[triod750]

"Of course various tubes sound different due to being used outside of their design specifications; the Little Dots have fixed parameters that mean they will sound different."

Spot on, and this is why you can find excellent synergy where input and output tubes compensate for the deficiances in each other and in the recordings you are listening to.
Simple.

 

[Cognomen]

So has my understanding. I expected someone to tell me I'm wrong. I just wrote what I have been told. I have asked previously if it is possible to use the pentodes EL41 and EL42 triodestrapped in pairs as output tubes and the answer was no.

Because of their ic internal connection pins? I glanced at an EL41 datasheet on frank.pocnet.net and it had data for triode connections and triodes in push-pull. I have 6AM5 tubes that a datasheet specified had an ic pin 6: do not connect anything to it. When I looked closely at the tube I noticed nothing was connected to that pin on my Amperex 6AM5. So I ran it in EF91/EF92 mode without chopping off pin 6 and it ran well. Another datasheet, however, was more accurate and specified pin 6 was nc not connected to anything in the tube..

 

[triod750]

Because of their ic internal connection pins? I glanced at an EL41 datasheet on frank.pocnet.net and it had data for triode connections and triodes in push-pull. I have 6AM5 tubes that a datasheet specified had an ic pin 6: do not connect anything to it. When I looked closely at the tube I noticed nothing was connected to that pin on my Amperex 6AM5. So I ran it in EF91/EF92 mode without chopping off pin 6 and it ran well. Another datasheet, however, was more accurate and specified pin 6 was nc not connected to anything in the tube..

I can't answer this since I don't speak electric. I have just used EL42 as input tubes in Little Dot and briefly tried EL41 for this duty too, these with external heater PSU. Tonight I use EL42 'Sakuma style' as both input and output tubes, four of them, in an amp with output transformers. This is just an experiment to hear their tone this way.

 

[Scooter64]

New LD MKIII user here so please bear with me if this has already been covered…….theres a huge number of pages here to digest.
I’m moving the jumpers to change EF91 tubes to EF95. I get that I have to move the jumpers from pins 2 & 3 to 1 & 2 but am I right in saying that pin numbers are 1, 2, 3 from left to right when the amp is upside down and the front is facing me?
I know it’s sounds like a pretty obvious question but doing it for the first time, I do want to make sure I’ve got exactly right.
Thanks

 

[Cognomen]

New LD MKIII user here so please bear with me if this has already been covered…….theres a huge number of pages here to digest.
I’m moving the jumpers to change EF91 tubes to EF95. I get that I have to move the jumpers from pins 2 & 3 to 1 & 2 but am I right in saying that pin numbers are 1, 2, 3 from left to right when the amp is upside down and the front is facing me?
I know it’s sounds like a pretty obvious question but doing it for the first time, I do want to make sure I’ve got exactly right.
Thanks

(When installing or removing jumpers, the amp should have been off and cooled down which makes it possible the electricity harboring capacitors have discharged. IF you shut off the amp with music playing, it will continue playing music while the capacitors are discharging.)

It seems you are probably on the right track for moving the jumpers.

When I turn my version of the MKIII upside down (removing the tubes makes the job easier for me)
with the volume knob pointed toward me, both jumpers should be connecting the two pins to the left for EF95 mode and vice versa for EF91/EF92 mode. When I look with a flashlight, 5654 i.e. EF95 appears near the Leftmost jumper pins and EF91 or EF92 near the rightmost jumper pins.

There are different versions of the MKIII. They do not all look the same when it comes to jumpers. With a flashlight, one can probably find the version number by looking through the housing holes when it's upside down. If you don't already have a manual knowing the version might help if you opt to look online.

It is common for people to lose hold of a jumper when trying to install it. Turning the unit upright and shaking can get it to fall out. Having spares can be good. Some people have bought aftermarket long-handled jumpers. I install the standard tiny jumpers using cotter pin pliers which are like a needle nose plier but much, much narrower, even narrower than tweezers, and not stout.

(IF the jumpers are installed for EF91/EF92 and one powers up the unit with EF95 tubes, the amp will not work and should be quickly turned off because one is shorting the EF95 tubes and probably risking other problems if left on. It is a somewhat common error and people have shut it off soon enough to avoid damage. IF the jumpers are set for EF95 and one powers up with an EF91 or EF92 tubes, another somewhat common goof, the amp is likely to work well but may risk being unstable with some tubes due to an unconnected grid in the tubes. In addition when running EF95 tubes in my MKIII, per my user manual, it makes no difference whether the jumpers are installed for EF95 or completely pulled out of the unit. I think of installing them in EF 95 mode as a good way of storing them and avoiding losing them.)

 

[Scooter64]

(When installing or removing jumpers, the amp should have been off and cooled down which makes it possible the electricity harboring capacitors have discharged. IF you shut off the amp with music playing, it will continue playing music while the capacitors are discharging.)

It seems you are probably on the right track for moving the jumpers.

When I turn my version of the MKIII upside down (removing the tubes makes the job easier for me)
with the volume knob pointed toward me, both jumpers should be connecting the two pins to the left for EF95 mode and vice versa for EF91/EF92 mode. When I look with a flashlight, 5654 i.e. EF95 appears near the Leftmost jumper pins and EF91 or EF92 near the rightmost jumper pins.

There are different versions of the MKIII. They do not all look the same when it comes to jumpers. With a flashlight, one can probably find the version number by looking through the housing holes when it's upside down. If you don't already have a manual knowing the version might help if you opt to look online.

It is common for people to lose hold of a jumper when trying to install it. Turning the unit upright and shaking can get it to fall out. Having spares can be good. Some people have bought aftermarket long-handled jumpers. I install the standard tiny jumpers using cotter pin pliers which are like a needle nose plier but much, much narrower, even narrower than tweezers, and not stout.

(IF the jumpers are installed for EF91/EF92 and one powers up the unit with EF95 tubes, the amp will not work and should be quickly turned off because one is shorting the EF95 tubes and probably risking other problems if left on. It is a somewhat common error and people have shut it off soon enough to avoid damage. IF the jumpers are set for EF95 and one powers up with an EF91 or EF92 tubes, another somewhat common goof, the amp is likely to work well but may risk being unstable with some tubes due to an unconnected grid in the tubes. In addition when running EF95 tubes in my MKIII, per my user manual, it makes no difference whether the jumpers are installed for EF95 or completely pulled out of the unit. I think of installing them in EF 95 mode as a good way of storing them and avoiding losing them.)

Thank you for a comprehensive response - that’s really useful and gives me the confidence I have done it right.
I did do it with the unit off, and it had been overnight. I also used modelling long nose spring loaded tweezers so grabbing hold of the jumpers, and keeping them firm, was pretty straightforward.
I have a got a manual but it’s only a generic one I found on the internet so not specific to the model I have, although from what it says about jumpers and gain control, I think it does cover my unit.
Thanks again

 

[Scooter64]

Jumpers changed, tubes changed from Mullard 8161 EF91s to Voshkod 6ZH1P-EV EF95s and listening on my DT770 Pros……well impressed with the difference

 

[Cognomen]

Or you can build a Christmas Tree like me

These are Novosibirsk 6S2S, the Soviet version of the 6J5GT. As @triod750 mentioned, you can also use the 6C5 family of tubes. I have a pair of almost 80-year-old VT-65 Ken-Rad's that, in a blind test, I'm pretty sure I wouldn't distinguish from the 6HM5.

There are literally hundreds of triodes that can be used in Little Dot. For some of them, there are off-the-shelf adapters; for others, you'll need to build a specific one.

Here's the list of families I found compatible for drivers (6,5V, <= 450mA):
2C22, 37, 3A/167M, 437A, 5842, 6AC5G, 6AC5GT, 6AE5GT, 6AF4, 6AM4, 6AQ4, 6C2, 6C5, 6C8P, 6CW4, 6DS4, 6ER5, 6ES5, 6F12, 6F5, 6FQ5, 6GK5, 6HM5, 6HQ5, 6J4, 6J5, 6J5G, 6J5GT, 6K5G, 6K5GT, 6K5MG, 6L5G, 6P5G, 6S3P, 6S45P, 6SF5, 6T2, 7245, 7586, 76, 7895, 7A4, 7B4, 8556, 8627, 8628, 8808, 9002, A2521, A2599, CV5112, CV6, E20C, E88C, EC52, EC80, EC8010, EC8020, EC86, EC866, EC88, EC88C, EC90, EC92, EC97, NY67

 

[Cognomen]

Or you can build a Christmas Tree like me

These are Novosibirsk 6S2S, the Soviet version of the 6J5GT. As @triod750 mentioned, you can also use the 6C5 family of tubes. I have a pair of almost 80-year-old VT-65 Ken-Rad's that, in a blind test, I'm pretty sure I wouldn't distinguish from the 6HM5.

There are literally hundreds of triodes that can be used in Little Dot. For some of them, there are off-the-shelf adapters; for others, you'll need to build a specific one.

Here's the list of families I found compatible for drivers (6,5V, <= 450mA):
2C22, 37, 3A/167M, 437A, 5842, 6AC5G, 6AC5GT, 6AE5GT, 6AF4, 6AM4, 6AQ4, 6C2, 6C5, 6C8P, 6CW4, 6DS4, 6ER5, 6ES5, 6F12, 6F5, 6FQ5, 6GK5, 6HM5, 6HQ5, 6J4, 6J5, 6J5G, 6J5GT, 6K5G, 6K5GT, 6K5MG, 6L5G, 6P5G, 6S3P, 6S45P, 6SF5, 6T2, 7245, 7586, 76, 7895, 7A4, 7B4, 8556, 8627, 8628, 8808, 9002, A2521, A2599, CV5112, CV6, E20C, E88C, EC52, EC80, EC8010, EC8020, EC86, EC866, EC88, EC88C, EC90, EC92, EC97, NY67

While listening to RCA Made in Great Britain 6HM5, I looked up this list of single triodes (and a few nuvistors) and queried them on all posts on this forum. This post was the first time approximately 85% of them were mentioned. In the past people tried and posted impressions of some triodes: 6AQ4, 6J4, EC90, short bottle 6HM5/6HA5/6HQ5 and perhaps EC92 and they did not bubble up to the top on lists of favorite tubes. More recently a limited number of people listened to the 6C5 and 6J5(GT) triodes and liked them. They are precursors of the twin triode 6SN7 which is used in a wide variety of good quality audio kit. Double triodes have been extensively auditioned on this forum both as driver tubes and as output ("power") tubes and some of them in addition to the 6SN7 incorporate similar tubes available as single triodes so the 85% 'statistic' errs on the high side.

The RCA Britain 6HM5s (Mullard Blackburn same year) have getter flashing running far down its side like the Yugo. Upon close examination the RCA has about 1 mm less. I also noticed very similar internals except for a slight difference in their plates. While the Yugo 6HM5 emits a flash of light when powered up, the RCA filaments burn very bright for the first second or so and then calm down. I find the RCA is slightly more forward than the Yugo in terms of mids and highs which suits my somewhat laidback speakers, ADS L620, well. I also found the RCA slightly warmer/euphonic. The RCAs sounded better than the Yugos on old Benny Goodman Big Band jazz recordings. Perhaps the Yugo whose mids sounded a bit harsh sometimes in comparison more accurately reflected the quality of 70 to almost 100 year old recordings, though. I like the warmer euphonic presentation for some genres of music: some classical and some jazz that I don't enjoy nearly as much on solid state. The RCA might be very, very slightly rolled off in the lower bass region (i.e. electronica and lower notes bass guitar) than the Yugo. Sometimes when switching back and forth I wondered about it and sometimes felt I could not hear a difference. I listened to them with RCA dissimilar double triode 6JK8s as output (power) tubes with my Little Dot MKIII. Due to brain and/or tube burn in I'm still learning about the sound of the 6JK8 which I consider competent to very competent so far.