Power tube heater glowing to bright

[navdave]

A customer brought me an amp to re-tube with tubes he bought. Well when switching the amp from standby to on one of the tubes heaters starts to glow very bright like a little light bulb. I've never winessed this with any power tube ever. News replacement tubes are in order right?

[stratele52]

Chance you must replace ALL four tubes if a new one is not match ( within 3 to 8 MA cathode current)

[alerich]

If you swap the position of the tubes does the bright filament follow the tube? Are all of the other parameters of the bright tube normal? Measure the 6.3VAC heater string. Is the bright tube pulling it down?

[stratele52]

If you swap the position of the tubes does the bright filament follow the tube? Are all of the other parameters of the bright tube normal? Measure the 6.3VAC heater string. Is the bright tube pulling it down?

+1

Easy test to do before buying new tube.

Heater voltage are parallele and can't be more than 6.3 VAC on one tube .
This tube's heater must have low resistance , kind of short.

[navdave]

Yes if I move the position of the tube it will still glow brightly when coming off of standby in standby mode it glows normal like the other three tubes. I have not checked the filament voltage on that tube yet before or after coming off of standby that's something I'll do tonight when I get off work.

If you swap the position of the tubes does the bright filament follow the tube? Are all of the other parameters of the bright tube normal? Measure the 6.3VAC heater string. Is the bright tube pulling it down?

[navdave]

He bought the tubes new from antique electronics they match them so it's something their matcher didn't catch that it's going now but it only glows brightly when the high-voltage is turned on.

+1

Easy test to do before buying new tube.

Heater voltage are parallele and can't be more than 6.3 VAC on one tube .
This tube's heater must have low resistance , kind of short.

[stratele52]

"Yes if I move the position of the tube it will still glow brightly  ........
    
                                         _____Navdave


Tube any where still glow brightly . It is the tube for shure .    Don't forget to check and adjust bias on the amp with these new tubes .

 

[stratele52]

Schematic is here ;

http://blueguitar.org/schems.htm#MiscSchem

Look at Misc amps Scheamtic . Down on the list ; Yamaha t100 zip , 158 k

But you don't need it , just replace tube and readjust bias

[stratele52]

Owner manual ;

www2.yamaha.co.jp/manual/pdf/emi/english/gtamp/T50_T50C_T100_T100C_en1.pdf

It is V9 glow too much

[navdave]

Yeah I don't trust these jj's from Antique Electronics the always drift because they don't burn them in long enough. Wish I could open that zip file but I'm on my iPhone.

Tube any where still glow brightly . It is the tube for shure .    Don't forget to check and adjust bias on the amp with these new tubes .

 

[stratele52]

I bought often JJ's tube from many dealer with no problem . But JJ's are they the same quality today ?

[alerich]

Yeah I don't trust these jj's from Antique Electronics the always drift because they don't burn them in long enough. Wish I could open that zip file but I'm on my iPhone.

It's not just JJ tubes nor it is just Antique. My last two sets of EL34 tubes were Tung Sol and Winged C - both sets from Tube Depot and neither set really closely matched. I actually modded my Mig60 for independent bias controls just to deal with it. I think I am going to go back to buying power tubes from Lord Valve.

[stratele52]

What is close matched ?

From some Weber Book's I read anything between 3 to 8 ma is a good match . Better than 0 ma wich is less musical