Hello Guys,
I have an odd one, 6080 OTL amplifier, I plugged in a new preamp and it blew all of the tubes (they exploded) on both channels.
So, changed the coupling caps, same thing, tested the cathode resistor, perfect on the money.
Checked all caps for leakage on the LCR, not an issue could be found.
Checked the loading resistors on the speakers, checked out...
B+ is as it should b, -75 rail is on the money bias, I just do not know.
I have NO schematic nor values, but I have the spec sheets for the tubes (EEC82 Driver 6080 Output), I know that too much current is passing to the K1 K2 but I cannot work out how...
I say this as I dissected one of the tubes and the connection from the K to Pin has gone.
Also, I put in a 6080, turned it off then on then off then on and bang... same again.
Any help would be great, I am scratching my hair away.
Björn
I have an odd one, 6080 OTL amplifier, I plugged in a new preamp and it blew all of the tubes (they exploded) on both channels.
So, changed the coupling caps, same thing, tested the cathode resistor, perfect on the money.
Checked all caps for leakage on the LCR, not an issue could be found.
Checked the loading resistors on the speakers, checked out...
B+ is as it should b, -75 rail is on the money bias, I just do not know.
I have NO schematic nor values, but I have the spec sheets for the tubes (EEC82 Driver 6080 Output), I know that too much current is passing to the K1 K2 but I cannot work out how...
I say this as I dissected one of the tubes and the connection from the K to Pin has gone.
Also, I put in a 6080, turned it off then on then off then on and bang... same again.
Any help would be great, I am scratching my hair away.
Björn
Do you know if your 6080 OTL amp has dc-coupling throughout (except maybe for coupling capacitors at the output)? If so, than maybe the output of your new preamp has a dc-offset (meaning: the output is not on 0 Vdc) which could cause the 6080 to start to pass way too much current.
What happens if you connect your 'old' preamp (if you still have it)?
What happens if you connect your 'old' preamp (if you still have it)?
That is consistent with too much current. Odd that it happens to all tubes. What do they have in common? Answer: the heater probably. If there is a short between the heater winding and the cathode somewhere that could lead to extreme high current, depending on how the cathode is biased. Worth a check.
Jan
Hej Guys,
Thanks so much for the responses, and to put you all to rest, I have bled every capacitor before I went any further, all CAPS measure -/+ 1VDC, I have had too many bad days to not.
I have checked for shorts on the heater, they are fine, the 82's are 6.3VDC loaded and the 6080 are 6.3VAC loaded they are separate and the drivers are rectumfried.
As far as video evidence, I am going to be honest and say that there is no chance I referencing this to mains voltage again until I solve the problem, I am looking for my trusted lightbulb dimmer current sharer but I think my ultra efficient wife has put it in a safe place, however I think she put it somewhere safe from me.
I have an autotransformer and isolation transformer at work, so I think I will hook it up to that at safe voltages and see what I can see, after changing the coupling caps and checking the heaters are fine it is not an obvious one.
It is SS rectumfried, checked the diodes in the packages and they test fine.
When I spun her up yesterday the 6080 got hot quick, with no signal or load, maybe this is characteristic of the tube, I cannot tell from the spec sheet, only watt dissipation, but in the real world, maybe they just get hot quick, this is my first experience with them.
I am getting a 46 at the weekend, but still, would like to fix this.
Thanks for all the help, I shall test the heater again tomorrow and post some pics, it is all p2p circuits and not that tidy, it was not my build I have to qualify!!!
Thanks
Björn
Thanks so much for the responses, and to put you all to rest, I have bled every capacitor before I went any further, all CAPS measure -/+ 1VDC, I have had too many bad days to not.
I have checked for shorts on the heater, they are fine, the 82's are 6.3VDC loaded and the 6080 are 6.3VAC loaded they are separate and the drivers are rectumfried.
As far as video evidence, I am going to be honest and say that there is no chance I referencing this to mains voltage again until I solve the problem, I am looking for my trusted lightbulb dimmer current sharer but I think my ultra efficient wife has put it in a safe place, however I think she put it somewhere safe from me.
I have an autotransformer and isolation transformer at work, so I think I will hook it up to that at safe voltages and see what I can see, after changing the coupling caps and checking the heaters are fine it is not an obvious one.
It is SS rectumfried, checked the diodes in the packages and they test fine.
When I spun her up yesterday the 6080 got hot quick, with no signal or load, maybe this is characteristic of the tube, I cannot tell from the spec sheet, only watt dissipation, but in the real world, maybe they just get hot quick, this is my first experience with them.
I am getting a 46 at the weekend, but still, would like to fix this.
Thanks for all the help, I shall test the heater again tomorrow and post some pics, it is all p2p circuits and not that tidy, it was not my build I have to qualify!!!
Thanks
Björn
WHAT exploded?
Filaments?
Plates?
Molten metal inside tube?
Shattered glass flying all over the place?
Pictures please.
Did you blow another set of tubes?
Again, pictures.
Pictures please.
Please pictures of the exploded tube remains.
Glad to help but we have ZERO data to work with.
Can you attach a photo of the underside of the point to point? We should be able to spot some gotchas.
I suspect you will need to start breaking the issue down and working backwards.
Too much current is normally todo with a operating point change:
* B+/B- out of spec (could be the transformer or reserve/smoothing caps fail as a short)
* shorting tube (but to have all do this is not common)
* duff capacitor (the cap is shorting allowing a DC current draw from the output to B+.
* resistors wrong values/shorting
* bad design - overall
* bad design (for 6AS7 and the like) is that it's using fixed biasing so it's possible to have a run-away tube(s).
Next step is to use HV capable multimeter/leads to check the voltages and if you use a 1ohm resistor (oe any other) it's possible to check the current flowing.
It's obviously not too much current - as the power supply or fuses haven't blown. So it's likely that either (a) it's running A2 and pushing too much, (b) the bias and operating point is wrong or (c) component failure/bad design.
I suspect you will need to start breaking the issue down and working backwards.
Too much current is normally todo with a operating point change:
* B+/B- out of spec (could be the transformer or reserve/smoothing caps fail as a short)
* shorting tube (but to have all do this is not common)
* duff capacitor (the cap is shorting allowing a DC current draw from the output to B+.
* resistors wrong values/shorting
* bad design - overall
* bad design (for 6AS7 and the like) is that it's using fixed biasing so it's possible to have a run-away tube(s).
Next step is to use HV capable multimeter/leads to check the voltages and if you use a 1ohm resistor (oe any other) it's possible to check the current flowing.
It's obviously not too much current - as the power supply or fuses haven't blown. So it's likely that either (a) it's running A2 and pushing too much, (b) the bias and operating point is wrong or (c) component failure/bad design.
It is a Tektron OTL
Yes it worked great, unfortunately Tektron do not want anything to do with it, they are not great with after sales.
I worked out the mystery with the heater, they are all in series.
I was selling it on EBAY, it did not sell so I got some new tubes and popped them in, had my new preamp, turned everything on, let it settle, put some vinyl on, boom!
Yes it worked great, unfortunately Tektron do not want anything to do with it, they are not great with after sales.
I worked out the mystery with the heater, they are all in series.
I was selling it on EBAY, it did not sell so I got some new tubes and popped them in, had my new preamp, turned everything on, let it settle, put some vinyl on, boom!
The diagnosis is clear: ALL the tubes draw too much current, the open connection between the K and it's pin shouts that out.
Since the B+ is OK as you measured, something else is increasing the current and it is on all tubes!
Please check if there is a low impedance connection between the heater winding and the cathode(s) and the grids. It must be something that is common to ALL tubes and the only thing I can think of is the heater winding.
Does the heater winding float on some DC voltage?
Or: (lightbulb) does this amplifier has a negative DC biasing for the grids that has given up the ghost - that would cause massive currents too! Can you measure the DC at the grids?
Jan
Since the B+ is OK as you measured, something else is increasing the current and it is on all tubes!
Please check if there is a low impedance connection between the heater winding and the cathode(s) and the grids. It must be something that is common to ALL tubes and the only thing I can think of is the heater winding.
Does the heater winding float on some DC voltage?
Or: (lightbulb) does this amplifier has a negative DC biasing for the grids that has given up the ghost - that would cause massive currents too! Can you measure the DC at the grids?
Jan
Just looking at the Tektron Italy website. I can't see a model that uses 6080s or an OTL (except for the headphone amps). It uses 6550s or 2a3/300s etc most with output transformers.
The only TekTron search result is this: TK One Head - Tektron Audio which lists technology as "OTL". Matched tubes: ECC82 x 2 – 5687 x 4 – 6ZY5 x 2 OR 6X5 so no mention of 6080. That uses big bottle for rectification.. the signal path is all B9A tubes.
Given TekTron has only been trading since 2014.. I assume that either the amp is an old model that is nolonger listed.. or it wasn't a TekTron amp (unknown to you) which may be why they are refusing to have anything todo with it.
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Hej Guys,
Sorry if my English is not tip top, boom I mean to say the tube implodes (vacuum) however it did not want to get into the nuances of pressure differentials and fluid dynamics.
The cause of the tube reaction is what I am interested in, the cathode lead has failed, this must be as a result current, which we have ascertained.
I have tried the old preamp, same condition, equally correlation is not causation so the new preamp may be an independent variable, however the dependant variable is the tubes blowing, we can vary the conditions as I have, with a passive preamplifier, a 12AU7 and 6SN7, all have the expected result, BOOOOOOOOOM!
I have just done some testing with no load on the speaker terminals and all seems stable, the speakers I have are 4ohm, but it drives/drove them fine before the ill fated day.
There are 4 6080 per channel, top 2 measure 160VDC to GND, K1 and K2 are tied directly to ground on this half and Bottom 2 measure 160VDC to K1 and K2 respectively. -75VDC is solid on both channels.
There is a ground wire from the 6.3VAC rail to the filter caps of the B+ so there is a short from the winding to GND, but that is not new.
I am going to put a load on the speaker and see what magic occurs......
Thanks again guys!
Sorry if my English is not tip top, boom I mean to say the tube implodes (vacuum) however it did not want to get into the nuances of pressure differentials and fluid dynamics.
The cause of the tube reaction is what I am interested in, the cathode lead has failed, this must be as a result current, which we have ascertained.
I have tried the old preamp, same condition, equally correlation is not causation so the new preamp may be an independent variable, however the dependant variable is the tubes blowing, we can vary the conditions as I have, with a passive preamplifier, a 12AU7 and 6SN7, all have the expected result, BOOOOOOOOOM!
I have just done some testing with no load on the speaker terminals and all seems stable, the speakers I have are 4ohm, but it drives/drove them fine before the ill fated day.
There are 4 6080 per channel, top 2 measure 160VDC to GND, K1 and K2 are tied directly to ground on this half and Bottom 2 measure 160VDC to K1 and K2 respectively. -75VDC is solid on both channels.
There is a ground wire from the 6.3VAC rail to the filter caps of the B+ so there is a short from the winding to GND, but that is not new.
I am going to put a load on the speaker and see what magic occurs......
Thanks again guys!
I don't think you can say without an osciliscope attached if it's stable. Probably worth draining out and then checking the resistance of the output capacitor (I assume it has them). If it's direct output (ouch!) then it's the tube bias out of whack.
If the operating point is out of whack then a signal could cause an overload but typically class A would simply have a problem idling and not be stable. Which is why I'm thinking that there's some thing causing either (a) a bad operating point or (b) a bad input on the grid (ie operating in an unintended A2 due to a DC leak).
All of this is hearsay - can you upload a photo (amp and the inside P2P wiring). It allows us to understand what is connected to where and if there's component failures.
The only way a speaker would cause a OTL to fail is if (a) the speak is a short and there's no isolating output.
The picture would also show us if it's a straight push-pull power or a circlotron but the latter shouldn't (in theory) cause the other tubes to die.
If the operating point is out of whack then a signal could cause an overload but typically class A would simply have a problem idling and not be stable. Which is why I'm thinking that there's some thing causing either (a) a bad operating point or (b) a bad input on the grid (ie operating in an unintended A2 due to a DC leak).
All of this is hearsay - can you upload a photo (amp and the inside P2P wiring). It allows us to understand what is connected to where and if there's component failures.
The only way a speaker would cause a OTL to fail is if (a) the speak is a short and there's no isolating output.
The picture would also show us if it's a straight push-pull power or a circlotron but the latter shouldn't (in theory) cause the other tubes to die.
Well I see there are some cynics amongst us!
I most certainly bought this from Attillio, it was an amp he assured me was their state of the art OTL..............
Please take a look at the images attached, Tektron is not exactly world renowned fellas and I do not think the Chinese would go to any length to copy the design.
Anywho......
Let us not get drawn into such arbitrary matters gentlemen, the battle front is not between us, it is on this god damn amplifier!!!
Note the blue caps, Jenzen 5.4uF, the old ones were RSPRO nasties..
Kiitos!
I most certainly bought this from Attillio, it was an amp he assured me was their state of the art OTL..............
Please take a look at the images attached, Tektron is not exactly world renowned fellas and I do not think the Chinese would go to any length to copy the design.
Anywho......
Let us not get drawn into such arbitrary matters gentlemen, the battle front is not between us, it is on this god damn amplifier!!!
Note the blue caps, Jenzen 5.4uF, the old ones were RSPRO nasties..
Kiitos!
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