[Cognomen]

Nope. Maybe you could make some kind of adapter.

The Little Dot MKIII has little jumpers that connect pins 6 and 7 underneath the amp for EF91 and EF92. One removes them for 5654. If I lost the jumpers, it would be easy enough to carefully connect pins 6 & 7 on an EF91 or EF92 tube with a wire. I have used small paper clips to connect other pins - cut to size, bend as needed, and wrap almost once around something similar in diameter to pins like a small nail so the wire fits snug and then carefully plug it in the tube socket with the amp cold and off and also remove when the amp is cold and off. Be sure the wire will not make contact with anything unwanted in the socket or other pins, or you etc. I do not know if such wire mods would work well for another brand amp or even all little dots. P. 77 has a list of wire mods that work on some little dot amps (there may be some models that were introduced later), and page 10 has a schematic of the Little Dot MKIII that might be helpful. Tube audio can have lethal voltages even when off. Strapping pins on tubes is do at your own risk. Insertion and removal when the amp is cold and off reduces risk as well as making sure you do not come into contact with pin(s) or the wire when the tube is in the amp. Tubes that draw too much current (mAh) or heaters that need different voltage than specified by the Little Dot typically require additional modifications.

Nope. Maybe you could make some kind of adapter.

P. 77 has information about how to run many different driver tubes in some Little Dots and p 10 a schematic of the Little Dot MK III. I have no clue whether or not any of the info could be useful for Fosi. One can strap pins together on some tubes with a homemade wire and use them in some Little Dots. For example, if I lost the little jumpers that bridge pins 6 and 7 for EF91/EF92 on my Little Dot III, it would be easy to make a wire that connects pins 6 and 7 on the tube. It is a do at your own risk activity because it could damage equipment and because tube audio can have lethal voltag

What you say is very plausible. Westinghouse was an old tube manufacturer but had some kind of lawsuit that forbade them from making tubes for a number of years. When they came back into the business some of the tubes were rebranded and there is the possibility that the tubes you mentioned were made by someone else.

Indeed seems very likely! The eBay vendor had a photo of a crate full of unbranded tubes Westinghouse marketed to the military. The vendor has been very honest so it's possible the story is true. They are actually tall bottle 6HQ5's which I have read are sensibly equivalent to 6HM5 and 6HA5. I briefly re-listened to them the other day and prefer them over my latest roll: Vinnitsa (USSR Ukraine probably) short bottle 6J2P-EV voltage amplifiers. Both with 6N6P-T power tubes.

At page 59 of this thread, the user Audiofanboy wrote this:

"Note that for EF92/91 tubes, one could also imagine placing a small wire between pins 6 and 7 to strap grid 2, grid 3 and anode together by hand and stay in the 6AK5 jumper setting all the time -if you really hate jumpers that much."

Is that a way to use EF91/92 tubes in EF95 mode?

If yes, would the red line I've drawn be the correct way to join pins 6 and 7?

Yes, it should work the same. If one has them, the jumpers may be a better solution because they allow one to fully seat the tube and may reduce the possibility of a loose homemade connection. They may also be safer especially if the wire is a bit long and has a kink in it. Some people have prefered solid wire instead of twisted. For some tubes, one has options to wire jump different pins as explained in the extensive chart toward the bottom of p. 77 of this forum. I don't recall that anyone identified one of those wiring modes as providing the best sound from their Little Dot, but more experimenting and different ears and equipment might reveal something. (Sometimes people like me make the not good temporary mistake of inserting an ef95 tube into EF91/EF92 mode and vice versa. To prevent myself from doing that again, I have a small post-it note on my amp noting the mode and keep my tubes sorted in terms of EF95 vs EF91/EF92.)

 

[mordy]

The Little Dot MKIII has little jumpers that connect pins 6 and 7 underneath the amp for EF91 and EF92. One removes them for 5654. If I lost the jumpers, it would be easy enough to carefully connect pins 6 & 7 on an EF91 or EF92 tube with a wire. I have used small paper clips to connect other pins - cut to size, bend as needed, and wrap almost once around something similar in diameter to pins like a small nail so the wire fits snug and then carefully plug it in the tube socket with the amp cold and off and also remove when the amp is cold and off. Be sure the wire will not make contact with anything unwanted in the socket or other pins, or you etc. I do not know if such wire mods would work well for another brand amp or even all little dots. P. 77 has a list of wire mods that work on some little dot amps (there may be some models that were introduced later), and page 10 has a schematic of the Little Dot MKIII that might be helpful. Tube audio can have lethal voltages even when off. Strapping pins on tubes is do at your own risk. Insertion and removal when the amp is cold and off reduces risk as well as making sure you do not come into contact with pin(s) or the wire when the tube is in the amp. Tubes that draw too much current (mAh) or heaters that need different voltage than specified by the Little Dot typically require additional modifications.

P. 77 has information about how to run many different driver tubes in some Little Dots and p 10 a schematic of the Little Dot MK III. I have no clue whether or not any of the info could be useful for Fosi. One can strap pins together on some tubes with a homemade wire and use them in some Little Dots. For example, if I lost the little jumpers that bridge pins 6 and 7 for EF91/EF92 on my Little Dot III, it would be easy to make a wire that connects pins 6 and 7 on the tube. It is a do at your own risk activity because it could damage equipment and because tube audio can have lethal voltag

Indeed seems very likely! The eBay vendor had a photo of a crate full of unbranded tubes Westinghouse marketed to the military. The vendor has been very honest so it's possible the story is true. They are actually tall bottle 6HQ5's which I have read are sensibly equivalent to 6HM5 and 6HA5. I briefly re-listened to them the other day and prefer them over my latest roll: Vinnitsa (USSR Ukraine probably) short bottle 6J2P-EV voltage amplifiers. Both with 6N6P-T power tubes.

Yes, it should work the same. If one has them, the jumpers may be a better solution because they allow one to fully seat the tube and may reduce the possibility of a loose homemade connection. They may also be safer especially if the wire is a bit long and has a kink in it. Some people have prefered solid wire instead of twisted. For some tubes, one has options to wire jump different pins as explained in the extensive chart toward the bottom of p. 77 of this forum. I don't recall that anyone identified one of those wiring modes as providing the best sound from their Little Dot, but more experimenting and different ears and equipment might reveal something. (Sometimes people like me make the not good temporary mistake of inserting an ef95 tube into EF91/EF92 mode and vice versa. To prevent myself from doing that again, I have a small post-it note on my amp noting the mode and keep my tubes sorted in terms of EF95 vs EF91/EF92.)

I remember way back then using extremely thin wires to wrap around the pins - they did not interfere with inserting the tube pins into the sockets.

 

[Cognomen]

Re p. 77, post 13,171, the comprehensive wiring mod chart:

I am a beginner when it comes to figuring out wiring mods and do not understand what "Yes" means in the narrowest column for the following 5 tubes which all draw .4 mAh or less:

6J4 has pinout g, k, h, h, g, g, a. Can one run it well in EF91/92 mode?

6AQ4 has pinout g, k, h, h, k, g, a. Can one clip pin 5, the second k pin, and run it well in EF91/EF92 mode?

6AQ6, 6AT6, 6AV6 are all double diode with pinouts g, k, h, h, anodediode, anodediode, a. Can one clip pins 5 and 6, the two anodediode pins, and run them well in EF91/92 mode?

I also wonder about 6AM5 aka EL91, a .2 mAh tube designed specifically for audio. It has pinout g, k, h, h, a, ic, g. "ic" designates an internal connection and nothing should be connected to it. Should it run well in EF91/92 mode with ic pin 6 clipped?

 

[TrollDragon]

At page 59 of this thread, the user Audiofanboy wrote this:

"Note that for EF92/91 tubes, one could also imagine placing a small wire between pins 6 and 7 to strap grid 2, grid 3 and anode together by hand and stay in the 6AK5 jumper setting all the time -if you really hate jumpers that much."

Is that a way to use EF91/92 tubes in EF95 mode?

If yes, would the red line I've drawn be the correct way to join pins 6 and 7?

Pin 7 is not connected to anything on the Little Dot since EF95 tubes are already bridged internally between pins 2 and 7. There is a permanent bridge on the circuit board between pins 5&6. The only way we can use EF92 tubes is to install the jumper which bridges pin 7 to the permanent connection between 5&6. If you were to install a EF95 tube with the EF92 jumper installed you would be shorting the anode and cathode together.

So for him to just use a jumper might not be a good idea, it really all depends on how his tube sockets are wired.

 

[barbazz]

Re p. 77, post 13,171, the comprehensive wiring mod chart:

I am a beginner when it comes to figuring out wiring mods and do not understand what "Yes" means in the narrowest column for the following 5 tubes which all draw .4 mAh or less:

6J4 has pinout g, k, h, h, g, g, a. Can one run it well in EF91/92 mode?

6AQ4 has pinout g, k, h, h, k, g, a. Can one clip pin 5, the second k pin, and run it well in EF91/EF92 mode?

6AQ6, 6AT6, 6AV6 are all double diode with pinouts g, k, h, h, anodediode, anodediode, a. Can one clip pins 5 and 6, the two anodediode pins, and run them well in EF91/92 mode?

I also wonder about 6AM5 aka EL91, a .2 mAh tube designed specifically for audio. It has pinout g, k, h, h, a, ic, g. "ic" designates an internal connection and nothing should be connected to it. Should it run well in EF91/92 mode with ic pin 6 clipped?

6J4, 6AQ4, 6AQ6, 6AT6, 6AV6 -> EF92 + You need to cut pins 5 & 6 (or, as I do, use a clipped tube saver)

I had too some problems reading page 77, so I have rewritten it in Excel and added some more info that might be useful. Let me know if you find some errors or if it can be refined with your experience.

Families	Alternative Names	Type	EF95	EF91/92	EF95 + 2/7-Socket Wire Mod	EF91/92 + Cut off and tape pins 5 & 6	EF95 + 1/7-Socket Wire Mod
6AG5, 6BC5, 6CE5	EF96, 6J3P(-E), 6186	Pentode	yes	no	yes (2)	no	no
6AH6	6J5P, 6485	Pentode	no	no	yes	no	no
6AJ5 (15)		Pentode	yes	no	yes (18)	no	no
6AN5 (11)		Pentode	yes	no	no	no	no
6AQ5 (19)		Beam Power Tube	yes	no	no	no	no
6AQ6, 6AT6, 6AV6		Double Diode Triode	no	no	no	yes	no
6AS6 (17)		Pentode	no	no	yes	no	no
6AU6	EF94, 6136, 8425, 7543 = mil spec 6AU6	Pentode	no	no	yes	no	no
6BA6 (7)	5749, EF93, CV454, Shuguang 6K4	Pentode	no (8)	no	yes	no	no
6BD6		Pentode	no	no	yes	no	no
6BE6, 6CS6, 6BY6	6BE6 = EK90, CV4012, 5750, 6A2P, 1217 , 1680, 6H31; 6BY6 = EH900, 6687, EH900S, EH960, E91H, 5915; 6CS6 = EH90	Heptode	yes (4)	yes	yes (5)	no	yes (6)
6BH6 (13)		Pentode	no	yes	no	no	no
6BJ6 (9)	CV3909, 6662, 7694, E99F	Pentode	no (3)	yes	yes	no	yes
6CB6, 6CF6	6676	Pentode	no (3)	yes	yes	no	no
6DE6 (18)		Pentode			yes
6DK6	8136	Pentode	no (3)	yes	yes	no	no
6DT6A	6DT6A	Pentode	yes	yes		no	yes
6EW6		Pentode	no (3)	yes	yes	no	yes
6GM6, 6AM6	6AM6 = CV4014, EF91, CV138	Pentode	no (3)	yes	yes	no	no
6GY6/6GX6		Pentode	no (3)	yes	yes	no	yes
6HA5, 6HM5, 6HQ5 (12)	6HA5 = EC900	Triode	yes	no	no	no	no
6HZ6, 6DT6 (10)		Pentode	yes	yes	yes	no	yes
6J4, 6AQ4	6J4 = 8532, 6J4WA = M8248, CV5311 / 6AQ4 = CV4070, CV417, EC91	Triode	no	no	no	yes	no
6Zh38P (14)		Pentode	yes	no	no	no	no

Recommended modes of operation are highlighted in green.

(1) EF91/92 = EF95 + 6/7-wire mod. See figure below.
(2): Mod doesn't add a function. Tubes are already internally strapped between pins 2 and 7. Use at higher risk only.
(3): Operation with "floating" grid 3 is strongly not recommended.
(4): Offers a great standard setting. Floating grid 3 but different grid architecture to (1).
(5): works flawless, preference dependent, bass heavy with rolled off treble for some 6BE6, for other 6BE6 and generally heptodes, this setting sounds brighter and more foreward than unstrapped.
(6): "Grid-to-grid strap", possibly, favourite option for 6BY6 heptodes, generally a good setting to try.
(7): Tested with Shuguang 6K4.
(8): Not recommended but works with Shuguang 6K4.
(9): Tubes of this family have not been tested yet (29/07/2013)
(10) 6HZ6 uses 0.45 A heater current, 6DT6 0.3 A. Similar to heptodes, these pentodes are FM-detectors.
(11) 6AN5 tubes follow the EF95 pinout and grid design but utilize a higher heater current (0.45 A).
(12) ~ 0.19 A heater current triodes with µ ~ 72 that internally strap pins 2 and 7 to the cathode.
(13) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9205498
(14) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9215096
(15) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-8916024
(16) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9829394
(17) https://www.head-fi.org/threads/little-dot-i-tube-rolling.364043/post-12973068
(18) https://www.head-fi.org/threads/little-dot-mk-ii-rebuild.933415/post-15641777
(19) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9737985

Tubes with A, W, WA, WB, WC specification share the same settings as the ones without.
CV versions usually indicate (improved) mil spec versions, specifically when used with four letters.

 

[Cognomen]

6J4, 6AQ4, 6AQ6, 6AT6, 6AV6 -> EF92 + You need to cut pins 5 & 6 (or, as I do, use a clipped tube saver)

I had too some problems reading page 77, so I have rewritten it in Excel and added some more info that might be useful. Let me know if you find some errors or if it can be refined with your experience.

Families	Alternative Names	Type	EF95	EF91/92	EF95 + 6AU6/6BH6 adapter	EF91/92 + Cut off and tape pins 5 & 6	EF95 + 1/7-Socket Wire Mod
6AG5, 6BC5, 6CE5	EF96, 6J3P(-E), 6186	Pentode	yes	no	yes (2)	no	no
6AH6	6J5P, 6485	Pentode	no	no	yes	no	no
6AJ5 (15)		Pentode	yes	no	yes (18)	no	no
6AN5 (11)		Pentode	yes	no	no	no	no
6AQ5 (19)		Beam Power Tube	yes	no	no	no	no
6AQ6, 6AT6, 6AV6		Double Diode Triode	no	no	no	yes	no
6AS6 (17)		Pentode	no	no	yes	no	no
6AU6	EF94, 6136, 8425, 7543 = mil spec 6AU6	Pentode	no	no	yes	no	no
6BA6 (7)	5749, EF93, CV454, Shuguang 6K4	Pentode	no (8)	no	yes	no	no
6BD6		Pentode	no	no	yes	no	no
6BE6, 6CS6, 6BY6	6BE6 = EK90, CV4012, 5750, 6A2P, 1217 , 1680, 6H31; 6BY6 = EH900, 6687, EH900S, EH960, E91H, 5915; 6CS6 = EH90	Heptode	yes (4)	yes	yes (5)	no	yes (6)
6BH6 (13)		Pentode	no	yes	no	no	no
6BJ6 (9)	CV3909, 6662, 7694, E99F	Pentode	no (3)	yes	yes	no	yes
6CB6, 6CF6	6676	Pentode	no (3)	yes	yes	no	no
6DE6 (18)		Pentode			yes
6DK6	8136	Pentode	no (3)	yes	yes	no	no
6DT6A	6DT6A	Pentode	yes	yes		no	yes
6EW6		Pentode	no (3)	yes	yes	no	yes
6GM6, 6AM6	6AM6 = CV4014, EF91, CV138	Pentode	no (3)	yes	yes	no	no
6GY6/6GX6		Pentode	no (3)	yes	yes	no	yes
6HA5, 6HM5, 6HQ5 (12)	6HA5 = EC900	Triode	yes	no	no	no	no
6HZ6, 6DT6 (10)		Pentode	yes	yes	yes	no	yes
6J4, 6AQ4	6J4 = 8532, 6J4WA = M8248, CV5311 / 6AQ4 = CV4070, CV417, EC91	Triode	no	no	no	yes	no
6Zh38P (14)		Pentode	yes	no	no	no	no

Recommended modes of operation are highlighted in green.

(1) EF91/92 = EF95 + 6/7-wire mod. See figure below.
(2): Mod doesn't add a function. Tubes are already internally strapped between pins 2 and 7. Use at higher risk only.
(3): Operation with "floating" grid 3 is strongly not recommended.
(4): Offers a great standard setting. Floating grid 3 but different grid architecture to (1).
(5): works flawless, preference dependent, bass heavy with rolled off treble for some 6BE6, for other 6BE6 and generally heptodes, this setting sounds brighter and more foreward than unstrapped.
(6): "Grid-to-grid strap", possibly, favourite option for 6BY6 heptodes, generally a good setting to try.
(7): Tested with Shuguang 6K4.
(8): Not recommended but works with Shuguang 6K4.
(9): Tubes of this family have not been tested yet (29/07/2013)
(10) 6HZ6 uses 0.45 A heater current, 6DT6 0.3 A. Similar to heptodes, these pentodes are FM-detectors.
(11) 6AN5 tubes follow the EF95 pinout and grid design but utilize a higher heater current (0.45 A).
(12) ~ 0.19 A heater current triodes with µ ~ 72 that internally strap pins 2 and 7 to the cathode.
(13) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9205498
(14) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9215096
(15) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-8916024
(16) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9829394
(17) https://www.head-fi.org/threads/little-dot-i-tube-rolling.364043/post-12973068
(18) https://www.head-fi.org/threads/little-dot-mk-ii-rebuild.933415/post-15641777
(19) https://www.head-fi.org/threads/little-dot-tube-amps-vacuum-tube-rolling-guide.563884/post-9737985

Tubes with A, W, WA, WB, WC specification share the same settings as the ones without.
CV versions usually indicate (improved) mil spec versions, specifically when used with four letters.

Hi, Very kind of you to do this! It references text in green as the best mode, however, I don't see any green in the update. (The prior version may have had red also?) (I am somewhat dyslexic and a horrible proofreader and am a beginner at wiring mods so I'm not a great reviewer for the updated chart.) The 6DL5 aka EL95, another carradio tube, looked to me after a too superficial glance at the pins that it would run well in EF91/EF92 mode. I tried that and it did not work well at all. I quickly shutdown the amp. Then I looked at the LDIII schematic and then the tube datasheet which revealed pins 1 and 7 are grid 1 so I converted to EF95 and it worked well with only 1 appropriate connection to g1. The 6AR5 works just as well in EF95 and EF91/EF92 because for that tube all modes have the same connection in the Little Dot III because pin 7 is not connected to anything in the tube. I just looked at the diagrams for 6J4 and 6AQ4 and can see why one needs to clip pins as in the table. I re-looked at the 6AM5 aka EL91 diagram and believe I am hopefully right to think it should be run in EF91/EF92 mode with pin 6 clipped. It intrigues me because it was specifically designed for audio.

 

[rudesssolo]

Is this the right way to join pins 6-7 in a EF91 tube?

 

[TrollDragon]

Is this the right way to join pins 6-7 in a EF91 tube?

You can do that ONLY IF you are plugging this tube into a Little Dot amplifier that supports the EF95/EF91 tube option via the internal jumper. Your Fosi T20 is NOT designed to take EF91 tubes! You would need to see how the tube sockets are wired inside your amp by making a schematic of the tube circuit. Only then you might be able to modify the amps board to allow you to use EF91 tubes.

The tubes in the Fosi T20 are no more than a gimmick and a selling feature, so I would just stick to using the tubes that work with that amp.

 

[barbazz]

It references text in green as the best mode, however, I don't see any green in the update.

You're right. The copy/paste from Excel "forgot" the colors. Just edited for better viewing.

 

[barbazz]

It's been quiet around here... No new experiments?

Just received some interesting JAN/CV military tubes:

Ken-Rad VT-65 (1943)

RCA 6K7 (1951)

Sylvania 12AT7WC (1971)

Mullard CV3998 (Mitcham, probably 1962 and 1973)

I also got a pair of STC CV131 (Footscray, probably 1966) that I haven't tried yet (must change to EF92 setting and I'm lazy ).

First impressions: Ken-Rads very mellow (reminds me of the EI 6HM5), RCAs a bit thin, Sylvania very energetic, and Mullards being Mullards .

 

[TrollDragon]

Love it! It brings back the crazy days of this thread.

 

[kvtaco17]

It's been quiet around here... No new experiments?

Just received some interesting JAN/CV military tubes:

Ken-Rad VT-65 (1943)


RCA 6K7 (1951)


Sylvania 12AT7WC (1971)


Mullard CV3998 (Mitcham, probably 1962 and 1973)


I also got a pair of STC CV131 (Footscray, probably 1966) that I haven't tried yet (must change to EF92 setting and I'm lazy ).

First impressions: Ken-Rads very mellow (reminds me of the EI 6HM5), RCAs a bit thin, Sylvania very energetic, and Mullards being Mullards .

really reminds me of my jank tower of adapters and external power adapter... Speaking of which its in a box somewhere... I should start messing with the LD1+ again...

 

[Acapella11]

Hi, good to see that life is back in this thread and thanks for making the table from p. 77 clearer!

Just for completeness, I compiled a second table with more information about later stage tube families on page 585. It can be found here:

https://www.head-fi.org/threads/lit...ube-rolling-guide.563884/reply?quote=11155053

Enjoy the rolling guys!

 

[barbazz]

Hi, good to see that life is back in this thread and thanks for making the table from p. 77 clearer!

Just for completeness, I compiled a second table with more information about later stage tube families on page 585. It can be found here:

https://www.head-fi.org/threads/lit...ube-rolling-guide.563884/reply?quote=11155053

Enjoy the rolling guys!

Thank you! If I had any doubt that the Little Dot was the right amp for tube rolling, after seeing your table, I stopped having any questions and jumped on the wagon.

With the right adapters, there's an unimaginable amount of possibilities of tubes we can try. I've done some research using radiomuseum.org and also a number of different catalogues and came to the conclusion that there are 348 tube families (1427 different tubes if you count military, brand specific and regional references) usable in our LDs. And this is only for drivers and without any external power supply....

 

[triod750]

And when you have tried them you can take another step. I am now listening to RCA 6BX7GT as input and Philips E182CC as output in my Little Dot MKIVSE. Pretty good result.