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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 386

post #5776 of 10501
Quote:
Originally Posted by hypnos1 View Post

 

First off I heartily agree with you re 6SN7 tubes as powers...the more I listen to my Sylvania VT231s (with the C3GSs as drivers) the more I am liking them - they are absurdly good for the money. They really are giving my MUCH more expensive Psvane CV181-T IIs a run for their money (and that's before I make my own silver wire adapters!).

 

Secondly, just for interest's sake, I am awaiting a Tung Sol 7N7 - the loctal version of the 6SN7GT...more adapter-making!! Looking forward to seeing how they compare to the Sylvanias...

 

And thirdly - don't ask me why (perhaps iluvmusic's pioneering spirit with 6AS7s has lit a fuse in me!) - but I have just bought some very nice-looking RCA "coke bottle" 6AS7Gs...wait for it...to try as power tubes. I know, I know...I am putting it down to early onset dementia! Whatever, I am determined to at least see if it is a complete no-no.

As for heater power, I am wondering if it is possible to have one tube fed by the LD, with the other fed externally...suppose a peek inside would show if each is fed separately or not...

And I would need to take off the front panel and stick my finger inside to test for excessive heat...NO, ONLY KIDDING!! - the dementia isn't that far advanced?? A thermometer - carefully positioned! - should do the trick.

 

You could try to dissuade me, mordy, but I am all fired up at the moment!...Still, I have probably a fortnight to reflect on my madness...This rolling game has become too addictive, lol...:eek:

 

Glad to hear that the Sylvania's are growing on you. And as you like the VT-231, you would probably like most of the Sylvanias, Even the often maligned GTBs are quite good. And it is very likely that the Tung Sol 7N7s on their way to you are also a Sylvania. To the best of my knowledge, only Sylvania and National Union made 7N7 and the vast majority of the ones I have seen are Sylvania-made. (The Sylvania have chrome tops and the NUs do not.)

 

And I would be very leery about trying to run one 6AS7 off the internal Little Dot heater circuit and the other off an external power supply. It is quite likely (TrollDragon please weigh in here) that the two power tubes are wired separately and drawing that much current through just one side may well overload your wiring (smoke and flames?). But for sure, if you are willing to go to the trouble of feeding one separately, it would be simple matter to feed both off the same external power supply (tie the tubes' heaters together, pin 7 to pin 7 and pin 8 to pin 8) as long as your power supply and regulator have sufficient capacity, I am guessing more than 5amps to be safe.

 

So by all means do this! But be careful. :)

post #5777 of 10501
Quote:
Originally Posted by gibosi View Post
 

 

Glad to hear that the Sylvania's are growing on you. And as you like the VT-231, you would probably like most of the Sylvanias, Even the often maligned GTBs are quite good. And it is very likely that the Tung Sol 7N7s on their way to you are also a Sylvania. To the best of my knowledge, only Sylvania and National Union made 7N7 and the vast majority of the ones I have seen are Sylvania-made. (The Sylvania have chrome tops and the NUs do not.)

 

And I would be very leery about trying to run one 6AS7 off the internal Little Dot heater circuit and the other off an external power supply. It is quite likely (TrollDragon please weigh in here) that the two power tubes are wired separately and drawing that much current through just one side may well overload your wiring (smoke and flames?). But for sure, if you are willing to go to the trouble of feeding one separately, it would be simple matter to feed both off the same external power supply (tie the tubes' heaters together, pin 7 to pin 7 and pin 8 to pin 8) as long as your power supply and regulator have sufficient capacity, I am guessing more than 5amps to be safe.

 

So by all means do this! But be careful. :)


16 awg will be plenty safe @ 5A

 

http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

 

That's assuming you run both heaters off an external regulator in parallel


Edited by kvtaco17 - 4/8/14 at 11:12am
post #5778 of 10501

This is a good recommendation to use with an external power supply. But what we don't know is the wire gauge Little Dot is using to to supply heater current to power tubes in his LD !V. The 6N30s draw only about .9amps each, so it is not at all clear that it would be safe to draw 2.5amps through that same wiring for a single 6AS7.....

post #5779 of 10501

Hi hypnos 1,

 

Seems that everybody agrees that the the 6AS7 tubes draw more power than the LD can put out. These tubes draw 2.5A each, and the LD MKIII can put out max 1.5A/channel if I remember correctly, so external power supplies are a must.

 

I don't know how to rig up the adapters for two separate power supplies with voltage regulators for power tubes, but if you can figure it out it is certainly an interesting and rewarding project. And don't forget the aesthetic aspect:

 

"Here is a picture showing the open design of the 6AS7 electrode architecture. This tube (and the 6080) is a real glower - a perfect show-off tube."

 

amp10.jpg

 

So I am definitively encouraging you to try; just exercise caution. Who knows, maybe you will end up with a bargain MK9!

 

1000x1000.jpg

 

Personally, I would like to try the 6AS7/6080 as a driver tube with the 6SN7 tubes for power tubes. Or maybe a 5A 6338 tube? My voltage regulator can handle 5A ......

post #5780 of 10501

Heaters aside, perhaps a single 6AS7G could replace both power tubes. What do you think?

post #5781 of 10501

Many thanks to you all - gibosi; mordy;kvtaco17; oskari - it really is comforting to know so many good people are here to keep an eye on us keen amateurs, who otherwise could get into so much trouble!

 

Yes, the obvious safe course is to externally heat both tubes - just in case. Thanks for the reassurance...

 

Yes, these tubes (especially the "coke bottles") are real sexy. And the "cokes" seem to attract more pluses than the others - or is it all in the mind?...(Mind you, the real stars seem to be that shape...viz WE 421A; 5998...).

 

A single 6AS7? With amplification of just 2, would that be sufficient?

 

There are a lot of factors to ponder in this experiment...not forgetting artsi's concerns.

 

Thanks again for all your encouragement, folks, and be assured I shall be as careful as possible. It's such a shame it will be a while yet before I can venture forth into the unknown, what with postal systems etc. Not to mention sorting external power supplies. Ah well, such is the nature of what we do, no?

 

ps. So gibosi, it looks like my 7N7 will just be replicating my VT231? Those adapters will have to wait, methinks!!

 

pps....mordy - the 6338 seems to attract interest, but were there other differences to accommodate also?

 

Cheers folks.


Edited by hypnos1 - 4/8/14 at 12:08pm
post #5782 of 10501

I love the idea of using 6SN7GT more (great tube) but remember the GTB can take twice the power of our lovely GT fron the 40s. I would be interest in knowing where you got Tung Sol 7N7s :) re the 6AS7G, my favourite tube type for OTLs and I use it loads, however I would not be thinking to use it here. Just a bit too different, PSU issues sorted. The E182CC might make another intersting power tube also.......anyone tried a 3A/167M as a pre?


Edited by Nic Rhodes - 4/8/14 at 12:56pm
post #5783 of 10501
Quote:
Originally Posted by hypnos1 View Post
 

A single 6AS7? With amplification of just 2, would that be sufficient?

 

ps. So gibosi, it looks like my 7N7 will just be replicating my VT231? Those adapters will have to wait, methinks!!

 

 

I think a single 6AS7 could be used. but it is not at all clear what it would sound like. As the LD runs the double triodes in parallel, the resisters used to bias the tube are sized accordingly, and they may be too far out of spec for a single triode. But even so, I think it may well be worth trying.

 

And actually, the 7N7 will be less like your VT231 and more like a chrome-top 6SN7GT or GTA. At the least, you should notice more bass. :)

post #5784 of 10501

Recieved a Tungsam ECC40 the other day. Casual inspection suggests that it is perhaps mid-1950's, with the rather dirty, multi-hued getter splash and foil getter. But on closer inspection, I see the little tag "75" and according to the Tungsram tube codes, this suggests mid-1970's. So at this point, I do not know what to think....

 

post #5785 of 10501
Quote:
Originally Posted by Nic Rhodes View Post
 

......The E182CC might make another intersting power tube also.......anyone tried a 3A/167M as a pre?

 

The E182CC looks very interesting, unfortunately, is has a different pin-out than either the 6DJ8 or the 12AU7. It is closer to the 12AU7, but the heater center tap is on pin 8, instead of 9. It draws 640amps in the 6v mode and .320amps in the 12v mode

 

http://tdsl.duncanamps.com/dcigna/tubes/sheets/amperex/7119-1g.gif

 

For those of us using breadboard sockets, we would need to reconfigure three connections and use an external PS to use this as driver. And to use as a power tube, it would require a special adapter.

 

And the 3A/167M is a single 6v loctal triode and would therefore require two custom adapters to be used as a driver, similar to the C3G. It draws .45amps, which is the same as the 6AH6 pentodes many of us used to run.

 

http://www.retrovox.com.au/3A167M.pdf

 

Two very interesting tubes, but both would require some work to use with our LDs.....

post #5786 of 10501
Quote:
Originally Posted by gibosi View Post
 

Two very interesting tubes, but both would require some work to use with our LDs.....

 

Nothing that hasn't been done before :) and certainly the E182CC is a very friendly tube to the LDs. Some great Mullard box plates out there in good numbers :)

post #5787 of 10501

Then we have the synergy of running certain combinations of tubes together. My choice of investigating synergy is based on which tubes sounded good as drivers, and what I have that is a pair. Or, based on a sign I saw in a shoe store Midwest many years ago: A 7 and 71/2 shoe was labeled as a "near pair".

 

Been running two RCA 6SN7 (Hoffman rebrand and RCA from the mid fifties) with mysterious dark blue glow and top mounted heater wires with a GE 6BX7 as driver. Time for a change. Found to my surprise two mid 50's identical Sylvania chrome tops with the same date in my 6SN7 box. (They were bought separately). Since it is a pair they got to play the power tube role. Then I took my 6SN7 Japanese Channel Master MatsuHiToTen and plugged it in as the driver tube. Checked the voltage - needed a little less than the 6BX7, but the LED readout reads 6.5V to get 6.3V at the tube pins.

 

First impression: You got to wait. About 20 minutes before the tubes are up to speed. Then: Beautiful sound - sounds best without any adjustments in bass and treble. The bass is very powerful and the highs are sizzling. Very wide soundstage. All is well, nothing bothers me. The BX set up sounds different with more heft; this one is a little lighter, but everything sounds just right.

 

Amazing how you cannot go wrong with 6SN7 tubes.....

post #5788 of 10501
Quote:
Originally Posted by Rossliew View Post

Btw, anyone have pictures on how to change the jumpers from ef95 to ef92 on the LD Mk 3?

    On the first picture you see 3 pins (arrows) on the right side its the EF95 JUMPER SETTING so you would use the 2 pins on the right and if you want to use EF92 you use the 2 pins to the left and you do the same thing for the other channel. On the 2 nd picture the jumper is on the EF95 setting these peep holes are under the Littledot remember to put jumpers the same way on both channels                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

 

 

 

010.JPG

post #5789 of 10501

Regarding power supply i'am using a old desktop PS IMO it have more than enough current to roll  tubes (12V-15A) and i'm currently using a 12A voltage regulator.

TD here is the picture of LD 1 transformer.I just butchered mine i can't wait for that speed boat from Chinada.The wire size from LD 1 are 22AWG i don't know about the MK III yet i'am about to find out soon.I'am replacing the transformer wires to 18awg the headphone socket are 18awg and the Pot is 22awg.

 


Edited by i luvmusic 2 - 4/8/14 at 4:05pm
post #5790 of 10501
Quote:
Originally Posted by Nic Rhodes View Post
 

I love the idea of using 6SN7GT more (great tube) but remember the GTB can take twice the power of our lovely GT fron the 40s. I would be interest in knowing where you got Tung Sol 7N7s :) re the 6AS7G, my favourite tube type for OTLs and I use it loads, however I would not be thinking to use it here. Just a bit too different, PSU issues sorted. The E182CC might make another intersting power tube also.......anyone tried a 3A/167M as a pre?

 

Nic. Got the 7N7s off fleabay - one had just part of "Tung Sol" on it, the other no discernible markings but looking identical. Both chrome top short-bottles...so Sylvanias, according to gibosi...

 

Am hoping against hope the 6AS7G is not too different - and that the MKIV SE can continue its magical versatility...what a feat that would be - the Klondike revisited perhaps?! (I do actually feel like I'm in the grip of goldrush fever lol!).

 

Quote:
Originally Posted by gibosi View Post
 

 

I think a single 6AS7 could be used. but it is not at all clear what it would sound like. As the LD runs the double triodes in parallel, the resisters used to bias the tube are sized accordingly, and they may be too far out of spec for a single triode. But even so, I think it may well be worth trying.

 

And actually, the 7N7 will be less like your VT231 and more like a chrome-top 6SN7GT or GTA. At the least, you should notice more bass. :)

 

So,g, the 7N7 look to be Sylvania short-bottle chrome-tops. I believe you've said the short-bottles have a more detailed bass than the talls. Well that would suit me fine, because the VT231s - in my setup anyway - are giving me plenty of bass, and I would prefer a little less weight and a bit more detail. I am sure it's that bass, plus the greater mids, that are giving me a little less "air" compared to my Psvanes (and the 6N30P-DRs). So perhaps I have not wasted my money after all...thanks once more :bigsmile_face:

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