g'%20is%20used,so%20its%20notation%20is%20gm.

The VCM 163 is a great tester. I‘m “biased” tho - as a calibrated 163 seems to give very similar test results to my Amplitrex.

For headphone amps a low testing tube will probably work fine. The only reason I don’t like using low testing tubes is because my OCD kicks in and I start trying to listen to problems/noise with the tubes rather than listening to and enjoying the music. A higher testing tube allows me to relax more.

Yes, a higher testing tube might still be noisy, but I find this case to be rare if all test results are good - and you’ll tend to know it’s noisy as soon as you start listening.

 

[leftside]

The testing of tubes is a dark art! So many variables between testers and what they measure, and of course is the tester calibrated. I am able to give you some help with your query as I have sent my 5998/421a to a professional for testing, and he gave me an explanation regarding the results, which I quote below. Also a pic of one of my tubes which is pretty much reading nos, new old stock.

PC Plate Conductance, TC Transconductance. Measured on an AVO VCM 163.

“The PC/TC figures are pretty much a standard that people use to buy / sell valves to give an idea of their ‘goodness’, but in reality the 421A / 5998s are very high power triodes used mainly in Military applications back in the day, so to be honest for the purposes of matching the valves for your preamp, the PC score is really irrelevant, whether a valve can drive 90mA or 40mA is of no consequence when it is in circuit driving 5/6mA, they will pretty much all work until they become noisy or completely exhausted. A more useful parameter to match against is the TC (transconductance, loosely described as the gain of the valve), so use that as a basis for matching, but again don’t worry unduly, because I think you would be hard pushed to hear the difference between a valve with a TC of 9 or 14, but always good practice to get as close as possible. The main criteria with your amp I would suggest is how noisy they are, as that directly affects the listening experience, old valves can become noisy and microphonic, as you know.”

I’m certainly not a professional when it comes to tube testing, but I’ve tried to learn as much as I can the last couple of years. There is some good advice there - it coincides with what I’ve read from others much more knowledgeable than me in this field. Chris from Amplitrex has been great at answering all my questions.

 

[theredmantra]

I bought a lot of 421a tubes and 3 of them look as expected. One is Tung Sol which was surprising but I saw one like it posted earlier on this thread. My question is what's up with the two without date codes? The font is slightly different from the ones I am used to. Does anyone have insight on these two tubes in particular? I suspect they might be rebranded 5998 tubes. Especially the one in the bottom middle with the side/top getters. Thanks for any insights!

 

[JTbbb]

I bought a lot of 421a tubes and 3 of them look as expected. One is Tung Sol which was surprising but I saw one like it posted earlier on this thread. My question is what's up with the two without date codes? The font is slightly different from the ones I am used to. Does anyone have insight on these two tubes in particular? I suspect they might be rebranded 5998 tubes. Especially the one in the bottom middle with the side/top getters. Thanks for any insights!

The top three are early 421a’s. The date code obviously, but also the top mica supports are rectangular, not curved.

 

[JTbbb]

I bought a lot of 421a tubes and 3 of them look as expected. One is Tung Sol which was surprising but I saw one like it posted earlier on this thread. My question is what's up with the two without date codes? The font is slightly different from the ones I am used to. Does anyone have insight on these two tubes in particular? I suspect they might be rebranded 5998 tubes. Especially the one in the bottom middle with the side/top getters. Thanks for any insights!

The bottom left is early 421a due to the rectangular mica supports. Others will know more about the bottom middle, but I do believe these 421a’s with top and bottom getters have been seen before. As you suspect, the bottom right looks like Tung Sol 5998.

Anyways, that’s my thoughts. But there are many here far more knowledgeable than I.