Adjusting the Bias on the Apetite....

[Jerome W]

Hello folks,

I changed my power tubes and the driver tubes in my Apetite about 2 months ago because I had the feeling that it wasn't sounding at its best but did not adjust the bias.
Bought tubes at Tube Depot : the Apetite was bought used from Des here on the market place so I did not contact any Shindo dealer to buy the same tubes that came with it originally ( I have been told that no original "Shindo" tubes can be bought for used units not bought from a Shindo dealer so I did not even try ! ).
The sound improved clearly, with better dynamics and a fuller, more natural presentation but I was asking myself now about the bias adjustment that I completely ignored !
Does someone know how to do that and what is the recommended voltage ?


On a side note, life is clearly easier with autobias amps like McIntosh. Does this autobias system degrades the sound ? I wonder how it works....
I had some trouble with the bias of my Snappers during a few months, probably until the EL34s become fully broken in. Now I checked once every 2 to 3 months and they are straight on the recommended voltage all the time.
Manley Labs say that the bias should be checked once per month or once every two months like the pressure in your auto tires.
Since Shindo amos are not autobiasing, wouldn't it be recommended to check the bias regularly also ?
Does an incorrect bias level affect the sound quality or does it affect the longevity of the tube or both ? Is it dangerous for the amp when the bias is not set correctly ?

Many thanks in advance !

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[Cucumber_Jones]

My montille is auto bias.

[Cucumber_Jones]

What tubes did it have and what did you buy?

[Jerome W]

Originally Posted by Cucumber_Jones

What tubes did it have and what did you buy?

It had original tubes : United Electron ( ics ).
I bought Tung Sol 6V6GT tubes and I also bought a quad of NOS JAN Philips to try but I'm waiting for them.
Driver tubes were changed for NOS GE. Those made the biggest difference in sound.

Interesting to know that your Montille is autobias. Is it a 6V6 version ?

An other question about the Apetite : tubes are paired back to front or left to right ?

I did not open at all the bottom of the amp so I cannot tell...

[Cucumber_Jones]

My montille is 6v6 and came with nos jan Phillips.

[Jerome W]

Originally Posted by Cucumber_Jones

My montille is 6v6 and came with nos jan Phillips.

Interesting. Thanks. The ones I just bought !

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[GaryB]

Originally Posted by Jerome W

An other question about the Apetite : tubes are paired back to front or left to right ?

I did not open at all the bottom of the amp so I cannot tell...

Jerome,
I've got an Apetite, which I've opened up and looked over. It came with the same United Electron 6V6GTs and Philips 6AW8As were used for the input tubes. I recently bought some NOS 6AW8As of different brands to try out but haven't had a chance to listen to them yet.

The amplifier section is self biasing so there is no adjustment needed. One should get matched tubes for the left channel and the right channel to make sure that the current is roughly equal. It's not hard to measure this in the amplifier if you're willing to run the amp with the bottom off and do some measurements. There are dangerous voltages exposed, so you should only do this if you're comfortable working around high voltages. Otherwise get a friend or a good tech to do this for you. Each 6V6 has a cathode resistor. In my Apetite this was a Takman 5W resistor that is relatively big and square in cross section. The voltage across this resistor should be the same for the 2 6V6 tubes in the same channel. The left channel tubes are all in the back, farthest from the front panel. The right channel tubes are in the front, nearer to the front panel.

If you just bought new tubes then they were probably matched when you got them and then you don't need to worry about this for a while.

---Gary

[GaryB]

Here's a picture of the cathode resistor.
---Gary

[Jerome W]

Originally Posted by GaryB

Jerome,
I've got an Apetite, which I've opened up and looked over. It came with the same United Electron 6V6GTs and Philips 6AW8As were used for the input tubes. I recently bought some NOS 6AW8As of different brands to try out but haven't had a chance to listen to them yet.

The amplifier section is self biasing so there is no adjustment needed. One should get matched tubes for the left channel and the right channel to make sure that the current is roughly equal. It's not hard to measure this in the amplifier if you're willing to run the amp with the bottom off and do some measurements. There are dangerous voltages exposed, so you should only do this if you're comfortable working around high voltages. Otherwise get a friend or a good tech to do this for you. Each 6V6 has a cathode resistor. In my Apetite this was a Takman 5W resistor that is relatively big and square in cross section. The voltage across this resistor should be the same for the 2 6V6 tubes in the same channel. The left channel tubes are all in the back, farthest from the front panel. The right channel tubes are in the front, nearer to the front panel.

If you just bought new tubes then they were probably matched when you got them and then you don't need to worry about this for a while.

---Gary

Thanks a lot Gary !
Wonderful and useful information !