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Little Dot Tube Amps: Vacuum Tube Rolling Guide
May 7, 2017 at 11:48 AM Post #11,041 of 13,434
Topodomain said:
C3g's seem to get ridiculously expensive and rare. I wonder would it be possible to make adapters and heater voltage source (like in 6as7 power tube mod.) and get c3m or something similar working? Would it be safe for LD IV SE?

C3c's would look cool :)
Click to expand...

Yes, compared to the standard recommended LD tubes, C3g are expensive. However, compared to other premium tubes used in audio, such as 6AS7, 6SN7 and 6DJ8, they are not ridiculously expensive. A pair of C3g can often be found for around 100 US dollars. Premium double triodes (equivalent to a pair of C3g) often go for hundreds of dollars. Further, these are 10,000 hour tubes, so two pairs will very likely outlast your amp. :)

As to running a C3m? Sure. As the old adage goes, "If there is a will there is a way." :)

First, you would need to be provide the tube with 20 volts to heat it. Second, the pinout is completely different than a C3g, so you would need to built a custom adapter, 8-pin loctal to 7-pin miniature, to reroute the pins. This should not be all that hard to do, but would the end result be worth the required time and treasure? I have no idea....
 
May 8, 2017 at 4:38 AM Post #11,042 of 13,434
Two pairs? Do you mean like use C3G also for the power tubes? What I have tried was to put C3G as driver + 6SN7 as power tubes, but I see that these 6SN7 are usually found on other amps in driver position. It is not very clear to me what to choose best as power and what to choose best as driver....
 
May 8, 2017 at 11:16 AM Post #11,043 of 13,434
The C3g is not suitable for use as an output tube. What I am suggesting is one pair for daily use as drivers and a second pair for backup. And given their 10,000 hour life time, it is likely that they would never need to be replaced.

Yes, 6SN7 are often used as drivers in other amps. However, these amps typically use the 6AS7 as an output tube, which draws 2.5A of heater current and is much more powerful than the 6H30-types recommended for the LD. The LD cannot use the 6AS7 without serious modification, including an external heater power supply, and in my opinion, upgrading key resisters on the circuit board to handle significantly more DC current.

I suggest that it is best to respect the design limitations of the LD and use output tubes drawing at most 0.9A of heater current. The 6SN7, which draws 0.6A works well with efficient high-Z cans. For less efficient low-Z cans, output tubes requiring more heater current, up to 0.9A, such as the 6H30 or the 5687 (which draws 0.9A) will work better. And if money is no object, the Mullard ECC32, which also draws 0.9A, would be a good choice.
 
May 8, 2017 at 11:50 AM Post #11,044 of 13,434
Thanks gibosi for your help and explanations. Unfortunately the new design of the forum, which I have to say does not please me very much, does not have the Thanks button but a Like one. This new design adds too much advertising and looses the simplicity of the other one, or maybe I am too old to accept changes anymore.
Anyway, I will stick than to the plan of C3G as drivers + 6SN7 as output for my T1. Impedance should not be a problem.
 
May 8, 2017 at 4:22 PM Post #11,046 of 13,434
May 9, 2017 at 6:14 AM Post #11,047 of 13,434
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May 15, 2017 at 6:33 AM Post #11,048 of 13,434
My adapters just arrived. I think I might try them today or latest tomorrow. But before that, I am wondering if it makes sens to test them somehow.
Can they damage in any way the LD? Or just plug-n-play and nothing bad can happen?

Adapters.jpg
 
May 15, 2017 at 9:04 AM Post #11,049 of 13,434
OctavianH said:
My adapters just arrived. I think I might try them today or latest tomorrow. But before that, I am wondering if it makes sens to test them somehow.
Can they damage in any way the LD? Or just plug-n-play and nothing bad can happen?
Click to expand...

If you want to check them, use a multimeter to see if there is continuity between the socket holes on top and the associated pins on the bottom according to the pin-out diagrams on the datasheets.

http://drtube.com/datasheets/ecc88-philips1958.pdf

http://www.nj7p.org/Tubes/PDFs/Frank/093-GE/6SN7GTB.pdf

https://frank.pocnet.net/sheets/190/c/C3g.pdf

But in my experience, even if the adapter is defective, nothing bad happens. Either the tube heats up and plays or it doesn't. And if it doesn't, then you might want to pull out the muitimeter to see which connections are bad.
 
May 15, 2017 at 11:40 AM Post #11,050 of 13,434
It seems I need some help. I mounted the adapters and the new tubes, but I hear a quite loud buzz in the headphones, more pregnant in the left channel.
I assumed it is related to the power tubes, so I replaced them with the old 6N6P-IR and the problem seems solved. I switched them left-right and the buzz remained in the same form (I was expecting to move to right channel). I switched Jan Philips 6SN7WGTA with russian 6HC8 and the same.
So the tubes seem fine, the adapters seem fine... what is the problem?
 
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May 15, 2017 at 11:57 AM Post #11,051 of 13,434
The buzzing happens with the C3g's on my LDMK11 in low gain, mid and high do not display the symptoms.
 
May 15, 2017 at 12:00 PM Post #11,052 of 13,434
So question, should I switch to high gain? Will damage the sound in any way? Because yes, I remember I let it to low gain.

These C3G need burn in like other normal tubes?

Later edit:

It seems I have solved the mistery via Gain settings. But I think mine was on high gain and now it is set to low. I mean both jumpers are towards 1 and 2 and not ON on the switch:

2017_05_15_19_12_40.jpg


Before both were towards ON (which I think is high gain according to the manual)
Even the volume knob now is lower for the same output level. Anyway, many thanks for help.
 
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May 15, 2017 at 12:11 PM Post #11,053 of 13,434
Depends on your headphone impedance and also how you like the sound, high gain can add tad more slam and sparkle.

I have the monoprice M1060 and they like high gain even though the are 50ohm.

Med gain is also good.

Mine sounded great right away, I would say after 30 minutes of every listening session they start to really sound their best for me.
 
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May 15, 2017 at 12:32 PM Post #11,054 of 13,434
I use T1 here, 600Ohm, but the only Gain setting which does not buzz is this one. So I think it is a kind of "take it or leave it". I have no choice of setting the gain in other way.
Another option would be to replace 6SN7WGTA with 6N6P-IR but I want to try these new ones to see what is happening.

Last but not least, a picture with the "monkey":

2017_05_15_19_26_17.jpg
 
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May 15, 2017 at 12:45 PM Post #11,055 of 13,434
High gain for the T1 anyhow which I also have (T1.1)

Seems like its the adaptors making the issue.
 
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