Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: buddha2015 on June 30, 2015, 09:02:16 AM
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Hi there,
I finished building my Crack amp with Speedball upgrade. It measured and worked flawlessly right from the start with stock tubes.
To lower output impedance I purchased a Tung Sol 5998 from a seller on Head-Fi. Right from the start it just got hot but it was not glowing and there is no output at all. I tried with different ECC82s with the 5998 in place but no difference.
I measured voltages with the Tung Sol installed:
B1: 82V B2: 210 V B3: 1,4 V B4: 80V B5: 210 V B6: 1,4 V B7: 0V B8: 0V
How to interpret this ? Could anything be wrong with my Crack ?
The seller says the tube was working perfectly when he sent it.
Is there any way of knowing if the tube could have been damaged in shipping ?
thanks for your help
Guenther, Austria
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Pull the 5998 out of the socket. Set your meter to read resistance in a low range. Measure resistance across the 5998 pins 7 and 8. You should read some low number. If you read OL or infinity the heater is open and the tube is dead. If you read a good, low resistance from 7 to 8 plug the tube back in. Set your meter to read AC volts in a low range, like 20VAC. Take a voltage reading from B7 to B8. It should be around 6.3 volts. If the voltage is correct turn your room lights down and look for any kind of glow from the 5998 that would indicate the voltage is getting to the heater. The glow may be faint. If it is not glowing at all, try cleaning the pins and rocking the tube in the socket a tiny bit.
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Thanks for your help, Doc.
The resistance between pin 7 and 8 is somwhere around 1 Ohms or below.
The meter reads 5,5 V AC voltage between B7 and B8.
The tube does not glow at all but it gets hot !
I have plugged it in and out numerous times with same results.
Strangely I found the 4 red LEDs on the larger circuit board of the Speedball Kit are not glowing with the 5998 plugged in. All the LEDs are glowing with the stock tube in place.
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I run a 5998 with great results. I'm inclined to think you have a bad tube
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5.5V is a little low, and that may have some bearing on whether the tube will conduct. What is your AC mains voltage? Also, what AC voltage do you measure from B7 to B8 with the stock 6080 installed?
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My AC voltage measures 233 V.
The AC voltage from B7 to B8 is 5,6V with the stock tube.
The 4 LEDs not glowing - does that indicate any problem ?
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The LEDs not glowing are indicative of the same problem as the low B3 and B6 voltage, the tube is not conducting. My hunch is the 5.5VAC is just a bit low for the 5998 (I think it wants more like 5.7VAC minimum) and it's getting warm but not hot enough to emit properly. The 6080 you have seems to have a heater that emits better at the slightly low voltage.
You might try removing the 5998, leaving the ECC82 in its socket and measuring AC voltage across terminals B7 and B8. That will give us an idea of whether the 5998 is pulling the heater supply voltage down excessively.
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The voltage is 6.15 V from B7 to B8 with the tube removed.
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OK, that's about right for the line voltage you are getting. The 5998 is just pulling that voltage down quite a bit, probably just below the threshold of sufficient emission. My hunch is that to get the tube to work you would need to increase the AC mains voltage to the amp by 3%, about 7 volts. The easiest way to do this is with a variac.
You might also reflow all of the solder joints from pins B7 and B8 back to the power transformer. Just a little bit of added resistance from a cold solder joint could affect the heater voltage. For example, an added .1ohm of resistance from a cold joint with the 2.4A current draw of the 5998 heater could drop the heater voltage .24V. It may or may not help, but it's something simple to try. Also clean the tube pins really well.
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Ok I will resolder the joints tomorrow, it is getting close to midnight where I am.
At my workplace we should have variacs and different high voltage power supplies. Both are not tools that I want to use at home but they should do for testing.
Is there any way of stabilizing the voltage at B7 B8 or cranking it up somehow by changing components on the circuit boards ?
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The heater supply is very simple and direct, going from the transformer right to the tube socket. There aren't any components in between that could be changed to get more voltage. To see higher heater voltage you either have to reduce any unnecessary resistance in the wiring connections, use a tube that draws less current like the original tube (and thus pulls the voltage down less), or put more voltage into the primary side of the power transformer.
The Variac will be a great way to see if a little more voltage will get the 5998 hot enough to play.
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OK so I used a variable transformer to crank up AC mains voltage up to 250V which brought up AC voltage from B7 to B8 to 6 V.
No change whatsoever, the 5998 gets hot but no glowing and the LEDs on the large Speedball circuit board do not glow either.
Bad tube ? Any other tests I can run ?
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Sure sounds like a bad tube! Just double check that the amp is still happy with your other 6080/6AS7 tubes.
-PB
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The amp happily accepts the stock tube.
Anything else I can try/measure with the 5998 tube ?
Can a tube get damaged like that from shaking/in transit ? I paid more than $100 and I need to argue with the seller...
:-[
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It would be best if you could get the tube tested locally, if at all possible.
-PB
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Do I need a tube tester ? I work in a service center for electronic appliances and we have lots of tools available.
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Yes, being able to tell the seller of the tube that you tested it on a specific tube tester and obtained failing results is helpful information on the road to getting a refund.
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Thank you guys for great & immediate support so far :)
I am still open to other suggestions that could help resolving the problem.
Not sure if there is a tube tester around at my workplace.
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You could try measuring the tube for a short. Clip one test lead to pin 7 and then see if you find a very low resistance reading to any other pin beside pin 8, which of course will read very low since 8 is connected internally to 7. I don't think you will find a short based upon your description of the problem, but it's easy to check.
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Thanks. No short.
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I think PB is right that you feel you need to support your case you might find a tube tester and document that the tube has low emission or low/zero transconductance. It certainly should be working with 6V on the heater.
It is possible that some wire that extends from the tube structures down into one of the pins is broken or loose. Unfortunately this is pretty much impossible to measure. In rare circumstances one can reheat the pins and reflow the solder that anchors the wire to the inside of the pin. I have saved a few tubes this way, but I would be hesitant to take an iron to a tube that I might try to return for refund.
You might also clarify with the seller how he determined the tube was working. If he just checked to see if it got hot then he would have assumed it to be working. If he used a tube tester he might have recorded the reading he got. If he tested it in an amp to check function and heard music then it most likely did get damaged in shipping.
The last resort I can think of would be to double check that all of the pins are getting adequate contact in the socket. Sometimes pins are slightly different diameters or they might be slightly bent and it's possible that a pin is not making full contact even thought that same pin on the 6080 is connecting well to the socket. Wiggling the tube in the socket can sometimes show that there is an intermittent connection.
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Hi if you put added your location to your profile maybe you might live close to someone with a tester who might help.
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In my experience any tube that gets hot but doesn't visibly glow has got air inside it. Does it still have the shiny getter material on the glass?
Go back to the seller anyway, i have bought tubes from eBay that have died in transit and always got a refund from the seller.
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I've been running a 5998 tube in mine for some time with no issues. I'd go with the bad tube theory also.
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To summarize, they are saying a good 5998 works in the Crack.
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I'm listening through my 5998 right now- no issues at all
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In my experience any tube that gets hot but doesn't visibly glow has got air inside it. Does it still have the shiny getter material on the glass?
Go back to the seller anyway, i have bought tubes from eBay that have died in transit and always got a refund from the seller.
Thank you everybody for their input.
My tube does not have the shiny getter material on the glass. There is a very clear circle above the getter and some whitish material around.
There are some glass pieces inside the tube (seller told me about them) and on close inspection also white powder.
I just found out that I can rotate the black base slightly against the glass part.
I guess my tube has sucked in air ?
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That whitish material doesn't sound so good. That usually the color the flashing turns if it is worn out or air has snuck in.
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Ok folks, here comes the solution. It is bad news for me I guess.
I had almost forgotten, that pictures had been taken of the tube when it was in transit. I used a freight forwarder to ship the parcel from the US to Austria and for insurance reasons photos had been taken from the contnents of the parcel when it arrived at the depot in the US. The photos were uploaded to my account.
Here they are:
the tube when it arrived at the depot:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fabload.de%2Fimg%2Ftube1g5phn.jpg&hash=f7993da323f9e7edd5249ee7e9993c5f8f599be7)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fabload.de%2Fimg%2Ftube27uqlq.jpg&hash=71e503bcfc5a8b712a5ed6900c3838e66b2bf6ac)
the same tube when I received it:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fabload.de%2Fimg%2Fresizeof20150704_1347x1onj.jpg&hash=a7f94f4cc60031e6eb879878f33ce869379f8de2)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fabload.de%2Fimg%2Fresizeof20150704_13478tr0z.jpg&hash=4de7db54d642b268b3a2a1291d4138f59fcbcc5a)
You can clearly see that the dark getter material has vanished from the glass.
In this case it is most likely that the tube has been damaged when on the way to Europe.
I am unsure if I can still start a claim with the transport insurance, as I received the parcel visible undamaged and I accepted it from the post office without hesitation. I must admit the parcel was packed well and I cannot really blame the seller. Maybe someone at customs dropped it ?
Or I was just unlucky. :(
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Yup thats what i suspected, the inside has filled up with air so its useless now. Most likely a crack developed where the pins enter the tube, due to said wobbly base.
Are you saying the tube was unpacked and photographed at a shipping Depot? You can clearly see the getter starting to erode in those first few pics which implys to me that is when it got damaged.
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Are you saying the tube was unpacked and photographed at a shipping Depot? You can clearly see the getter starting to erode in those first few pics which implys to me that is when it got damaged.
Yes it was unpacked and photographed. The getter starting to erode ? How do you see that ?
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When new the getter material would have had a shiny mirror coating on the glass, your tube is unusual in that had the getter material on the top and on the side. In those pics you can see the top circle is getting smaller as the outer ring is still visible. Likewise on the side the material is being eaten away from the center of the material out. Eventually that material will turn milky white once it has fully reacted with the air. In your last pic there is no visible trace of the getter material, all that will remain is a white power floating around inside the glass. The fact the materiel is visibly reacting with air tells us that the tube had already started to leak at that stage. i.e. it was damaged before you received it.
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Do you mean it must have been damaged before it arrived at the depot ?
How long does it take the getter material to react with air/to be eaten away ? Is that a process that takes seconds, hours, days ?
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I dont know how long it takes, i've never broken one to find out :)
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The getter turns white nearly instantaneously when the vacuum is lost. That tube is definitely dead.
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Hi folks,
someone is offering two 5998 tubes and claims that they are both working.
I seriously doubt that when I look at the picture that has been posted with the ad (please look at the right one, the silvery material on the inside of the tube is missing):
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fabload.de%2Fimg%2F_57q8kfc.jpg&hash=cd943a716bb67e87742509ed2fad909d9f920481)
What is your opinion ?
Thanks
G
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The getters and getter material are on the bottom of the glass in the early versions. Personally i think those versions sound better too. The same differences can also be found in the TS 421a tubes.
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You mean they could be from different batches ?
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Different years of manufacture, so yes. The other obvious difference is the plate colour, early tubes had a light grey colour, where as later years had a dark black, almost shiny finish.
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The seller just confirmed that the tubes are from different batches and indeed one has the getter on top, the other one on the bottom.
Thanks for your help, mcandmar ! :)