[samwell7]

Quote:

 
tubes...it's a love hate relationship.  yours might be going, can you swap?

 
On the plus side this sounds amazing, definitely got that ballsy tube sound I've been looking for, it overdrives nicely as well.  I will swap and try soon, the sound is gone when I just use it as a preamp before some powered speakers.  It was pretty much gone when I was using my headphones as well.  I'm using a JAN spec Phillips 6922
 
here's a photo also

 

[ludoo]

I had a similar issue, and fixed it by thouroughly cleaning with some fine sandpaper the tube and tube socket contacts, which were slightly oxidized. It might also be due to a grounding problem, check if the sound changes when you touch the sockets or metal case with your hand.
 
It's a great little amp, isn't it?

 

[samwell7]

I had a similar issue, and fixed it by thouroughly cleaning with some fine sandpaper the tube and tube socket contacts, which were slightly oxidized. It might also be due to a grounding problem, check if the sound changes when you touch the sockets or metal case with your hand.

It's a great little amp, isn't it?

Well the socket I have at the moment is really hard to get the tube into and doesn't quite fit in properly, I've ordered a new socket which should fit the tube more snug. Pretty sure I considered it not a grounding problem because it didn't change when I touched stuff. I think it might be the ground problem because it didn't go in properly and when I moved the amp on its side the noise came back a little louder. Will report back with the new socket, and also bought a switched potentiometer for it so those wires and running through, I reckon they will melt on the heatsink of the MOSFET. It is an amazing amp for the money, it sounds awesome. How I thought a tube would sound before I started listening to them.

 

[Zigis]

Anyone know replacement part for 2sk117, preferably available in Farnell?
I am waiting for package from Thailand, but it is too long time.
 
What parameters I need to look for similar working in CCS? Similar gate current (14mA) ? anything else?

 

[Zigis]

Can BF254A work?
 
Or NTE312 maybe, datasheet:
 
http://www.nteinc.com/specs/300to399/pdf/nte312.pdf

 

[duncan1]

The BF254  isnt a fet but an NPN transistor. The   2SK117 is an N channel fet that works to  50V. A 2SK68 would  do/2SK106/2SK163/2SK184 would all work.

 

[Zigis]

Typo, I mean BF245 N channel fet, of course.
 
Actually I ordered NTE312 from Farnell and it work great in amp, so if anyone have parts problem, this is good and easy to get replacement part, only pins are different.
 
I buy some BF245A locally, not tested yet. Yes, and package with 2SK117 arrived yesterday

 

[duncan1]

The BF245 is only good for  30V I wouldnt use it . But glad to hear your amp is now working great.

 

[DKJones96]

  Are you certain the 12AU7 can be used as a replacement for the 6DJ8? Retailers seem to sort these as two different types of tubes. I'd verify this amp can use a 12AU7 before buying a new tube.

You know, with a little bit of circuit modding a 12A*7 series tube could work.
 
The standard circuit is setup for 6.3V across pins 4 and 5, if you were to re-calculate the constant current supply resistors and snip the shield connector at pin 9 you'd not only have the option of any of the 9A based dual triodes but your regulators would work MUCH cooler. A 12AY7 would be a good tube for matching gain but an AU7, AT7, or AX7 should all work and since they all have the same heater current rolling is a simple swap.
 
Great, now you have me wanting to build another one of these!

 

[DKJones96]

Simple mod actually works!
 
I used a 12AY7 for my quick test but haven't tested the others yet(exams). Swap in a 8.2 ohm resistor on each LM317 for a CC of 150mA. They end up both going to the same pin(3 I believe) and if you leave one of them alone but send the other one to pin 4(should be to ground so cut that) the shield should already be grounded on pin 9 which completes the heater/output circuit. With that setup you should only need to re-bias between tube swaps(it might not even need that really) from 12AU7, 12AY7, 12AT7, 12AX7, and a multitude of other dual triodes if you aren't afraid of air wiring(I have my tube air wired to make the tube stick out of my chassis more).
 
I want to play with it a little bit more because there is no reason why an LM317LZ(to-92 packaged LM317) couldn't be used in place of the 2SK117(pinout might be different). It's just a simple plate CCS with a depletion mode jfet. If this is the case it might be possible to also make this a super cheap build seeing as it would just use 4x LM317s and a couple of output MOSFETs.
 
Unfortunately, I might not be able to test the LM317 idea since I don't want to mess up my original. If anybody has some boards they could sell I could play a bit more.