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Little Dot Tube Amps: Vacuum Tube Rolling Guide - Page 329

post #4921 of 10502
Quote:
Originally Posted by mab1376 View Post
 

The Sylvania 6SL7WGT I have from 1955 hums less and does sound amazing, the sound stage and instrument separation are amazing compared to the 6AV6 and 6HM5 tubes i've been using. The new production TS 6SL7GT from '05 I have hums a bit more and sounds OK, but nothing mind blowing.

 

Its really troubling me what is causing the humming, as you tried grounding isn't the issue.

 

From the interwebs... "6v octal preamp tubes (6SC/L/N7)are more prone to hum than 12v noval preamp tubes (12AX/T/Y/U7)"

The octals are more microphonic than other tubes as well for some reason.

 

Here is a little test I read about, wrap a piece tinfoil around the whole tube and base from top to bottom and then ground the tinfoil to the chassis to see if the hum goes away.

Also it is highly recommended to have a DC heater when using octals as preamps to try and get rid of the hum.

 

:beerchug:

post #4922 of 10502

I have only two 6SL7s, a Tung-Sol 6SUL7GTY, with black glass, and a Sylvania GB-6SL7WGT, and both are completely silent. And I can add that all the 6SN7s I have tried are also completely silent. However, I am using an external DC heater power supply, which tends to be quieter than the LD's internal AC heater supply.

 

The cathode voltage tends to be a little lower than desired when using 6SL7s in our Little Dots. However, if the cathode voltage is too low, it is my understanding that this would manifest itself as distortion, not as a ground hum. My best guess is that the hum you are hearing is due to the heater power supply, but again, this is only guess. Mordy has used 6SL7s, both with and without an external power supply. Perhaps he would be willing to add his two cents.

post #4923 of 10502
Quote:
Originally Posted by gibosi View Post
 

I have only two 6SL7s, a Tung-Sol 6SUL7GTY, with black glass, and a Sylvania GB-6SL7WGT, and both are completely silent. And I can add that all the 6SN7s I have tried are also completely silent. However, I am using an external DC heater power supply, which tends to be quieter than the LD's internal AC heater supply.

 

The cathode voltage tends to be a little lower than desired when using 6SL7s in our Little Dots. However, if the cathode voltage is too low, it is my understanding that this would manifest itself as distortion, not as a ground hum. My best guess is that the hum you are hearing is due to the heater power supply, but again, this is only guess. Mordy has used 6SL7s, both with and without an external power supply. Perhaps he would be willing to add his two cents.

 

it sounds more like radio static than a ground hum, i think you're onto something here.

 

Do you have ebay links to the voltage regulator and breadboard i would need to make a powered adapter?


Edited by mab1376 - 2/6/14 at 8:35am
post #4924 of 10502
Quote:
Originally Posted by mab1376 View Post
 

it sounds more like radio static than a ground hum, i think you're onto something here.

 

Do you have ebay links to the voltage regulator and breadboard i would need to make a powered adapter?

 

All you need is a voltage regulator and an AC to DC adapter. You may already have a suitable AC adapter. I am using a 24VDC adapter that came with an old cordless drill/driver. So if you have an adapter putting out 15V or more (to allow you to use 12 volt tubes as well) you are good to go. And I bought my regulator here:

 

 http://www.ebay.com/itm/131062144956?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649


Edited by gibosi - 2/6/14 at 8:46am
post #4925 of 10502

Hi mab1376,

 

Please look at the page 301 post 4507 where you have a guide to make an adapter using a breadboard.

 

There are many sources for a voltage regulator - can be bought for less than $5. In retrospect I would look for one from China rather than Hong Kong since it took 30 days to arrive from HK. Get one with a LED volt meter.

 

http://www.ebay.com/itm/DC-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-SSY-2510-/221302164468?pt=LH_DefaultDomain_0&hash=item3386a30bf4

 

This is one link of many. You can get it a little cheaper, but shipping time may be shorter from China.

post #4926 of 10502

Disconnect the wires currently connecting the LD's AC heater (Vector pins 3 and 4) to the 9-pin socket, pins 4 and 5 (or if you are using an octal socket, pins 7 and 8).

 

Run wires from the voltage regulator OUT to pins 4 and 5 on the 9-pin socket (pins 7 and 8 on an octal socket), and connect negative OUT to chassis screw to establish a common ground.

 

LL 

post #4927 of 10502

Hi Gibosi,

 

I use an external PS with a grounded voltage regulator as per your advice, and I do not have any major problems with hum using 6SL7 or 6SN7 octals (or any other tubes for that matter).

 

Since I listen through speakers, I run my LD KMIII at the highest volume without clipping, and keep the volume low on my power amp (110W ss). If I play very loud  (louder than I need), there is a hum, but it is drowned out by the music, and I can only hear it with nothing playing and turning up the volume very loud.

 

Even though the 6SL7 is a very nice tube, I find that the 6SN7 is a better sounding tube for me. The 6SN7s are plentiful, and I am able to buy tubes for $4 - 9 (incl shipping). I have a couple of Sylvanias form the 50's that are just plain wonderful sounding. They are so good that I am almost tempted to stop looking for better, although I have another tube that is exceptional - have to do a shoot-out before I report. And yes, this tube is also very inexpensive.

 

I do note that the Little Dot MK9 uses a Chinese variant 6H9C of the 6SL7 family as the driver tube.

 

It has been a three year odyssey for me to find these tubes.  It was a lot of fun and excitement to explore dozens and dozens of tubes to reach this level, but in one way I wish I would have known about them earlier and how to use them with the LD amps.

 

But I guess that you wouldn't really appreciate these tubes unless you went through all the trouble, experimenting and searching. In the words of my old dentist: "If I knew how fun grand children were, I would have had them first."


Edited by mordy - 2/6/14 at 10:41am
post #4928 of 10502
Quote:
Originally Posted by mordy View Post
 

Hi mab1376,

 

Please look at the page 301 post 4507 where you have a guide to make an adapter using a breadboard.

 

There are many sources for a voltage regulator - can be bought for less than $5. In retrospect I would look for one from China rather than Hong Kong since it took 30 days to arrive from HK. Get one with a LED volt meter.

 

http://www.ebay.com/itm/DC-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-SSY-2510-/221302164468?pt=LH_DefaultDomain_0&hash=item3386a30bf4

 

This is one link of many. You can get it a little cheaper, but shipping time may be shorter from China.

 

Is this the right vector adapter?

 

http://www.radiodaze.com/product/15450.aspx

 

I ordered this: http://www.ebay.com/itm/8-pin-octal-breadboard-prototype-tube-socket-for-DIY-experimenting-/150913780305?ssPageName=ADME:L:OC:US:3160

 

and this: http://www.ebay.com/itm/DC-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-SSY-2510-/221302164468?ssPageName=ADME:L:OC:US:3160

 

so far.

 

I just need to but some wire and find a power supply (which I'm sure i have one somewhere, at least 12v).


Edited by mab1376 - 2/6/14 at 11:18am
post #4929 of 10502
Quote:
Originally Posted by mab1376 View Post
 

Is this the right vector adapter?

 

http://www.radiodaze.com/product/15450.aspx

 

Yes.

 

And I am curious...  What is your current setup for listening to octals?


Edited by gibosi - 2/6/14 at 11:20am
post #4930 of 10502
Quote:
Originally Posted by gibosi View Post
 

 

Yes.

 

And I am curious...  What is your current setup for listening to octals?

 

Sweet, all parts ordered, just need to find a PSU and get some wire.

 

I bought an adapter off MIKELAP, it just has the buzz issue so i wanna take the DIY route with the PSU to see if that fixes it.

post #4931 of 10502

U got all the parts right. I am sure u have a little flat blade screwdriver for the breadboard.

 

The wires I use I got from an old computer power supply. Most anything will do.

 

Make sure you read about how to handle the Vector adapters in the post on page 301.

 

I think that an old laptop adapter would do fine as well since they usually are rated for around 20V.

 

Good luck!


Edited by mordy - 2/6/14 at 1:09pm
post #4932 of 10502
Quote:
Originally Posted by mordy View Post
 

U got all the parts right. I am sure u have a little flat blade screwdriver for the breadboard.

 

The wires I use I got from an old computer power supply. Most anything will do.

 

Make sure you read about how to handle the Vector adapters in the post on page 301.

 

I think that an old laptop adapter would do fine as well since they usually are rated for around 20V.

 

Good luck!

 

Thanks, i'm sure i have some old power adapters around to use.

 

Thanks for the tip on the adapters, i would be irritated if they came apart and i wasn't able to get them back together.

post #4933 of 10502

I finished my latest DIY amp. It uses one 6X5GT as rectifier, two 6SN7 powertubes and one octal socket for driver. I optimized this to use 6SL7 tubes as driver, cathode resistor 1.5k and to anode through 68k. No feedback connection.

 

After listening a while this amp with Tung-Sol 6SU7GTY i have realized how badly little dot is suitable for 6SL7 tubes. With little dot 6SL7 tubes work very limited way. With 6SL7 optimized amp 6SU7GTY tube sounds insanely good, it gives so much details, that i get chills. Music sounds weird, this amp will dig out all the little things from music, that i have not even noticed before. This is going to take time to get used to. Now i can focus on adjusting my other DIY tube amps even better.

 

In brief i suggest to use 6SN7 tubes with little dots. 6SL7 tubes are much more sensitive to any electric interference, and they won't sound as good how they could sound.

post #4934 of 10502
Quote:
Originally Posted by Artsi View Post
 

I finished my latest DIY amp. It uses one 6X5GT as rectifier, two 6SN7 powertubes and one octal socket for driver. I optimized this to use 6SL7 tubes as driver, cathode resistor 1.5k and to anode through 68k. No feedback connection.

 

After listening a while this amp with Tung-Sol 6SU7GTY i have realized how badly little dot is suitable for 6SL7 tubes. With little dot 6SL7 tubes work very limited way. With 6SL7 optimized amp 6SU7GTY tube sounds insanely good, it gives so much details, that i get chills. Music sounds weird, this amp will dig out all the little things from music, that i have not even noticed before. This is going to take time to get used to. Now i can focus on adjusting my other DIY tube amps even better.

 

In brief i suggest to use 6SN7 tubes with little dots. 6SL7 tubes are much more sensitive to any electric interference, and they won't sound as good how they could sound.

 

Got any pics? sounds interesting, i'd love to see your work.

 

Do you feel tube rectification provides any benefit?

post #4935 of 10502
Quote:
Originally Posted by mab1376 View Post
 

 

Got any pics? sounds interesting, i'd love to see your work.

 

Do you feel tube rectification provides any benefit?

http://kuvaton.com/k/yYqo.jpg Needs some paint...

 

Chassis is way too small! And there is inside transformer, 15H choke etc. Do not know is there any benefit to use tube rectifier, but it makes electric field and many 6SL7 tubes are rather sensitive to it. At least with tube rectifier amp does not seem to sound worse than with diodes.

 

Amp uses AC heaters without any problem.

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