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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 278

post #4156 of 10559
Quote:
Originally Posted by gibosi View Post
 

On the 7308's top mica there is a metal plate covering almost the entire surface:

 

Could it be another mica sheet rather than metal?

post #4157 of 10559
Quote:
Originally Posted by gibosi View Post
 

 

Yes, I can these "mica springs", and for sure, the 6922 doesn't have them. Further, perhaps due to all that extra metal, the 7308 feels noticeably heavier in my hand.

 

And now I am very curious to see what the Holland-made Amperex 7308/E188CC looks like....  (Tracking indicates that it arrived in NY from France in only four days... and it sat in NY for two weeks! lol  But finally, as of today, it is on the move again.... Soon I hope.... ) 

 

*cough* darn customs *cough*

 

Yeah, I'm very curious about the European Philips E188CC for a few different reasons now. I'd expected the US 7308 to not be better than the US 6922 - some versions are even supposed to sound worse - but as far as Holland tubes go, the E188CC are supposed to be equal or better to the E88CC - at least for mid to late 60's tubes, early 60's and late 50's seem to be a bit more iffy to compare, as people's opinions are all over the place (the proverbial "all those tubes are great!" which doesn't help much...).

post #4158 of 10559

Just a quickie from someone in a mild state of shock - the combination of direct soldering of headphone cable to PCB and 30+ hours on the Tesla E88CCs (gold pins AND grids from the '60s) is producing something rather magical...even more detail (especially in the upper range) and soundstage than the TFK ECC88s. Plus all the bass you could wish for, which is a nice surprise after one of our esteemed colleagues found it not quite so hot in that department. Thankfully the over-bright aspect has now toned down and is transforming into even more sparkle than before, not to mention that wonderful treble detail. These could be my new love...once more...:wink_face:

post #4159 of 10559
Quote:
Originally Posted by Kestovitutus View Post
 

Hi.
This might be silly question with all this modding and other tinkering, but has anyone any good tips how to change jumper position easily :D I'm using sharp-nosed tweezers to fish them out. Not a big problem tho, because I only use one pair with EF92 setting. It's the Mk 3 with big brown nichicon capacitators? right next to jumpers.

Use long jumpers like this way easier to change

Processed By eBay with ImageMagick, z1.1.0. ||B2

post #4160 of 10559
Quote:
Originally Posted by Oskari View Post
 

Could it be another mica sheet rather than metal?

 

It very well could be another mica sheet... It has a very lustrous and smooth sheen to it, like chromed metal, but looking at the edges, I am not sure...  My cheap magnifying glass isn't all that good, and while I understand it would further the interests of our research here, I am simply unwilling to break the tube in order to be sure. :)  

post #4161 of 10559
Quote:
Originally Posted by hypnos1 View Post
 

Just a quickie from someone in a mild state of shock - the combination of direct soldering of headphone cable to PCB and 30+ hours on the Tesla E88CCs (gold pins AND grids from the '60s) is producing something rather magical...even more detail (especially in the upper range) and soundstage than the TFK ECC88s. Plus all the bass you could wish for, which is a nice surprise after one of our esteemed colleagues found it not quite so hot in that department. Thankfully the over-bright aspect has now toned down and is transforming into even more sparkle than before, not to mention that wonderful treble detail. These could be my new love...once more...:wink_face:

 

I have only about 20 hours on my Tesla...  So I guess I'll have to burn them in for another 10 or 20 hours...  :)

post #4162 of 10559
Quote:
Originally Posted by Audiofanboy View Post
 

 

*cough* darn customs *cough*

 

 

It's actually a little funny... Packages from Moldova and Ukraine have been getting through customs faster than this package from France! lol  While it is probably just a random delay, it does seem a bit strange....

post #4163 of 10559
Quote:
Originally Posted by gibosi View Post
 

 

I have only about 20 hours on my Tesla...  So I guess I'll have to burn them in for another 10 or 20 hours...  :)

 

Hi g.

 

Sincerely hope they deliver more for you - would hate to think I'm deluding myself! (They do LOOK so beautiful :tongue_smile:). But then - different set-up + tubes (even if from the same batch) : who knows?!

 

Still keeping an eye out for some early '60s Amperexes (for not silly money), but methinks I am in for the long haul...just hope the patience doesn't run out!

post #4164 of 10559
Quote:
Originally Posted by Ctritical Bill View Post
 

 

A better candidate in this circuit would be the 6SN7. Has anyone tried this as a driver ?

Oops, i have somehow forgot totally to try my 6SN7's as a driver. This is easily fixed. They work perfectly. Gain is perhaps little bit lower than 6SL7, but this is no problem. From now on i'm really listening different 6SN7's as a driver and try to find differences.

 

I know you guys love tube porn, so here is something to drool.

RCA 6SN7GT

700

Sylvania 6SN7GTA

700

Tung-Sol 6SN7GTB

700

post #4165 of 10559

Here was an interesting experiment... 12AX7 sealed in oil.

Quote: ZennAudio
Oil sealed tube. Jan GE 12AX7. Part of an interesting experiment to find out how the tube sounded when immersed in an oil environment. Sounded great. Very quiet and dark background in the soundstage.
post #4166 of 10559
Quote:
Originally Posted by TrollDragon View Post
 

Here was an interesting experiment... 12AX7 sealed in oil.

and smooth as a baby's butt

post #4167 of 10559

Artsi, you beat me to it. I have just tried a 6SN7 and, I agree, it works perfectly and still has that fabulous soundstage of the 6SL7. Mine is a NOS Russian from 1983 and of course I took some measurements ( stock values with no added resistors ) :

 

Heater  -  6.12v

Plate (R) - 86.0    Grid (R) - 2.13

Plate (L)  - 85.8    Grid (L)  - 2.13

 

So you can see the heater voltage is down quite a bit from the 6SL7 which was 6.36v . This is the unregulated power supply doing it's thing of dropping the voltage as the current draw increases. The 6SL7 draws 300ma and the 6SN7 draws 600ma so that all makes sense. Under-volting the heaters a little is no bad thing as it increases tube life.

 

The plate voltage is down below 100v which I think is the ideal in this circuit and it is a lot closer than the 6SL7 so a good result. Also the grid voltage is up around 2v where it should be.

So the technical results are all very good.

 

Speaking of ideals, in this circuit with a B+ of 200v , the ideal plate voltage would be 100v and grid 2v , which results in about 3ma through the tube. The Little Dot resistor values work to give these results as long as the tube is suitable. So if you are looking at graphs in the datasheets then you want to find tubes with graphs where the values of plate volts = 100, grid volts = 2,  and current  = 3ma roughly converge.


Edited by Ctritical Bill - 12/2/13 at 1:36pm
post #4168 of 10559

Can it always be seen, if a tube is faulty if you take closeup fotos? I have a matched pair voskhod tubes and one seems to be faulty, especially after switching from left to right the dropouts followed especially when i had the volume on 12 O`clock with 5 gain setting. Does this sound familiar to anyone? I couldn´t see any faulty wires that were detached and the silver lining in the tube head seemed intact too.

The seller asked me if i could make some closeup fotos before he decides towards a refund.

post #4169 of 10559
Quote:
Originally Posted by Ctritical Bill View Post
 

Artsi, you beat me to it. I have just tried a 6SN7 and, I agree, it works perfectly and still has that fabulous soundstage of the 6SL7. Mine is a NOS Russian from 1983 and of course I took some measurements ( stock values with no added resistors ) :

 

Heater  -  6.12v

Plate (R) - 86.0    Grid (R) - 2.13

Plate (L)  - 85.8    Grid (L)  - 2.13

 

So you can see the heater voltage is down quite a bit from the 6SL7 which was 6.36v . This is the unregulated power supply doing it's thing of dropping the voltage as the current draw increases. The 6SL7 draws 300ma and the 6SN7 draws 600ma so that all makes sense. Under-volting the heaters a little is no bad thing as it increases tube life.

 

The plate voltage is down below 100v which I think is the ideal in this circuit and it is a lot closer than the 6SL7 so a good result. Also the grid voltage is up around 2v where it should be.

So the technical results are all very good.

 

Speaking of ideals, in this circuit with a B+ of 200v , the ideal plate voltage would be 100v and grid 2v , which results in about 3ma through the tube. The Little Dot resistor values work to give these results as long as the tube is suitable. So if you are looking at graphs in the datasheets then you want to find tubes with graphs where the values of plate volts = 100, grid volts = 2,  and current  = 3ma roughly converge.

 

I've been looking at driver tube datasheets for over a year - since we started this non-native tube rolling silliness - and everytime I looked at graphs, I never really knew what values to use a base (though the graphs were still useful for misc. reasons). These values are actually pretty convenient to have, thanks!

post #4170 of 10559

Hi TrollDragon,

 

So basically this is an oil cooled tube. In the past I found that having a de-commissioned computer fan blow on the tube (actually drawing air away from the tube) on a hot summer day was detrimental to the sound if the tube got too cool. Apparently the tube needs a certain temperature to function properly. It should not be a problem with the oil, since one has to assume that it heats up somewhat.

 

I am sure that for an all American GE tube corn oil was used. The next step would be to put in an Amperex Herleen tube and surround it with Special Reserve Cold Pressed Extra Virgin Olive Oil. Wonder if different oils have different effects on the sound.

 

For those who prefer a wetter more sparkly sound, may I suggest Perrier sparkling mineral water.

 

For the car enthusiasts out there, I think that the Toyota OEM red radiator fluid would look good. Seriously, we need research here if the best sounding oil is a 5-20W or a straight 50 weight oil. (I know that there are protagonists for both.) And yes, we got to try Johnson's baby oil as well.

 

DISCLAIMER: This is an international forum, and we all come from different cultures and react differently to different inputs (just like tubes). What I wrote here was NOT intended to make fun of this interesting experiment, but to try to be funny, exploring the LOL quotient.

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