Some strange thinks occur with my 300B filament supply. This is the schema: http://www.homepages.hetnet.nl/~rjonkers/psu.gif (one from the bottom).
1) Startposition: If I adjust R11 to deliver exactly 5.0vDC the circuit draws 1.41A. The 300B filament is grounded via the '-' of the DC supply and a 10R resistor (fixed bias circuit: http://www.homepages.hetnet.nl/~rjonkers/amp.gif ).
2) If I connect the 300B filament to ground with two 100R series resistors, the circuit only delivers 4.7V so I have to re-adjust R11 to get it back to 5V. Voltage drop over R12 is 1.5A, so for some strange reason the 300B's start drawing more current. How is this possible?
3) Back to startposition. If I don't connect the B+ of the 300B's right away in order to heat them up first, the circuit only delivers some 4.6V and never gets to 5.0. If I connect the B+ the normal 5.0V is delivered. Now the main issue, if I use a LM350 as a current source and set it to 1.41A why doesn't it deliver 5.0V without the B+?
Ralph
1) Startposition: If I adjust R11 to deliver exactly 5.0vDC the circuit draws 1.41A. The 300B filament is grounded via the '-' of the DC supply and a 10R resistor (fixed bias circuit: http://www.homepages.hetnet.nl/~rjonkers/amp.gif ).
2) If I connect the 300B filament to ground with two 100R series resistors, the circuit only delivers 4.7V so I have to re-adjust R11 to get it back to 5V. Voltage drop over R12 is 1.5A, so for some strange reason the 300B's start drawing more current. How is this possible?
3) Back to startposition. If I don't connect the B+ of the 300B's right away in order to heat them up first, the circuit only delivers some 4.6V and never gets to 5.0. If I connect the B+ the normal 5.0V is delivered. Now the main issue, if I use a LM350 as a current source and set it to 1.41A why doesn't it deliver 5.0V without the B+?
Ralph
MR. OHM.
Hi,
Well of course the 100R resistors will cause a voltage drop and the circuit will draw more current.
Yes...that is to be expected.
Cheers,
Hi,
If I connect the 300B filament to ground with two 100R series resistors,
Well of course the 100R resistors will cause a voltage drop and the circuit will draw more current.
3) Back to startposition.
Yes...that is to be expected.
Cheers,
Thought there were some sonic benefits so I use a current source for both the 5687 and the 300B. Are BOTH those tubes not 'specified' for that?
Don't know about floating, I think they are. 5687 supply is only grouned via pin 8 of the 5687 and the 300B supply only via the '-' pin of the 300B's supply. But please remember that you are 1000 steps ahead of me so I may not understand you correctly.
Don't know about floating, I think they are. 5687 supply is only grouned via pin 8 of the 5687 and the 300B supply only via the '-' pin of the 300B's supply. But please remember that you are 1000 steps ahead of me so I may not understand you correctly.
ACHTUNG.
Hi,
Correct.
What I mean is that you don't "have" to reference the heater to ground...quite often you will be injecting ground currents back into the circuit by running it that way.
Give it a try,
Hi,
Are BOTH those tubes not 'specified' for that?
Correct.
Don't know about floating, I think they are.
What I mean is that you don't "have" to reference the heater to ground...quite often you will be injecting ground currents back into the circuit by running it that way.
Give it a try,
You mean this I think http://www.zwengelamps.com/heater.html , correct? Will try, thanks for the suggestion.
PROBLEMS IN PARADISE.
Hi,
With cathode bias, you mean?
Cheers,
Hi,
I think there could be some problems leaving the heaters of DHT's "floating"
With cathode bias, you mean?
Cheers,
dhaen said:I think there could be some problems leaving the heaters of DHT's "floating"
I'll say there's a problem. They won't work! The filament in a DHT, since it is the cathode, cannot be isolated. It must be referenced to B-, C+, and possibly chassis "ground" if it's the same as the other two.
REGS.
Hi,
Wasn't that a current reg. he was using?
Cheers,
Hi,
with a voltage regulator...
Wasn't that a current reg. he was using?
Cheers,
John,
I don't understand this. At this moment I use (just measured it, all relative to ground):
5687: +6.17v and -6.39v
300B: +6.34v and +1.31v
now I want to elevate both circuits approx 40V. Is it OK to try?
Ralph
I'll say there's a problem. They won't work! The filament in a DHT, since it is the cathode, cannot be isolated. It must be referenced to B-, C+, and possibly chassis "ground" if it's the same as the other two.
I don't understand this. At this moment I use (just measured it, all relative to ground):
5687: +6.17v and -6.39v
300B: +6.34v and +1.31v
now I want to elevate both circuits approx 40V. Is it OK to try?
Ralph
A MAN WITH A CONSCIENCE.
Hi,
What you've understood so far still stands.
Huh?
No heater, no sound.
Hi,
If there is any particular post that you don't understand, just ask.
What you've understood so far still stands.
PS I think most of us are unsympathetic with messing with heater supplies
Huh?
No heater, no sound.
Ralph,
In the case of the KR300, it is already elevated by the cathode bias.
On the 5687, you can if you want, but I see no reason to.
In the unlikely event of emission from the heater to the cathode, you'd only have to raise the heaters a few volts to stop it.
I really think your time and effort would be better spent in perfecting the layout and earthing scheme of this magnificent amplifier.
Cheers,
_____________________________
Frank,
"Messing" implies making unnecessary changes to an already working system
Strange, your understanding of English nuances is usually better than mine....
Cheers,
In the case of the KR300, it is already elevated by the cathode bias.
On the 5687, you can if you want, but I see no reason to.
In the unlikely event of emission from the heater to the cathode, you'd only have to raise the heaters a few volts to stop it.
I really think your time and effort would be better spent in perfecting the layout and earthing scheme of this magnificent amplifier.
Cheers,
_____________________________
Frank,
"Messing" implies making unnecessary changes to an already working system
Strange, your understanding of English nuances is usually better than mine....
Cheers,
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