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Old 2nd July 2011, 01:08 PM   #1071
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Quote:
Originally Posted by andyjevans View Post
Just a quick observation - I tried the globe 26 against the ST version, and found I preferred the globes. Slightly more definition in the mid and treble. Anyone else have views?

andy
Could you post a pic to see the differences?

Felipe
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Old 2nd July 2011, 03:24 PM   #1072
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I can't post a pic of the sound!!! You can see globe and ST shapes by googling "26 globe tube" and "26 ST tube".

andy
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Old 2nd July 2011, 04:15 PM   #1073
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Quote:
Originally Posted by andyjevans View Post
Just a quick observation - I tried the globe 26 against the ST version, and found I preferred the globes. Slightly more definition in the mid and treble. Anyone else have views?

andy
For my ears as well, the globe are certainly better than ST's. Globes are having better control across all the frequencies I believe. Very rich sound that pleasing to the ears. Super Silvertone and Tung-sol are the only ST's coming closer to the sound of the globes as I observed. I prefer Silvertones above all other ST's because of the faster sound they produce. Cunningham is the best overall sound from globes that I found. Both are very musical tubes and pleasure to listen. Tested Cunningham, RCA, Silvertones, Tungsol, Blue Acturus, Philco, and Superairlines so far.

Last edited by coolzero; 2nd July 2011 at 04:23 PM.
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Old 2nd July 2011, 04:20 PM   #1074
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ST
Click the image to open in full size.

Globe
Click the image to open in full size.
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Old 2nd July 2011, 05:01 PM   #1075
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coolzero you have p.m.
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Old 2nd July 2011, 05:39 PM   #1076
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by andyjevans View Post
Just a quick observation - I tried the globe 26 against the ST version, and found I preferred the globes. Slightly more definition in the mid and treble. Anyone else have views?

andy
Fully agree. I listened today Andy's pre-amp and it's superb. Globes had a better treble indeed.
Worth following Andy's advice on DHTs...
Cheers, Ale
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Old 3rd July 2011, 03:10 PM   #1077
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Default Removing output ground resistor

Will there be any serious implications of removing R3. Bass and treble became more tuneful without it.
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Old 3rd July 2011, 03:20 PM   #1078
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Hi!

R3 is there to avoid static charge build up on the output when nothing is connected. This avoids that you hear a loud plop when you plug the preamp into a power amo which is on.

R3 should not have a big impact since it is in parallel with the input resistance of your power amp anyways. If the preamp reacts to such tiny changes in load impedance, something is not optimal.

Do you really run at -16V bias? The way the filament is drawn this results in an average of -16,75V. At 140V thats maybe 2-3mA or even less. That marginal op point is probably the reason why you hear a difference when you remove R3.

What you don't really need is R1. The 26 is low transconductance and not prone to parasitic oscillation. I'd use it without a grid stopper.

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Old 3rd July 2011, 03:25 PM   #1079
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Hi!

Another comment:

The 26 has a rather highish miller capacitance of about 65pF. Driven from a high impedance pot, this can already impact treble response audibly.

If your sources allow it, go for a lower impedance pot.

Of course a transformer volume control driven by a 26 through a step down transformer is even better.

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Old 3rd July 2011, 04:39 PM   #1080
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Coolzero - is that a 5uF output capacitor? Is this going straight into a tube amp stage? Is it so close to it so leads can be very short? If that is true, and you have say 270k to 470K total input resistance on the amp (your two resistors in parallel) then a smaller capacitor would give you much better sound, because you could use a better quality capacitor. I'd use Russian 0.1uF Teflon FT-2 or FT-3 in whatever numbers give you a good enough bass response. Parallel for 0.2, 0.3 etc.

I have short leads to my amp and I use a single Teflon 0.1uF FT-2 cap. Inevitably capacitors will have some effect on the sound so this part must be optimised.

If you have a transistor amp that's another story, but surely you don't?

Andy
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