Luxman SQ38u bias adjustment

[TLL]

The photo is from 6moons

[henry218]

The photo is from 6moons

nothing comes up , perhaps check your link or attachment?

[TLL]

http://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=1n13T4d7j-GoqM&tbnid=3Lot9Se_VVOCoM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.6moons.com%2Faudioreviews%2Fluxman2%2F38_2.html&ei=XqybU8XUK8bNkgW0roGoAw&bvm=bv.68911936,d.dGI&psig=AFQjCNFuV4f_9e47BUZjbWBd4FQUjSLsoQ&ust=1402797499682950

 

I'm trying to upload the above photo, but don't know how, someone may be able to help?

 

Anyway, here is the instruction to adjust the bias current (warning, do at your own risk as it is high voltage)

 

1. To check V plate voltage put your DDM probes across pin #3 & #8 (I measured 475V) of the EL34 tube

 

2. What bias current should used? My reference is based on the following web site

    http://www.webervst.com/tubes1/calcbias.htm

 

3. To check cathode voltage and adjust bias current, put your DDM probes across the 10 ohm resistor

 

If you could see the above photo, from left to right, there are four white pots with a cross on the top  VR1, VR2, VR3, VR4

 

- VR1 and VR2 is one group, adjustment for one channel (left or right, cannot remember)

- VR3 and VR4 is for the other channel

 

First, use VR2 to adjust the cathode current flows to both tubes, turn it anticlockwise to reduce current, but slowly as it is very sensitive

Second, use VR1 to adjust the balance between the two EL34 tubes until the DDM readings are equal.

You may need to repeat the adjustment of VR2.

 

Then repeat with VR3 and VR4 for the other channel.

 

A little more information about wires colour and EL34 pins

 

Brown  EL34 pin #2 and #7 - heater

Thin white wire from circuit board pin #5 of EL34 - signal input to EL34

White wire to pin #3 of EL34 - it is the plate of EL34, connect ot output transformer

EL34 pin #1 and pin #8 - shorted in pp amp configuration

EL34 pin #6 - not use

EL34 pin #8 - the cathode, where a 10 ohm resistor is connected to the ground

 

Plate voltage pin#3 and pin#8

Cathode voltage pin #8 and ground

 

Ground is the thick copper wire connected across all the tubes

 

I wish it may help someone who has the Luxman SQ-38u

 

Cheers

Edited June 14, 2014 by TLL

[TLL]

http://www.webervst.com/tubes1/calcbias.htm

[VanArn]

The H.T. (B+) voltage that matters is measured from the centre tap of the O/P transformer and ground.This for a model with a  240V a.c. mains transformer,should be 420 to 430V,d.c. to achieve the rated 30W into 8 Ohms. The Lux SQ 38 U uses the EL34 in a fixed bias,class AB, U.L. mode.I would expect that the  bias current should be set to around 50 to 60mA for the best performance ( .5 to .6V across the cathode resistor).Precautions when setting the bias include  fitting dummy load resistors  at the speaker outputs and ensuring that no signals are arriving at the O/P valve grids.

[TLL]

Hi VanArn

 

I think you are right, as I'm no expert on tube amps circuitry. I thought the bias was adjusted as per plate voltage of the EL34.

Thanks for your input and clarification.

[VanArn]

It has  indeed been a difficult time for owners of Lux/Luxman products with the various ownership buyouts of the original company leaving a vacuum for clients seeking  maintenance or manuals for the product.  With the Lux brand being re-established following the mores of the original founders,hopefully the new distributors  under the auspices of Audio Active Australia Pty. Ltd. can eventually fill the void and assist in supplying some of the required service information.

[aaleks]

Well, I decided I am keeping my luxman and would like to do some experimenting with the tubes (never even attempted something like this before).

 

thinking of Electro Harmonix 6ca7 EH.  Do I need a matched quad or 2 matched pairs. Will I need to adjust bias after replacing ...

[rodders3]

I wish someone answered the above question five years ago.

 

I have the Luxman SQ38u and recently changed the power tubes from Tung-Sol el34B to a matched quad Genelax Gold Lion KT77. The difference in sound is quite profound in a very good way. It has made my speakers really sing.

 

It is the first time I ever changed a tube and did a straight swap. I don't pretend to know anything about biasing at all and clearly didn't do anything to adjust.

 

I did a lot of research on the net and one particular site suggested the SQ38u is NAB which I suspect meant it was non adjustable biasing.

 

Well the system sounds great but can I expect a mini catastrophic explosion anytime soon?

[Guest Muon N']

In this review it  says that the SQ38u is auto bias.

https://stereonomono.blogspot.com/2010/05/luxman-sq-38u.html

 

"Luxman's retro-styled SQ-38u is the 11th installment of a now 25wpc EL34 push/pull integrated with auto bias and a classic Ultralinear Mullard circuit."

 

Edit:

Also in this review

http://www.stereomojo.com/Luxman SQ-38u Tube Integrated Amplfier Review.htm/LuxmanSQ-38uTubeIntegratedAmplfierReview.htm

 

"I believe the easiest way to sum up the SQ-38u is it is a classic tube product but with some improvements like modern parts, voltage regulation, auto bias, and a remote control.  The best elements of vintage and modern design in one versatile package." 

 

 

I couldn't find a manual, maybe there is one...likely in Japanese though.

 

 

 

Edited May 12, 2019 by Muon N'

[rodders3]

Cheers @Muon N'. I did read similar but seeing the OP, wondered if it was necessary or just the OP wanted to have a fiddle with it to satisfy him/her self it was correct.

 

Either way, thanks mate, I'll leave it well alone.

 

Cheers, Rod

[Guest Muon N']

These reviews go against a discussion around the amp being fixed bias in some previous posts on the subject, so I'm not sure what is going on.

 

 

Edited May 12, 2019 by Muon N'

[rodders3]

SNAP!!!

[Guest Muon N']

I'd contact Luxman and see if they are good enough to respond.

[Guest Muon N']

Also, and I'm hesitant to say this as I know VanArn is very smart and experienced, but biasing EL34's at 50 to 60mA is like...wow! in a guitar amp I'd have less qualms, but in a hifi amp for a KT88, sure!

Edited May 12, 2019 by Muon N'
typo

[F18]

50 to 60ma is nothing out of the ordinary for kt77’s or el34’s. Considering they measure up to 90-110ma for a new tube.

 

Depends on what plate, grid and cathode voltages is present for the valves. The sq38u is fixed bias, newer gen sq38u may be different. The biasing is usually done near the transformers and back to the valves through a 100ohm or 10ohm resistor measuring links.

Edited May 12, 2019 by F18

[Guest Muon N']

So depends on the model of the sq38u with the older models fixed? and newer auto?

 

Well others can bias their EL34's at those specs with a 475v plates, I'll continue to bias mine at 30ma to 40ma where a plate voltage is around the 450v area. I prefer the sound at these specs, and the tubes will last a lot longer.

 

 

[Guest Muon N']

These things are all over the place, looks like Luxman have at times provided incorrect information to some reviewers, this review says

"The fixed-bias design, with a rail of about 420V (at power)"
Read more at https://www.stereophile.com/content/luxman-sq-38u-integrated-amplifier#Rx9rGI4G746OP5rE.99

 

The current owners manual is not in the least helpful, has not reference to bias circuit at all, or anything related.

https://onahighernote.com/oahn/wp-content/uploads/2015/01/SQ38u_eng.pdf

 

 

 

 

 

[Guest Muon N']

Looks like this model is from 2008 according to this write up.

http://www.highfidelity.pl/@main-68&lang=en

 

 

OK, in Japanese but can see the procedure for setting the bias, and as you can see he is setting it at 350mv/35ma as recommended for this amp by Luxman. So it is fixed bias. Bloody internet reviews!

 

I have translated via google and added the pertinent bits with pics, just in case this page disappears like happens on the internet at times.

https://nack-audio.com/wordpress/luxman-sq-38u-el34/

-----------------------

In the case of EL34 When the output tube is replaced, "almost" bias adjustment is required.
I said "almost" because I said "almost" because some amplifiers and designs use self-biasing circuits and some amplifiers do not require bias adjustment from the beginning.
Well, for most triode amps, bias adjustment is required.

Most of the resistors in the tube amps are distracting on this "bias adjustment" wall.
For those who don't understand, "No way" For those who don't know "Unknown work"
Let's say that this is "bias adjustment" syndrome.

Speaking in advance, this article does not explain "bias adjustment" at all.
Or say. . I can not explain.
In terms of work, I just turn the volume (pod), but what about "what"?
There are a few things that you must at least know in order to know the "what".

Basic knowledge of electricity and electrons (plus, minus and electron relations, basics of alternating current and direct current)
Basic structure and characteristics of vacuum tube (meaning of amplification)
Basic configuration of circuit and specifications of parts used (Resistor-Transformer-Capacitors etc ,,)
Ohm's law (relationship of current, voltage, resistance)
Basic usage of the measuring instrument (tester)

Well, it is the source of an accident if you do not know the above level at least.
If you think the above thing is easy, you can create a tube amplifier designed by yourself, more than bias adjustment.

The person who knows the bias adjustment is a matter of course There is such a high hurdle that the stranger does not know at all.

However, this time, I will make an article about “bias adjustment” like this.
It would be nice if you read this article and think "Let's study a little".

 

First of all, it consists of this amplifier "push-pull".
It is also called "PP amplifier" for short.
Speaking so simply that super can be attached, the two L2 R4 output tubes are responsible for the L side and the R side.
If you assign the numbers 1.2.3.4 from the left, you can take L side ch with 1 and 2 and R side ch with 3 and 4.

The adjustment position of "adjustment" of "bias adjustment" is the adjustment volume of photo ○ mark (pod)
There is a + plus shape of the driver.

Be sure to use a dedicated adjustment driver when turning this adjustment volume.
There is nothing that even a normal driver can not do, but please think that there is a considerable "risk".
If you use a metal driver and touch any other electrode part, it will be an outrageous accident.
There are places in the tube amp where a high voltage is flowing that can not be imagined from the appearance.
If the equipment only breaks down, there is still no risk of electric shock.
I also have the experience of touching my hands and my hair was upset ww
No, because it is real.
Also, if it is something on the board of ultra-high precision equipment, just inserting a metal driver will affect the frequency and magnetism, and it may interfere with adjustment.
Why use an adjustment driver to adjust these electronic circuits?
In the past, I have made my own driver by scraping the bamboo chopsticks. . .
Some things are cheap and sell for 200-300 yen, and there are high-quality ceramic drivers.

When making this adjustment, be sure to create a basic "None" situation in the circuit.
In the case of SQ-38u this time, there is a switch between pre-main and separate, so separate. Speaker output switching is also ON / A / B and switched to OFF so there is no volume. Or, there are things that put resistance of about 8 Ω virtually)

As we explained earlier, since 1ch is amplified with 2 tubes, please think that 2 tubes are interlocked.
If you adjust one, the other will also change the value in conjunction.
The turning order is different depending on which tube is the first stage.
Even if you say "turn", it doesn't mean turning round, but moving just a very small amount little by little, we will match the numbers of the two combinations.

What is "bias" in the first place?
Plate voltage, cathode voltage, grid voltage, heater etc. . . . . .
I can not explain it in this article anymore, so I will omit super.

Simply measure the resistance of KOCO in the picture.
By the way, the resistance contains the "pattern" of the shimma. If you match the color of this shim, you can read this resistance value.
The voltage (current) flowing through this resistor is "bias". (Insufficient explanation)

It is unnecessary to explain if you see it. . .
I omit here too. . . .
EL34 has eight pins. (No. 6 is unnecessary)
Short No. 8 and No. 1 to the body ground.
If you put any resistance between them, that resistance .... . Anyway I understand!
Although SQ-38u is installed with a 10Ω resistor this time, there is no particular problem if it is another 1Ω.
If you really want to know the meaning, please study the structure of the vacuum tube separately.

Once you add it, if you say that this measurement method is "the main line", it is actually a "virtual" measurement.
Hmm. Although the reason is also difficult, I will omit it. . . .
Since this resistance was already prepared when I saw this SQ-38u, it is interpreted that the maker is probably saying "it is good". I will go with that flow.

 

 

 

 

Originally, when measuring the value of this resistance, I measure the both ends of the resistance with a tester, but if it is a measurement of the bias voltage (current), the negative terminal of the speaker or the ground terminal of the phono is OK. (For convenience)

The bias current value of this SQ-38u is about 35mA.
why?
Even if it is asked, I can not explain it as above, so I will omit it.
(Please note that we can not explain even if you inquire by e-mail or telephone etc.)
(If you need an explanation, please contact Laxman directly for bias adjustment)
Are other EL34 amplifiers also 35 mA?
I do not know that.
The circuit of the amplifier, the limit value of the parts used, and the original design intention are totally different depending on the amplifier.

Anyway it's 35mA.

It is 350mV when it sees with a tester.

I have omitted the explanation so far, but I think that it is a little study and I raise a problem in the mood of the teacher.

35mA = 0.035A 350mV = 0.35V resistance 10 Ω

Ohm's law voltage (V) = resistance (R) × current (I)
Current (I) = Voltage (V) 抵抗 Resistance (R)

Please think that it is a mental exercise.

In the first place, "bias value" may be called "current" or "voltage"

 

---------------------

Note that a load needs to be on the speaker outputs when doing this, as VanArn stated earlier a dummy load is advised to simulate a speaker connection.

 

I just leave the speakers connected with no input signal and volume zeroed, maybe not best tech' practice *shrug*

 

Owners might like to have a look at the translated page as well. But looks straight forward to anyone that has done this.

 

 

 

Edited May 12, 2019 by Muon N'

[Guest Muon N']

Caution is needed doing this as there are high voltages in there, and you don't want to slip and cause damage with a probe either.

[Guest Muon N']

Deleted, as I was mistaken.

Edited May 12, 2019 by Muon N'
typos