[mordy]

A normally microphonic NU 12SL7 in the MK9...piece of pool noodle foam keeps it listenable...

Was just listening to some Steve Grossman (Tenor Sax man) when I realized that the gear....tubes...amp...cans, had all disappeared!
I was there, man!

This NU is a fantastic sounding tubular device. Look at those beautiful copper rods

Happy Thursday, Y'all!

Was looking for a microphonic tube to try your ingenious hack - found a National Union 6F8G that I had problems with in the past. (The tube is labeled Philco and was made the 3rd Q 1943 but it is a NU rebrand).
I once tried to put on a piece of high temperature self sealing silicone tape to cure the microphponics but it did not help.
Could not find my Glenn box with the pool noodles ATM, but found a similar piece of foam pipe insulation and sliced off a piece - was surprisingly easy.

Happy to report that it works - I am able to adjust the volumes on the headphone amp and power amp so that I don't hear any microphonics.
Score a win for JV!

 

[Shane D]

… was? …

Then I had to go the Clears. And then I had to go to the LP. These decisions are out of my hands.

 

[JazzVinyl]

Was looking for a microphonic tube to try your ingenious hack - found a National Union 6F8G that I had problems with in the past. (The tube is labeled Philco and was made the 3rd Q 1943 but it is a NU rebrand).
I once tried to put on a piece of high temperature self sealing silicone tape to cure the microphponics but it did not help.
Could not find my Glenn box with the pool noodles ATM, but found a similar piece of foam pipe insulation and sliced off a piece - was surprisingly easy.

Happy to report that it works - I am able to adjust the volumes on the headphone amp and power amp so that I don't hear any microphonics.
Score a win for JV!

Yeah! Glad to hear it worked for you too @mordy. BTW pool noodles are available at the Dollar Tree...one noodle should cure 'many a dozen' micro-phonic tubes

This clear top NU 12SL7 is positively amazing! So inexpensive and so incredibly good sounding! Easy to find these 12v versions, in true NOS condition.

BTW Mordy...your image is espicially good! Sharp as a tack! Would also be interested in the NU date code info....if you have that handy.

 

[mordy]

Yeah! Glad to hear it worked for you too @mordy. BTW pool noodles are available at the Dollar Tree...one noodle should cure 'many a dozen' micro-phonic tubes

This clear top NU 12SL7 is positively amazing! So inexpensive and so incredibly good sounding! Easy to find these 12v versions, in true NOS condition.

BTW Mordy...your image is espicially good! Sharp as a tack! Would also be interested in the NU date code info....if you have that handy.

Don't know anything about photography. Never had any luck with cameras until they became digital, and then available on cell phones. All I did was to point and shoot with my iPhone, but the technology is such that you get good pictures.
The date code is MR 3U. MR means Manufacturers Replacement. During WW2 most tubes were set aside for the military with some rationed for civilian use. Those tubes got the designation MR. The rationing lasted from 1942 until 1945 so the MR designation dates a tube to those years.
3 means 1943. U is the month. One 12 month sequence went from A until M (skipping the letter I which looks like 1). Another sequence went from N to Z (skipping Q that looks like a 0). Using my built in calculator (my fingers) U = 7 = July.
I have an Arcturus 6N7G tube with the date codes N4 N4. After much searching and finding no answers I decided that the date of manufacture and shipping was the same. N = January and 4 = 1944.
Many Sylvania tubes have two date codes - one for when it was made and one when it was shipped. One code is on the top of the tube or on the glass under the tube designation, and the other on the base near the Sylvania EIA number of 312. An example would be L9M on the glass and 026 on the base.
L = November; 9 = 1949 (M - factory?)
0 = 1950; 26 is the week of the year = June
Tube date codes are very mysterious. Apparently, the Tung Sol date codes indicate the expiration of the warranty, and we still don't even know what the TS letter codes mean. - Somebody solved the GE dots codes...

 

[JazzVinyl]

MK9 PSA:

You see many a set of National Union grey glass on the 'ole famous auction site, like these:

https://www.ebay.com/itm/304689588288

This JV 'Public Service Announcement' is to not fall for the looks! I have tried a couple of these (much cheaper 12v versions) and I am here to say I do not like them in the MK9. They are very thin, brittle and bass shy. The clear top versions of the National Union SL7's are better balanced, top to bottom and have that clear/rich beautiful National Union house sound.

I have also had the exact same experience with RCA grey glass in SL7.

NO, NO, NO to this one...


The less sexy looking clear tops sound far richer:

YES, YES, YES to this one!

As always....YMMV

 

[JazzVinyl]

Don't know anything about photography. Never had any luck with cameras until they became digital, and then available on cell phones. All I did was to point and shoot with my iPhone, but the technology is such that you get good pictures.
The date code is MR 3U. MR means Manufacturers Replacement. During WW2 most tubes were set aside for the military with some rationed for civilian use. Those tubes got the designation MR. The rationing lasted from 1942 until 1945 so the MR designation dates a tube to those years.
3 means 1943. U is the month. One 12 month sequence went from A until M (skipping the letter I which looks like 1). Another sequence went from N to Z (skipping Q that looks like a 0). Using my built in calculator (my fingers) U = 7 = July.
I have an Arcturus 6N7G tube with the date codes N4 N4. After much searching and finding no answers I decided that the date of manufacture and shipping was the same. N = January and 4 = 1944.
Many Sylvania tubes have two date codes - one for when it was made and one when it was shipped. One code is on the top of the tube or on the glass under the tube designation, and the other on the base near the Sylvania EIA number of 312. An example would be L9M on the glass and 026 on the base.
L = November; 9 = 1949 (M - factory?)
0 = 1950; 26 is the week of the year = June
Tube date codes are very mysterious. Apparently, the Tung Sol date codes indicate the expiration of the warranty, and we still don't even know what the TS letter codes mean. - Somebody solved the GE dots codes...

Thanks Mordy....isn't it amazing that all these years later....almost 80 years - that these tubes would still be delighting the ears of audiophiles.

 

[mordy]

MK9 PSA:

You see many a set of National Union grey glass on the 'ole famous auction site, like these:

https://www.ebay.com/itm/304689588288

This JV 'Public Service Announcement' is to not fall for the looks! I have tried a couple of these (much cheaper 12v versions) and I am here to say I do not like them in the MK9. They are very thin, brittle and bass shy. The clear top versions of the National Union SL7's are better balanced, top to bottom and have that clear/rich beautiful National Union house sound.

I have also had the exact same experience with RCA grey glass in SL7.

NO, NO, NO to this one...


The less sexy looking clear tops sound far richer:

YES, YES, YES to this one!

As always....YMMV

Can you interpret the date code EC?

 

[JazzVinyl]

Can you interpret the date code EC?

@mordy ... I don't think I have enough info to decipher EC into a year / month. But...
When it comes to National Union they only made tubes in the 30's/40's/early 50's - stopped in 1954 - so as long as they are Genuine NU (and not the grey glass ones) it is probably a good sounding.

 

[mordy]

@mordy ... I don't think I have enough info to decipher EC into a year / month. But...
When it comes to National Union they only made tubes in the 30's/40's/early 50's - stopped in 1954 - so as long as they are Genuine NU (and not the grey glass ones) it is probably a good sounding.

Haven't seen a code listing for NU but I made my own, comparing writing on boxes and tubes:

First letter:
G 1943
H 1944
I 1945
J 1946
GU is July 1943
HU is June 1944
IN is May 1945
IU June 1945
IU April 45
IU March 45
HC Oct 44
Quarters?:
U is March April June/July May maybe
N is March April May probably
R June
C October?

If you extrapolate the years E=1941. The second letter designates the quarter or the month, but it seems that it is changing for different years. EC for sure means 1941 but I am not sure which month C is.

 

[JazzVinyl]

Haven't seen a code listing for NU but I made my own, comparing writing on boxes and tubes:

First letter:
G 1943
H 1944
I 1945
J 1946
GU is July 1943
HU is June 1944
IN is May 1945
IU June 1945
IU April 45
IU March 45
HC Oct 44
Quarters?:
U is March April June/July May maybe
N is March April May probably
R June
C October?

If you extrapolate the years E=1941. The second letter designates the quarter or the month, but it seems that it is changing for different years. EC for sure means 1941 but I am not sure which month C is.

Very nice, thank you!

 

[jonathan c]

Hey Shane, did the fan for your LD MK9 cool down the amp or just blow the amp smoke all over the East Coast of North America ?

 

[Shane D]

Hey Shane, did the fan for your LD MK9 cool down the amp or just blow the amp smoke all over the East Coast of North America ?

The fan is Awesome on hot days!

There is a big wildfire about ten minutes from my house, but it is under control now. That is due to getting rain from Friday straight through Tuesday.

There is a much bigger fire out in the country (Shelburne/Barrington) that has already burned about 57,000 acres and is still out of control.

Plus Quebec and Ontario have lots of fires too. Worst wildfire season ever and we are only in June.

 

[Shane D]

I haven't commented here in quite a while.
I tend to go off this amp for a while sometimes and then think about selling it. And then I plug in some headphones and discover it all over again.

Lately I have been A-B'ing with the Valhalla 2. I figured I would run them for a while and then move one. It turns out that I like both of them.

I find the Valhalla 2 more crisp and clear, the MK9 more thick and tubey. And it is a lot fun going back and forth with the right headphones. Lately I bought yet another Senn, the HD660S2's. Really nice on the MK9 and very easy to drive. I don't even need high gain.

Only downside to a 2-tube amp set up is the heat. The Valhalla 2 has cooled considerably after installing four tube risers.
But I am using my fan for both in the summer.

Last note: I was in the mood for a trip down memory lane the other day and chose my "Best of 60's pop" playlist. Some of the songs don't sound perfect after 55-60 years. A little bit of noise in the Violectric and iFi amps. But smooth as silk on this amp. A very nice option to have.

 

[jonathan c]

I haven't commented here in quite a while.
I tend to go off this amp for a while sometimes and then think about selling it. And then I plug in some headphones and discover it all over again.

Lately I have been A-B'ing with the Valhalla 2. I figured I would run them for a while and then move one. It turns out that I like bother of them.

I find the Valhalla 2 more crisp and clear, the MK9 more thick and tubey. And it is a lot fun going back and forth with the right headphones. Lately I bought yet another Senn, the HD660S2's. Really nice on the MK9 and very easy to drive. I don't even need high gain.

Only downside to a 2-tube set up is the heat. The Valhalla 2 has cooled considerably after four tube risers.
But I am using my fan for both in the summer.

Last note: I was in the mood for a trip down memory lane the other day and chose my "Best of 60's pop" playlist. Some of the songs don't sound perfect after 55-60 years.** A little bit of noise in the Violectric and iFi amps. But smooth as silk on this amp. A very nice option to have.

** … does the ‘missus’ say the same about you?

 

[Shane D]

** … does the ‘missus’ say the same about you?

Very much so!