6G6 b+ voltage & 5881 tubes

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Stevem
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Re: 6G6 b+ voltage & 5881 tubes

Post by Stevem »

Back when these amps where made the electrical grid in this country was very light weight and a normal for then 110 volts from the outlet would drop off down to even 103 no less 105 during day time hours!
When your amp is up at that crazy 490 plus plate volts what is your filament voltage at?

Lower or higher by 10% of 6.3 volts and your going to change the gain structure of the amp a bunch , and 10% More on the high side will shorten the life of the tubes filament wise and Cathode wise.
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pdf64
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Re: 6G6 b+ voltage & 5881 tubes

Post by pdf64 »

Yes the heater voltage is the key indicator for whether the amp is being supplied with its intended mains voltage.
tubeswell
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Re: 6G6 b+ voltage & 5881 tubes

Post by tubeswell »

What Stevem and pdf64 said. What is the VAC across the heater winding with all tubes installed?

Only then will you know if the wall voltage is too high for the PT.

Once that is sorted, the next thing to check is output tube bias. If the -ve bias voltage is set too high, it will run the output tube plate voltage on the high side.
He who dies with the most tubes... wins
scooter_trasher
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Re: 6G6 b+ voltage & 5881 tubes

Post by scooter_trasher »

Variac came last night, today my wall voltage is at 123,7v giving 6.8v heater 488v plates
heaters like 114v at variac giving 6.3v 450v at plates
110v at variac gives 6,1 at heater 440 at plates
so I'm figuring it likes 114v and is going to be 450v unless it's biased wrong which I haven't checked yet
my specs for a 6G6 A show 470v at plates w 5881 tubes, 6G6B shows 428v at plates 5881 tubes, looks like I'm close to being in the middle at 114 wall voltage
I'd like to run it a little lower on the plates for 5881 tubes, would it starve the heaters at 6v ?
may just stay with the JJ6L6 tubes , keep the nos 5881 tubes with it for history's sake (their money in the bank) and not try to fix whats not broke, sounds great as it is and I'm never going to be SRV or Albert Lee any how, there's a reason they don't make 5881s,I have no need to sniff corks, I've always preferred Boone's Farm or PBR :)
Checked bias at 114v variac plate v 460v outside tube plate dissipation 14.72w inside tube 14.72w a tad on the cold side
once amp fully warm 114v variac 438v at plates outside tube 27.15w inside 27.46w
may have a bit of component drift as amp builds heat
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martin manning
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Re: 6G6 b+ voltage & 5881 tubes

Post by martin manning »

Manufacturers specify heater voltage at +/-10%, so you could go down to 5.7 no problem. There are some new-made 5881's available, short, fat bottle and all.
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ToneMerc
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Re: 6G6 b+ voltage & 5881 tubes

Post by ToneMerc »

scooter_trasher wrote: Thu Jun 08, 2017 1:03 pm
I'd like to run it a little lower on the plates for 5881 tubes, would it starve the heaters at 6v ?
6.3V plus/minus 10% = 5.67 - 6.93V

TM
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pompeiisneaks
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Re: 6G6 b+ voltage & 5881 tubes

Post by pompeiisneaks »

Also most manufacturers post a max heater voltage, and in many it's 50v and a few I've seen 100, so it won't destroy them, probably just shorten the life a bit if it goes higher.

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martin manning
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Re: 6G6 b+ voltage & 5881 tubes

Post by martin manning »

pompeiisneaks wrote: Thu Jun 08, 2017 5:24 pm Also most manufacturers post a max heater voltage, and in many it's 50v and a few I've seen 100, so it won't destroy them, probably just shorten the life a bit if it goes higher.
Never heard of that. Maybe you're referring to max Vh-k? 100-200V would be typical for that.
scooter_trasher
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Re: 6G6 b+ voltage & 5881 tubes

Post by scooter_trasher »

Got the NOS rca labeled tung sol 5881s today, plugged them in to check plate current,( pop ) must have blown a bias cap or resistor, 32% spread on plate dissipation, either way I switch them, I guess matched is same color base to some people,(they were pretty) sending back, now my 6L6s are at 42 whopping watts dissipation , he they still match either way I switch them, must have blown a cap or burnt a resistor, going to have to mail order, bummer :(
scooter_trasher
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Re: 6G6 b+ voltage & 5881 tubes

Post by scooter_trasher »

weirdest thing , after letting the amp sit for a couple hours , checked again plate dissipation on the cold side at 13.1 & 12.9W left amp on for a half hour & played a bit rechecked, 444 b+ , 24.36w & 23.8 w plate dissipation, a resistor or cap must have gotten hot to the point of failure and is now ok
still sending those mismatched tubes back
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ToneMerc
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Re: 6G6 b+ voltage & 5881 tubes

Post by ToneMerc »

scooter_trasher wrote: Fri Jun 09, 2017 12:10 am weirdest thing , after letting the amp sit for a couple hours , checked again plate dissipation on the cold side at 13.1 & 12.9W left amp on for a half hour & played a bit rechecked, 444 b+ , 24.36w & 23.8 w plate dissipation, a resistor or cap must have gotten hot to the point of failure and is now ok
I don't know of any component that is self healing, no parts fail and revert back to normal.

TM
scooter_trasher
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Re: 6G6 b+ voltage & 5881 tubes

Post by scooter_trasher »

Something caused my 6L6gcs to spike up to 42w plate dissipation, dragging my b+ down to 415v and then go back to normal after the amp cooled back down and still stay normal after warming back up & being played through for about a half hour, all I can think of is component drift due to excessive heat, seems to be running fine now, I'll be keeping an eye on it.
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ToneMerc
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Re: 6G6 b+ voltage & 5881 tubes

Post by ToneMerc »

scooter_trasher wrote: Sat Jun 10, 2017 6:05 pm Something caused my 6L6gcs to spike up to 42w plate dissipation, dragging my b+ down to 415v and then go back to normal after the amp cooled back down and still stay normal after warming back up & being played through for about a half hour, all I can think of is component drift due to excessive heat, seems to be running fine now, I'll be keeping an eye on it.
You need through it replace all those several decades old filter caps.

TM
scooter_trasher
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Re: 6G6 b+ voltage & 5881 tubes

Post by scooter_trasher »

well it doesn't hum , quiet as a church mouse, I hardly think the filter caps caused my plate dissipation to go through the roof, if they were failing to ground my B+ would drop and my dissipation would be less, not to mention a fuse blowing , the bias circuit opening up would more than likely be the culprit,(keeping the screen from doing it's job),possibly a bad soldier joint in it
tubeswell
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Re: 6G6 b+ voltage & 5881 tubes

Post by tubeswell »

Don't forget that the bias supply circuit has filter caps in it too. They also need replacing
He who dies with the most tubes... wins
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