Discussion in 'Audio Hardware' started by RockAddict, Mar 25, 2021.
Right, was just gonna say that
Hopefully having the higher value resistor is what is causing the bias anomaly. At least I know it is not totally dead.
Just looked at a schematic for the R8 on the Aussie website and it shows the cathode resistor value as "10R" which I am guessing is 10 ohms. Just have not seen a resistor value expressed with an "R" before.
Yes, that is the way it is often written on schematics, especially outside the US. That avoids confusion with decimal points that may not be clear on drawings, ie 10R3 = 10.3 ohms.
Have you figured out what has caused the damage?
I assume I got a bad tube. I ordered a quad of KT77's and it smoked when I was bringing up the bias on V3. VivaTubes was very decent about the problem and is taking the tubes back for a refund and also provided a return label. I currently only have the stock tubes in the amp and will probably keep that way for now.
What a luck and a scary experience It is very fortunate no major damages otherwise it is really PITA to send it in for repair. Hope everything turns out OK.
Looks like you are on the way to a functioning R8 soon. Nice sleuthing and I'm looking forward to hearing about great listening sessions moving forward!
I'm glad that you were able to salvage your amp after all!
Yeah it's definitely good to have a hand-wired p2p amp when push comes to shove and repairs are needed.
Having been away for a few I'm sure I've missed a thing or two, and since it's been so hot here and I've been so busy I haven't turned on the amp once. (Though I do have high ceilings and the amp doesn’t really get that hot anyway.)
Meanwhile what I have done is buy new boxes for my ever-growing tube collection. Couldn't find any to match the actual brands I bought NOS so I just ordered Tesla and Telefunken. Have several extras which I will send free to any regular contributor in this thread. These are the large size about 1.5" x 1.5" x 4.75"... just PM me your address, first-come, first served.
These were shipped from Bulgaria! And the shipping cost was the main thing. Hope I'm not violating forum rules with a giveaway of trivial paper items but I'm sure someone will correct me if so.
Those are cool... and my original tube boxes are held together with Scotch tape. I appreciate the info!
I got an acceptable response from CHA regarding the issue with my R8. Yong said the factory suspected a faulty tube caused one of the three resistors attached to the V3 pins to fail. He also provided a close up picture showing the resistors and provided so advice to check that there were no other issues. I thanked him for his response and said that I could replace the resistor myself.
Now I am going to be very leary when comes to have to replace the power tubes. I am going to stick with the stock KT88's until they fail to minimize any chance of this happening again.
So you meant you are not going to roll tubes for the next 1 or 2 years???.... No, really, it is not that scary as long as you take precaution steps, like buying from reputable tube vendor and check for short yourself with a multimeter before using the new tubes.
Sorry to hear about the failure and nice job on the self save. I wouldn't be overly concerned with rolling tubes, bad tubes can happen. I've had a tube blow, a rectifier in my case, and take a resistor out it's nothing to do with the amp itself. FWIW I've had excellent luck buying KT77's from Upscale, they cost a little more but I've found their tubes very reliable. I hope you do try the GL KT77 again sometime I suspect it would be a marked upgrade over the stock tubes.
The tubes that gave me a problem were from Viva Tubes who I think is a reputable dealer. It is possible something happened to the tube during transit.
Maybe just invest in a tube tester
That is probably pretty pricey.
Davey…you are a tech in heart, that’s for sure
You could always get one of those cheap Chinese EL34 amps and use it as a test bed before installing them in the big rig, I've seen some of them for around $100
Now that's an interesting idea. Or buy from Upscale Audio. They claim all power tubes are burned in to weed out defects. Also right on their page for the Gold Lion KT77's, they say that they have a high failure rate but for some people, they might accept the risk for great sounding tubes.
Well, I've drawn a lot of schematics and circuit boards in my time, and made a lot of parts lists, so this is just second nature even though I don't do much of that type of work anymore.
They are correct in fact the reason I started buying them from Upscale is I loved the tube but was buying them from whoever was cheapest and having lots of early failures. That pretty much subsided with the switch to Upscale.
More than you probably ever wanted to know about tube testers. I think in most cases a multimeter would be just fine to check for shorts or opens. Even the most reputable seller cannot control for damage during shipping.
Separate names with a comma.