[Xcalibur255]

I'm sure towards the end demand for the 6J5 was very low and it made no sense to have dedicated tooling to make them so we get interesting things like this as a result.

 

[Xcalibur255]

I used to have a pair of Sylvania 6j5s that sounded phenomenal, except for a pretty strong buzz. I tried to re flow the solder, but ended up killing the tubes instead.
In my attempt to get another "magic" pair of Sylvanias, I mustve bought 8-10 pairs of 6 and 12j5s....all of them sounded pretty bad.
To this day I have no idea what made that one pair sound so good and the rest were not. Oh well....

This is why I don't attempt the solder re-flow on my buzzing tubes. I feel that the solder joint isn't always the source of this type of noise, sometimes it's actually a tiny speck of debris lodged inside the grid from manufacturing and a good "thwack" in your palm can knock it out. Other times it's a grid tolerance issue and the tube will technically work but will always buzz. My last few 6J5 purchases have all turned out to have unfixable buzzing issues, I sort of feel like the world is telling me to stop. You just can't stop being curious about the ones you haven't heard yet though!

 

[Isaacc7]

I'm sure towards the end demand for the 6J5 was very low and it made no sense to have dedicated tooling to make them so we get interesting things like this as a result.

Yup. I'm sure Sylvania had a contract to fulfill, probably with the government/military, and was not about to retool a whole production line when they already had a perfectly good tube being made. All they had to do was redo some connections and voila, a tube that worked just fine for whatever the government needed it for.

Sylvania did a ton of this. Keep your eyes out for 807 or 6bg6ga with 7581a guts in them, often times labeled Philips. A 7581a rated tube could drop into a circuit designed for an 807 no problem. Don't try the other way around though! There are also lots of TV tubes that were upgraded over time. You'll see 6av5 with the guts of much more powerful 6fw4. The most notorious example of this is Sylvania using a 6av5 (probably actually a 6fw4), wiring it as a triode, and selling it as a 6b4ga. The 6b4 is a triode (an indirectly heated version of the 6a3, the 6v version of the 2a3), the 6av5 is a beam tetrode I think. Rewiring the 6av5 as a triode made it close enough to a 6b4 *for whatever purpose the government had for it* so that Sylvania didn't 't have to revive the ancient 6b4 tooling. I'm pretty sure they were being used as pass elements in voltage regulators. Some Techtronix equipment used them that way. Needless to say, audio quality wasn't the driving factor of fulfilling the contract!

 

[mordy]

The tube world is full of surprises. Here is a GE metal 6N7 pair from the 50's that sound excellent. - Maybe they are old Ken-Rad tubes with new logos and dates?

The days of $2 tubes are mostly over, but you can still find these for little money.
If you have the right amp and adapters for the 6N7 it is well worth trying.

 

[Xcalibur255]

Yup. I'm sure Sylvania had a contract to fulfill, probably with the government/military, and was not about to retool a whole production line when they already had a perfectly good tube being made. All they had to do was redo some connections and voila, a tube that worked just fine for whatever the government needed it for.

Sylvania did a ton of this. Keep your eyes out for 807 or 6bg6ga with 7581a guts in them, often times labeled Philips. A 7581a rated tube could drop into a circuit designed for an 807 no problem. Don't try the other way around though! There are also lots of TV tubes that were upgraded over time. You'll see 6av5 with the guts of much more powerful 6fw4. The most notorious example of this is Sylvania using a 6av5 (probably actually a 6fw4), wiring it as a triode, and selling it as a 6b4ga. The 6b4 is a triode (an indirectly heated version of the 6a3, the 6v version of the 2a3), the 6av5 is a beam tetrode I think. Rewiring the 6av5 as a triode made it close enough to a 6b4 *for whatever purpose the government had for it* so that Sylvania didn't 't have to revive the ancient 6b4 tooling. I'm pretty sure they were being used as pass elements in voltage regulators. Some Techtronix equipment used them that way. Needless to say, audio quality wasn't the driving factor of fulfilling the contract!

I actually have a bit of experience with the whole 6AV5 6B4G thing. The 6AV5 oscillated like crazy in the particular amp I tried it in.

 

[triod750]

I've only used genuine 6B4G in Triod750 .

 

[Isaacc7]

I actually have a bit of experience with the whole 6AV5 6B4G thing. The 6AV5 oscillated like crazy in the particular amp I tried it in.

I wonder if using "snubbers" in an adapter would prevent that. I don't actually know what they are but I've seen people talk about using them to prevent oscillations. I have some 12av5 I'm interested in using In my next amp but am worried about problems.

 

[bcowen]

PS…Long-plate Lansdale 12AU7 s are fantastic tubes !

So are the tall-bottle 7N7's.

 

[raindownthunda]

I was planning on "just" cleaning the pins and giving these a quick test run, but I'm getting sucked into tonight's tube roll and having trouble taking off the headphones. Here are the Philips Miniwatt 6C5V. I believe these are manufactured by RT? Not the prettiest examples, but they are dead silent and sound quite nice. Spacious, detailed, full, and musical paired with the Chatham 6AS7G.

 

[mordy]

I was planning on "just" cleaning the pins and giving these a quick test run, but I'm getting sucked into tonight's tube roll and having trouble taking off the headphones. Here are the Philips Miniwatt 6C5V. I believe these are manufactured by RT? Not the prettiest examples, but they are dead silent and sound quite nice. Spacious, detailed, full, and musical paired with the Chatham 6AS7G.

Are these tubes glass tubes with an RF coating? There is a possibility that you could find the RFT logo on the bottom of the base near the tube pins if they were made by RFT.

 

[raindownthunda]

Are these tubes glass tubes with an RF coating? There is a possibility that you could find the RFT logo on the bottom of the base near the tube pins if they were made by RFT.

Hey mordy - I just checked both tube bases and don’t see any markings at all. They are glass with a textured metallic coating. They look identical (other than the logo) to the ones pictured here: https://www.radiomuseum.org/tubes/tube_6c5v.html
Looks like Langrex also has them for sale.

 

[mordy]

Packed up the Cetron 6336B tubes, being mindful of the joint Army & Navy instructions:

According to the spec sheet, one pair of 6336B can take the place of 4 or 6 6AS7G tubes.
https://frank.pocnet.net/sheets/077/6/6336B.pdf

What about? Mrs Ling Xu did not plan for 6 x 6AS7 tubes in her adapter (not enough spacing to make room for 6 tubes) so we have to settle for four tubes.
Is it going to melt my voltage regulator? Make the listening room into a sauna? How will it sound compared to the 6336B?
Only one way to find out:

You know what they say about cars - you cannot have enough horse power. How many horsepower is 10A?
Common Amps to Horsepower Conversions

Amps	Horsepower	Efficiency
10 A	1.45 HP	90%

Throw in another 1.6A for the driver tubes and we should have at least 1.5 HP.

It is getting warm in here - time to turn on the AC. So far everything is holding up. The sound is different than the 6336B - more background detail, less slam and the sound stage isn't as wide. The presentation is more laid back and distant compared to the Cetron's in your face sound. Need more volume - the amplification factor for the RCAs is 2.2 and 2.7 for the Cetrons. The RCAs are supposed to be warm sounding tubes - need more time to form a clearer opinion of the sound in this setup. I don't own planar headphones but 1.5HP sounds like enough to drive them lol.

 

[maxpudding]

1.5HP AC is enough to cool down a hot room within minutes too lol

 

[bcowen]

Packed up the Cetron 6336B tubes, being mindful of the joint Army & Navy instructions:

According to the spec sheet, one pair of 6336B can take the place of 4 or 6 6AS7G tubes.
https://frank.pocnet.net/sheets/077/6/6336B.pdf

What about? Mrs Ling Xu did not plan for 6 x 6AS7 tubes in her adapter (not enough spacing to make room for 6 tubes) so we have to settle for four tubes.
Is it going to melt my voltage regulator? Make the listening room into a sauna? How will it sound compared to the 6336B?
Only one way to find out:

You know what they say about cars - you cannot have enough horse power. How many horsepower is 10A?
Common Amps to Horsepower Conversions

Amps	Horsepower	Efficiency
10 A	1.45 HP	90%

Throw in another 1.6A for the driver tubes and we should have at least 1.5 HP.

It is getting warm in here - time to turn on the AC. So far everything is holding up. The sound is different than the 6336B - more background detail, less slam and the sound stage isn't as wide. The presentation is more laid back and distant compared to the Cetron's in your face sound. Need more volume - the amplification factor for the RCAs is 2.2 and 2.7 for the Cetrons. The RCAs are supposed to be warm sounding tubes - need more time to form a clearer opinion of the sound in this setup. I don't own planar headphones but 1.5HP sounds like enough to drive them lol.

Love it! Maybe some 6AS7GA's? Then you could fit 6.

 

[Xcalibur255]

I wonder if using "snubbers" in an adapter would prevent that. I don't actually know what they are but I've seen people talk about using them to prevent oscillations. I have some 12av5 I'm interested in using In my next amp but am worried about problems.

That's what I was trying for, but that amp is long gone now anyway. It had grounding issues and when I sent it off for repairs I never got it back.