[leftside]

A little more info....

The 4-digit Special Purpose code designation for WE's 421A, "5998," was reserved with the RTMA (Radio-Televsion Manufacturers Association) in August, 1950. Thus, there were no 5998's before that date. And the very first 5998's were in fact, WE 421A. It's not clear when WE and Chatham worked out an arrangement allowing Chatham to manufacture the 5998. The earliest 5998s I have are dated 1957, week 10 (7-10). If anyone has older ones, please let me know.

I always thought that must be the case (i.e. 5998 were 421A) and not the other way around, as I have WE 421A from 1984 and TungSol no longer existed as a company then.

 

[gibosi]

Where do the 6520 tubes with domino plates fit in?

For reasons we do not understand, it appears that on occasion Tung-Sol deliberately mislabeled 5598 as 6520. Perhaps a customer ordered 6520 and Tung-Sol didn't have any in stock? So a 5998, which is after all a premium tube, was mislabeled and shipped out.

But again, this is just a guess.

 

[gibosi]

My pair of Tung-Sol 5998 has code 55-35. So must be 1955 week 35?.

Probably so... But I would expect to see them labeled as Chatham, not Tung-Sol. And that date code implies they were JAN tubes? I would like to see a picture of the base.

 

[VanHai]

Probably so... But I would expect to see them labeled as Chatham, not Tung-Sol. And that date code implies they were JAN tubes? I would like to see a picture of the base.

The label is Tung-Sol, not JAN and the code is not on the base, but edge on the top of the glass 55-35 then 5998 then 5.

 

[gibosi]

The label is Tung-Sol, not JAN and the code is not on the base, but edge on the top of the glass 55-35 then 5998 then 5.

I'm not sure I understand "the code is...on the edge on the top of the glass". I have twelve 5998, manufactured between 1957 and 1969. None of them have any text or graphics printed on the glass, only on the base. So while it seems likely that yours were manufactured in 1955, every 5998 I have seen has text and graphics printed on the base, not the glass. I would really like to see a good picture of yours showing text and graphics and the internal construction. Construction is very helpful when dating these tubes.

 

[VanHai]

I'm not sure I understand "the code is...on the edge on the top of the glass". I have twelve 5998, manufactured between 1957 and 1969. None of them have any text or graphics printed on the glass, only on the base. So while it seems likely that yours were manufactured in 1955, every 5998 I have seen has text and graphics printed on the base, not the glass. I would really like to see a good picture of yours showing text and graphics and the internal construction. Construction is very helpful when dating these tubes.

Here are the pictures. It is very hard to photograph and see the graphics clearly. Hope these help, i missed reading the top code. It should be 5538.

 

[gibosi]

Thank you! And yes, I have no doubt that these were manufactured in 1955, week 38. And the code printed on the right tube base indicates that they were then packed into a box and shipped in 1956, week 6.

 

[raindownthunda]

Listening to TFK 6080's tonight when I noticed the first tube has two heaters lit up, while the second tube only has one heater lit up. Both channels are producing audio and they seem to be at around the same volume, no obvious differences between the channels.

Has anyone experienced this before or have any insight into how a tube with 1 of 2 heaters being dead can still produce sound? Does it just mean it's on it's way out? Is there a reason to avoid using it?

 

[LobalWarming]

Listening to TFK 6080's tonight when I noticed the first tube has two heaters lit up, while the second tube only has one heater lit up. Both channels are producing audio and they seem to be at around the same volume, no obvious differences between the channels.

Has anyone experienced this before or have any insight into how a tube with 1 of 2 heaters being dead can still produce sound? Does it just mean it's on it's way out? Is there a reason to avoid using it?

I can't say for sure. Best to send both the good one and the half-heated one to me for the definitive analysis.

However, since your BH+ uses one or more 6080s per channel, the sections are operated in parallel. The tube with only one heated section would have to perform the work of two sections. Which means it probably won't last as long as one with both sections in operation. Again this is only my preliminary hypothesis. Sending them to me will be the only way (for me) to know for sure.

 

[raindownthunda]

I can't say for sure. Best to send both the good one and the half-heated one to me for the definitive analysis.

However, since your BH+ uses one or more 6080s per channel, the sections are operated in parallel. The tube with only one heated section would have to perform the work of two sections. Which means it probably won't last as long as one with both sections in operation. Again this is only my preliminary hypothesis. Sending them to me will be the only way (for me) to know for sure.

Thanks for the (almost?) free advice! I would have thought there would have been some noticeable difference in sound, so was surprised that the half-heated tube was managing to keep up. Makes sense it would have a much shorter life though...

I got this lot a while back from an ebay gamble - no real description, and they appear to have seen some good use... NOS prices for these tubes are too crazy, not worth it IMO! I went through the rest of the lot and happened to find a 2nd TFK 6080 that also has only a single heater powering up, as well as one with both heaters working. Coincidence multiple tubes with dead heaters in such a small sample? Perhaps a common failure with these tubes? Either way, I've set the "half-heated" tubes aside as a sad pair that can limp along together, hand-in-hand towards their inevitable demise.

 

[LobalWarming]

Thanks for the (almost?) free advice! I would have thought there would have been some noticeable difference in sound, so was surprised that the half-heated tube was managing to keep up. Makes sense it would have a much shorter life though...

I got this lot a while back from an ebay gamble - no real description, and they appear to have seen some good use... NOS prices for these tubes are too crazy, not worth it IMO! I went through the rest of the lot and happened to find a 2nd TFK 6080 that also has only a single heater powering up, as well as one with both heaters working. Coincidence multiple tubes with dead heaters in such a small sample? Perhaps a common failure with these tubes? Either way, I've set the "half-heated" tubes aside as a sad pair that can limp along together, hand-in-hand towards their inevitable demise.

You make it sound almost romantic.

 

[mordy]

Thanks for the (almost?) free advice! I would have thought there would have been some noticeable difference in sound, so was surprised that the half-heated tube was managing to keep up. Makes sense it would have a much shorter life though...

I got this lot a while back from an ebay gamble - no real description, and they appear to have seen some good use... NOS prices for these tubes are too crazy, not worth it IMO! I went through the rest of the lot and happened to find a 2nd TFK 6080 that also has only a single heater powering up, as well as one with both heaters working. Coincidence multiple tubes with dead heaters in such a small sample? Perhaps a common failure with these tubes? Either way, I've set the "half-heated" tubes aside as a sad pair that can limp along together, hand-in-hand towards their inevitable demise.

I always wondered about parallel wired dual triode driver tubes. Many amps do just fine with a single dual triode, so why have a double setup with two tubes in parallel? One dual triode = two channels.
The Feliks amps such as the Elise/Eiuforia have parallel dual triode drivers- sometimes I wondered if it is only for aesthetics; a more symmetrical look with four tubes instead of three.
Re the TFK tubes I would make a pair of the single heater tubes and use them without worries.

 

[bcowen]

Thanks for the (almost?) free advice! I would have thought there would have been some noticeable difference in sound, so was surprised that the half-heated tube was managing to keep up. Makes sense it would have a much shorter life though...

I got this lot a while back from an ebay gamble - no real description, and they appear to have seen some good use... NOS prices for these tubes are too crazy, not worth it IMO! I went through the rest of the lot and happened to find a 2nd TFK 6080 that also has only a single heater powering up, as well as one with both heaters working. Coincidence multiple tubes with dead heaters in such a small sample? Perhaps a common failure with these tubes? Either way, I've set the "half-heated" tubes aside as a sad pair that can limp along together, hand-in-hand towards their inevitable demise.

It's possible that you can bring that dead heater back to life by resoldering the pins (if you have the means to do that). It's usually the cathode coating wearing away that causes a tube to die naturally, and not the filament. If a filament isn't lit, it's either broken internally (possible), OR it could be that its lead is not making good contact inside the pin due to degraded solder. Common issue these days with Russian tubes from the '50's, and I've had a few US-made tubes with that problem.

 

[mordy]

It's possible that you can bring that dead heater back to life by resoldering the pins (if you have the means to do that). It's usually the cathode coating wearing away that causes a tube to die naturally, and not the filament. If a filament isn't lit, it's either broken internally (possible), OR it could be that its lead is not making good contact inside the pin due to degraded solder. Common issue these days with Russian tubes from the '50's, and I've had a few US-made tubes with that problem.

I have had such problems with degraded solder in Melz tubes from the 60’s and Sylvania tubes from the 40’s.

 

[triod750]

And I have 'repaired' heaters by heating the heater pins for about a minute with a solder gun...