Manley Chinook Owners Tube Rolling

The Steelhead, and possibly the Chinook, uses a 30 µF metallized film capacitor for output coupling between the phono section and the line section. Then there is a second 30 µF metallized film capacitor between the line stage section and the output. The single most revealing improvement you could make in the circuit is to replace both of those capacitors with better quality and lower value film capacitors. The question then becomes what is the minimum value of capacitance that would be sufficient. So far as I can tell the motorized volume control on the steelhead has a 5000 ohm input impedance. That is very low as volume controls go. Therefore you do need a fairly high amount of capacitance between the phono stage and the volume control. I chose to use 10 µF value, because that will still give you a very extended low bass response. For the output from the line stage to the amplifier, you can use any value that will give you an appropriate bass cut off in conjunction with the input impedance of the amplifier you are driving. So for example if your tube amplifier has an input impedance of 100K ohms, you could use a 1 µF capacitor. For amplifiers with a lower input impedance, you would want to increase the value of the coupling capacitor accordingly. That will give you a bass cut off at 2Hz. In addition to those capacitor changes, you could remove each of two 47 ohm resistors that are in series with the output of the line stage and the phono stage, respectively. Unless you are using very very high capacitance interconnects between your preamplifier and your amplifier, these changes will have absolutely no deleterious effect on performance.To the contrary the improvement in sound quality is very significant, far more significant and lasting than tube rolling can achieve. In my opinion, of course.

I posted last time above that if the chinook is laid out like the steelhead, then the gain tubes are the pair of tubes nearest to the centerline of the chassis looking from front to back. the cathode follower output tubes are to the left and to the right respectively of the gain tubes in each channel. I hope that’s not too confusing. And if it is ask manley  or your tube dealer.

Apparently the Chinook uses two 6922s per channel. If that’s not correct, stop reading this, because I don’t want to mislead you. If it is correct then you would mess around with the tubes closest to the centerline of the chassis. That’s if it’s constructed like my Steelheadwhich seems a reasonable bet. OR ask Manley which of the two tubes in each channel is part of the gain circuit. They’re cool.

As to SLN tubes, who could argue against the idea? Problem is that the SLN characteristic is transitory. And there’s no telling how long it will be before any given tube will go noisy. Also, in the particular case of the Chinook the single gain tube is part of a hybrid cascode where the bottom element is a FET. In such a topology the noise characteristic of the tube section is less crucial to output noise,partly because the tube per se does less work on gain. Not that it still isn’t a good idea to use a low noise tube.

Tubes of the same type made by different manufacturers do sound different to me. But in my experience differences don’t hold up over time. Then too, same tubes from same maker can sound different from one another; there’s a sample to sample difference. There is no substitute for understanding how the circuit works in the first place. But I admit there are some tubes and makers  I really dislike. In my Steelhead I use Siemens CCa for that one gain section. 

Cords are only a little more overrated than tube rolling. Which is overrated.

Keep in mind that only one of the tubes per channel in the Chinook (6922, I think)  is actually being used for gain and is therefore likely to have an affect on sound quality. The other tubes in each channel are used as part of fancy Cathode follower output stages. Cathode followers add no gain, and usually have little to no effect on sound quality, so long as they are in good working condition. Also, I would agree with others who suggest that you listen to your unit extensively before thinking about tube rolling.