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Can I ask the valve brains trust in this thread what they think of the capabilities of the maximatcher as a valve tester?

 

https://www.maximatcher.com/maximatcher.html

 

It's obviously designed for matching valves primarily but it does measure transconductance, however it doesn't measure emissions. Is measuring transconductance enough to give you some perspective on valve age? I know emissions drop over time and others have mentioned checking emissions to get a vague idea of valve condition but can you get a better/enough perspective based on transconductance?

Edited by Ittaku
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20 minutes ago, Ittaku said:

Can I ask the valve brains trust in this thread what they think of the capabilities of the maximatcher as a valve tester?

 

https://www.maximatcher.com/maximatcher.html

 

It's obviously designed for matching valves primarily but it does measure transconductance, however it doesn't measure emissions. Is measuring transconductance enough to give you some perspective on valve age? I know emissions drop over time and others have mentioned checking emissions to get a vague idea of valve condition but can you get a better/enough perspective based on transconductance?

 

 

It also measures plate current for a given plate voltage and bias setting.  If emission is weak, plate current will be down.

 

As I mentioned elsewhere, they don't mention small signal valves like the 12AX7.  I would want to be able to test and match them too.

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Just now, aussievintage said:

It IS very simple.  But for some, it is all they might need.

Sure thing. I'd already read about it and it just gives pass fail results for very coarse endpoints. I'm looking for something slightly more sophisticated. There are very few new testers in production...

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12 hours ago, Ittaku said:

They are reasonably tightly packed, but fortunately my amps are actively cooled with ventilation fans, which I always leave on high speed unless it's for very quiet listening, and I run them with the covers off, and regularly check them with IR thermometers. The hottest power tubes are at 150 degrees; they range from 130-150 depending on their location. The bias in my amp is adjustable but with an ideal targeted range of 65mV. I basically never run them out of class A, but the amps are fairly heavily class A biased.

 

IMG_20190428_210350.thumb.jpg.b953d17ca13adf7ad59da2595f790b21.jpg

 

You can see the fan at the back (Nexus, the quietest PC fans you can buy). Don't be fooled by any red colour in this photo, it's a reflection of my inductors in my speakers as the amp is actually off here.

 

That's good work, a good start.

I'd try get the envelope temp down much more, there's a lot of investment there ;)

130 degC  = 265degF.

Using the 'chimney' effect iis the usual design strategy - try rig up fans over the top (drawing upward).

If they're unacceptably noisy, drop the supply voltage (eg series wire the fans to slow them.

That's just what i'd do.

 

At least ARC always design for available modern production tubes, not burning up rare vintage GE6550As for example in a modern design.

Back in the 90s, when I had ARC, they were just switching over to Russian tubes.

 

Cheers, Owen

Dark Lantern blog - http://darklanternforowen.wordpress.com/

Edited by Owen Y
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1 hour ago, Owen Y said:

That's good work, a good start.

I'd try get the envelope temp down much more, there's a lot of investment there ;)

130 degC  = 265degF.

Depends if that was measured with the amp going full belt or just idling.  In any event, that graph indicated nearly 100% survival at 220 degC

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Re. the graph - that's just an example, the 6AQ5 is just a small tube, like an EL84.

It depends on the tube, envelope size/shape, operating point/dissipation, etc, etc.

Wider envelope tubes (KT88) tend to have cooler glass envelope temps than slim power tubes (like say EL34, KT90).

But the principle still applies - keep 'em cooler for for long life.

 

Cheers, Owen

Dark Lantern blog - http://darklanternforowen.wordpress.com/

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image.png.bcae3fb3fd01ce88893643fa36559448.png

Of course it's just a guideline but they list 250 degrees as the max hottest envelope temperature. On this amp I've never seen temperatures even close to that, but yes I always try to keep any of my valves as cool as I can for longest life. As I said earlier, I never manage to get it into class B operation so they're always the same temperature as when the amp's completely idle.

 

At any rate I'm tempted to get a maximatcherII to keep an eye on the valves since it's about half the cost of revalving.  If they keep sounding okay and there are no grossly abnormal measuring valves I might be able to recoup its cost by delaying revalving for longer.

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  • 2 weeks later...

Finally rolled in some CVC branded GZ34 rectifier tubes in to the PrimaLuna Prologue Classic CDP to replace the standard 5ar4’s and the results are very positive.

They have noticeably reduced sibilance and a low level of what could be best described as harshness that was previously apparent but not annoying.

 

I have not changed rectifier tubes previously and had read various comments in different forums as to the value of changing them, well after this experience I am in the camp that says that rolling them can make a big difference.

 

This interesting combination of Mullard Box Plate CV 4004’s, Tungsram Tilburg 12au7’s and the CVC GZ34’s has really transformed the little PrimaLuna CD player, I did try a number of different combinations prior to settling on this one which I’m very happy with.

 

cheers Terry

 

 

899DFC46-D2D7-43EB-BE2D-EF2889F612A9.jpeg

24FC81A3-8791-44FE-841C-77154D584C74.jpeg

Edited by TerryO
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9 hours ago, TerryO said:

Finally rolled in some CVC branded GZ34 rectifier tubes in to the PrimaLuna Prologue Classic CDP to replace the standard 5ar4’s and the results are very positive.

They have noticeably reduced sibilance and a low level of what could be best described as harshness that was previously apparent but not annoying.

 

I have not changed rectifier tubes previously and had read various comments in different forums as to the value of changing them, well after this experience I am in the camp that says that rolling them can make a big difference.

 

This interesting combination of Mullard Box Plate CV 4004’s, Tungsram Tilburg 12au7’s and the CVC GZ34’s has really transformed the little PrimaLuna CD player, I did try a number of different combinations prior to settling on this one which I’m very happy with.

 

cheers Terry

 

 

899DFC46-D2D7-43EB-BE2D-EF2889F612A9.jpeg

24FC81A3-8791-44FE-841C-77154D584C74.jpeg

In some preamps I have built which require a 12AX7 I have heard some harshness. If I swapped the 12AX7s out for 12AU7s the harshness goes away. You will get a little less gain but shouldn’t be a problem. 

 

These days I’m favouring the Psvane T series MKIIs. Pricey but I think an excellent performer. 

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29 minutes ago, mwhouston said:

In some preamps I have built which require a 12AX7 I have heard some harshness. If I swapped the 12AX7s out for 12AU7s the harshness goes away. You will get a little less gain but shouldn’t be a problem. 

 

These days I’m favouring the Psvane T series MKIIs. Pricey but I think an excellent performer. 

Interesting that you and some others find the PSvane T mk2 12au7’s a good performer, I have tried to like these tubes and have swapped them in and out a number of times in both the PrimaLuna amp and the PL CD player and in my system they lessen the sq noticeably. 

I actually have a brand new octet of their el34’s that I have never used and will one day try and sell (cheaply).

 

cheers Terry

Edited by TerryO
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1 hour ago, mwhouston said:

In some preamps I have built which require a 12AX7 I have heard some harshness. If I swapped the 12AX7s out for 12AU7s the harshness goes away. You will get a little less gain but shouldn’t be a problem. 

 

A lot less gain actually.  Amplification factor of 20 vs 100.   Have you tried any of the different types in the family (in terms of gain).  The 12AT7 is a fine valve I have used and liked in some of my designs.  There are many others, such the 12AY7.  Both have more gain than the 12AU7 but less than the 12AX7.

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And 5751 as well if you need something between ax and at

 
A lot less gain actually.  Amplification factor of 20 vs 100.   Have you tried any of the different types in the family (in terms of gain).  The 12AT7 is a fine valve I have used and liked in some of my designs.  There are many others, such the 12AY7.  Both have more gain than the 12AU7 but less than the 12AX7.
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Swapping 12ax with 12at and other 12 variants will affect the sound because if a circuit is deigned for a 12ax7 it will not be operating a 12at7 at it's optimal operating point.

It does not take much to just have a look at the tube curves to realise this.

 

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7 hours ago, Ihearmusic said:

Swapping 12ax with 12at and other 12 variants will affect the sound because if a circuit is deigned for a 12ax7 it will not be operating a 12at7 at it's optimal operating point.

It does not take much to just have a look at the tube curves to realise this.

 

 

Good thing about triodes, for small signals, just about anywhere in the main part of the curves is an acceptable operating point.

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I started the 4S small tube preamps many years ago. Many on a Canadian site have built them.  One of the engineers on the site came up with the 4SU - the universal version of the 4S. Into the preamp you can install any 12A?7 tube with no changes to any components for good (but not of course optimum) performance. Also a chart of distortion/ tube has been posted. So you can match gain and distortion profile. The 4SU is a tube rollers dream. 

 

Also the 4S and 4SU can be used as a driver stage to most tube power amps. Once more, in the power version, a tube rollers dream. 

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22 minutes ago, mwhouston said:

I started the 4S small tube preamps many years ago. Many on a Canadian site have built them.  One of the engineers on the site came up with the 4SU - the universal version of the 4S. Into the preamp you can install any 12A?7 tube with no changes to any components for good (but not of course optimum) performance. Also a chart of distortion/ tube has been posted. So you can match gain and distortion profile. The 4SU is a tube rollers dream. 

 

Also the 4S and 4SU can be used as a driver stage to most tube power amps. Once more, in the power version, a tube rollers dream. 

A nice little project.  I just found it with a search  https://diyaudioprojects.com/Tubes/Universal-Tube-Preamplifier/   

 

Not knocking it at all, but it's pretty much a standard amplification stage with fairly typical values, 100k in the plate and about 1 k for the bias.  The tables show the variation in gain due to the differing amplification factors for the different types. Roughly varying  from 20 to 30db for that one gain stage.

 

I find it interesting to try  valves at different operating points.  I once put 6550 valves in a SET amp initially designed for 6V6 valves.  They are pin-compatible.  Of course the 6550s ran at the lower operating point of the 6V6s  but I found I actually liked the sound.   I eventually modified that SET amp to be able to take most of the compatible, or near pin-compatible types, including 6V6, 6L6 and EL34s and 6550 and others.  all in triode mode.   Another tube-rollers dream?  

 

 

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Since this is a show-and-tell thread, here's some photos of that prototype with Sylvania Chrome Dome 6SN7s and GE 6550s in it (ignore the printed valve types - I re-used an old PA amp chassis and power transformer).

 

DSC_0180.jpg.b6657fa98acd9d4ca3e4a811b90120ce.jpg

 

This is the sloppy mess I make when lashing together a prototype :)   This one never made it into "production" as I discovered directly heated triodes, and went on to build a 2A3 style SET amp.

DSC_0179.jpg.1577b6823159289f5e312518ac744c51.jpg

 

Edit: stupid mistake corrected

Edited by aussievintage
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