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stereo SE kt88 build ... abdellah diyaudioprojects design

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Hi all,

Nice thread and congrats to the builders of this amp.
I have few questions regarding the amp and appreciate reply from anyone who build it.

1. How much current per channel required?
2. How much power typically this amp has.
3. Is it any benefit if regulated HV power supply is applied? I'm not much into rectifiering tubes, I'd rather use SS.
4. Any brand recommended for KT88?

Thanks
 
Hi all,

Nice thread and congrats to the builders of this amp.
I have few questions regarding the amp and appreciate reply from anyone who build it.

1. How much current per channel required?
2. How much power typically this amp has.
3. Is it any benefit if regulated HV power supply is applied? I'm not much into rectifiering tubes, I'd rather use SS.
4. Any brand recommended for KT88?

Thanks


1) Typically 80mA, I would get a transformer that can handle 200-220m
2) depends on the tubes, but for the kt88 you should have 8w
3) I am using a regulator. It makes the amp silent. You can use just diodes, but in this case you need a lower voltage transformer and, for longer life of tubes, a way to delay B+
4) I have the Svetlana

D
 
Bad tube failure, is it an amp build failure?

Hey folks,

Been rocking this design for about a year now with no issues to speak of. Today, I received some NOS Sylvania 6dj8s via Ebay and plugged them in. It was my understanding that these could be used as drop in replacements for the 6N1Ps, albeit with a lower heater current (the datasheets confirm this). Well, after about one hour the plate on one of them was about to go Chernobyl :(. I immediately unplugged it and detected the oh so sinister odor of silicon smoke. It took me a minute to find the source, but it ended up being the 47k plate resistor, which had turned to charcoal. My question is, was this a probable tube failure from these supposedly perfect NOS tubes, or something that went haywire elsewhere?

Some additional info: (1) the Rp on the other channel was testing at 33k which does not make sense as I had confirmed them at 47k before building; (2) all passive components checked out -- no other fried resistors, no blown caps; (3) I briefly turned it back on before finding the burnt resistor and the rectifier tube started arcing internally; (4) finally, I have modded it to include switchable plate to plate feedback between output and input tubes (it doesn't seem to me that would have any effect, but I'm a little green with this stuff still). Thoughts and opinions would be greatly appreciated.
 
Hey folks,

Been rocking this design for about a year now with no issues to speak of. Today, I received some NOS Sylvania 6dj8s via Ebay and plugged them in. It was my understanding that these could be used as drop in replacements for the 6N1Ps, albeit with a lower heater current (the datasheets confirm this). Well, after about one hour the plate on one of them was about to go Chernobyl :(. I immediately unplugged it and detected the oh so sinister odor of silicon smoke. It took me a minute to find the source, but it ended up being the 47k plate resistor, which had turned to charcoal. My question is, was this a probable tube failure from these supposedly perfect NOS tubes, or something that went haywire elsewhere?

Some additional info: (1) the Rp on the other channel was testing at 33k which does not make sense as I had confirmed them at 47k before building; (2) all passive components checked out -- no other fried resistors, no blown caps; (3) I briefly turned it back on before finding the burnt resistor and the rectifier tube started arcing internally; (4) finally, I have modded it to include switchable plate to plate feedback between output and input tubes (it doesn't seem to me that would have any effect, but I'm a little green with this stuff still). Thoughts and opinions would be greatly appreciated.

The 6N1P and 6DJ8 are very different. The only thing they share is same pin connections. Perhaps sometime in the past someone made a typo when selling them, and put 6DJ8 instead of 6AQ8 as the equivalent. That confusion has persisted since.
To make things worse, the Chinese have a 6N11, which IS a 6DJ8 equivalent.:confused:

With the high gm of 6DJ8 coupled with too high B+, I am not surprised the plate resistor smoked out. Hopefully, the 6DJ8 is still OK, as it is only recommended to have 100v on their plates.

The circuit would have to be re-designed to suit the 6DJ8.
Some other tubes to try in place of the 6N1 are the 6AQ8 (ECC85), 6BQ7.
Either of those will work, but whether any sonic improvement is unknown.
Of course, there are a number of 6N1P variants you can try (6N1P-EV, 6N1P-IR etc)

Gary
 
Thanks for the input, Gary!

I was afraid of that. I'm not sure about the poor little 6dj8. Her plates were glowing orange and some of the Sylvania lettering turned black. I've got no tube tester, so until I acquire one way down the road, I'm just going to assume it's toast. I guess I'll just go back to the 6N1P, which I love sonic-wise (I was just looking to mix things up a bit).

Do you think I might get off as easy as just having to replace the plate resistors? Anything else you think I should be sure about before plugging her back in? Again, all the passives were reading at normal, and I don't think I cooked the PT, but I'll check that tomorrow when I have the time.
 
Replaced the resistor and my LED string (the heat took the diodes out as well). All is right as rain. I also switched the Rp's from NOS carbon composite to new metal oxide which seems to have had a pleasant effect on the tone. I'm not sure if it's just my imagination, but the bass seems a little tighter and more pronounced. So happy ending I guess.
 
I've got an issue with mine. It does great with most music but anything that has a lot of pretty continuous high notes, like pop where they just kind of fill in the background, I get a static sort of high pitch crackle sound with it. This morning it even did a completely separate crackle after the music.
On jazz or any other music that doesn't run a long stretch of higher notes it works flawlessly. The tubes have all been swapped out over time and it still does it.

Suggestions?
 
Hi all,

Reviving this thread is a must :) especially when help is required.

Question:
I can purchase OT Ra=5K I=200 mA and Power=30-40W for this design, and before i do that, will be any benefit if I connect two KT88 tubes in parallel (PSE) regarding output power?
Usually PSE OT for 2xKT88 Ra is 1.5kOhms. Any help is appreciated.

Thanks in advance.
 
I've got an issue with mine. It does great with most music but anything that has a lot of pretty continuous high notes, like pop where they just kind of fill in the background, I get a static sort of high pitch crackle sound with it. This morning it even did a completely separate crackle after the music.
On jazz or any other music that doesn't run a long stretch of higher notes it works flawlessly. The tubes have all been swapped out over time and it still does it.

Suggestions?

Sounds like a bad connection somewhere or bad solder joint.
 

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