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Tube Change/Biasing a Stax 006t II - Page 2

post #16 of 35
We are talking about direct drive electrostatic amps here that swing 400+V P-P so 10V is nothing, let alone 6v.

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post #17 of 35
Thread Starter 
Quote:
Originally Posted by spritzer View Post
We are talking about direct drive electrostatic amps here that swing 400+V P-P so 10V is nothing, let alone 6v.
Yeah... after sending out the message I started thinking about it and from a percentage view it's pretty small. If I'm writing this up for others I figure that anything under a few hundred mV is more than acceptable and anything under 100 mV is just plain not worth the effort.

Thanks for the help... listening to some Rippingtons and everything sounds just fine. I'll take some pictures and write things up later today or tomorrow and post it under a thread called:

"Changing Tubes in a STAX 006t II"

Thanks for all the help............

Tom
post #18 of 35
Anything under 1v is more then good enough but it's fine to shoot for the mV range.

You could also add to the title of your thread what other amps are basically identical. In chronological order: SRM-T1, SRM-T1S, SRM-T1W, SRM-006t and SRM-006tA/II
post #19 of 35
Thread Starter 
Quote:
Originally Posted by spritzer View Post
Anything under 1v is more then good enough but it's fine to shoot for the mV range.

You could also add to the title of your thread what other amps are basically identical. In chronological order: SRM-T1, SRM-T1S, SRM-T1W, SRM-006t and SRM-006tA/II
Thanks... will do. I think I'll put the text up here for review and add the pictures afterwards.

Tom
post #20 of 35
Thread Starter 

Procedure text w/o pictures for review

Changing Tubes in a STAX Tube Headphone Amplifier

The following description is specific to the STAX 006t II vacuum tube output driver unit but much of the procedure is similar for any of the STAX tube units (SRM-T1, SRM-T1S, SRM-T1W, SRM-006t and SRM-006tA/II)

WARNING – DON’T BE STUPID. If you cannot read English very well, are uncomfortable around high voltages, describe yourself as “all thumbs”, “ham-fisted” or “awkward” and have never worked inside of any electrical component that has potentially lethal voltages DO NOT attempt any of the procedures listed below. Do yourself and your equipment a favor and find someone who can, or take a copy of this to a local audio/video repair shop and ask them if understand what is being described and can they can do it for you.

Disclaimer – I make no warranty and accept no responsibility for suitability of any materials listed below. I assume no responsibility or liability for errors or inaccuracies. Reader accepts all responsibility for any and all results obtained. Use of any supplied materials constitutes acceptance and understanding of these disclaimers.

STAX clearly states on the Operating Manual for the 006t II that “This product operates with a high voltage. It is extremely dangerous to attempt to dismantle or modify the unit in any way, and under no circumstance should any such attempt be made.” What I have done has clearly violated the manufacturer’s warranty – YOU HAVE BEEN WARNED!


What follows is a description of how I changed and adjusted the tubes in my personal STAX 006t II vacuum tube amplifier.

The tools I used were a philips screwdriver (to remove the cover), an insulated (plastic) slot head screwdriver (to adjust the internal potentiometers), and a good quality multimeter that is set to measure volts .... NOT AMPS!

Procedure I used:

I disconnected the headphones, unplugged the unit from the wall power, and using a Philips screwdriver, removed the four screws that hold the top.

I removed the two 6FQ7 (6CG7) tubes and replaced them with the new tubes (that were checked with a tube tester prior to insertion in the unit).

With the cover still off I plugged in and powered up the unit leaving it on for about and hour to stabilize. WARNING – at this point the cover is off and the unit is powered. I NEVER leave an electrical unit in this state unattended for any reason.

Below is a diagram of the earspeaker connector as it would appear if you were looking at it from the front of the unit. There are two of these connectors with the words “PRO ONLY” above them. They will not have "L+", "L-", "R+".... those labels identify the holes for the purpose of the discussion below.

*** See Attached STAX Connector image ***

WARNING - DO NOT under any circumstances put a probe into the socket shown on the bottom right labeled above as “Bias”. In fact, I covered it with a small piece of tape so that I wouldn’t have the possibility of an accident that could damage the unit or myself.

I set my multimeter to measure volts and inserted the positive probe into the slot shown above labeled “L+” and inserted the negative probe into the slot labeled “L-”. At this point I was measuring dc balance. My first measurement was in the 6 volt range, the reading could have been higher or lower, the goal is to get it under 1 volt. To adjust the value I used a plastic (NOT METAL) slot head screwdriver and adjusted the potentiometer labeled “TVR1” for the left channel. The potentiometer is EXTREMELY sensitive and the meter reading will have a tendency to drift around a bit. With some effort I was able to get the reading stabilized at about 0.250 volts.

*** See attached inside view of STAX 006t II ***

I then removed the negative probe from the slot labeled “L-“ and attached the probe to the ground post labeled “GND” at the back of the unit. At this point I was measuring dc offset. Initially, the dc offset was around 1.5 volts. Again, the object was to get the dc volts under 1 volt. To adjust the value I used a plastic (NOT METAL) slot head screwdriver and adjusted the potentiometer labeled “TVR2” for the left channel. Again, the potentiometer is EXTREMELY sensitive and the meter reading will have a tendency to drift around a bit With some effort I was able to get the reading stabilized at about 0.090 volts.

I confirmed that the dc balance was still below 1 volt by removing the negative probe from the ground post and re-inserting it into the slot shown above labeled “L-”. If needed I could have adjusted the dc balance again and lowered it under 1 volt, but it still measured close to 0.250 volts. This process of going back and forth between the adjustment of dc balance and dc offset could have happened several times.

At this point the left channel adjustments were complete. I followed the exact same procedure for the right channel with similar results for the measured and adjusted voltages.

With both channels adjusted I turned off and unplugged the unit. With the unit unplugged I attached the top using the four screws and then plugged in the unit into the wall power and I was done.
LL
LL
post #21 of 35

I was tube rolling my STAX SRM-006t and needed to adjust balance and offset. I was puzzled because the printed "BALANCE" and "OFFSET" on the PCB have changed placed in SRM-006t and the newer SRM-006tII. I believe there is a misprint on the PCB of SRM-006t which is corrected on the new version. They have practically identical PCB layout and components. Does any one have another explanation to this?

 

Here you can see how it looks:

 

Sammenligning SRM-006t ny og gammel.jpg

post #22 of 35

Looks like it is just mislabled

post #23 of 35
Quote:
Originally Posted by ColoradoTom View Post

Changing Tubes in a STAX Tube Headphone Amplifier

The following description is specific to the STAX 006t II vacuum tube output driver unit but much of the procedure is similar for any of the STAX tube units (SRM-T1, SRM-T1S, SRM-T1W, SRM-006t and SRM-006tA/II)
....
 

 

I went ahead and made this a Wiki for it to be easier to find. Big thanks to ColoradoTom and others

 

http://www.head-fi.org/a/adjusting-bias-on-stax-tube-amplifiers

post #24 of 35
Just got a SRM-006ts from Price Japan and waiting for my headphone to arrive. While tuning the offset for the tubes, I discovered that 2 of the 4 big capacitor and the 3 small ones around the transformer has about 370Vdc leaking on top of its body. Would appreciate if any user of this amp would verify on their set. It definitely looks not right to me.
post #25 of 35

So are the TVR screws on the 007t/ii (that I have) clearly and accurately marked if I want to do biasing myself? Thanks.

post #26 of 35

^ I had no problem finding them :)

post #27 of 35

OK, thanks. Is it easy to tell which is the Left/Right channel for each of the TVR1 and 2 screws?

Thanks again.

post #28 of 35
Quote:
Originally Posted by rgs9200m View Post
 

OK, thanks. Is it easy to tell which is the Left/Right channel for each of the TVR1 and 2 screws?

Thanks again.

 

I had no problem with that. But you can of course open up your amp to look for yourself ,)

post #29 of 35

Ok, thanks again. When I get my voltmeter, I'll go at it.

post #30 of 35
Quote:
Originally Posted by rgs9200m View Post
 

Ok, thanks again. When I get my voltmeter, I'll go at it.

 

Just be careful where you stick your fingers... 

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