I like crazy ideas.JamesD wrote:I had a crazy idea...
Filament bias!!!
72V bias at 3A filament current only 24 ohms!!!
and 216Watts - Ooooooopppppppsssssssssssssssssssssssss!
Oh well I said it was a crazy idea...
GK-71 - economical build.
- pre65
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#391
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#392
I'm not sure how to calculate filament bias, I've searched Google but there seem no easy explanations.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#393
The HT is a bit low (500v - 70v) so I'm changing the PSU a bit. Rather than go cap input, I'm going to retire Mikes E-choke/regulator and replace it with another 10H choke and 500uf of capacitance.
The caps are 2 X BHC 1000uf 450v low ESR in series.
This is similar to what was on the "old" GM70 amp.
Is 500uf too much for this amp ?
The caps are 2 X BHC 1000uf 450v low ESR in series.
This is similar to what was on the "old" GM70 amp.
Is 500uf too much for this amp ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#394
Difficult. You raise the filament supply voltage by the bias voltage. Don't expext you can with Andrew's module. Then filament ground to one end of your bias resistor other end to one filament pin, other filament pin to supply plus out.
Other end of bias resistor to circuit ground and filament minus
Bias resistor ohms law incorporating bias voltage devised by filament current. Wattage is bias volts x filament current. Cathode current insignificant in this instance but you could add it to be pedantic.
Other end of bias resistor to circuit ground and filament minus
Bias resistor ohms law incorporating bias voltage devised by filament current. Wattage is bias volts x filament current. Cathode current insignificant in this instance but you could add it to be pedantic.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#395
Thanks Paul, I'll do my sums later.
I'm head nurse today as Jean has "woman flu".
The mods are coming along. As the HT has (or should have) increased I'm in the process of adding a 4K7 50W resistor in the 12HG7 CCS feed. The CCS heatsink gets quite hot so I don't want to make it worse.
The drill I was using to make the resistor mounting bracket broke, and attacked my thumb, so now it's bleeding a bit and throbbing.
Ivimeys law strikes again.
I'm head nurse today as Jean has "woman flu".
The mods are coming along. As the HT has (or should have) increased I'm in the process of adding a 4K7 50W resistor in the 12HG7 CCS feed. The CCS heatsink gets quite hot so I don't want to make it worse.
The drill I was using to make the resistor mounting bracket broke, and attacked my thumb, so now it's bleeding a bit and throbbing.
Ivimeys law strikes again.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#396
One amp is done now, and when plugged in has lost most of the hum it had before.
Just as I was re-assembling the amp I noticed I'd wired up the two caps after the first choke incorrectly.
Instead of the balancing resistor being between plus and minus on each cap I'd put a resistor between each cap. DOH.
Perhaps that was causing the hum ? Anyway, I tidied up a few wires, and re-routed the 12HG7 heater wires as well for good measure.
Just need to mod the other amp now.
Just as I was re-assembling the amp I noticed I'd wired up the two caps after the first choke incorrectly.
Instead of the balancing resistor being between plus and minus on each cap I'd put a resistor between each cap. DOH.
Perhaps that was causing the hum ? Anyway, I tidied up a few wires, and re-routed the 12HG7 heater wires as well for good measure.
Just need to mod the other amp now.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#397
2nd amp is done, and just played a couple of Eva tracks to see if everything is OK.
Almost no hum is good.
The anode HT is now 603v and the cathode is 83.3v (820R) so current is 102ma.
Everything sounds just right.
Will have a good session in the morning to see how it is on a selection of tunes.
Almost no hum is good.
The anode HT is now 603v and the cathode is 83.3v (820R) so current is 102ma.
Everything sounds just right.
Will have a good session in the morning to see how it is on a selection of tunes.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#398
I've got a Derek Bailey album you can borrow if you want to run it in Phil
"The fat bourgeois and his doppelganger"
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#399
Thanks Dave.
I hope you won't be offended if I decline your kind offer.
Yesterday I put a 4K7 resistor in the line feed to the CCS to drop the volts a bit and keep the CCS heatsink from overheating.
Should I decouple after the resistor with a cap ?
I hope you won't be offended if I decline your kind offer.
Yesterday I put a 4K7 resistor in the line feed to the CCS to drop the volts a bit and keep the CCS heatsink from overheating.
Should I decouple after the resistor with a cap ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#400
No need.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#401
I'm not sure the CCS should be fed from a high impedance ( 4.7k ) .... perhaps Nick can comment ?
"Once you find out ... the Circumstances ; then you can go out"
#402
I can't see how it would make any difference either way, as long as the CCS has enough voltage behind it to stay positively biased it should be fine. Of course there is equally no reason why you would not put the resistor after the CCS either.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#403
I'm doing the cascode CCS driver mod this morning.
I needed to reduce the voltage to the CCS a bit more, but could not find a suitable resistor. In the end I paralleled two 50W resistors, 10K and 22K, which was near enough.
I've got to put things back together now, and then test. If the first one is OK I'll do no 2 later.
EDIT. No 1 works OK.
I needed to reduce the voltage to the CCS a bit more, but could not find a suitable resistor. In the end I paralleled two 50W resistors, 10K and 22K, which was near enough.
I've got to put things back together now, and then test. If the first one is OK I'll do no 2 later.
EDIT. No 1 works OK.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#404
I've never been unhappy with the GK-71 sound, and it seemed to be well received at Owston.
But now, with the cascade CCS driver,Andrews filament supply and all the little details sorted out, it sounds REALLY good.
Last tweek will be to replace the 80uf Sprague Atom electrolytic cathode bypass cap on the GK-71 with a polywhosit version.
But now, with the cascade CCS driver,Andrews filament supply and all the little details sorted out, it sounds REALLY good.
Last tweek will be to replace the 80uf Sprague Atom electrolytic cathode bypass cap on the GK-71 with a polywhosit version.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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#405
I managed to find a pair of Solen MKP capacitors on Ebay at reasonable cost, so that should be it upgrade wise for a while.
May not be here for several days.
May not be here for several days.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)