the tube red plate very quickly.
Something is seriously wrong. but cant for the life of me work out what.
here is a pic if that helps
Something is seriously wrong. but cant for the life of me work out what.
here is a pic if that helps
An externally hosted image should be here but it was not working when we last tested it.
checking through each channel with schematics i see no errors.
I am using 6p14p, which have been said to be a direct substitue with the EL84. They glow red quicky, by which time i shut down.
If the plates are glowing, that suggests to me that the bias blocks arent working, however, checking witha 9v battery shows they give 34ma exactly - so what else could cause the red plates?
I am using 6p14p, which have been said to be a direct substitue with the EL84. They glow red quicky, by which time i shut down.
If the plates are glowing, that suggests to me that the bias blocks arent working, however, checking witha 9v battery shows they give 34ma exactly - so what else could cause the red plates?
Thanks for the help guys, all sorted. It was indeed the bias block.
I was using a datasheet for a different mje340, apparantly they do differ per manufacturer.
B+ is now 335v, ccs is giving 34ma. quick mental calc and that gives 11.5 watts dissipation per valve.
Its high but ok?
again, thanks for the advice
I was using a datasheet for a different mje340, apparantly they do differ per manufacturer.
B+ is now 335v, ccs is giving 34ma. quick mental calc and that gives 11.5 watts dissipation per valve.
Its high but ok?
again, thanks for the advice
Nice to know it worked out OK - without any black smoke and component damage.
Since you still have the cover off, could you measure the cathode voltage? I am a bit curious how much voltage the CCS takes up.
I think I would have preferred a small negative supply for this, but maybe Ian/Gingertube would like to comment on that.
Do you have any other measuring gear available (apart from the multimeter)?
SveinB.
Since you still have the cover off, could you measure the cathode voltage? I am a bit curious how much voltage the CCS takes up.
I think I would have preferred a small negative supply for this, but maybe Ian/Gingertube would like to comment on that.
Do you have any other measuring gear available (apart from the multimeter)?
SveinB.
no i dont, but give me a month and i will have an Oscope.
I have retired for the night, but will get the voltages for you tomorrow. I assume you want cathode to ground?
I'll go through final adjustments tomorrow, get the base plate on.
By the way, the 6p14p tubes glow blue inside (as others have experienced). Bit alarming at first!
It made some music, but oddly, i couldnt turn the volume all the way down......?
I have retired for the night, but will get the voltages for you tomorrow. I assume you want cathode to ground?
I'll go through final adjustments tomorrow, get the base plate on.
By the way, the 6p14p tubes glow blue inside (as others have experienced). Bit alarming at first!
It made some music, but oddly, i couldnt turn the volume all the way down......?
a rather unglamourous shot, without knob or the baseplate screwed on.
An externally hosted image should be here but it was not working when we last tested it.
Yvesm said:The CCS takes up exactly the voltage needed to bias each tube for it passes the expected current.
That's CCS job
Yes, of course.
I was for a moment there concerned that the CCS would require some volts to do its job and thus reduce the available g-k voltage swing. It is however not relevant here since the CCS only defines the DC current and is bypassed for AC.
SveinB.
a couple of questions...
My B+ is 340v, outputs are running at 34ma, so the power dissipation is roughly (340 – 8ish)*(0.034) = 11.3 watts, which is close to the upper limit of the 6p14p. Is this too high, or shall I risk it and just assume tube life will be reduced? The 6p14p is meant to handle slightly more power than the el84
Somewhere in the thread it was suggested that the 33ohm resistor between screen grid and UL tap should be increased if using a high B+. I only have a 33ohm 2w kiwame in there at the moment. Should I increase this to say 250ohms given my high(ish) B+.
There is a strong blue glow on the inner side of the anodes – Its certainly blue and not the dreaded purple/pink. Is this normal?
I haven’t spent any time listening yet, so I’ll report back after the ‘new toy’ effect has gone.
My B+ is 340v, outputs are running at 34ma, so the power dissipation is roughly (340 – 8ish)*(0.034) = 11.3 watts, which is close to the upper limit of the 6p14p. Is this too high, or shall I risk it and just assume tube life will be reduced? The 6p14p is meant to handle slightly more power than the el84
Somewhere in the thread it was suggested that the 33ohm resistor between screen grid and UL tap should be increased if using a high B+. I only have a 33ohm 2w kiwame in there at the moment. Should I increase this to say 250ohms given my high(ish) B+.
There is a strong blue glow on the inner side of the anodes – Its certainly blue and not the dreaded purple/pink. Is this normal?
I haven’t spent any time listening yet, so I’ll report back after the ‘new toy’ effect has gone.
adamus said:
Mmmmh ...
100 Ohms trimpot cannot have large effect !
Anyway, less than 10% anode voltage inbalance is really ... peanuts.
This phase splitter is as well balanced that the plate resistors are.
Don't bother about small DC differences due to tube tolerances, this has NO effect on AC balance cos the CCS in the cathodes forces the sum of anode current to be constant, thus any current change in one triode produces an absolutly equal change in the other one.
So, if plate load resistors are equal, voltage swings are.
Yves.