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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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25th Aug 2019, 1:43 pm | #1 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Tube amplifier output tubes cold, no sound
Hey Guys...happy Sunday !
It seems that I am either having too hot output tubes or cold ones... weird. I have this tube amplifier from last year, already went through with you guys as the 6V6 were way too hot, but it was sorted out, worked fine. I have put this amp away, in the meantime I did move... so this was packed from and to boxes etc... Now I am having a brand new set of tubes, Philips 6v6GT and thought why I don't switch this on and enjoy some music... turned it on... light comes on.. rectifier tube nice and hot...and no sound at all.. Output tubes aren't doing anything and cold, so the preamp tube... I am suspecting that during transportation something happened. I have another set of 6v6 output tubes, tried it one, again, nothing... All the soldering are intact. No loose connections, all in place. You see on the picture I have a JAN 5693, the red one... removed it and noticed that something is moving inside while I am shaking it... would you suspect that this tube in the meantime gone bad? it is odd as his amp was never really used and bought this tube as NOS...last year but I don't recall any moving elements inside... Any helping thoughts- as always!- would be greatly appreciate it. Last edited by Levente; 25th Aug 2019 at 1:44 pm. Reason: grammar |
25th Aug 2019, 1:50 pm | #2 |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
Posts: 513
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Re: Tube amplifier output tubes cold, no sound
Can you see if the filaments of the tubes other than the rectifier come on? If not, or if you can not see it good enough, i advise you to measure if the 6,3 V are on the filaments.
But be carefull if you do not have any experience in doing so. There are high voltages involved in tube amplifiers. Greetings, Robert |
25th Aug 2019, 1:51 pm | #3 |
Moderator
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Location: Ipswich, Suffolk, IP4, UK.
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Re: Tube amplifier output tubes cold, no sound
You say the valves are cold, but do the they light up?
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
25th Aug 2019, 2:01 pm | #4 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
Thanks guys, I do not see any lights and heat besides the rectifier...at this point.
The moving particle inside the preamp tube is no concern? |
25th Aug 2019, 2:05 pm | #5 |
Moderator
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Location: Ipswich, Suffolk, IP4, UK.
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Re: Tube amplifier output tubes cold, no sound
I like things you can measure.
Measure the voltage across the heater pins of the valve holders with the amp turned on. Measure the resistance between the heater pins of the valves. http://www.r-type.org/exhib/aai0136.htm Report results here and someone will advise you.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
25th Aug 2019, 2:29 pm | #6 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
OOOPS... first time I've got electrocuted.. went through my right hand... ****. the unit was unplugged..i think some leftover voltages...
will try and measure the heaters...was just poking around the light bulb ( with my finger) ...to see if the heather is connected to the bulb.. i think it is.. but my hand is sweaty due to heat.... ****... very bad feeling tho... |
25th Aug 2019, 2:41 pm | #7 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,869
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Re: Tube amplifier output tubes cold, no sound
You need to read up on how to handle valve amplifiers safely.
That amplifier CAN KILL YOU. Large capacitors store energy at high voltage, and can hold it for a long time. Good designers include bleeder resistors to discharge the capacitors over about 30 seconds after power is disconnected. BUT accountants want every penny saving. Even with bleeder resistors, the resistors sometimes fail open-circuit and don't do their job. So you always check before touching anything. In old equipment someone before you could have changed anything, so you check always. You survived, but you got a warning. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
25th Aug 2019, 2:46 pm | #8 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
Thanks David, yes I agree. Usually I am careful... right hand only...and yes, capacitors can be nasty... i think by mistake got too close to other parts with my ring finger to the filter capacitor next to the transformer...it is a very small box packed... i am uber careful usually, that is why i am shocked that this happened..
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25th Aug 2019, 3:13 pm | #9 | |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
Quote:
I am measuring 20 VDC across the heaters, pin 2 and 7 also on pin 7 and 8 at the 6SL7, and around the light bulb. And now I can see that the 6SL7 is lighting up gently ( turned now up side down, i can see that properly ) this is really high... no? Last edited by Levente; 25th Aug 2019 at 3:17 pm. Reason: thinking |
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25th Aug 2019, 3:20 pm | #10 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
..... now that the amp turned side ways, everything is on.. and the tubes are lighting and heating up... but the heater 20VDC is concerning right?
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25th Aug 2019, 3:21 pm | #11 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Tube amplifier output tubes cold, no sound
Measure using the AC range on your meter.
Lawrence. |
25th Aug 2019, 3:21 pm | #12 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,163
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Re: Tube amplifier output tubes cold, no sound
Set the test meter to AC volts.
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25th Aug 2019, 3:24 pm | #13 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
AC is 40 Volts
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25th Aug 2019, 3:27 pm | #14 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Tube amplifier output tubes cold, no sound
Are the heaters referenced to chassis or isolated from chassis?
Lawrence. |
25th Aug 2019, 3:29 pm | #15 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
Yes, referenced to chassis.
I did measure the heather's with negative to chassis. |
25th Aug 2019, 3:32 pm | #16 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Tube amplifier output tubes cold, no sound
You might be measuring a "ghost voltage" or there's something wrong with the meter.
Are one side of the valve heater pins connected to chassis? Lawrence. |
25th Aug 2019, 3:43 pm | #17 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
No heather pins connected to chassis. I took another DMM ( i have 3 in total) measuring the same 42VAC on the heather with negative to chassis.
While i was doing that the the power went out and the main fuse shut down in my flat... definitely not a good sign i guess.. |
25th Aug 2019, 3:48 pm | #18 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Tube amplifier output tubes cold, no sound
With the valve heaters glowing normally measure the heater voltage across the valve tags on the valve holder.
Lawrence. |
25th Aug 2019, 3:52 pm | #19 |
Hexode
Join Date: Nov 2016
Location: Budapest, Hungary
Posts: 386
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Re: Tube amplifier output tubes cold, no sound
Each tag has 42.3 VAC precisely.
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25th Aug 2019, 3:59 pm | #20 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Tube amplifier output tubes cold, no sound
If the 6V6 valve(s) are glowing normally you will not have 42V RMS AC across the heater pins....
Lawrence. |