I don't know how accurate this is, but here:
Hi
My first post on this forum. Greetings from Scotland.
I am very much a newcomer to the joys of valve amps and am currently tearing my hair out. Here's why:
About four years ago, I acquired my first valve amp - a KONES TA-801. It came with no literature at all (secondhand)- I got it at a very good price, so thought I'd give it a spin and it has served me very well. I have never found any info or references to this amp - have you heard of it?
I believe it was made in china and it uses the following tubes:
4x KT88 (so far so good), 2x 6N2, 2x 6N6 and 2x 6N11.
Problem: recently I have noticed the following problem. Switch on the amp - everything sounds just as it should. Twenty minutes later (and this fault always starts after about twenty minutes) i notice bad distortion in one channel. I've tried switching over the power tubes and the preamp tubes, but the fault stays in the same channel, so I'm guessing it isn't the tubes(?)
What could be the cause? I've had trouble finding a valve technician in Scotland, so I might have to send the amp away for repair. Any tips as to where I might go would be very welcome.
My next query - and this really has got me stumped - relates to replacement valves. As I said, KT88s are obviously no problem (mine are, I think, chinese, branded 'national' or something like that), but I simply can't get hold of 6N2, 6N6 and 6N11. I've tried loads of suppliers, but most can't help, and the few that can will need to place a special order (which will take time and be expensive). Can anyone help me?
someone kindly provided the following list of equivalents:
6N2 = 6AX7
6N11 = 6922, ECC88, 6DJ8
6N6 = No equivalent?
Is this info accurate?
does 'equivalent' mean 'identical' - in other words, can I simply substitute any of the above without modifying the amp?
I'd be extremely grateful for any info/help you can provide.
Many thanks
Martin
andyjevans
http://www.edicron.com/ are dealers that have stocks of russian tubes and should be able to help you, though sometimes the russian and chinese names vary. The 'N' in russian is written as 'H' so 6N6 would look like 6H6 in russian.
fdegrove
Hi,
quote:
Twenty minutes later (and this fault always starts after about twenty minutes) i notice bad distortion in one channel.
That's probably a cap going on the blink...
It may be a coupling cap but it can also be a PS cap.
The problem occurs after warm up so it can be a cold solder joint too...
As for the valves; I'll look into that tomorrow but I don't see anything "problematic" so far.
The National KT88s are quite likely Richardson Electronics Chinese scams...not my friends, these folks.
Cheers,
NickC
Could be the bias going off after it gets hot. Common thing, i have come across this too many times myself. i speculate it could be utilizing fixed bias that means voltage on the plate of the tube normall for kt88 pp. The fixed bias circuit could then change value causing the voltage to increase thus biasing the amp further into class B. Another possible problem is the circuit being run on cathode bias opose to fixed bias. IN this way the resistor below the tube could get very hot thus changing its values as well as the cap parallel to it as they are normally in close proximity. Hope this sheds some light on the matter
horace
Thank you all for your help.
It looks as if a trip to the repair man is on the cards.
If anyone can help with a source of replacement valves (or a list of 'fit and forget' equivalents) I'd be grateful.
Many thanks
Martin
TG
6N2P - may be substituted with 12AX7/ECC83, but heater pins should be rewired (12AX7 has pins 4-5 - 12.6V, pin 9 - heater center tap; 6N2P has pins 4-5 - 6.3V, pin 9 - screen between triodes).
6N11 - I believe this is actually 6N1P, and if I'm right then it may be directly substituted with 6DJ8/6922/ECC88, although they are noticeably different. Or you may try Svetlana 6N1P.
6N6P - may be substituted with 12BH7 (different heater pinout) or 5687 (totally different pinout). 5687 is electrically closer.
Goog luck!
fdegrove
Hi,
quote:
6N2P - may be substituted with 12AX7/ECC83, but heater pins should be rewired (12AX7 has pins 4-5 - 12.6V, pin 9 - heater center tap; 6N2P has pins 4-5 - 6.3V, pin 9 - screen between triodes).
None of the Russian "equivalents" qualify as such comapred to Europen or U.S. tubes.
As a designer you'd better sort them out. Some are great, but equivalent they rarely are.....
Cheers,
Colt45
when the chinese copied soviet sojuz tubes, they usually dropped the last letter (ie. 6N6P = 6N6).
6N2P - no real sub, similar to 12AX7, different pinout. 6N2P is very common though, so its not an uphill battle finding this.
6N6P- similar to 12BH7< i forget if pinout is the same though. 6N6P shouldnt not be hard to find though. (although not as common as 6N2P)
if 6N11 = 6N1P as our ukrainskij friend suggests, then it is also very easy to find.
