Two Rock Custom Reverb Artist TubeSync Fitted

[lovetone]

I thought I would share this, A Two Rock Custom Reverb artist with TubeSync Installed. You can see the Tube Sync board mounted to the right above the mains transformer.

For those who have not seen or heard of this, its like an ECU for the Valve / Tube amplifier. It controls the current through the tubes by measuring the cathode current and adjusting the –ve bias on each tube to maintain the correct bias level.

I like to run 6L6’s at 35ma this is set via a computer interface through the USB on the PC. Once this is set the controller measures the current and adjusts the grid volts to maintain the correct bias level, neat eh? You can also use any 8 pin octal tube (except 6V6 these use lower current) in fact mixed tubes at the same time and the amplifier will still operate with out problem.

If the unit detects a faulty tube it switches it off running the amp on the remaining tubes, you can also switch between full and half power for a 100 watt 4 tube amp.

I install these in all of the amplifiers I build, these are made in the U.K. Orange are distributing a product called the OV4 which uses the same module

[Structo]

Interesting, I hadn't heard of that before.

How much cost does it add to an amplifier?

Not so sure that would work on the average ODS clone because of the bias board and foot pedal supply being there on that end of the chassis.

[lovetone]

This version is £249 around $400 installed, that’s the control board, the small board mounted transformer and the ribbon cable that connects to status LED’s that are mounted on the back panel. It was quite tight to fit in this amplifier. I agree it would be difficult with the power supply board mounted in the end. The Orange version is a self contained unit that has what are called intercepters that plug in to the tube base and then the tube push in the intercepter. The control unit mounts on to the chassis but it is still very tight.

Here is the early type unit I fitted to a Mesa MK4

[alvarezh]

I guess something of that sort is what Fender is using on their new (NAMM '12) Bassman Pro series with automatic bias:

http://www.fender.com/products/bassmanpro/

Here is a link to the TubeSync site:

http://www.tubesync.co.uk/

Cheers.

[lovetone]

I'm not sure how the Fender amp system works, i'll have a look at the schematic when it's available.

With this there is no need to think about the bias, you don’t need matched tubes as each tube is biased individually. Even tubes that might red plate in one amp will work O.K.

[martin manning]

lovetone, do you know any more about how this gadget works? Does it do what it does by adjusting bias voltage only? The website suggests it controls the temeprature of the tubes, but maybe it's calculating plate dissipation? This is done continuously, while playing? If so, it seems like "bias" in the usual sense is unknowable under those conditions. Also, without knowing more I'm skeptical of the claim that matched tubes are not needed. Can it compensate for tubes that are not matched in transconductance as well as in plate current at static conditions?

[alvarezh]

Good questions Martin.

Furthermore, what happens if the system breaks? Who or what controls the bias? Would there be tubes running away? What about output impedance with two tubes out of the circuit, would it control that automatically too?

Here is a given general explanation on what it does to control the bias:

http://www.tubesync.co.uk/tubesync-gene ... -1-346.htm

For sure you guys will come up with a few more questions that need to be answered.

[martin manning]

Thanks, Horacio, that FAQ answers most of my questions. I thought maybe it detected quiescent operation and only adjusted bias at idle, and that is apparently what it does. The overload protection and the turn-down at idle are neat features to protect the amp and save the tubes, and I guess it wouldn't affect the tone at all. Some of the claims are a little far reaching, though, I think.

[lovetone]

Martin, I've attached an operation guide that explains the workings of the unit, i'll try and answer any other questions you might have.

[martin manning]

Thanks for posting the detailed info, interesting read!

"To prevent damage to the cathode
emissive material, which can occur if an attempt is made to draw electrons from it, before
it reaches working temperature (a process known as ‘cathode stripping’), during this
period, the cathodes of the valves remain disconnected from 0V and maximum grid bias
is applies to each of the control grids."

Cathode stripping is debated, but the consenus seems to be that it is not an issue in low-power (i.e. audio) tubes. A recent experiment by a member of this board, I believe, ran low filament voltages (ca. 2V) as a means of reducing power for several days with no ill effect, supposedly the worst case for cathode stripping.

"In the former case, it is a known fact that valves left for long periods with their heaters
running, but with no appreciable cathode current draw, will suffer a failure mode known
as ‘cathode poisoning’."

My understanding of cathode poisoning is that electrons flowing from cathode to plate strike gas molecules and dislodge positively charged ions which are then attracted to the cathode. In light of that, the above seems confused, perhaps with cathode stripping? Also, the device reduces idle current flow (by 33%) during quiescent periods with the heaters on which would seem to be detrimental according to this statement.

"When TubeSync detects that the amp has not been played for a preset time, it
automatically switches between the two biasing modes [two fixed bias levels actually - MPM], the current settings may be
adjusted using the bias runner software, for example, to run at the ‘normal’ current
setting, when the amp is being played, but drop back to a lower current setting when it is
not, thereby reducing power consumption, heat generation and extending valve life,
whilst eliminating the possibility of cathode poisoning."

This seems to be in the right direction to reduce (eliminate is a bit strong) cathode poisoning. However, reducing the operating temperature at idle might actually reduce tube life from the standpoint of increased thermal cycling, which is known to cause cathode coatings to fail.

The major benefits of this device as I see it are the automated ajustment of bias to compensate for deterioration over the life of the tube, and the protection against colateral damage in the event of tube failure. I don't see it eliminating the need for tube matching as claimed, as it compensates for static idle current draw only. I'd rather have higher and more consistent quality tubes, in both static and dynamic characteristics, than find a way to make do with poor quality ones.

[llemtt]

Very coool product!

Years ago I managed to build an all analog circuit working exactly like that but it ended up to much complicated and I convinced myself that a microprocessor solution was needed.

Once understood it wouldn't be cheap I abandoned the project.

But 2 month ago I discovered an incredible, fantastic and cheap microprocessor architecture called Arduino!

My project will be back on track sooner or later...

cheers
teo