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Old 27th March 2007, 10:29 PM   #1
jarthel is offline jarthel  Australia
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Default referencing DC heater to B+

somewhat silly question but i haven't reference heater supply (whether AC or DC) to B+ before so I have to ask.

schematic: http://img225.imageshack.us/my.php?i...titled2fc6.gif

the 12.6V box in the schematic represents a DC linear regulator using LT1084 (similar to LM317) with it's own trasformer. It is nothing fancy just the usual way of using an LM317.

I believe that the resistor divider is connected to the negative (i.e. ground) side of the DC supply.

Is this correct?

thank you.
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Old 27th March 2007, 10:53 PM   #2
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You can connect it to a water pipe for the same results...

AC powered heaters usually bias in regard to cathode to eliminate a hum. DC, especially regulated, no need to bias in regard to cathode.
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Old 28th March 2007, 12:06 AM   #3
jarthel is offline jarthel  Australia
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Quote:
Originally posted by Wavebourn

AC powered heaters usually bias in regard to cathode to eliminate a hum. DC, especially regulated, no need to bias in regard to cathode.

somehow I believe hum elimination is not the purpose but to reduce heater-to-cathode voltage difference.

BUT the topic is not about the why in regards to referencing heater supply to B+. But the question being asked is "how".
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Is my understanding correct in connecting the resister divider to the DC supply ground?

thank you.
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Old 28th March 2007, 03:28 AM   #4
jarthel is offline jarthel  Australia
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The circuit was obtained from this document: http://www.tubecad.com/Nine-Pin_Aikido_PCB.pdf (page 2)
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Old 28th March 2007, 03:43 AM   #5
billr is offline billr  New Zealand
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Default Re: referencing DC heater to B+

Quote:
Originally posted by jarthel
somewhat silly question but i haven't reference heater supply (whether AC or DC) to B+ before so I have to ask.

schematic: http://img225.imageshack.us/my.php?i...titled2fc6.gif

the 12.6V box in the schematic represents a DC linear regulator using LT1084 (similar to LM317) with it's own trasformer. It is nothing fancy just the usual way of using an LM317.

I believe that the resistor divider is connected to the negative (i.e. ground) side of the DC supply.

Is this correct?

thank you.

hi,

there are really two things here,

the first is the heater cathode voltage, this is specified in the tube specs, this has to be maintained, hence the need to elevate heater supplies.

The second thing is that the heater cathode voltage differential must be defined. So if an elevated potential is not required, then the heater supply must be referenced to the HV ground.

this can be done several ways,

the obvious is to get a centre tap on the 12.6v transformer and connect it to the HV ground,

another way is to put a 100ohm humbucking pot across the lt suppy and ground the wiper [normally used for ac heater supplies], msybe overkill as you have a regulated supply

the third way is to use 2 47 ohm resistors across the LT supply and ground the junction.

all of these will do. hope that this helps.

kind regards

bill
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