MPX3 6BL7 question
Jul 16, 2009 at 11:50 PM Thread Starter Post #1 of 22

thathertz

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Hi all

Please bear with me since I'm new to this
wink.gif


Ok my MPX3 SLAM has the following upgrades:

Power Input adapter for 12Volt tubes
Noble Volume Pot
Cardas Quad-Eutectic Solder
Cardas Copper Litz Wire
Additional RCA Input(2 Total)
Giant 47mf 630VDC Solen Capacitor
Jensen Paper-In-Oil Coupling Capacitors
Blackgate Cathode Capacitors
Solid Silver Audio Circuit
Silver Teflon Power Capacitors
Upgraded cathode gain tube capacitors
Upgraded output capacitors (low ESR)

I've heard that the 2c51 + 2x 6BL7 is a great combination.

SACD Lover said in an earlier post:

6BL7GT/A and 6BX7GT @ HIGH VOLTAGE. Some later MPX3 SLAM SE's
can accept either tube and do not have a high/ low voltage switch because of a "universal bias (my term).

I don't have the SE upgrades. Does that mean I cannot run 6BL7's?

Input appreciated, thanks!

Also, I've heard of people using 6V and 12V wall-wart adapters with
the MPX3. I don't understand how this amp which is rated at 110v
can perform with a 6/12v adapter. Does it switch internally to accept
this voltage?

Still playing major catch-up
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Jul 17, 2009 at 3:12 PM Post #2 of 22

takezo

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no, don't use a 6bl7 or 6bx7 in your mpx slam. the 6sn7 draws .6A of current from
your power transformer... the 6bl7/6bx7 draws 1.5A of current, more than double...
it may work for several seconds or minutes...followed by smoke and power failure.

when you put the 12v adapter cord into the back of your mpx slam, it bypasses
the 6.3v heater line to give 12v to the heater pins of the socket. regarding the
110v, that's why a transformer is used.
 
Jul 17, 2009 at 3:26 PM Post #3 of 22

Skylab

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I think that is good advice. Given that some SP amps have had problems, and that getting them fixed is a dicey proposition, why stress the amp out unnecessarily?
 
Jul 17, 2009 at 4:07 PM Post #4 of 22
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The typical Supra and SDS can handle the extra current draw easily. The Hammond power transformer in my SDS lists the filament supply as 6 Amps at 6.3 Volts. No problem for 3.6 Amps worth of draw from the tubes.

If you can, take a look at that transformer to see what you're dealing with. I wouldn't want to run it very close to the limit.

Edit: Wait, on second thought DON'T go digging around inside this amp by yourself - the parts can maintain deadly voltages especially since Mikhail is known for ignoring typical safety measures like installing bleeder resistors.
 
Jul 17, 2009 at 4:51 PM Post #5 of 22

thathertz

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Quote:

Originally Posted by takezo /img/forum/go_quote.gif
no, don't use a 6bl7 or 6bx7 in your mpx slam. the 6sn7 draws .6A of current from
your power transformer... the 6bl7/6bx7 draws 1.5A of current, more than double...
it may work for several seconds or minutes...followed by smoke and power failure.

when you put the 12v adapter cord into the back of your mpx slam, it bypasses
the 6.3v heater line to give 12v to the heater pins of the socket. regarding the
110v, that's why a transformer is used.



Ok, I got it. Thanks once again Takezo!

Quote:

Originally Posted by Skylab /img/forum/go_quote.gif
I think that is good advice. Given that some SP amps have had problems, and that getting them fixed is a dicey proposition, why stress the amp out unnecessarily?


Absolutely Skylab, I wanted to confirm this first though. Given my recent
problem with the MPX3 I intend to play it very safe from now on.

Ok, I'm sticking with the 6SN7's and 5687's for a good while.
I also have 6GU7, 6CG7 and 7N7's which are fine with this amp.

I have yet to switch it back on after the previous problem was 'fixed'
so that's my next hurdle..
biggrin.gif


Thanks for the help guys!
 
Jul 17, 2009 at 4:55 PM Post #6 of 22

thathertz

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Quote:

Originally Posted by mulveling /img/forum/go_quote.gif
The typical Supra and SDS can handle the extra current draw easily. The Hammond power transformer in my SDS lists the filament supply as 6 Amps at 6.3 Volts. No problem for 3.6 Amps worth of draw from the tubes.

If you can, take a look at that transformer to see what you're dealing with. I wouldn't want to run it very close to the limit.

Edit: Wait, on second thought DON'T go digging around inside this amp by yourself - the parts can maintain deadly voltages especially since Mikhail is known for ignoring typical safety measures like installing bleeder resistors.



Yep, I've read the horror stories and I'm not going under the hood.
Thanks for the input mulveling.
 
Jul 17, 2009 at 7:08 PM Post #7 of 22

Frihed89

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PM SACD Lover about this. He will know for sure. I have the high low power switch. I also have a Supra power supply. So, I have happily run these tubes. But don't do it unless SACD Lover says it is OK.

I urge you to look inside your amp and make sure these upgrades were all installed. There are two 1/16" (usually) hex head screws on the bottom of the front and back of the amp. Turn the amp upside down; unscrew these and lift off the bottom to expose the inside. The screws are generally torqued down very very tight. Make sure you have a very hefty 1/16" hex head (allen) key, bit or screw driver. It helps to heat the head of the screws with a soldering iron. Also make sure the tool is well-seated in the screw top and twist slowly, but forcefully, maintaining max pressure just up to the point where you may break the shaft of the tool. With enough heat and pressure, it will give eventually. Take a pic and circulate it. Again SACD Lover knows the inside of these amps better than almost anyone else.

Good luck.
 
Jul 17, 2009 at 11:40 PM Post #8 of 22

thathertz

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Frihed99: I'll PM SACD lover for his input.

Many thanks for the detailed instructions on opening the box.
The most comprehensive notes I've yet read.

However, I have no intentions at this stage to open up the amp.
Mainly because it's just not in my comfort zone and there is a good
chance of damaging the amp or me given my lack of experience.

Also, I've had one problem with this amp in my first week of ownership
and I don't want to temp fate. There's alot of investment in this amp,
both financially and emotionally so we're going to take each day as it
comes
wink.gif


A big thanks to everyone for their input over the last couple of days
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Jul 19, 2009 at 9:48 PM Post #11 of 22

moredes

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I've been running 6BL7GT/A's in my MPX3 SLAM since forever after trading emails with SACD-Lover.

Here is the information he sent me, verbatim and unedited:

Quote:

The MPX3 SLAM .... can use the 6BL7GT/6BX7GT. But the amps built with the 5687 in mind are not optimized for the 6BL7GT type tubes. So, what I am saying is the tube will not cause any problems, but the tube, and consequently the amp, will not sound their best. That, however, doesnt mean that you still wont like them.

The 6BL7GTA types can take 550 volts on the plate and can be biased up to 50-55 ma's at around 400 volts. The 5687 runs at 300 volts max and is biased at around 10-12 ma's. Therefore, if your amp was designed with 5687's in mind the 6BL7GTA types will not be producing nearly the power they are capable of producing and they sound sort of dull at this 5687 operating point, to me.

Now, you can use the 2c51 for more gain and this will drive the 6BL7GTA harder and produce more power. THE 2C51/5670, by the way, has its own adapter. The ECC type # 1 adapter WILL NOT work with the 2c51. The higher gain tubes you can use with the type #1 adapter .... 12AV7/ 5695/ 6414/ 6829/ 7062 will have the same effect because they are even higher gain than the 2c51. 2c51 = mu/ gain of 36 .... 12AV7/ 6414 etc .... = mu/ gain of 43-48. I dont know if the 12AV7's higher gain will work with the 5687's .... you may get some hum from excessive gain.

Next, the 6BL7GTA/ 6BX7GT sound more like 6SN7GT's, in that they have a more laid back, larger, less defined soundstage and a slightly warm tone. With the Denon that is supposedly on the richer, darker side the brighter sounding 5687's may be a better choice. Also, if you think the sound is to dark, rich or dull with the 6BL7GTA types try a brighter gain tube besides 6SN7GT's. If you have the ECC type #1 adapter the GE 6414 or 6829 will definitely give you a brighter and clearer sound with the 6BL7GTA types. You can also try the 7062 and the 12AV7's. I like the Raytheon 12AV7, again, for a brighter presentation. The Raytheon 6414 or 6829 black plate tubes are very detailed and smooth but not quite as clean and clear sounding as the GE's; atleast in my setup.

The Mullard ECC32 is a very nice tube. I would think the Mullard would be a very good match for the 5687's. I dont know about this tube with 6BL7GTA's. I am guessing the sound may be a little dark for my tastes, but very possibly .... not yours. In these cases you just have to try the combinations and see what you like. With different equipment and different ears I dont know what your reaction will be. Anyway, I hope this helps.


and in answer to other questions I had:

Quote:

What allows the amp to drive low impedances better is the tubes themselves. The 6sn7 is a 4.5 watt dissipation tube, the 5687 a 7.5 watt dissipation tube and the 6bl7gta a 12+ watt dissipation tube. The more power output by the tube the more current available at lower impedances. The bias and voltage are set for the 6sn7. But read on ....

Now the 5687 has the same essential operating points as the 6sn7 and you will get that tubes full power (approximately 2-2.5 x a 6sn7) in your amp by just adding the adapters. The 6bl7gta or 6bx7gt really need to be rebiased and/ or have the voltage increased to get their full performance. However, even used sub-optimally they will have more power than a 6sn7. You can make them operate more optimally by driving them harder with a higher voltage gain tube. Warning, if you try and drive the 5687's with the higher voltage gain tubes you will likely get to much gain and consequently get hum when the signal is muted .... or possibly overdrive the 5687's.

I would use the 5687's with a 6sn7/ 7n7 or 6cg7/ 6gu7. I would try the 6bl7gta's first with the same lower gain tubes and see how the headphone sounds. If it sounds underpowered try a 6414/12av7 for gain. A lot depends on how loudly you listen. If you are a low level listener the power requirements are obviously much less which makes the demands on the amp much more manageable for the amp. I hope that clarifies your question.


Beyond the TungSol2c51's, you should hear a Bendix 6385 coupled with NU 6BL7GTA'S... DAYUUMMM. I t's like comparing a Mullard EE32 against a Russian tube.

also, from here: http://www.head-fi.org/forums/f5/sin...on-hum-343447/ comes this response to a query about hum in an MPX3 SLAM :

Quote:

This may be a tube issue. Do you have a spare set or spare driver tube to
sub in?
You can use the following tubes:

6SN7, 5692, or any other variant of the 6SN7 tube in driver without
adapters. With an adapter you can use the following:

ECC1: 12AU7, 5751, 5814, 6189, 12AT7, 12AY7 (very nice), 12AV7, 5965
(Nice), among others.

ECC2: 6922, E88CC, ECC88, 6CG7, 6GU7, and others.

2C51: 5670, 6385, and of course the 2C51. These are excellent drivers.

7N7 driver tubes with the 7N7 adapters.

Output tubes: 7044, 5687 native to the Slam version. If you have the
Slam version with the 5687 adapter tubes, you can also use the 6BL7 tubes
in the output positions (center and rear).

If you have a native 5687 version with the 9 pin sockets as standard in
the chassis, we do make adapters to go the other way to accept the 6SN7
and 6BL7GT versions.


Thank You and let us know if you have any other questions.

Mikhail Rotenberg
Singlepower Audio Inc.


 
Jul 20, 2009 at 12:19 AM Post #12 of 22

thathertz

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To Moredes:

A big thank you for digging this info up and sharing it here!

Those combinations open up alot of possibilities
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May I ask if you had any issues with your amp / phones running any
of these combinations?

Cheers.
 
Jul 20, 2009 at 3:13 AM Post #13 of 22

moredes

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Frankly, I don't have a lot of hours on my set up. Earl's email replies date from 5/28/08, and I probably have 2hr/week on the MPX3 SLAM since then, so to be safe, call it 80hr with the 6BL7GTA's mostly driven by the 2c51. No problems at all.
 
Jul 20, 2009 at 9:08 AM Post #15 of 22

thathertz

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Quote:

Originally Posted by moredes /img/forum/go_quote.gif
Frankly, I don't have a lot of hours on my set up. Earl's email replies date from 5/28/08, and I probably have 2hr/week on the MPX3 SLAM since then, so to be safe, call it 80hr with the 6BL7GTA's mostly driven by the 2c51. No problems at all.


Great to hear that, thanks.

Quote:

Originally Posted by forcecommand /img/forum/go_quote.gif
My MPX3 is SE style with SE transformer. Running 2c51 6BL7 combo for hundreds of hours with no problem.


Thanks forcecommand, my MPX3 doesn't have the SE transformer but
Moredes has had no problems with his MPX3 Slam so I should be OK.

As for sources for the 2C51 adapter: Mikhail or FS forums?
 

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