My Ultravalve Just Dropped the Left Channel!

adydula · « **on:** 21 Oct 2010, 12:58 am »

Well after almost 3 month of ear problems I finally started to listen again and my wonderful Ultravalve amp decided to stop functioning on the left side. I was listening at a low level and heard a pop and them all right channel no sound from the left speaker.

Oh boy, I measured the bias, -1.3 vdc on the right, -27.1 on the left. I swapped the output tubes around and the probelm stays on the left side. Tubes seem fine, I tried the rectifier tube as well, still left ch has very low volume and its very distorted. I have a new set of tubes and tried these as well. Nada.

Swapping speaker cables left and right the problem stays with no output from the left side. I connected the preamp outs from my AVR and the same thing.

I took the bottom panel off looking for something that may have 'fried' but nope...oh well I am glad I saved the shipping box.

Call Frank in the am and hope we can get this gem running and back soon, I really like the sound from this amp!

All the best
Alex

jaw5279 · « **Reply #1 on:** 21 Oct 2010, 01:11 am »

Alex, so sorry to hear about your Ultravalve. Please keep us in the loop as you find out more about what has happened.

John

Gopher · « **Reply #2 on:** 21 Oct 2010, 01:16 am »

Alex,

I was just reading about your ear issues earlier today--this is a miserable way to celebrate hearing again, but isn't that always how crap like this works out?

That Ultravalve was high on my list of amps to try with my Zu Soul Superflys--I suspect it is worth the wait for a warranty repair.

Lefty052347 · « **Reply #3 on:** 21 Oct 2010, 01:18 am »

I am sorry to hear about your problem. I certainly enjoy my Ultravalve.

Did you try swapping the small signal tubes?

Regards,
Dean

gjs_cds · « **Reply #4 on:** 21 Oct 2010, 01:34 am »

Sometimes electronics give us headaches, but I know from personal experience that Frank and his team Will Take Care Of You. That's why I'll buy from no one else...

adydula · « **Reply #5 on:** 21 Oct 2010, 01:58 am »

Yes, I did try swapping the left with the right small signal tubes first, and then the output tubes and a new rectifier....the left side still was the issue.

I then changed the entire set with a new set of valves.

I also noticed that the left bias pot adjust does not affect the right side bias at all.

Sure wish I had a schematic!

I used to do troubleshooting of electronic circuits for a living, fuel gauges for jet aircraft, servo circuits etc...all kinds of stuff. I have an Amateur Radio Extra Class Operators licnese and have built all kinds of stuff over the years. But I have been out of that for 20 yrs or so. Used to run sampling scopes on high speed digital circuits etc.

The swapping of removeable parts is the easy part. Its when its a part the has just let go or opened or shorted when it gets a little harder to figure out.

Thank God the speaker was not damaged. I have the AVR hooked up again in the interim and they are just fine.

Yes I partially bought this because of Frank and his honesty and no BS attitude!! lol

Its just sitting here in its shipping box waiting for its journey back home for resurrection!!

Alex

Tom Alverson · « **Reply #6 on:** 21 Oct 2010, 02:27 am »

Power it down and measure the resistance to ground on each channel on the bias test points. They should both be the same (around 16 ohms probably). If one is way higher you could have a bad resistor or maybe a bad ground connection on the cathode resistor. Check out the stock ST-70 schematic as the output tube stage is probably very similar to the Ultravalve. You can download it from http://www.triodeel.com/schindex.htm

73 de NU8D

Tom Alverson · « **Reply #7 on:** 21 Oct 2010, 02:52 am »

Check out this thread to see if maybe this applies?? http://www.audiocircle.com/index.php?topic=84622.0

adydula · « **Reply #8 on:** 21 Oct 2010, 03:20 am »

Hey Tom...

de AG1Q/4

I checked the 16 ohm resistor to ground and on the right side its 15.9 on my el cheopo meter. The left side is 1 meg!!! on the 20 ohm scale it looks open!!. The grounds look mechanically solid, there is a star lug on the uvalve...I read Franks comment and these bias resistors seem to be the culprit on the left side, dont know why one would all of a sudden decide to become a 1 meg resistor!!

I will call Frank in the am and ask him to send me a 16 ohm resistor etc.. this should do the trick i hope!!

All the best...CQ, CQ CQ AvaHiFi De AGIQ/4

Alex

Tom Alverson · « **Reply #9 on:** 21 Oct 2010, 03:24 am »

I would open it up and measure right across the resistors to see if they are OK or the problem is just the connection.

Tom

adydula · « **Reply #10 on:** 21 Oct 2010, 12:25 pm »

Tom , I did that. There is a piece of tubing on the hot side nothing on the gnd side. its 1.01 meg right across the resistor itself. I must have measured it 459 times....also all gnds look tight and good. Frank is using a lug fastened to the chassis and tube socket, very secure no movement. If this is it... its a simple fix. willng to try it if Frank will send me a 16 ohm precision resistor, looks like a small 1/8 watt all brown resistor, no color bands on this one..

Hopefully nothing else was affected. Something made this resistor change, could be a shorted tube, high current etc...I spoke to Frank this morning and I got a few 15 - 16 ohm resistors and will replace this one tonight and see if thats it. Stay Tuned.

Alex.

Tom Alverson · « **Reply #11 on:** 21 Oct 2010, 07:34 pm »

A tube could have shorted out and burned out the resistor, but usually the fuse will go first. It sounds like the tubes worked OK when you swapped them to the other side, so maybe it was just a resistor failure (not caused by something overloading it).

avahifi · « **Reply #12 on:** 21 Oct 2010, 08:01 pm »

Alex just called me to let me know the issue was (as I had suggested to him) a 16 ohm bias resistor fried open on one channel.

Replacing the resistor fixed the problem.

The only remaining problem is that he did not keep track of which output tube shorted (the only possible cause of killing that resistor). He put the same set back in and all are working again. However, we suspect this will only be temporary until the defective output tube shorts out again and repeats the issue, unless he catches it promptly.

Regards,

Frank Van Alstine

gjs_cds · « **Reply #13 on:** 21 Oct 2010, 08:22 pm »

So would the safest response be to replace all the tubes then? Or is there a poor-man's way of testing them?

adydula · « **Reply #14 on:** 22 Oct 2010, 12:41 am »

Hello,

Its working again, the 16 Ohm resistor changed values from 16 ohms to about 1meg! Not open but 1meg is a far enough away from 16 ohms!!! Funny the resistor looks fine, not burn or any color change...just like it brother in the other channel!

I was fortunate to have a lab in the my workplace that was well stocked with 15 and 16 ohm thin metalfilm resistors that I was able to hand select one that was 16 Ohms spot on. It took 10 minutes to changeout. Bias set to -1.6vdc no problem.

As Frank indicated this was probably caused by a tube short, high current draw....enough to heat the resistor up enough to change its value.

Unfortunately I laid the tubes down and mixed them up and dont know really which tube 'might' be the culprit. So I replaced all of the tubes with a new set. The original tubes maybe got 50 or so hours on them (groan).

The original tubes play great, sound fine but if this is a thermal thing then it could come back short and maybe cause the same type of failure. So not going down that path..hence the tube replacement.

So the question I have now for Frank is tubes do go bad, they do short out, open etc...so can this resistor etc be protected somehow so this type of component failure does not happen?

I always will be worried that another tube down the road will do the same thing someday and voila here we go again...I dont want to have to have a supply of 16 ohm resistors lying around...even though I enjoy troubleshooting and soldering!!

That said, the Amp sounds absolutely WONDERFUL, I played 2 cds both demo disks from RMAF and it was an awe inspiring experience....I love my Ultravalve.

All the best
Alex

rlee8394 · « **Reply #15 on:** 22 Oct 2010, 03:21 am »

Sometimes when power tubes go Tango Uniform, their getter splash changes from a bright and shiny silver to a powdery white or chalk-like appearance. See if any of your tubes look like this, if so, they are probably the culprits of the 16 ohm resistor demise. You could also put a 200 ma fast-blo fuse in-line with the resistor. Then try each tube until you find the one that blows the fuse.

Ron

adydula · « **Reply #16 on:** 22 Oct 2010, 12:25 pm »

rlee,

Good Idea!!

I might just do that...

Alex

Tom Alverson · « **Reply #17 on:** 22 Oct 2010, 09:09 pm »

Glad you got things working again. Here is what I do to test and match tubes:

Put two good tubes in the left channel and set the bias normally (This is to keep some loading on the amp power supply and keep the voltages from getting too high). In the right channel, just install one tube and set the bias for 1/2 the normal value. I then try each suspect tube one by one and write down the measured voltage on the bias test point (Without adjusting anything). Then I pair up the closest tubes to use in the same channel. In your case I would watch the bias current for anything funny. If you want to get fancy you can get a cheap Digital Voltmeter with a USB or serial port and capture the voltage vs. time on a PC (some even come with a graphing application). The bias should rise to a normal value and stay pretty steady (it may vary a few percent with line voltage variations). If you see the bias start to climb well after warmup then that tube is probably bad.

adydula · « **Reply #18 on:** 23 Oct 2010, 12:53 am »

Hey Tom, thanks for the input. I will first inspect the tubes carefully in daylight to see if i can see anything, i kind of doubt that.

I could do the meter with only 1 tube on one side at half the bias voltage and see what happens over time...or try the 200 ma fast blow fuse which i think is kind of ingenious in its own right!!!

I also thought of buying a tube tester .....I actually am bidding on one on ebay!! like i really need one, but boy it would be a neat toy!! (LOL)...

I do have a friend at work that has 3 tube testers ,and he is going to let me borrow one so I will try that as well.

He also has a BIG box of NOS tubes he doesnt know what to do with !!! oh boy!!

Mucking around with the soldering iron is making me want to build something again!!

All the best
Alex

adydula · « **Reply #19 on:** 23 Oct 2010, 01:36 am »

Another thought and question. When the failure occurred it was sudden, just a "pop" sound that really caught my attention the no sound from the right channel.

So the question is is there a voltage where the tubes on the offending side just suffenly STOP hence the pop? OR did the bias voltage keep climbing to a point where the "pop: occurred...be a long time since I drew load lines etc!! (lol).

or did the resistor just have the idea to change its value....Frank is pretty sure its a tube and I thing I am also, but the sudden part of the failure has me baffled.

I guess if the tube gets hot thermally something in the tube could 'grow' and touch something it isnt suppose to and draw lots of current and bang the pop and the resistor failure...

just thinking
Alex