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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 75

post #1111 of 5906
Quote:
Originally Posted by mordy View Post

I've been waiting for this post, and I am looking forward to see what you will find. I have my eyes on a cheap deal of RCA/Sylvania 6J4 tubes. Should I hold off and wait to find out if the diode/triode tubes are better sounding? Half of 12AX7/12AT7 sounds enticing.

 

I encourage you to go for them. My Syl 8532W/6J4s are my current favorites, and I seriously doubt that standard Syl 6J4s wouldn't sound just as good. As for these newly discovered diode/triodes, it is impossible to know how they will sound at this time. As usual, I have ordered some inexpensive samples, but don't expect delivery until the end of this week, or early next.

post #1112 of 5906
Quote:
Originally Posted by Audiofanboy View Post
Note that you should supposedly be grounding those unused diodes, though many people apparently could care less and leave them floating, but that is not an ideal case. But the 6AT6 and 6AV6 are often recommended as "single 12AX7" and just too interesting not to test, and pretty cheap too apparently.

 

Oh, no. Absolutely, you can't do that, lol wink.gif

 

 

Quote:
Originally Posted by Audiofanboy View Post

The fun never stops, here are a few new tube rolling ideas. As usual, each new tube type is even more obscure than the previous one lol.

 

This time, it's 7-pins double diode-triodes. Yeah, it seems barbaric, but it's actually pretty simple. It's a triode, with two useless diodes in the same glass bulb, which you can just, well, not use, getting a triode in the end. Many of these are described in the datasheets as having similar characteristics to half of a -famous- 12AX7 or 12AT7 type tube. They tend more towards the high or very mu and low gm, meaning they should be perfect for a voltage gain section (driver tube) in the MK III & IV, just like their 12V heater double triode counterparts massively used in preamps and headamps around the globe. Well, used by a few thousand people at least...

 

So far I've identified the 6AT6, 6AQ6 and 6AV6. There are more 7-pins diode-triodes (one diode plate pin and one extra cathode lead pin) and double diode-triodes (same shared cathode, two diode plate pins), but they aren't all easy to make compatible (if the anode is on pin 1 instead of the grid, it's seems difficult to adapt with wire mods, unless making a whole 7-pin adapter, which is entirely possible btw). Like the 6J4, albeit for different reasons, these would require you to chop off pins 5 & 6 (diode 1 & diode 2, simple really) and use EF92 jumpers!

 

Excellent, more exotic food for us and let us know how they sound, then I'll update the table =D

 

Quote:

 

This one is great.

 

Btw, anyone of you at the Head-fi meet in London on Saturday?


Edited by Acapella11 - 4/23/13 at 2:49pm
post #1113 of 5906

In my relentless quest for the Unobtanium tube, I came across some tubes labeled Sonotone. Thinking that they must be re-branded, I did a little research. True, they used re-branded tubes from Mullard and Telefunken among others, but they also manufactured their own tubes in the 40's - 60's in the USA. The tubes I looked at say "Made in USA".

 

Does anybody know anything about the quality of their US made tubes (as compared to the major US brands)?

 

"By the 1950's Sonotone was making over 400 different tubes. The automated tube manufacturing equipment was located at the Elmsford factory. The progressive line was circular, about 20 feet in diameter. There were many gas jets at each step to heat the glass and shape it. It was very impressive to watch. Some of the tubes were made by other manufacturers with the Sonotone name on them. Some were made by Telefunken, Mullard and Amperex. An economy line was later introduced with tubes made in Japan and were sold in green boxes. By the mid-sixties, tube sales decreased with the advancement of transistors. The tube manufacturing equipment was sold."
 

post #1114 of 5906
Quote:
Originally Posted by mordy View Post

Hi AFB,

 

I've been waiting for this post, and I am looking forward to see what you will find. I have my eyes on a cheap deal of RCA/Sylvania 6J4 tubes. Should I hold off and wait to find out if the diode/triode tubes are better sounding? Half of 12AX7/12AT7 sounds enticing.

 

Truth is, I thoroughly enjoy almost all of the new tubes I've tried, such as the 4825/6AU6 and the 6AH6. But if good is good, better is better......

 

I also notice that the new tube categories you list above come in European designations, so in addition to the standard Sylvania, RCA, Tung Sol and GE variants, it seems that you can get Phillips, Mullard and Siemens tubes as well etc. .

 

If you really want to get into the 6AV6 tube rolling mode, there is a T shirt available LOL.

 

http://www.ebay.com/itm/12AX7-VACUUM-TUBE-T-SHIRT-LRG-RCA-6AV6-ECC83-/320961636314?pt=Vintage_Electronics_R2&hash=item4abacde7da

 

I'd love to tell you to wait for the 6J4 because they're great or something, but as haven't even gotten my Sylvania 8532W yet, I can't. I keep bringing up new tube types that I'm not even the first person to test; I've basically fallen behind in my own game lol...

 

Which reminds me I finally got my replacement TS 6485 (1971-72, O-getter, last version), and these are still some great awesome tubes. I realize that even more now after spending a full week with my French 6J4S in the meantime. Those 6485 are a grade in themselves, and anyone ought to try a pair; they are my current best tubes by a fair margin.

 

Now, a few pictures, as I just realized I hadn't actually taken pictures of the last three tubes I tested. No pics of the boxes this time, as I just didn't feel it added much information, and I preferred to focus on close-ups of the tubes for once (pics are full high resolution if you click on them). I do hate how doing macro at silly small apertures reveals how dirty you camera's sensor is; you never see those dust specks at normal apertures...

 

First, a bit of tube porn. I think I'd mentioned how I broke a 6J4S tube by bending its pins, and that the glass broke off so neatly, I thought I should take a picture of it, well here it is. See how the grid (the only grid, it's a triode) goes further than the anode width.

 

 

The 6J4 (all the ones I've seen have this exact same construction, save for minor mica changes) has a pretty peculiar build with weird shaped anodes held by a U bent sheet of metal; fascinating to look at outside of the glass.

 

 

The unbroken, yet mutilated Thomson-CSF 6J4S. See how a little bit of glass got chipped off when I bent the pins.

 

 

My West German mil-spec Valvo (Mullard Blackburn) EF94, very well built tubes I have to say, nice and heavy feel. Good luck finding those!

 

 

And my current favs, the Tung Sol 6485. This is the first pair I got, and the left tube is now dead (new pair is on the amp). Notice how the left tube has some degree of black grainy screening and the other one has none. It's weird, as these two tubes have the exact same code on them, and the same export dates (Germany) on the boxes. It's even more evident on my replacement pair, where one tube is almost all black, and the other one is perfectly transparent.

 

post #1115 of 5906

Dear AFB,

 

I am trying out these Tung Sol 6AH6WA tubes. As you noted, the glass on my tubes also have a black sooty looking screening which makes it a little hard to see everything clearly. These are the only tubes I have with two dates on them: On the glass on top over the silver cap is etched a date 6210 followed by USA 7. The printed date on the tube is 6251. Could the earlier date be the manufacturing date and the second date the packing date?

 

The sound is excellent. They look very similar to your 6485 tubes, but the getter is rectangular:

 

 

 

 

 

 

post #1116 of 5906

I did not know that by double clicking on the picture you get a full view. If you click on the third picture the two dates are visible - one date on each tube on this picture.

post #1117 of 5906

Audiofanboy, Thumbs up from me: TS 6485 o2smile.gif

Mordy, Interesting to see the differently build JTL-6AH6WA. Would be curious to hear these.
 

Edit: Yes, Gibosi, you posted also the JAN 6AH6 with square getter. Sorry, forgot about that.


Edited by Acapella11 - 4/24/13 at 3:02pm
post #1118 of 5906

The reason I put up the pictures was that I thought that the TS 6H6WA should be very similar to the TS 6485. Now I have another proof: The left tube died suddenly; the same experience AFB had.

 

Luckily I have four tubes, so I don't have to go through TS 6H6WA withdrawal, but I really find it strange that one tube died after around 30 hours. This is the first time for me that a tube died in use suddenly. Makes me worry about the others...

post #1119 of 5906

And on page 61, post 915, I uploaded a picture of a pair of 1961 TS JAN-6AH6. Your tubes, my JAN tubes and my TS 6485 (page 67, post 1005) are all 1960s vintage and seem to be identical, including the square getter.

 

Oh, I am happy to report that none of mine have failed...

post #1120 of 5906

Hey guys,

 

Just now I found something interesting in terms of power tubes, a possibly useful alternative, which is also well used in audio.

 

 

"The 12BH7 double triode is pin compatible with the ECC81, ECC82 and ECC83 series from Mullard but has slightly different characteristics. Brimar give the intended use as TV frame oscillator and frame output. The construction is compatible with audio through to low VHF use. The thin glass tube envelope is 19 mm in diameter and, excluding the B9A base pins, is 68 mm tall."

 

Here is the layout of the base. The two cathode sections are interchanged, but I think that shouldn't be a problem. Only relevant difference between 6N6P and 12BH7(A) seems pin 9, which is a center tap heater for 12BH7 and a center shield pin for 6N6P. Sounds to me like a heater bridge wire mod from one of the other two heaters to pin 9 should make 12BH7 compatible. What do you guys think? I have merged the pin layouts in the figure below.

 


Edited by Acapella11 - 4/24/13 at 3:03pm
post #1121 of 5906
Quote:
Originally Posted by Acapella11 View Post

Hey guys,

 

Just now I found something interesting in terms of power tubes, a possibly useful alternative, which is also well used in audio.

 

 

"The 12BH7 double triode is pin compatible with the ECC81, ECC82 and ECC83 series from Mullard but has slightly different characteristics. Brimar give the intended use as TV frame oscillator and frame output. The construction is compatible with audio through to low VHF use. The thin glass tube envelope is 19 mm in diameter and, excluding the B9A base pins, is 68 mm tall."

 

Here is the layout of the base. Only variation between 6N6P and 12BH7(A) is pin 9, which is a center tap heater for 12BH7 and a center shield pin for 6N6P. Sounds to me like a heater bridge wire mod from one of the other two heaters to pin 9 should make 12BH7 compatible. What do you guys think? I have merged the pin layouts in the figure below.

 

 

I do wonder what they mean by "heater center tap". I'd assume the heater works fine powered through the usual B9A pins 4 & 5, and that pin 9 just has some weird random function, that may not be necessary. I guess whether to just chop off pin 9 on this one or bridge it depends on what pin 9 is connected too at the socket level (if it is indeed used as the shield, it should/would/I guess it is connected at the source, therefore the cathode (?)). I'd take a look at the MK III PCB pics to figure it out and make sure.

 

Out of curiosity, and before I check it out tomorrow at fresher times of the day for my time zone, what is the 12BH7's selling point compared to the 6N6P?

 

At any rate, yey to more options lol! (though 6N6P & 6N30P are recognized as very very good double triodes in the first place)

 

Edit: I see, 12AT/U/X7 lineage. That explains the interest. And it has a high-ish heater current compared to its counterparts, though low compared to a 6N6P. To be investigated I guess, though the amp may be more sensitive to power tube type changes than driver tube types (power types being quite critical). Of course being a 12v heater tube makes things a bit more complicated...


Edited by Audiofanboy - 4/24/13 at 3:14pm
post #1122 of 5906
Pin 4 to 5, 12V heater....pin 4/5 to 9 6v use. Pin9 is a center tap.
Quote:
Originally Posted by Audiofanboy View Post

I do wonder what they mean by "heater center tap". I'd assume the heater works fine powered through the usual B9A pins 4 & 5, and that pin 9 just has some weird random function, that may not be necessary. I guess whether to just chop off pin 9 on this one or bridge it depends on what pin 9 is connected too at the socket level (if it is indeed used as the shield, it should/would/I guess it is connected at the source, therefore the cathode (?)). I'd take a look at the MK III PCB pics to figure it out and make sure.

Out of curiosity, and before I check it out tomorrow at fresher times of the day for my time zone, what is the 12BH7's selling point compared to the 6N6P?

At any rate, yey to more options lol! (though 6N6P & 6N30P are recognized as very very good double triodes in the first place)
post #1123 of 5906

Audiofanboy- In Europe unlike America those   tubes with a center tap were used in series heater configurations in European TVs .

                        European TVs used the dangerous engineering construction of one side of the electrical mains connected DIRECTLY to the chassis[think of reversal of plug connections so LIVE is connected to chassis.]

                           The US used mainly MAINS TRANSFORMERS there bye isolating the electrical supply from the TV.

                             And yes  some died here from electrocution so everything that had bare metal was shrouded.

                                 The only logical engineering concept  in those TVs was in series  with the live [240V-here] connection.

                                    But to make them more "universal" the center tap was added.

                                        Series heaters usually had to have the same current drain as each other to even up the flow of current through them.

                                             You could add a resistor across the heaters-SERIES working ONLY to even out one with a different current drain

                                                But that was inefficient as the resistor could be several Watts and radiated a lot of heat.

                                                     Why did manufacturers use direct mains connection rather than an isolation mains transformer???--

                                                         Think -money.

post #1124 of 5906

So basically this type of tube will work of a 6V heater source if you "double connect" the heater pins to the center tap (and the whole thing to 6V at the socket level), so in parallel I guess?

post #1125 of 5906

Look on the heaters as 2 resistors connected together at the center tap the  current flow through both will be the same 2 equal resistances connected in parallel the total resistance is HALVED[more current used] if connected to the other heater connection at the center  tap.    Applying  12V across -4+5 without using the CT will reduce the amount of current through them for use in other equal current heater circuits.by INCREASING the total resistance[lower resistance=higher current].[higher resistance=lower current]

                    So "double connect"-IE- shorted together 4+5 and the other heater connection to 9-AFTER you have removed the earth connection to it.

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