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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

SE 6CB5A amp with 6N7 driver

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Joined 2008
Vinylsavor said:
Hi!

A detailed description of testing and measurements is now on line:

VinylSavor: Low Cost Single Ended 6CB5A Amplifier - Part 5

Best regards

Thomas
Click to expand...

Nice!
This is also a clear demonstration about the truthfulness of Lundahl transformers specs. The LL1682 is specified for 8W (undistorted) at 30Hz with 5R speaker. Looks like it's true!!:D
At 20Hz that should mean about 3.5W (undistorted). The little core saturation at 20Hz for 7W out is normal and better than I would have guessed...
 
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germantuby

Member
Joined 2014
Hi folks, now my experiences with the 6CB5A sweep tubes. Good sound and perfect (a little bit exagerated bass response) in pentode-op but poor in triode. I did a lot of listening to find out that this tube and the 6CD6 as well does'nt really like high screen voltages. I tried 300V in PP and triode circuit providing 150 Ohms screen resistor for current protection at 1,9kohms plate2plate resistance. Didn´t really sound good at high frequencies. I would recommend SE-mode at 1kOhms Plate resistance in pentode-op.
 
Vinylsavor

Vinylsavor

Member
Joined 2002
vinylsavor.blogspot.com/
Hi!

Your experience is quite contrary to mine and to that of many builders of 6CB5a amps. It actually sounds very good in triode and can compete with many 300B amps. One of my amps has been tested by the german DIY magazine Klang+Ton and they had nothing but praise for it. So I assume it is your implementation which resulted in poor sound. (Driver, output transformer, power supply, etc)

Best regards

Thomas
 
Vinylsavor

Vinylsavor

Member
Joined 2002
vinylsavor.blogspot.com/
Hi Jazbo

I know you talked tongue in cheek but I would never generally say pentode sounds better than triode or vice versa. Or a certain tube sounds better than another. These are wrong generalisations which are very common in audio. Conclusions are drawn from a single experience in a specific environment. It is always the overall implementation which is responsible for the result. And if a single person has contrary results than many others, I'd first suspect the implementation. Output transformer and matching to the speaker can have a huge impact especially on distortion at certain frequencies. Such things are rarely caused by the tube.

Best regards

Thomas
 
G

germantuby

Member
Joined 2014
I was surprised about the result of my listening. I guess, that a better output transformer or SE would improve the sound. Btw. I lost one tube by self-ignition after red glowing of the plate. 6CB5A really dont like a plate load of more than 20 watts. I could improve the sound by replacing the 6829 driver with an ECC99 but the upper range still kept on sounding quite harsh. Now I switched to the british 12E1 tube with better results providing the same PP output transformer (1,9kohms). If anyone has an explanation for that effect, help would be appreciated.
But indeed: triode mode should sound better than pentode, thats why I´m posting.
 
Vinylsavor

Vinylsavor

Member
Joined 2002
vinylsavor.blogspot.com/
Hi!

germantuby said:
guess, that a better output transformer or SE would improve the sound.
Click to expand...

Without knowing the circuit and OPT you used it is difficult to judge your findings


germantuby said:
Btw. I lost one tube by self-ignition after red glowing of the plate. 6CB5A really dont like a plate load of more than 20 watts.
Click to expand...

This is another indication that your circuit might not have been ideal. I never lost a single 6CB5a and I run them around 25W plate dissipation and even more. They are tough and last long. The first 6CB5a amp I built is running since more than 5 years now, still with the first set of tubes

germantuby said:
I could improve the sound by replacing the 6829 driver.
Click to expand...

Look at the plate curves of the 6829. It is a very non linear tube and will dominate the sound when used as driver. No wonder you got bad results. But it was definitely not the fault of the 6CB5a


Best regards

Thomas
 
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