Mesa Boogie Mk4 design shennanigans

[Gareth Magennis]

This is a bit strange, never noticed it before.

The Mesa Boogie Mk4 has a switch for "Tweed", or "Full Power". Basically a
PSU voltage drop for reduced power output.

I had one in that just would not perform in Tweed mode, but was fine in Full
Power mode.


I discovered that all 4 of the Electro Harmonix ECC83 pre-amp tubes would
not work with the reduced voltage, but substituting 4 new JJTesla ECC83
solved the problem.
The EH tubes were actually branded "Watford Valves Cryo" - Watford Valves
put these things into liquid nitrogen to make them work better.
Apparently.
Cough.


Anyway, after a bit of investigation I discovered that this Tweed switch is
actually on the mains transformer Primary, and switches in some extra
windings.
The result of which is all the secondary HT voltages are reduced by around
20%, BUT, so is the heater supply voltage.
In this case dropping from 6.1v to 5.1v.

I'm no expert in valve amp design, but this seems to be rather a strange
design choice.


But then Mesa Boogie design their amps to work with their own branded
valves, so they presumably know the reduced voltages, including heater, will
mean their tubes will still carry on working.



Interestingly, I had another (non Cryo) Electro Harmonix ECC83 which didn't
bug out at the reduced voltage, so perhaps this was a dodgy quad of ECC83,
of perhaps something to do with the Cryogenic process?




Gareth.

 

[Phil Allison]

Gareth Magennis wrote:

The EH tubes were actually branded "Watford Valves Cryo" - Watford Valves
put these things into liquid nitrogen to make them work better.
Apparently.
Cough.


Interestingly, I had another (non Cryo) Electro Harmonix ECC83 which didn't
bug out at the reduced voltage, so perhaps this was a dodgy quad of ECC83,
of perhaps something to do with the Cryogenic process?

** I doubt they put the valves directly in liquid N2 - as it would destroy them instantly by cracking the glass. Even if done some other and safer way, the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal between the pins and the glass base - cos steel and glass do not have the same tempco of expansion. Typically, steel has a higher tempco so the fit get tighter as the glass envelope heats - conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into the vacuum and spoil the operation.


..... Phil

 

[pfjw@aol.com]

On Tuesday, November 29, 2016 at 9:37:28 PM UTC-5, Phil Allison wrote:

** I doubt they put the valves directly in liquid N2 - as it would destroy them instantly by cracking the glass. Even if done some other and safer way, the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal between the pins and the glass base - cos steel and glass do not have the same tempco of expansion. Typically, steel has a higher tempco so the fit get tighter as the glass envelope heats - conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into the vacuum and spoil the operation.

I do not believe they do, either. Here is one "Cryo" vendor describing their process:
_______________________________________________________________

The BLACK SABLE process is far more than putting tubes in a chamber and lowering the temperature. The BLACK SABLE process starts with tube selection. Only the best preamp, power and rectifier tubes are chosen to undergo this arduous process. All tubes undergo a 24 hour burn-in under load. The tubes are then placed in the Cryo-Processor where a computer-controlled proprietary system lowers the temperature to -300 Fahrenheit / -184 Celsius for 24 hours and then slowly ascends back to room temperature. Preamp tubes are tested and rated for Gain, Microphonics and Noise. Next, all 7/9 pin tubes have their pins cleaned for a better electrical connection. Power tubes are matched to within 3% for both Ip (Plate Current) and Gm (Transconductance). No other cryogenic process comes close. When only the best will do, choose BLACK SABLE.
__________________________________________________________________________

Which is 21F above the boiling point of liquid nitrogen, a cheap and readily obtainable material in liquid form. That being written, most metals, including coated steel, copper, cupro-nickel and other solderable materials have a vastly greater coefficient of expansion/contraction than even the softest glass (Pyrex). So either the pins are going to shrink out of their surroundings, or all this is done in a *hard* vacuum. There is no real danger of shattering the glass if done slowly, but as the pins will be *smaller* than the opening during the process - that is where all the 'magic' must take place.

Color me dubious.

Peter Wieck
Melrose Park, PA

 

[Phil Allison]

et...@whidbey.com wrote:

Especially dubious because if the pins really did shrink away from the
glass the glass/metal seal would be broken and the tube would leak air
in once exposed to the atmosphere again. When tubes are made the glass
really does seal to the pins, just like glue.

** True when the steel pins are as hot as the molten glass that is formed around them.

But this happens at a very high temp ( about 1500C ) so during cooling thermal contraction will put considerable stress on this seal even at room temp.



..... Phil

 

[Gareth Magennis]

"Phil Allison" wrote in message
news:efdd5f94-6779-43ba-aa28-0a9fb53520a1@googlegroups.com...

Gareth Magennis wrote:

The EH tubes were actually branded "Watford Valves Cryo" - Watford Valves
put these things into liquid nitrogen to make them work better.
Apparently.
Cough.


Interestingly, I had another (non Cryo) Electro Harmonix ECC83 which
didn't
bug out at the reduced voltage, so perhaps this was a dodgy quad of ECC83,
of perhaps something to do with the Cryogenic process?

** I doubt they put the valves directly in liquid N2 - as it would destroy
them instantly by cracking the glass. Even if done some other and safer way,
the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal between the
pins and the glass base - cos steel and glass do not have the same tempco of
expansion. Typically, steel has a higher tempco so the fit get tighter as
the glass envelope heats - conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into the vacuum
and spoil the operation.


..... Phil







My bad, their website makes no mention of N2. Maybe they just stick them in
the freezer and call it Cryo.
Interesting info though.

Anyway, any thoughts on 5.1v heater voltage as a viable propostion?


Cheers,



Gareth.

 

[Gareth Magennis]

"Phil Allison" wrote in message
news:efdd5f94-6779-43ba-aa28-0a9fb53520a1@googlegroups.com...

Gareth Magennis wrote:

The EH tubes were actually branded "Watford Valves Cryo" - Watford Valves
put these things into liquid nitrogen to make them work better.
Apparently.
Cough.


Interestingly, I had another (non Cryo) Electro Harmonix ECC83 which
didn't
bug out at the reduced voltage, so perhaps this was a dodgy quad of ECC83,
of perhaps something to do with the Cryogenic process?

** I doubt they put the valves directly in liquid N2 - as it would destroy
them instantly by cracking the glass. Even if done some other and safer way,
the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal between the
pins and the glass base - cos steel and glass do not have the same tempco of
expansion. Typically, steel has a higher tempco so the fit get tighter as
the glass envelope heats - conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into the vacuum
and spoil the operation.


..... Phil








Oh, OK, rather late to the party on this one - so there is no bonding at all
between the pin and the glass, just an interference fit?


Gareth.

 

[Phil Allison]

Gareth Magennis wrote:

The result of which is all the secondary HT voltages are reduced by around
20%, BUT, so is the heater supply voltage.
In this case dropping from 6.1v to 5.1v.

I'm no expert in valve amp design, but this seems to be rather a strange
design choice.


** The same idea was used by MusicMan in several models to create a half power switch.

I did a quick test on a few 'X7 and 'U7 types and found good operation was maintained to under half voltage on the heaters. At about 2 volts instead of 6.3V, voltage gain is low or sub unity.


..... Phil

 

Low filament voltage was used to do a "life test", at least on CRTs. If the emission dropped like a rock it was deemed that the tube was close to failure. I do not really know how accurate the test was, no way to get the data really.

But it did not drop it to half, something like maybe 70 % or so.

This liquid nitrogen bullshit really sounds like audiophoolery. First of all how would it work ? What would be the theory behind it. Just because it got cold it somehow changed the characteristics of the cathode coating ? Because it can't do much else. The grids are just wires and the plate is just a piece of metal. I think if they wanted to make a better tube they would bombard it more with heat, like they do CRTS, which were put into a very demanding application and required special treatment. Don't depend on the getter. That would evaporate more gases out of the elements before the getter is even involved, and I would guess this was done before the glass envelope was on it. That would seem logical.

However it still doesn't make sense. The solubility of a gas into a solid goes down with higher temperature and of course the reverse is true. What does that mean in this case ? I am not sure.

Maybe they want some nitrogen in the tube, but only a small amount. This would of course increase leakage and slow the electron flow, but some might find the sound more pleasing. Seems to me it would add distortion but if you are talking a guitar amp that distortion is like gold to some artists.

However, the leakage and probably lower gain would probably make it more likely that reduced heater voltage would take it out of the operating range where it was intended in the amp. Then of course it does not work.

And then we got the thermal coefficient of the resistance of the heater itself which would inherently pull more current at a lower voltage. The tube book is kinda like the transistor book, when it says so many mA at a certain voltage it means it, but not so much at lower voltages. How that curve would be affected by dunking it in liquid nitrogen is beyond me, it could but it would take a metallurgist to figure it out. Like heat treating, now they got cold treating. OK.

It still sounds like a bunch of audiophoolery to me. What's more the customer should have noticed that the low power ode quit working when the tubes were changed and simply changed them back, but he took it to a shop. No accounting for brains with some people.

Like where I used to work at the music store. These fuckers don't know the difference between line level and mic level. They have an effects box and the complaint is that it pops when switching modes. Well they got it plugged in between the guitar and amp when it is supposed to be in an effects loop on a mixing board. And they are selling this shit not even knowing how it is supposed to work ? And how many times I had a problem with hum come back to them using a speaker cable for low level input. And then blowing the low level cables using them for multi-hundred watt amps.

So now I am working where they sell karaoke machines. ALL of one model seems to have low mic gain. They gave me a 400 ohm mic for the bench, it is simple that ALL of this model has low mic gain, it needs a high impedance mic. One comes in with that complaint and the customer says "I use good mics, Shure SM-58 (I think)". So I look it up and the thing is even lower impedance than what I have. That is like trying to use a moving coil cartridge on a stereo that does not have the proper input for it. (preamp that is) Some mics have a built in transformer for that, but not the SM-58 as far as we could tell if I got the model number correct.

I am almost thinking that this problem is due to the characteristics of the heaters of these tubes, not any cryogenic process. Unless it literally is nitrogen in the tubes.

What does nitrogen do to the getters ? Anyone know ? Air turns them all white and flaky, whatever boils out of the elements in the tube makes them brown, the atmosphere makes them white and it is mostly nitrogen. But nitrogen is generally non-reactive except when you burn it so hot it oxidises like in a car combustion chamber, thus the need for an EGR valve. Other than that, while not a noble gas, it is pretty close. And tubes do not reach those temperatures encountered in a combustion chamber.

Another interesting but useless subject, but then what are we here for anyway ? Maybe we gain knowledge and take advantage of some of the audiophoolery. I got kicked off one forum and the one I am on now is even more nuts. A twenty grand preamp, and get your own phono stage and DAC while you're at it. Five subwoofers but never turn the bass up. Move the furniture to where the Wife is pissed off to get the best sound. Like people used to do home theater, they do home sound rooms. I am talking additions to the house just for the stereo. Of course you can stick a big TV in there, but those listening sweet spots are not all over the place. And the more shit you got the worse it gets.

And now we got guitar amps that automatically bias the tubes no matter what you put in there, and sockets that will accept a 6BQ5 as well as a 6550. (KT88//6L6 or whatever)

I think this is getting a bit out of hand myself, but if it is a way to make money fine. Just charge enough.

 

On Wed, 30 Nov 2016 13:44:18 -0800 (PST), "pfjw@aol.com"
<pfjw@aol.com> wrote:

On Tuesday, November 29, 2016 at 9:37:28 PM UTC-5, Phil Allison wrote:

** I doubt they put the valves directly in liquid N2 - as it would destroy them instantly by cracking the glass. Even if done some other and safer way, the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal between the pins and the glass base - cos steel and glass do not have the same tempco of expansion. Typically, steel has a higher tempco so the fit get tighter as the glass envelope heats - conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into the vacuum and spoil the operation.

I do not believe they do, either. Here is one "Cryo" vendor describing their process:
_______________________________________________________________

The BLACK SABLE process is far more than putting tubes in a chamber and lowering the temperature. The BLACK SABLE process starts with tube selection. Only the best preamp, power and rectifier tubes are chosen to undergo this arduous process. All tubes undergo a 24 hour burn-in under load. The tubes are then placed in the Cryo-Processor where a computer-controlled proprietary system lowers the temperature to -300 Fahrenheit / -184 Celsius for 24 hours and then slowly ascends back to room temperature. Preamp tubes are tested and rated for Gain, Microphonics and Noise. Next, all 7/9 pin tubes have their pins cleaned for a better electrical connection. Power tubes are matched to within 3% for both Ip (Plate Current) and Gm (Transconductance). No other cryogenic process comes close. When only the best will do, choose BLACK SABLE.
__________________________________________________________________________

Which is 21F above the boiling point of liquid nitrogen, a cheap and readily obtainable material in liquid form. That being written, most metals, including coated steel, copper, cupro-nickel and other solderable materials have a vastly greater coefficient of expansion/contraction than even the softest glass (Pyrex). So either the pins are going to shrink out of their surroundings, or all this is done in a *hard* vacuum. There is no real danger of shattering the glass if done slowly, but as the pins will be *smaller* than the opening during the process - that is where all the 'magic' must take place.

Color me dubious.

Peter Wieck
Melrose Park, PA

Especially dubious because if the pins really did shrink away from the
glass the glass/metal seal would be broken and the tube would leak air
in once exposed to the atmosphere again. When tubes are made the glass
really does seal to the pins, just like glue. But glass is elastic
(more elastic than the metal pins) and the movement would be small so
maybe the glass does move with the pins. Steel pins on a tube would
shrink about .0001" going from room temp to 300 below. Glass would
move about .000067" so about 33 millionths of an inch difference. So
the glass/steel seal would probably hold.
Eric

 

[Phil Allison]

Jeff Layman wrote:

And why would they do it to a rectifier tube?

What would they expect to gain?

** You are kidding - right ??



.... Phil

 

[Jeff Layman]

On 30/11/16 21:44, pfjw@aol.com wrote:

On Tuesday, November 29, 2016 at 9:37:28 PM UTC-5, Phil Allison
wrote:

** I doubt they put the valves directly in liquid N2 - as it would
destroy them instantly by cracking the glass. Even if done some
other and safer way, the whole idea is completely nuts.

One of the design issues with valves is the vacuum tight seal
between the pins and the glass base - cos steel and glass do not
have the same tempco of expansion. Typically, steel has a higher
tempco so the fit get tighter as the glass envelope heats -
conversely it gets looser at very low temps.

Prolonged exposure at very low temps could let air ( or N2) into
the vacuum and spoil the operation.

I do not believe they do, either. Here is one "Cryo" vendor
describing their process:
_______________________________________________________________

The BLACK SABLE process is far more than putting tubes in a chamber
and lowering the temperature. The BLACK SABLE process starts with
tube selection. Only the best preamp, power and rectifier tubes are
chosen to undergo this arduous process. All tubes undergo a 24 hour
burn-in under load. The tubes are then placed in the Cryo-Processor
where a computer-controlled proprietary system lowers the temperature
to -300 Fahrenheit / -184 Celsius for 24 hours and then slowly
ascends back to room temperature. Preamp tubes are tested and rated
for Gain, Microphonics and Noise. Next, all 7/9 pin tubes have their
pins cleaned for a better electrical connection. Power tubes are
matched to within 3% for both Ip (Plate Current) and Gm
(Transconductance). No other cryogenic process comes close. When only
the best will do, choose BLACK SABLE.
__________________________________________________________________________

Which is 21F above the boiling point of liquid nitrogen, a cheap and
readily obtainable material in liquid form. That being written, most
metals, including coated steel, copper, cupro-nickel and other
solderable materials have a vastly greater coefficient of
expansion/contraction than even the softest glass (Pyrex). So either
the pins are going to shrink out of their surroundings, or all this
is done in a *hard* vacuum. There is no real danger of shattering the
glass if done slowly, but as the pins will be *smaller* than the
opening during the process - that is where all the 'magic' must take
place.

Color me dubious.

Peter Wieck Melrose Park, PA

How would they do this in practice? If it had to be done in a hard
vacuum, how would you transfer the heat away from the valve to cool it
down to -184? Maybe they hire a rocket to fire the valve into space and
let it cool down by radiation, obviously keeping it out of sunlight
while it's up there. ;-)

And why would they do it to a rectifier tube? What would they expect to
gain?

--

Jeff

 

[Michael A. Terrell]

Jeff Layman wrote:

How would they do this in practice? If it had to be done in a hard
vacuum, how would you transfer the heat away from the valve to cool it
down to -184? Maybe they hire a rocket to fire the valve into space and
let it cool down by radiation, obviously keeping it out of sunlight
while it's up there. ;-)

And why would they do it to a rectifier tube? What would they expect to
gain?

Your money. if you are gullible enough


--
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)