[toddc2]

Sometimes one tube glows brightly and the glow in the other one is barely discernable...

Yes I have found the same to be true, particularly with driver tubes.

 

[Odin412]

Do you think it helps to run tubes without the load of headphones for a while? I know somebody who has a setup where he lets new tubes sit with the heaters on for three days before he starts to use them.

I think that for a transformer-coupled tube amp that is perfectly fine, but I read somewhere that you shouldn't leave an OTL tube amp on without a load connected. I have a transformer-coupled Woo Audio WA6 and I leave that on without a headphone connected with no issues, but my WA3 is an OTL amp and that's where i use my resistor-loaded plug if I leave it without a headphone.

 

[gibosi]

I think that for a transformer-coupled tube amp that is perfectly fine, but I read somewhere that you shouldn't leave an OTL tube amp on without a load connected. I have a transformer-coupled Woo Audio WA6 and I leave that on without a headphone connected with no issues, but my WA3 is an OTL amp and that's where i use my resistor-loaded plug if I leave it without a headphone.

My understanding is different. Transformer-coupled amps usually require a connected load, whereas it doesn't matter for OTL amps. But, perhaps we can't generalize? I can say that Glenn, the maker of my Glenn OTL, told me no load is required for my amp. So perhaps it is best to check with the manufacturer in each case.

 

[L0rdGwyn]

There were a number of folks in the Glenn forum who reported that their headphones were damaged by the loud popping sounds of 5998's as they warmed up. The consensus advice of those folks was to let 5998's warm up for about 30 minutes before connecting headphones to protect ears and headphone drivers.

This type of arcing often occurs not because the tubes are defective, but due to bad startup conditions. Tubes have maximum voltage ratings between their electrodes, for example there should not be more than 100V max between a 5998s cathode and its heater. Likewise, large voltage differences between grid and cathode should be avoided. Both of these things can cause arcing inside the tube. Depending on the circuit topology, during startup, these ratings might be exceeded as the tubes begin to conduct, which I believe is the cause of a large majority of the arcing issues associated with the 5998. I haven't looked at the SRPP startup conditions in detail, but that may be the reason why it is happening in the GOTL. I'll investigate. It certainly is an issue in direct-coupled cathode follower type 6AS7G OTLs. One solution is to put a diode connected between the output tube's grid and cathode so the voltage is clamped during startup.

I think that for a transformer-coupled tube amp that is perfectly fine, but I read somewhere that you shouldn't leave an OTL tube amp on without a load connected. I have a transformer-coupled Woo Audio WA6 and I leave that on without a headphone connected with no issues, but my WA3 is an OTL amp and that's where i use my resistor-loaded plug if I leave it without a headphone.

Most OTL amplifiers have a load resistor on the output in parallel with the headphone jack. The value is often much higher than the nominal impedance of the headphone, so in parallel, the load is predominantly the headphone, the parallel resistor will steal a very small amount of current. So if the headphone is unplugged, there is still a load connected. This is very common.

My understanding is different. Transformer-coupled amps usually require a connected load, whereas it doesn't matter for OTL amps. But, perhaps we can't generalize? I can say that Glenn, the maker of my Glenn OTL, told me no load is required for my amp. So perhaps it is best to check with the manufacturer in each case.

Correct, typically it is a transformer coupled amplifier that should always have some load connected, but OTLs typically have a parallel load resistor as well.

 

[Monsterzero]

This type of arcing often occurs not because the tubes are defective, but due to bad startup conditions. Tubes have maximum voltage ratings between their electrodes, for example there should not be more than 100V max between a 5998s cathode and its heater. Likewise, large voltage differences between grid and cathode should be avoided. Both of these things can cause arcing inside the tube. Depending on the circuit topology, during startup, these ratings might be exceeded as the tubes begin to conduct, which I believe is the cause of a large majority of the arcing issues associated with the 5998. I haven't looked at the SRPP startup conditions in detail, but that may be the reason why it is happening in the GOTL. I'll investigate. It certainly is an issue in direct-coupled cathode follower type 6AS7G OTLs. One solution is to put a diode connected between the output tube's grid and cathode so the voltage is clamped during startup.



Most OTL amplifiers have a load resistor on the output in parallel with the headphone jack. The value is often much higher than the nominal impedance of the headphone, so in parallel, the load is predominantly the headphone, the parallel resistor will steal a very small amount of current. So if the headphone is unplugged, there is still a load connected. This is very common.



Correct, typically it is a transformer coupled amplifier that should always have some load connected, but OTLs typically have a parallel load resistor as well.

So, about those bettas.....

 

[mordy]

I think that for a transformer-coupled tube amp that is perfectly fine, but I read somewhere that you shouldn't leave an OTL tube amp on without a load connected. I have a transformer-coupled Woo Audio WA6 and I leave that on without a headphone connected with no issues, but my WA3 is an OTL amp and that's where i use my resistor-loaded plug if I leave it without a headphone.

The person I referred to who lets the new tubes burn in for three days uses an external power source to sockets and does not use an amplifier to burn in the tubes.

 

[Odin412]

Thanks for the responses above! I checked the manual for my WA3 and it doesn't say anything about not running the amp without headphone connected, so I guess the moral of the story is to ignore random advice online and RTFM. Oh well, at least I got to practice my soldering skills...

 

[leftside]

Thanks for the responses above! I checked the manual for my WA3 and it doesn't say anything about not running the amp without headphone connected, so I guess the moral of the story is to ignore random advice online and RTFM. Oh well, at least I got to practice my soldering skills...

Definitely ignore the random advice, but you can trust the good fellas @L0rdGwyn for technical advice and @gibosi for general all around tube knowledge.

 

[bcowen]

Yea that's what I basically did, was just curious what you guys think about this.

As for others, I have 2 more pairs

But interesting thing about these is that they sure do not sound the same at all, to my ears.

I have 5998's branded Chatham and those sound quite transparent, while the other pair branded Tung Sol sounds sort of bloated in bass and this JAN branded 5998's do not have the bass bloat and sound more open/expansive. So out of the 3 pairs, this pair with this defective tube, sounds the best

One more thing I was thinking about was... is it possible that this problem goes away after some burn-in ? 100-200 hours ? Seller claimed the tubes are NOS and except for the pieces in this one tube, they both look excellent so they might actually be NOS.

Assuming those little pieces are actually chunks of mica (which won't hurt anything), then it's much more likely the noise you're getting is due to degraded solder in the pins. I have four TS 5998's, and three of them had varying levels of random rustling and squealing before resoldering. Afterwards? No noise at all. I've had two Chatham 6AS7G's with the same problem and fix. The pin solder issue pops up more frequently with the 1950's era Russian tubes (Melz, Fotons, etc), but I'm beginning to think Tung Sol must have bought their solder from Russia back then.

 

[bcowen]

Definitely ignore the random advice, but you can trust the good fellas @L0rdGwyn for technical advice and @gibosi for general all around tube knowledge.

+1 on that!

 

[Flisker]

Assuming those little pieces are actually chunks of mica (which won't hurt anything), then it's much more likely the noise you're getting is due to degraded solder in the pins. I have four TS 5998's, and three of them had varying levels of random rustling and squealing before resoldering. Afterwards? No noise at all. I've had two Chatham 6AS7G's with the same problem and fix. The pin solder issue pops up more frequently with the 1950's era Russian tubes (Melz, Fotons, etc), but I'm beginning to think Tung Sol must have bought their solder from Russia back then.

So I ran the tube basically all day everyday since the post, when it was squeaking/whining I would just move that one headphone of my ear

And I think after 30 something hours, it basically stopped completely. So that's quite interesting.

Added: I just thought... what the heck, if after 100 hours it's doing the same quite loud squeeking noise, I will just write it off complete/give it to a friend for resoldering or trying something more exotic with it, but as seller claimed those to be NOS and micas looked shiny/unused. (still not sure if this is good indicator or not, whether the tube is used or NOS, maybe someone can chime in on the topic ) And the tubes sounded probably the best out of all pairs I got, when not making the noise, it seemed to be worth a try.

Maybe this info helps someone with similar problem in the future

 

[Thaddy]

I have a question about these Tung-Sol branded 6AS7G's I have. I got them a while ago and only paid $40 for the pair. They have the '322' Tung-Sol factory code, however their internal construction does not look like other Tung-Sol 6AS7G's I've seen. These appears to be the exact same construction as the 1950's RCA black plates, with the flaps/protectors above and below the plates and a top getter. Think these are just rebranded RCA's?

I have many pairs of RCA 6AS7G's wearing various branding (Sylvania & Raytheon) but always thought Tung-Sol made their own tubes. I just noticed these tonight while going through some older tubes.

 

[bcowen]

I have a question about these Tung-Sol branded 6AS7G's I have. I got them a while ago and only paid $40 for the pair. They have the '322' Tung-Sol factory code, however their internal construction does not look like other Tung-Sol 6AS7G's I've seen. These appears to be the exact same construction as the 1950's RCA black plates, with the flaps/protectors above and below the plates and a top getter. Think these are just rebranded RCA's?

I have many pairs of RCA 6AS7G's wearing various branding (Sylvania & Raytheon) but always thought Tung-Sol made their own tubes. I just noticed these tonight while going through some older tubes.

Those most definitely look like RCA's. I have a Chatham branded RCA myself. but don't have any TungSol branded 6AS7G's.

 

[Thaddy]

Those most definitely look like RCA's. I have a Chatham branded RCA myself. but don't have any TungSol branded 6AS7G's.

That's exactly what I thought as well. It was a "Huh!" moment, I didn't realize I had a pair of Tung-Sol branded RCA's. Now, I just checked my Chatham 6AS7G's and they are closer to what I'd expect. The plates extend through the top and bottom mica and they have double bottom getters. I'm not sure if the copper rods are unique to Tung-Sol, I've seen them in silver as well. I think my Tung-Sol 6080's also have the copper rods.

These are some of my favorite tubes, I like them just as much as the top and bottom getter 5998's, and I only paid $40 for the pair before they became popular

 

[maxpudding]

That's exactly what I thought as well. It was a "Huh!" moment, I didn't realize I had a pair of Tung-Sol branded RCA's. Now, I just checked my Chatham 6AS7G's and they are closer to what I'd expect. The plates extend through the top and bottom mica and they have double bottom getters. I'm not sure if the copper rods are unique to Tung-Sol, I've seen them in silver as well. I think my Tung-Sol 6080's also have the copper rods.

These are some of my favorite tubes, I like them just as much as the top and bottom getter 5998's, and I only paid $40 for the pair before they became popular

I’ve seen some Japanese branded tube (NEC) with copper rods 6AS7s, but without the getters.