Sylvanias 7591 NOS vs EH 7591s Break in

[andreas75]

Hi guys long time since i dont post over here....

ok ive got a Mcintosh MC225 and planning to replace output tubes 7591.
I have a quad of electroharmonix 7591 "non" NOS and also
i have 4 Sylvanias 7591 NOS
Id like to know:

1)in terms of hours;which is easier or faster to break in of both: sylvanias vs Electroharmonix.

2) how long does it take aprox in terms of listening hours for the full break in also ...in both cases ¿?

thanx a lot

Andreas

 

[Dandy]

Hi Andreas. I guess not many people here will have the experience of comparing those two tubes from NOS condition.

All I can say is that I recently replaced some good used 7591 tubes with a quad of NOS Sylvania tubes in my rebuilt Heathkit AA50. Once fully warmed up, say after 30 minutes, I didn't notice any difference in sound quality.

What differences would you expect to observe after burn in?

 

[tubeactive]

With output tubes, my concern is potential burn-out rather than burn-in...LOL...

Small signal tubes and capacitors sometimes deserve "burn-in" times before making critical, sound describing comments.

Output tubes usually stabilize re: voltages and characteristics within about 12 minutes after turn-on, presuming correct bias, filament and high voltages.

 

[62caddy]

I would stop worrying and just enjoy the music.

I think some audiophiles are doing their listening pleasure a disservice by obsessing over trivialities.

 

[primosounds]

Caddy, makes an excellent point. Tubes don't have much of a "break in" at all. It is the circuit that is the major difference to sound. The tubes just do what they do after they reach their stabilized operating conditions.

 

[apachef1]

Stay with the Sylvania's if you have to make a choice - They are the original Westinghouse designed tube, EH will work fine, but I believe they run a little hotter compared to the Sylvania. Other option, the new Tung-sol 7591 built to the WH design and work fantastic in the Mc-225. I would save the Sylvania's, very rare to find anything NOS or ANOS.

 

[primosounds]

Stay with the Sylvania's if you have to make a choice - They are the original Westinghouse designed tube, EH will work fine, but I believe they run a little hotter compared to the Sylvania. Other option, the new Tung-sol 7591 built to the WH design and work fantastic in the Mc-225. I would save the Sylvania's, very rare to find anything NOS or ANOS.

I agree with you about the Sylvanias are a superior tube. But they are not made by Westinghouse unless there are marked on the top of the tube " 7591 made in USA" with a row or 2 of dots. Sylvania made their own 7591 which was marked 7591A on the side of the tube.

 

[apachef1]

I didnt say they were original WH tubes. WH contracted Sylvania and RCA to build the tube to the exact WH standard. RCA manufactured the 7591 branded WH, Sylvania may have done the same. I think GE is in the the group, I seem to remember having a few coin based 7591's, its a twisted web for this tube.

The new Tungsols are essentially the same build, EH is not exactly the same spec and wont hurt the bank as much.

 

[triode17]

All parts need break-in time, or maybe it should be called a stability time. In general, I find that 8-12 hrs, in two hour sessions will settle any initial inconsistencies. Amps. that are freshly rebuilt, new tubes all around tend to sound thin in the Bass and a bit screechy in the high end. When I needed replacement 7591s for my Scott LK-72, I used a matched quad of JJ's. Some don't like them, I do. Only ever had a problem with the JJ 5AR4 rectifier that arc'd.

 

[62caddy]

Regarding so-called "NOS" tubes, it's also important to bear in mind many of these were new tubes that hadn't met spec and were rejected when they were new, but never tossed out. This was especially true in the waning days of tube manufacture as quality began to deteriorate because when tube production was no longer profitable, it made little business sense to invest in the tooling needed to maintain quality.

In The McIntosh Clinics book, Dave O'Brien claimed that out of a brand new box of 50 Sylvania 7591s, he could not find 4 that would work properly in a McIntosh MA230. Therefore never assume an older tube will perform well simply because it's "NOS"; in some cases the equipment will perform better with modern production tubes even though they aren't from one of the respected tube tube manufacturers of the past.

 

[apachef1]

Regarding so-called "NOS" tubes, it's also important to bear in mind many of these were new tubes that hadn't met spec and were rejected when they were new, but never tossed out. This was especially true in the waning days of tube manufacture as quality began to deteriorate because when tube production was no longer profitable, it made little business sense to invest in the tooling needed to maintain quality.

In The McIntosh Clinics book, Dave O'Brien claimed that out of a brand new box of 50 Sylvania 7591s, he could not find 4 that would work properly in a McIntosh MA230. Therefore never assume an older tube will perform well simply because it's "NOS"; in some cases the equipment will perform better with modern production tubes even though they aren't from one of the respected tube tube manufacturers of the past.

I did hear that over the years. This was an oddball tube only used in a handful of applications. I purchased a quad of WH years ago from Tubeworld and they were fantastic. I was disappointed when their end of life came to be, about 5000+ hours 12 years of reliable service in the Mc-225. I purchased the very new Tung-sols for replacement and couldn't be happier with their performance, I feel they are sligtly better tone vs the WH. I had one red-plate after a year, purchased a replacement, and no issues three years into regular service. No need to chase down questionable so call NOS 7591's on Flea-bay

 

[primosounds]

Regarding so-called "NOS" tubes, it's also important to bear in mind many of these were new tubes that hadn't met spec and were rejected when they were new, but never tossed out. This was especially true in the waning days of tube manufacture as quality began to deteriorate because when tube production was no longer profitable, it made little business sense to invest in the tooling needed to maintain quality.

I have not heard that "story" before regarding factory Sylvania tubes. It makes no sense to me. During the heyday of tube manufacturing i have read actual factory workers relating how the rejects get summarily destroyed if they did not meet specs off the test racks. It makes more sense that in order to protect their reputation Sylvania would destroy all the rejects.
Now, being so called NOS tubes today is a total crap shoot as there is no real way to ascertain the provenance of the actual amount of hours on the tubes. And i have a whole box of NOS tubes that are stone cold dead, for what ever reason. NOS tubes should be purchased from trusted vendors to be sure you are not getting ripped off.

 

[c_dk]

After hosting a Mac smp clinic with DOB back in the late 80s we bench tested 3 MC240s that I had.

Found 4 OK tubes out of the 12 but was therefore short 8 tubes.

David sent me his last 8 GE6L6GCs that came out of the old RCA plant that I understand GE obtained when they aquired RCA.

The 8 tubes were culled out of a batch of 100 that he was sent from the plant that I believe was in Kentucky. The MC240s are long gone but I still have the tubes.

I had purchased 4 relabeled Russian tubes from the Canadian firm Groove Tube, there was a trade embargo, and since Gordon Gow was coming for a visit in a few months he did not think he would take too kindly having these amps functioning with these gray market tubes. So he sent me the last 8 the factory had.

 

[primosounds]

I did hear that over the years. This was an oddball tube only used in a handful of applications. I purchased a quad of WH years ago from Tubeworld and they were fantastic. I was disappointed when their end of life came to be, about 5000+ hours 12 years of reliable service in the Mc-225. I purchased the very new Tung-sols for replacement and couldn't be happier with their performance, I feel they are sligtly better tone vs the WH. I had one red-plate after a year, purchased a replacement, and no issues three years into regular service. No need to chase down questionable so call NOS 7591's on Flea-bay

Actually 7591 are not oddball tubes. They were developed as a way to get high power, up to 35 watts, in an envelope that was the same size as a 6v6. That is an amazing feat for a vacuum tube. Since they were a smaller dimension than a 6l6gc or el34 , they were employed in tens of thousands of integrated amps by Fisher, Scott, Eico, McIntosh, as well as many thousands of guitar and organ amps. Unfortunately, it showed up at the tail end of vacuum tubed audio and when people realized that the tubes for their amps were not being produced any longer the hoarding began.
Your story shows exactly why the original USA made 7591 are superior than the current production. 1 original WH quad lasting 50+ years and the replacement that burned out after 1 year. It probably makes more sense to get a matched quad of new productions since it would be impossible to get a matched quad of NOS tubes, unless you buy maybe 8 to 12 old stock and make matched pairs that way. Of course that would cost more but what price for superior product and reliability. When tubes go "Fukushima" there is a high likelihood of collateral damage. Sourcing a new output or power trans will be no picnic.

 

[apachef1]

Actually 7591 are not oddball tubes. They were developed as a way to get high power, up to 35 watts, in an envelope that was the same size as a 6v6. That is an amazing feat for a vacuum tube. Since they were a smaller dimension than a 6l6gc or el34 , they were employed in tens of thousands of integrated amps by Fisher, Scott, Eico, McIntosh, as well as many thousands of guitar and organ amps. Unfortunately, it showed up at the tail end of vacuum tubed audio and when people realized that the tubes for their amps were not being produced any longer the hoarding began.
Your story shows exactly why the original USA made 7591 are superior than the current production. 1 original WH quad lasting 50+ years and the replacement that burned out after 1 year. It probably makes more sense to get a matched quad of new productions since it would be impossible to get a matched quad of NOS tubes, unless you buy maybe 8 to 12 old stock and make matched pairs that way. Of course that would cost more but what price for superior product and reliability. When tubes go "Fukushima" there is a high likelihood of collateral damage. Sourcing a new output or power trans will be no picnic.

Fully agree, The 7591 was really developed for audio amplifiers unlike most tubes that had other applications, military, medical, Tv... Western electric is the only other tube manufacturer that made tubes mainly but not exclusively for audio type gear. That is really the odd factor to the 7591, there may be a few others, none that really come to mind.

 

[62caddy]

I have not heard that "story" before regarding factory Sylvania tubes. It makes no sense to me. During the heyday of tube manufacturing i have read actual factory workers relating how the rejects get summarily destroyed if they did not meet specs off the test racks.

I'm sure Dave O'Brien had no reason to fabricate his experience with Sylvania tubes in his published memoir, The McIntosh Clinics.

Keep in mind, this was toward the final days of tube production, not the "heyday" when quality control was more closely monitored. He specifically mentioned this to illustrate the serious decline in tube quality to the point that McIntosh could no longer guarantee tube equipment would meet original performance spec. On another occasion, he placed a large order with another major tube manufacturer but the manufacturer refused to fulfill it. "The writing was on the wall and the vacuum tube industry was dying", he said.

 

[primosounds]

Maybe so, but i still doubt that the factory would allow all the tubes that were made to just go straight into boxes without any testing.