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post #22291 of 24765

It held smoke smell as well but it is gone now.

 

Bleh, I know that feel. My SR-303 smelled strongly like a senior citizen's home when it arrived at my house. It was pretty gross, but it's gone now as well.

post #22292 of 24765
Quote:
Originally Posted by DefQon View Post

Ain't the newer line Stax tube amps auto biasing?

 

Well there is no such thing as auto bias, it's either fixed or not.  You can have servo control of the variable bias but that only goes so far.  The Stax amps all need to be adjusted but it is far more important to get properly matched tubes. Then the biasing is much easier and far more stable. 


Edited by spritzer - 5/16/13 at 8:08am
post #22293 of 24765

As far as self-biasing, someone wrote this on gearslutz.com:

 

Firstly, understand that VALVE/TUBES have insanely high voltages (HV) and an amp+ of current in places (some heaters)... you can DIE by playing with these voltages, and at best will get the shock of your life (like thrown across a room or to the floor)... and just remember, death is permanent!

If none of this scares you and you are happy to take your life into your own hands, acknowledge you do so at your own risk and are solely responsible for your actions (i.e, if you die or are hospitalized from your own stupidity or errors... you are to blame).

Right with that disclaimer out of the way, here is a good place to start RE working with amps: SafetyTips

RE biasing, the most common way is to do what is known as a 'cathode resistor bias', which measures the idle current across a resistor and you can retro fit this to most amps, general done on octal based output valves, many 9 pins don't need to be biased (or rather are 'preset').

You will need to place a 1ohm (best used for easy maths) resistor (2W-5W) from the cathode (pin 8 on most octal tubes) and ground and read the V across it.

What's nice about the cathode resistor method is that you're not dealing with high voltages. The cathode sits close to ground , which lessens your chances of death.... You're also reading each tube's bias current individually. 

To get a rough idea on BIAS points for the various tube families visit: Weber Bias Calculator

Since I could write a short book on how to do this all (and won't) your best bet is to purchase a tool like the Biasrite or BiasKing, which is much safer to use (you place it between the valve socket and valves).

RE meters, Fluke are the best (IMO), but expensive (and i don't use one because of that), there are a TON of Chinese ones that for most audio applications are more than sufficient. An autorange can be a nice feature to have if you are looking for one.

I hope that is of some help.

Cheers

Matt

post #22294 of 24765

SRM 600 LIMITED: DEAD LEFT CHANNEL
 

The headphones are good as I tried them with a different amp.  I tried switching the tubes and the left channel stayed dead, so not the tubes.

 

Cable and DAC are both confirmed good.

 

The problem first started with static in the left channel, then over the course of about 5 hours the sound gradually disappeared from the left channel.

 

Right sounds fine.

 

Any ideas about what I should check?

post #22295 of 24765

KG is going to make a post any second now. But I'd check if there is anything burnt or crispy looking inside.

post #22296 of 24765

Good call, how did you know?

 

Quote:

Originally Posted by rgs9200m View Post

As far as self-biasing, someone wrote this on gearslutz.com:

 

yada yada

 

Absolutely none of this applies to stax tube amps. You do not adjust the output stage bias current.

You DO adjust the output stage DC voltage at the plate of the tube.

 

The stax T2 has a servo which keeps the output DC voltage at zero within a limited range.

Newer versions of my kgsshv do the same thing.

 

As far as the srm600, likely the input fet pair is toast. on that one, a pair of 2sk170's glued together.

(goes looking for srm600 schematic)

 

Look carefully at the plate resistors. Measure with an ohmmeter after the thing is unplugged and

has been off for at least 30 minutes. remove both tubes and measure all 4 resistors.


Edited by kevin gilmore - 5/16/13 at 4:57pm
post #22297 of 24765

Thanks Kevin for the quick response.

 

I measured the 4 big resistors on each channel. They appear to be the original 30kohm AMRG.  Going left to right with the front panel facing me.

 

L channel: 30.6, OL, OL, 33.4

 

R channel: 65.3, 28.2, 29.7, 32.9

post #22298 of 24765
Quote:
Originally Posted by kevin gilmore View Post

Good call, how did you know?

 

Just had a good gut feeling that it was going to happen. wink.gif

post #22299 of 24765

The 30k AMRG death rate is about 50%+

 

every srm600 user should buy some spares....

you can get some cheap AMRG from amazon.co.jp

 

I've replaced  8-9 resistors, now they don't die

 

6 ARMG  in your srm600 are bad

they should be 27.5-29k


Edited by pkshan - 5/16/13 at 5:28pm
post #22300 of 24765

Any more reliable brands than AMRG that  ya'll recommend?  These are 5 watts right?

 

Did the bad resistors cause the FETs to fry?  I guess I can order some matched 2sk170 from Ebay; seem to be out of stock at Mouser.

post #22301 of 24765
Quote:
Originally Posted by pkshan View Post

 

6 ARMG  in your srm600 are bad

they should be 27.5-29k

 

Yikes! That would explain the somewhat disappointing SQ.

post #22302 of 24765

you can use two 15k AMRG, connect them in serial. so they never die

I've tried Caddock, Kiwame,Mills,AB resistors,

AMRG sound the best

post #22303 of 24765
Quote:
Originally Posted by pkshan View Post

you can use two 15k AMRG, connect them in serial. so they never die

I've tried Caddock, Kiwame,Mills,AB resistors,

AMRG sound the best

 

Amazon Japan has both the 15k and 30k 2 watts.  Is this the correct power rating?

post #22304 of 24765

yes, 2watts

post #22305 of 24765

Thanks PK.  I should probably test the resistors in my 007T.
 

EDIT:  Just ordered 16 of the 15k AMRG from Amazon Japan.  $99 (ouch), $40 of which was shipping (double ouch).


Edited by Argybargy - 5/16/13 at 6:51pm
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