[TrollDragon]

What would happen if I put tubes rated 4.9 volts, .45mA in the Little Dot MK III driver sockets? Could it damage the Little Dot? Or would it probably just wear out the tubes faster than at their specified lower voltage? Also, when one doubles volts does current decrease by 1/2 in a straightline relationship? Or is that variable and specific to each type of tube?

You would burn out the tubes faster running the heaters higher than they should be, it would be 30% over recommended voltage.

For your other question if a tube is usable in a 12V or 6V filament configuration running it at 12V will require 1/2 the current of running it at 6V.

 

[Cognomen]

You would burn out the tubes faster running the heaters higher than they should be, it would be 30% over recommended voltage.

For your other question if a tube is usable in a 12V or 6V filament configuration running it at 12V will require 1/2 the current of running it at 6V.

 

[Cognomen]

How (un)safe would it be to use the rca connectors in the photo to make preamp cables with capacitors to connect the little dot MkIII to a direct coupled amplifier? I briefly looked at an audio website, and they had a formula based on impedences of the specific power amp (Marantz midline late '70's 2238B receiver with main amp input option) that I believe indicated I would need a 2.4 microfarad capacitor. Would a cable with that on it be a way to risk death if one removed it and absentmindedly touched one end with one hand and the other end with the other hand? Intuitively it seems that if it had offset dc from the little dot upon startup or shutdown or when a tube wore out that it could contain something hazardous. I currently use the LDIII with a capacitor coupled power amp. I power up the little dot first and then turn on the power amp and don't have problems. And I reverse the process when turning everything off. I once turned off the little dot first and it threw the power amp into protection mode. Once I turned off the little dot first and it immediately sent the power amp into protection mode.

 

[TrollDragon]

How (un)safe would it be to use the rca connectors in the photo to make preamp cables with capacitors to connect the little dot MkIII to a direct coupled amplifier? I briefly looked at an audio website, and they had a formula based on impedences of the specific power amp (Marantz midline late '70's 2238B receiver with main amp input option) that I believe indicated I would need a 2.4 microfarad capacitor. Would a cable with that on it be a way to risk death if one removed it and absentmindedly touched one end with one hand and the other end with the other hand? Intuitively it seems that if it had offset dc from the little dot upon startup or shutdown or when a tube wore out that it could contain something hazardous. I currently use the LDIII with a capacitor coupled power amp. I power up the little dot first and then turn on the power amp and don't have problems. And I reverse the process when turning everything off. I once turned off the little dot first and it threw the power amp into protection mode. Once I turned off the little dot first and it immediately sent the power amp into protection mode.

It's a dangerous dice roll connecting an OTL amplifier to a DC amp, if one of the output tubes fail it will take out your whole system all the way to the speakers. Not worth the risk IMHO.

We looked into making a capacitor box years ago but nothing ever came of it. I'd try a pair of 10K 1:1 audio transformers instead of capacitors with those connectors. The 1:1 transformers can be picked up quite cheaply and if something does happen all that will be destroyed is the transformer. I've never used 1:1 transformers but have seen them in use with other circuits.

 

[barbazz]

And we have a new #3 in my Top 5 opamp/tube list.

I had already heard both the opamp and the tubes in other combinations, but once again, it was demonstrated that on the LD 1+, the combos between the two components are of great importance.

This time, the chosen pair was Linear Technology LT1364 and Mullard CV138.

The LT1364 is very well referenced in the LD 1+ rolling tubes thread, and, in the past, with a Northern Electric 408A it proved to be much more competent than the original MC33078P. Interestingly, the first time I heard the Voskhods 6Zh1P-ЕV was with this opamp, and I was really disappointed with the lack of detail, especially in the higher frequencies.

I had also heard the Mullards, this time with the LME49720NA, and I wasn't particularly convinced. In this case, the sound was too tubey for my taste.

The marriage between the LT1364 and the CV138, on the other hand, went smoothly. The more analytical aspect of the opamp married very well with the warmth of the tubes.

Here's my updated Top 5:

1. National Semiconductor LME49720NA + Voskhod 6Zh1P-ЕV
2. National Semiconductor LME49720NA + Mazda 6CB6
3. Linear Technology LT1364 + Mullard CV138
4. National Semiconductor LME49720NA + Elektronska Industrija 6HM5
5. Muses MUSES8820 + Voskhod 6Zh1P-ЕV

 

[Cognomen]

It's a dangerous dice roll connecting an OTL amplifier to a DC amp, if one of the output tubes fail it will take out your whole system all the way to the speakers. Not worth the risk IMHO.

We looked into making a capacitor box years ago but nothing ever came of it. I'd try a pair of 10K 1:1 audio transformers instead of capacitors with those connectors. The 1:1 transformers can be picked up quite cheaply and if something does happen all that will be destroyed is the transformer. I've never used 1:1 transformers but have seen them in use with other circuits.

I looked at 1:1 10k ohms. 10k ohms is the output impedence of the LD MK III. I saw some that had 2 wires per side. Does one need 2 transformers, 1 for each channel? Some had 3 wires on 1 side and 2 on the other. Some had 3 wire leads per side. What type is needed? 2 wire leads per side? Are the sides mirror images meaning either side can be upstream or downstream as long as one keeps + and - on the same side? I saw some cheap "audio"' ones on eBay. Will they transfer the entire audible range, 20hz to 20khz? I saw some "audio" ones that cost quite a bit more but were still relatively affordable that were rated 300hz to 20khz or more. Reducing or cutting out sound below 300hz in my opinion is not good audio. Not sure how to shop for them. Are there recommended, probably helpful vendors? Is it safe to assume that after everything is powered off for a few minutes, even if things stopped working due to Little Dot possible DC output that it would be safe to disconnect transformers with rca on each end? It would be easy enough for me to put them in a box with rca connections. Perhaps I just don't know enough for DIY and should rely on a capacitor coupled amp? Many direct coupled and cap coupled receivers and amps I have looked at have speaker DC output protection. Nonetheless, I agree with the point that connecting the LD MKIII to an amp risks destroying the amp and speakers because one can't be sure that the speaker protection will work, especially if the equipment is vintage and a technician has not expressly verified the speaker protection works or has replaced it with new parts that should work for a long while. I suppose that unless one asks a tech to focus on speaker DC protection that the "usual" replacement of old receiver/amp capacitors etc may or may not include a focus on speaker protection. Or, is the type of typical speaker protection in those units simply not up to snuff when it comes to what the LD can do? While I am happy with the LD MK III, IMHO marketing the LD MKIII as a preamp is a low point due to its limitations: incompatibility with a huge percentage of power amplifiers because since around 1980 +- most amplifiers have been direct coupled. I don't know if that applies or not to the small subset of power amplifiers that are tube.

 

[TrollDragon]

I looked at 1:1 10k ohms. 10k ohms is the output impedence of the LD MK III. I saw some that had 2 wires per side. Does one need 2 transformers, 1 for each channel? Some had 3 wires on 1 side and 2 on the other. Some had 3 wire leads per side. What type is needed? 2 wire leads per side? Are the sides mirror images meaning either side can be upstream or downstream as long as one keeps + and - on the same side? I saw some cheap "audio"' ones on eBay. Will they transfer the entire audible range, 20hz to 20khz? I saw some "audio" ones that cost quite a bit more but were still relatively affordable that were rated 300hz to 20khz or more. Reducing or cutting out sound below 300hz in my opinion is not good audio. Not sure how to shop for them. Are there recommended, probably helpful vendors? Is it safe to assume that after everything is powered off for a few minutes, even if things stopped working due to Little Dot possible DC output that it would be safe to disconnect transformers with rca on each end? It would be easy enough for me to put them in a box with rca connections. Perhaps I just don't know enough for DIY and should rely on a capacitor coupled amp? Many direct coupled and cap coupled receivers and amps I have looked at have speaker DC output protection. Nonetheless, I agree with the point that connecting the LD MKIII to an amp risks destroying the amp and speakers because one can't be sure that the speaker protection will work, especially if the equipment is vintage and a technician has not expressly verified the speaker protection works or has replaced it with new parts that should work for a long while. I suppose that unless one asks a tech to focus on speaker DC protection that the "usual" replacement of old receiver/amp capacitors etc may or may not include a focus on speaker protection. Or, is the type of typical speaker protection in those units simply not up to snuff when it comes to what the LD can do? While I am happy with the LD MK III, IMHO marketing the LD MKIII as a preamp is a low point due to its limitations: incompatibility with a huge percentage of power amplifiers because since around 1980 +- most amplifiers have been direct coupled. I don't know if that applies or not to the small subset of power amplifiers that are tube.

Like I stated earlier I don't have any experience with 1:1 audio transformers but have read a little on them when we were looking to solve the problem of hooking up a LD amp to a DC amp.

These are the transformers I would go with to test and see how well they work in your situation. https://edcorusa.com/collections/ma...-matching-transformers?variant=41117605331131 they have 3 wires per side so they can be used balanced or unbalanced but you will connect them up only using the + and - to an RCA leaving the CT not connected. You would need one for each channel. Edcor claims 20Hz - 20kHz in the specs so they should be fine.

I would connect these and power on the Little Dot first then power on your amp. If you were unhooking them I would power the amp off first then the Little Dot.

OTL amps come with the risk of DC on the output if a specific failure condition occurs (chances are rare but can happen), which will destroy a DC amp and probably just destroy the inputs of a non DC amp. The only way to avoid this issue completely is to use an OTC (Output Transformer Coupled) tube amp.

 

[Cognomen]

Thank you very much! While I was trying to figure things out, I was on the Edcor site. While looking at transformers, I noticed they have circuit board versions of Decware for the hobbyist at a fraction of the cost of Decware.

 

[Cognomen]

Today I hooked up 2 Little Dot Mk III's to switchboxes (Luxman AS-4 III and TC-7240) so I can switch between tubes on the fly and listen to them on speakers or headphones. I will also eventually be able to compare DAC's and solid state vs tubes etc. I do not regard it as scientific, just another subjective way to compare. I have a decibel meter and can get the volume close, but I've read .2 dB can make a difference. My dB meter reads within 1 db. And I suppose there is also the problem of dynamic range capabilities when trying to make both equal. Right now I have tall bottle Westinghouse 6HQ6 ( 6HM5 6HA5 ) drivers on one and Svetlana 6J2P short bottles with dashes of white paint on top of each tube on the other. I have the same power tubes on both, 6N6P-T. The two amps sound similar listening to classical concertos. My music collection is eclectic and it's possible I could hear differences with other music. The 6J2P may be a clone of 6AS6 and 5725 radar pentodes. I didn't find posts about these species on this forum. Either they have not been widely auditioned or they have another equivalent that I did not query. I also have Svetlana tall bottle double red dot on top 6J2P-E that I briefly heard the other day and consider promising. The short bottles did not sound so good iniitally but have improved.

We have not figured out with certitude what "T" signifies when it come to 6N6P-T tubes.

The Ukraine vendor recently emailed me:
"The "T" in 6N6P-T refers to the specific version or variant of the 6N6P vacuum tube. Different versions of the same tube may have different specifications or performance characteristics, and the "T" designation is often used by manufacturers to differentiate between different versions. In the case of the 6N6P-T, this variant is typically a higher quality or more ruggedized version of the 6N6P tube, with improved specifications for things like maximum plate voltage, power dissipation, and noise performance."

My heart goes out to Ukraine. However, circa 2000, I tried to do business there and found it too corrupt. So, I suppose we should take this response also with a grain of salt because it might not be what "T" designates but the type of info that sells tubes.

I enjoy 6N6P's, find them quiet, and have a hunch they are probably better but have yet to compare them with other power tubes. There are Chinese 6N6 and 6N6-T military tubes.

 

[TrollDragon]

Thank you very much! While I was trying to figure things out, I was on the Edcor site. While looking at transformers, I noticed they have circuit board versions of Decware for the hobbyist at a fraction of the cost of Decware.

The Decware amp kits on Edcor's site are just the transformers that Decware recommends using for their Zen kits. You would still have to purchase the unpopulated board from Decware and all the parts to put on it.

if you are looking for a tube amp kit,
Elekit's are highly recommended.
https://www.tubedepot.com/products/elekit-tu-8200-stereo-tube-amplifier-kit

Or any of the VTA ST kits.
http://www.tubes4hifi.com/amps.htm

 

[g0ldl10n]

This is a heptode with 5 grids.

http://www.radiomuseum.org/tubes/tube_12sa7gt.html

http://www.r-type.org/pdfs/12sa7.pdf

If you wanted to use this in your LD, it would be best to have an octal breadboard socket to facilitate strapping the extra grids to the plate and/or cathode, that is, to convert it to a triode. So it could be done. However, in my opinion, it probably wouldn't be worth the time....

So, I actually built myself a custom adapter for dual 12SA7GT strapped as triode running a Eufonika H5M (default 6SN7 input) with just normal 8 pin octal sockets and I tell you what, they sound freakin' fantastic, lol (Currently using external PS for the heaters since they run on 12.6v).

I was actually searching the entire Head-fi forum to see if I could come across any impressions out there, and found this. This is obviously a very old comment/post, but thought I would chime in, in case anyone else was wondering. A custom adapter can be built as easy as one is built for say, strapping dual EL32 pentodes -> 6SN7 and they're wonderful drivers.

Kinda funny story how I came to need an adapter for this tube type - I was shopping for 12SR7 tubes actually - bought a listing that I thought was two pairs of 12SR7GTs, and once I received them, realized I read the listing too fast, and one of the pairs were the 12SA7GTs.. so I thought, wth, let's see if I can build an adapter for these for fun - and results were much better than I expected!

Currently have a pair a pair of blacked out Sylvania's and a pair branded as Westinghouse coinbase variants (seller said they came in a sealed box marked as Sylvania, so guess both pairs could be Sylvania's) - both pairs sound wonderful.

Because of their SQ performance, I have some Tung-Sol, National Union, 'Los Gatos' (I believe these might be Tung-Sol looking at them, but might never be sure) and some "Fapesa/Miniwatt made on Philips tooling in Argentina" types on their way. I would assume the 6SA7 variants have the same SQ, so also grabbed a few pairs of those too (obviously run on 6.3v instead).

 

[GotNoRice]

I just got a pair of Sylvania 6HM5/6HA5 (tall version) tubes for my Little-Dot I+ and I'm very impressed so far... These are the first non- EF95/6J1/6AK5(W)/5654/403B tubes that I've ever used with that jumper setting. I had been switching back and forth between a pair of Sylvania Gold Brand 408A tubes and a pair of Ultron EF92 tubes for a long time, but I like these new 6HM5/6HA5 tubes better than both of those, and they are my new favorites at this point.

One thing that I noticed right away about the Sylvania 6HM5/6HA5 tubes is that the bass seems to have a lot more texture to it (in a good way). Very open and airy top-end and amazing vocals.

I've always liked my Little-Dot I+ a lot, especially for my lower-impedance headphones, but it never quite seemed to match that true tube sound that my Little-Dot II+ (OTL tube amp, predecessor to the MKII) had. With these 6HM5/6HA5 tubes it really seems to have helped close that gap, which I didn't think was really possible.

 

[barbazz]

That's interesting. I have a pair of Yugoslavian EI 6HM5 and while the treble and soundstage are great, I found them lacking some bass. For the EF95 setting without adapters, my favourites are still the Voskhods 6Zh1P-ЕV.

Are you using the stock opamp?

 

[GotNoRice]

That's interesting. I have a pair of Yugoslavian EI 6HM5 and while the treble and soundstage are great, I found them lacking some bass. For the EF95 setting without adapters, my favourites are still the Voskhods 6Zh1P-ЕV.

Are you using the stock opamp?

Currently using a LM4562 OpAmp.

These Sylvania 6HM5/6HA5 tubes are definitely not lacking on bass. Quite the contrary. I listen to a lot of bass-heavy music and push some of my headphones, like my DT770-Pro/80ohm headphones pretty hard, up to the limit of what the headphone drivers can handle. During my initial testing with the Sylvania 6HM5/6HA5 tubes I accidentally caused an over-excursion event with my DT770 headphones on a song that I play often, and where I'm very familiar with exactly how hard I can usually push them with most of my tubes.

 

[warp2600]

That's interesting. I have a pair of Yugoslavian EI 6HM5 and while the treble and soundstage are great, I found them lacking some bass. For the EF95 setting without adapters, my favourites are still the Voskhods 6Zh1P-ЕV.

Are you using the stock opamp?

Currently using a LM4562 OpAmp.

These Sylvania 6HM5/6HA5 tubes are definitely not lacking on bass. Quite the contrary. I listen to a lot of bass-heavy music and push some of my headphones, like my DT770-Pro/80ohm headphones pretty hard, up to the limit of what the headphone drivers can handle. During my initial testing with the Sylvania 6HM5/6HA5 tubes I accidentally caused an over-excursion event with my DT770 headphones on a song that I play often, and where I'm very familiar with exactly how hard I can usually push them with most of my tubes.

I have been running Sylvania 6HM5/6HA5 tall tubes in my LD MKIII for the last few weeks too. They seem to be very linear in the entire frequency range. There is nothing not to like about them. Earlier this year when I returned to reading this thread after a long hiatus, I found out that I missed out on a lot of tube types (I had stuck with 6AK5 types). So I ordered a bunch of new types like EH90, 6H31, 5915, 6HM5, 8425, all of which sound great.