Tube amplifier output tubes cold, no sound - UK Vintage Radio Repair and Restoration Discussion Forum

Levente · 25th Aug 2019, 1:43 pm

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.

Robert Gribnau · 25th Aug 2019, 1:50 pm

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

Station X · 25th Aug 2019, 1:51 pm

You say the valves are cold, but do the they light up?

Levente · 25th Aug 2019, 2:01 pm

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?

Station X · 25th Aug 2019, 2:05 pm

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.

Levente · 25th Aug 2019, 2:29 pm

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...

Radio Wrangler · 25th Aug 2019, 2:41 pm

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

Levente · 25th Aug 2019, 2:46 pm

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..

Levente · 25th Aug 2019, 3:13 pm

Quote:

Originally Posted by Station X

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.

Thank you !

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?

Levente · 25th Aug 2019, 3:20 pm

..... 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?

ms660 · 25th Aug 2019, 3:21 pm

Measure using the AC range on your meter.

Lawrence.

Silicon · 25th Aug 2019, 3:21 pm

Set the test meter to AC volts.

Levente · 25th Aug 2019, 3:24 pm

AC is 40 Volts

ms660 · 25th Aug 2019, 3:27 pm

Are the heaters referenced to chassis or isolated from chassis?

Lawrence.

Levente · 25th Aug 2019, 3:29 pm

Yes, referenced to chassis.

I did measure the heather's with negative to chassis.

ms660 · 25th Aug 2019, 3:32 pm

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.

Levente · 25th Aug 2019, 3:43 pm

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..

ms660 · 25th Aug 2019, 3:48 pm

With the valve heaters glowing normally measure the heater voltage across the valve tags on the valve holder.

Lawrence.

Levente · 25th Aug 2019, 3:52 pm

Each tag has 42.3 VAC precisely.

ms660 · 25th Aug 2019, 3:59 pm

If the 6V6 valve(s) are glowing normally you will not have 42V RMS AC across the heater pins....

Lawrence.

25th Aug 2019, 1:43 pm	#1
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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. Attached Thumbnails Last edited by Levente; 25th Aug 2019 at 1:44 pm. Reason: grammar

25th Aug 2019, 1:50 pm	#2
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 513	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
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Tube amplifier output tubes cold, no sound You say the valves are cold, but do the they light up? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

25th Aug 2019, 2:01 pm	#4
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	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. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

25th Aug 2019, 2:29 pm	#6
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	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 __________________ 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
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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..

25th Aug 2019, 3:20 pm	#10
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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?

25th Aug 2019, 3:21 pm	#11
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Tube amplifier output tubes cold, no sound Measure using the AC range on your meter. Lawrence.

25th Aug 2019, 3:21 pm	#12
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: Tube amplifier output tubes cold, no sound Set the test meter to AC volts.

25th Aug 2019, 3:24 pm	#13
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	Re: Tube amplifier output tubes cold, no sound AC is 40 Volts

25th Aug 2019, 3:27 pm	#14
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	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
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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
Levente Hexode Join Date: Nov 2016 Location: Budapest, Hungary Posts: 386	Re: Tube amplifier output tubes cold, no sound Each tag has 42.3 VAC precisely.

25th Aug 2019, 3:59 pm	#20
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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.