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Old 22nd July 2016, 08:22 PM   #11
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Guys, the transformer wiring is all soldered to the pcb on this one although aghreed the the pt output is the first thing to check.
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Old 22nd July 2016, 08:22 PM   #12
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Old 24th July 2016, 11:44 AM   #13
CalTurk is online now CalTurk  Germany
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So far I was able to test the heater wires as per Gavin's (Mudchute) instruction and they checked fine . . .
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Old 1st August 2016, 05:24 PM   #14
tomchr is offline tomchr  Canada
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Here's my suggestion: Pull all tubes except the rectifier tube. Measure the heater voltages on the driver tubes and the 300B tubes. Also measure the B+ (should be accessible on the anode pin of the 300B).

If the B+ is within spec (or a tad high as it's not loaded by the tubes when the tubes don't heat up) but the heater voltage is missing, debug the heater circuit starting from the transformer.

Measure the output voltage from the transformer on the filament winding. Follow the schematic and work your way to the tube sockets on the heater circuit. You can take all these measurements with the rectifier tube out. That will limit the number of nodes with high voltage and make the circuit a little safer to work on.

Tom
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Old 29th November 2016, 02:06 PM   #15
CalTurk is online now CalTurk  Germany
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From the day I got the amp, the large heat sink was wobbly and I was sure that it shook something loose in transit. I had no time so ended up taking it in to a repair man near me that said that whatever it was it wouldn't be a problem for him to fix.

Turned out that yes, the heat sink had shaken loose the filament regulator (D1). He replaced that and after 3 months of waiting (checking in with him every few weeks) he finally called to tell me it was ready. He had said he had done the check out according to the tubelab.com page I sent him and that I was set to go.

I get it home and hook up some cheap 8ohm speakers, cd player and finally plug it in and power it on. Pure magic. Definitely the best I had heard these little speakers sound. I shut everything down half way through 1 song and went to take care of errands.

Later a friend comes over and I put on the same cd but this time into newly run in Alpair 10p's. After about 4 songs I hear crackling and hear the music cutting in and out. I look over to see one tube glowing blue. I raced over and shut everything down.
An hour later I hooked everything back up again making sure that I had everything plugged into the right place and securely. Things seemed fine for about 10 seconds when the same thing started to happen so I just shut everything down again and contacted Gavin.

The only things that have been replaced are 1st the GZ34.

GZ34/5AR4-STR TAD PREMIUM SELECTED - TAD Rectifier Tubes SELECTED

and 2nd, the triode

5842 / WE 417A (aka CV2642 ) Triode USA - NOS Rare & Vintage

Then lastly the filament regulator.

I can't find specs on this replacement so I'm hoping that someone can confirm from the picture that this is the correct replacement. Or the tubes for that matter.

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Old 29th November 2016, 03:56 PM   #16
w5jag is offline w5jag  United States
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Well ...

Re: D1: D1 is the filament rectifier, it feeds the voltage regulator for the power tubes. I'm at the office, but that looks like the correct part - they're not hard to find.

I don't like the idea of a heat sink on a heat sink, that seems dicey to me, but if it works OK, I wouldn't try to fix it. If the voltage regulator overheats, however, it will shut down and the amp will malfunction - but I don't know that crackling would accompany that, as I've not experienced that type of malfunction.

Re: crackling: Often a symptom of a bad connection between tube pins and their repective socket contact. I would check the 5842's - pull them and then replace them, maybe rock them in their sockets a bit. This is probably your malfunction. Sockets can, and do, go bad, but I wouldn't worry about that now.

Re: blue glow: May, or may not be, bad. Blue glow on the inside of the glass is normal flourescence- don't worry about this.

Blue, pink, or some other color glow within the internal elements of the tube structure typically indicates gas, is bad, and might cause the problems you are experiencing.

Win W5JAG

edit: I'm not crazy about Chinese 5AR4's - I've fried every one I ever owned, without trying. That one in your link may be selected, or whatever, but I still wouldn't trust it any farther than I could throw it. That tube malfunctioning could cause the problems you are describing.

Those 5842's in the link are garden variety 5842's, and should be OK.

Last edited by w5jag; 29th November 2016 at 04:02 PM.
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Old 29th November 2016, 08:37 PM   #17
CalTurk is online now CalTurk  Germany
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Quote:
Originally Posted by w5jag View Post
Well ...

Re: D1: D1 is the filament rectifier, it feeds the voltage regulator for the power tubes. I'm at the office, but that looks like the correct part - they're not hard to find.

I don't like the idea of a heat sink on a heat sink, that seems dicey to me, but if it works OK, I wouldn't try to fix it. If the voltage regulator overheats, however, it will shut down and the amp will malfunction - but I don't know that crackling would accompany that, as I've not experienced that type of malfunction.

Re: crackling: Often a symptom of a bad connection between tube pins and their repective socket contact. I would check the 5842's - pull them and then replace them, maybe rock them in their sockets a bit. This is probably your malfunction. Sockets can, and do, go bad, but I wouldn't worry about that now.

Re: blue glow: May, or may not be, bad. Blue glow on the inside of the glass is normal flourescence- don't worry about this.

Blue, pink, or some other color glow within the internal elements of the tube structure typically indicates gas, is bad, and might cause the problems you are experiencing.

Win W5JAG

edit: I'm not crazy about Chinese 5AR4's - I've fried every one I ever owned, without trying. That one in your link may be selected, or whatever, but I still wouldn't trust it any farther than I could throw it. That tube malfunctioning could cause the problems you are describing.

Those 5842's in the link are garden variety 5842's, and should be OK.

Thanks very much Win.

Good to hear about the filament regulator.

The repair man had originally wanted to replace the heat sink with a smaller one because the weight of it bouncing in transit from England to Germany is what broke it in the first place. I insisted that it remain the same though as it won't move much at all now that it's home, Gavin said it's necessary and George Anderson wrote on his site;

" . . . It has virtually no ventilation (there is a Lexan cover which is removed in this photo), and plays for hours without issue. This is probably the worst case that you would encounter, so this is the largest heat sink that you would ever need. I used it because it was free. If you have a heat sink similar to this, and the space to use it, by all means do so. The cooler these parts run, the longer they will last."

Semiconductors | Tubelab


About the blue glow. It was actually quite pretty but as it was only one and I only saw it once I heard the crackle, I assumed the worst. It was in fact inside the bulbous part of the glass. Very much like photos I've since seen online so apparently no concerns there. No blue glow on the right side along with crackle then silence in the associated speaker was bad news but at least tells me it's something going on there. According to Gavin the right side has always been slower to warm up and the repair man mentioned it too. Apparently that wasn't a problem to actual functionality for either of them but I mention it just in case it is a hint towards possible fixes.


Very happy at the thought that it might simply be the 5AR4's. Which ones have you found to work best for you?

I'm tempted to swap in a spare of the same make I have BUT while taking the board out I noticed melted wire insulation from the volume pot to to R1 that concerns me. It was at the twist in the wires (white / orange wire ((R1)) melted onto the still intact white wire ((R2)) ) so I'll get small small heat shrink for it before I solder it back on.

In the mean time, even though the contacts all looked clean, I did as you recommended and cleaned them.


Sorry for such a long post but I wanted to be sure to mention everything up to this point for clarity. Thanks very much for your help so far!


-Deniz
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Old 29th November 2016, 10:26 PM   #18
w5jag is offline w5jag  United States
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Quote:
Originally Posted by CalTurk View Post
......

I'm tempted to swap in a spare of the same make I have .....

Very happy at the thought that it might simply be the 5AR4's. Which ones have you found to work best for you? ....
It won't hurt to swap your spare in, and it may solve your issues.

The vanilla Sovtek 5AR4 is fine, and and I would expect that the upscale versions of it would work fine also, although not necessarily any better for the extra expense.

Any U.S. made, British made, Western European made, or Japanese made, 5AR4 will be fine, regardless of brand, and would probably outlive you. Sylvania made some really robust 5AR4's that were marked as 5V4GA. They can be branded Sylvania, Phillips ECG, and even RCA.

Many tubes marked "made in england" or "made in germany" are communist counterfeits marked to avoid import bans, and should be avoided unless you are certain as to what you are looking at. These can even turn up in U.S. JAN boxes.

Win W5JAG
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Old 6th December 2016, 08:13 AM   #19
CalTurk is online now CalTurk  Germany
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I've checked all of the connections and they seem fine.
All solder points seem solid and I've cleaned all sockets and pins as well as made sure sockets are tight. Swapped out all of the glass as I had extras and problem still there.
Tube on left gets hot while tube on right only gets a faint glow. Left speaker has a soft crackle that doesn't change when turning the volume up or down. When playing music only the right speaker plays.
Since I don't have any spare 300b I let everything cool down for an hour then swapped those and same thing. No music from the left speaker, only a light crackle.
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Old 6th December 2016, 04:28 PM   #20
w5jag is offline w5jag  United States
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Quote:
Originally Posted by CalTurk View Post
....
Tube on left gets hot while tube on right only gets a faint glow. .....
Not entirely sure what this means.

By hot, do you mean the left tube has an orange or red glow coming from the outermost metallic part of the tube ( i.e. the anode or plate ) ? This is bad.

By faint glow, do you mean the right tube is only emitting light from the innermost filament like structure ( also known as the cathode ) ? This is normal.

Do you know how to measure and adjust, if necessary, the power tube bias?

Win W5JAG

Last edited by w5jag; 6th December 2016 at 04:30 PM.
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