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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 355

post #5311 of 7674
Quote:
Originally Posted by mordy View Post
 

Hi hypnos1,

 

Thank you for your kind comments. Truth is, I am perfectly happy to listen to the offspring of a 6SN7 and a 6DJ8. This baby is called 8FQ7 and made for Raytheon in Japan, probably by Hitachi. This tube has amazing clarity and musicality, and great treble and amazing bass detail and punch.

 

But I am not adverse to try 6SN7 as power tubes; I am just wondering if I am capable of building the adapters needed. Gibosi's solderless breadboard solution suits me fine,

 

 

 

Actually, mordy, I'm beginning to feel that rather than castigate you (and mab) I should be sending you (and him) my greatest thanks...I'm sensing in my bones that good things are on their way (literally!). So now, rather than with trepidation, I am awaiting the consequences of my rash decision with eagerness. :beerchug:

At the very least perhaps I may have helped gee things along a bit in this particular direction (but full marks go to mab, of course)...and to echo gibosi's sentiments, it amazes me also what we are able to do with our LDs...and still they beg for more! I can't think of any other units that are so forgiving, or that have made such massive improvements from stock without the need for equally massive (and costly) mods...perhaps somebody else knows differently?...

 

Cheers!

post #5312 of 7674
Quote:
Originally Posted by mab1376 View Post
 

 

Definitely give it a try with a 6SN7/6SL7/6SU7 driver tube if it doesn't seem all that impressive with the c3g's! I'm loving my 6SU7GTY.

 

As per my post to mordy, I feel thanks are in order after all...am feeling much more positive about the whole thing! :wink_face:

 

I must admit, though, I am putting all my faith in the Psvanes...from what I have been able to glean, it would appear they shouldn't have too negative an impact on the C3GSs, which are providing such an incredible signal to play with (but no guarantees, of course!).

 

And really don't fancy altering the look with the mods necessary to run 6SN7s as drivers. So wish me luck!!

 

Cheers!

 

ps. So glad you are still loving your new power tubes...you didn't have the DRs did you?

post #5313 of 7674
Quote:
Originally Posted by hypnos1 View Post

ps. So glad you are still loving your new power tubes...you didn't have the DRs did you?

 

I was running 6N6P-IR previously, and EH 6H30Pi prior to that.

 

I'm using these adapters: http://www.ebay.com/itm/250751485737?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

They sent me 2 sets of adapters BTW.


Edited by mab1376 - 3/10/14 at 10:33am
post #5314 of 7674

Hi mab1376,

 

If I understand correctly, you are running two 6SN7 tubes as power tubes and another 6SN7 as a driver tube?

 

Could you describe the difference between the IR power tubes and the 6SN7 power tubes? Is there a substantial difference that you feel will make it worthwhile to change from the IR tubes to the 6SN7 tubes?

post #5315 of 7674
Quote:
Originally Posted by TrollDragon View Post


Tube filaments change resistance (goes up) when they heat up, it might be 4 ohms cold and 90 when hot.

 

Shouldn't a hot one be simply Uf / I ? No?

post #5316 of 7674
Quote:
Originally Posted by mab1376 View Post
 

 

I was running 6N6P-IR previously, and EH 6H30Pi prior to that.

 

I'm using these adapters: http://www.ebay.com/itm/250751485737?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

They sent me 2 sets of adapters BTW.

 

Hi mab.

 

Things are looking up...if they are surpassing both those tubes - my EHs equipped themselves very well, even compared to the DRs - then I am filled with even more hopeful expectation...(just hope I'm not setting myself up for a fall!).

 

 

Thanks for the link...

post #5317 of 7674
Quote:

 

Thanks for the link - just ordered a pair.

 

Does anyone have a suggestion for a reasonably priced pair of 6SN7s to run as power tubes with these, apart from the re-issue tung sol 6SN7GTBs?

post #5318 of 7674
Quote:
Originally Posted by TrollDragon View Post
 

 

Sorry been out all day long and wasn't able to make this post for you.

 

The 12AU7 is run in 6V mode.

 

Are you sure that those two are IRF 630N's? They are the output mosfets and should be on the other side?

Ok then what are the numbers of the two on the other side? ;)

 

The LM317 max's out at 1.5A, it provides the current for the mosfets and the 12AU7 filament.

 

So you can test it by running wires out to a socket matching both sides of the 12AU7  Anode / Gate / Cathode with the 6SN7 pins.

You will use pin 5 and 9 from the bravo socket for your octal filaments, it does not matter which way you hook them up to the octal socket, 5 to 7 and 9 to 8 or vice versa.

 

The LM317's will probably get a LOT hotter from the doubled current draw, you will have to watch for this and if it gets TOO hot, I'd just forget about the octal in the bravo amp.

 

Thinking about this further, the two LM317's (to be confirmed by ILM2) are providing 6V to each side of the 12AU7's filaments with the center tap to ground. This also provides a load for the LM317 and for the IRF 630N mosfets. So no you will not be able to run a 6SN7 tube easily. I can't tell you to jumper pin 4 and 5 to 9 with a resistor and use an external power supply on the tube as I do not know what size and wattage resistor you would need to make this work.

Sorry.:(

 

You can feel free to experiment, but you do it at your own risk to the amp.

:beerchug:

Thank You for all the info/help(specially to TrollDragon and Gibosi)i tried all the method that you guys suggested but in the end it is not worth it using octal on BRAVO it HEAT UP a lot i may risk on burning the amp.Yes TD it is LM 317T and also by using octal the voltage measurment on those pins went up to 14V(pin 9 to 4 and 5)the sound was distorted and by strapping resistors i tried that too it did work(sound is distorted) and the IRF 630N(with resistors strapped) it gets overheated  soo i decided not to bother converting, after all we all have this AMAZING AMP(LITTLE DOT) Rolling all kinds of tubes and it sound amazing again THANK YOU for all you HELP!:beerchug:


Edited by i luvmusic 2 - 3/10/14 at 1:21pm
post #5319 of 7674
Quote:
Originally Posted by Oskari View Post
 

 

Shouldn't a hot one be simply Uf / I ? No?

Yes indeed, all he would have to do is measure the voltage between pins 5 & 9 with a voltmeter to get V.

Break the connection to pin 9 and put an ammmeter in series with it to get I.

Then the hot filament resistance R could be calculated.

 

R = V/I

post #5320 of 7674
Quote:
Originally Posted by i luvmusic 2 View Post
 

Thank You for all the info/help(specially to TrollDragon and Gibosi)i tried all the method that you guys suggested but in the end it is not worth it using octal on BRAVO it HEAT UP a lot i may risk on burning the amp.Yes TD it is LM 317T and also by using octal the voltage measurment on those pins went up to 14V(pin 9 to 4 and 5)the sound was distorted and by strapping resistors i tried that too it did work(sound is distorted) and the IRF 630N(with resistors strapped) it gets overheated  soo i decided not to bother converting, after all we all have this AMAZING AMP(LITTLE DOT) Rolling all kinds of tubes and it sound amazing again THANK YOU for all you HELP!:beerchug:

You are most welcome, anytime!

 

That is too bad though, I figured it probably would not work without some major board rework...

 

And like I said quite a few pages back. :tongue_smile: 

 

Quote:

Originally Posted by TrollDragon View Post

Personally I would not bother putting Octals on a Bravo Ocean. You probably won't be able to adjust the bias on that tube.
Just Kidding...

 

But you did have some fun and it was a great experiment to try out! Leave the little Blue amp just as it is and enjoy The LD Rolling Extravaganza!

:beerchug:

post #5321 of 7674
Quote:
Originally Posted by samtheman View Post

 

Does anyone have a suggestion for a reasonably priced pair of 6SN7s to run as power tubes with these, apart from the re-issue tung sol 6SN7GTBs?

 

In this forum we have very little experience using 6SN7s as power tubes in our LDs. To my knowledge, mab1376 is the only one. So my advice is to go by price. By a cheap pair of RCA,. Sylvania, Tung-Sol, Raytheon, or whatever, and see how they sound. You could get a pair of the old Russian equivalents, 6N8S, pretty cheap too. Personally, I think Sylvanias and Tung-Sols might be pretty good as they are fairly balanced and neutral, but this is just wild guess on my part.... :)


Edited by gibosi - 3/10/14 at 1:36pm
post #5322 of 7674
Quote:
Originally Posted by TrollDragon View Post
 

You are most welcome, anytime!

 

That is too bad though, I figured it probably would not work without some major board rework...

 

And like I said quite a few pages back. :tongue_smile:

 

 

But you did have some fun and it was a great experiment to try out! Leave the little Blue amp just as it is and enjoy The LD Rolling Extravaganza!

:beerchug:

Oh yeah i had alot of fun and learn something from it to DO NOT USED YOUR FINGER AS ATHERMOMETER FOR THOSE HEAT SINK lol:D

post #5323 of 7674

Thank you gibosi - you are always so helpful to everyone.

post #5324 of 7674
Quote:
Originally Posted by i luvmusic 2 View Post
 

Oh yeah i had alot of fun and learn something from it to DO NOT USED YOUR FINGER AS ATHERMOMETER FOR THOSE HEAT SINK lol:D


Been there, done that, got the blister or two... ;)

 

Now what you really need to do is work on a TV where the High Voltage wire going to the picture tube has a crack in the insulation, poking around taking measurements you happen to lean too close to the wire and SNAP, a 30 kV spark jumps to your nose... Yank your head back bumping it on the cabinet, just an excellent time, I really hated console TV sets.

 

But that was a long time ago, in a land far far away.

post #5325 of 7674

Well I dug out the old 6H9C again and decided to give it another listen.

 

Changed out the ceramic B9A for a machined pin ceramic Octal socket.

 

Not one of the prettiest tubes when it comes to glow...

 

This Great Album was sent to me and I thought I'd give it a listen with the 6H9C.

I don't remember the 6H9C sounding this good for a cheap soviet tube.

 

Listening with the GMP 8.300D's this Jazz Fusion album has some ultra sweet bass lines, and the 6H9C is providing a really nice punch to the GMP's. I am seriously impressed, a totally different experience than what I remember when I first tried the tube.

:beerchug: 

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