Hi, ..
measured at the base of the pins , with a 46 in it, I get 3.4 volts instead of 2.5 v. I'm using a seperate 2.5V filament transformer for each channel.
Is this okay? I suspect not.
Any suggestions for fixing this ? Would using the same filament transformer for both channels work (could it be that the filament transformer doesn't have a good enough load regulation and isn't loaded down enough by a single tube)?
Thanks
measured at the base of the pins , with a 46 in it, I get 3.4 volts instead of 2.5 v. I'm using a seperate 2.5V filament transformer for each channel.
Is this okay? I suspect not.
Any suggestions for fixing this ? Would using the same filament transformer for both channels work (could it be that the filament transformer doesn't have a good enough load regulation and isn't loaded down enough by a single tube)?
Thanks
Hi Zobsky,
Who made your filament transformers and what is the secondary current rating.. Lightly loading some filament transformers, umm Hammond comes to mind amongst others, may give this outcome.
If you are using a center tapped filament winding (using center tap) then a small pair of ~ 0.27 ohm 2W resistors would be about right if this is not the case then a single 0.47 ohm 5W resistor would be about right. The idea is to drop about 0.9V with a load current of 1.75A..
Who made your filament transformers and what is the secondary current rating.. Lightly loading some filament transformers, umm Hammond comes to mind amongst others, may give this outcome.
If you are using a center tapped filament winding (using center tap) then a small pair of ~ 0.27 ohm 2W resistors would be about right if this is not the case then a single 0.47 ohm 5W resistor would be about right. The idea is to drop about 0.9V with a load current of 1.75A..
kevinkr said:
These are some ancient vintage surplus filamnent trannys (White-Rodgers, model S81-288). I couldn't find any info on them (or their current rating), though they are rated for 2.5V secondary (I'm using A/C heaters).
They don't have a center tap. I guess I'll have to burn off some voltage. I only had the circuit on for a minute, so I doubt that any harm has been done.
Thanks
Hi Zobsky,
Do these transformers have more than one primary tap? I have run across old transformers that had taps at 105, 110, and 117V.. Also if they are rated at in excess of 5 - 10A they may produce excessive voltage when this lightly loaded.
I agree it's unlikely that this short exposure caused any harm..
Do these transformers have more than one primary tap? I have run across old transformers that had taps at 105, 110, and 117V.. Also if they are rated at in excess of 5 - 10A they may produce excessive voltage when this lightly loaded.
I agree it's unlikely that this short exposure caused any harm..
No kevin, .. they have only one primary tap. I know what you mean about some trannys having multiple primaries but not these.
Before trying some inline resistors, i'm thinking of attach both channels to one filament transformer to load it down some more.
1. is this okay (the tranny doesn't have any load specs on it)?
2. would this have a negative effect on the sound?
I'll try and post some pics on this (long overdue) project sometime soon.
thanks.
Before trying some inline resistors, i'm thinking of attach both channels to one filament transformer to load it down some more.
1. is this okay (the tranny doesn't have any load specs on it)?
2. would this have a negative effect on the sound?
I'll try and post some pics on this (long overdue) project sometime soon.
thanks.
zobsky,
Loading the trans should not make more than a 5% difference maybe 10%. When you do this, you are only moving the heat dissipation from a resistor to the trans. Now.... that's OK, but you need more than 10%.
It would be worth your time to investigate all these voltages. It seems the error is greater than it should be... are you measuring the 3.4 volts on the 200 volt setting of your meter? Check the little things carefully.
Resistors are probably your best bet here...
Also, how you reduce the voltage will not affect your sound... issues of hum aside. You either have hum or you don't... usually not. Don't worry about it...
But you need some resistors anyway. You need to create a voltage divider across your heaters with 2 resistors, so that you can ground, or reference, your heater supplies. They cannot be left "floating"... it makes makes noise and sometimes other mysterious problems (feedback).
Loading the trans should not make more than a 5% difference maybe 10%. When you do this, you are only moving the heat dissipation from a resistor to the trans. Now.... that's OK, but you need more than 10%.
It would be worth your time to investigate all these voltages. It seems the error is greater than it should be... are you measuring the 3.4 volts on the 200 volt setting of your meter? Check the little things carefully.
Resistors are probably your best bet here...
Also, how you reduce the voltage will not affect your sound... issues of hum aside. You either have hum or you don't... usually not. Don't worry about it...
But you need some resistors anyway. You need to create a voltage divider across your heaters with 2 resistors, so that you can ground, or reference, your heater supplies. They cannot be left "floating"... it makes makes noise and sometimes other mysterious problems (feedback).
poobah said:zobsky,
Resistors are probably your best bet here...
Also, how you reduce the voltage will not affect your sound... issues of hum aside. You either have hum or you don't... usually not. Don't worry about it...
But you need some resistors anyway. You need to create a voltage divider across your heaters with 2 resistors, so that you can ground, or reference, your heater supplies. They cannot be left "floating"... it makes makes noise and sometimes other mysterious problems (feedback).
Yes, .. I'm measuring using the 200V setting on the multimeter.
I do have a hum reducing potentiometer across the two ends of the filament but adjusting that shouldn't affect the voltage across the heater. See the filament wiring scheme on the referenced link (not my schematic, but similar filament wiring and cathode biasing scheme).
http://www.angela.com/catalog/how-to/SE.2A3.html
poobah said:OK then,
Repeat your measurements using the 20 Volt scale... you should always use the lowest scale possible. You may have less of a problem than you think.
I don't have a 20V scale on the A/C measurement scale of my multimeter, .but I tried measuring again with my secondary (autoranging) multimeter with the same results ie. voltages around 3.5 V AC or so.
Well, I tried paralleling the heaters of both channels to the secondary of A SINGLE filament transformer, resulting in a rather drastic voltage drop. I now measure 2.8 V across either heater (the trannys are rated for 2.5V).
Can I live with this, or would I still need dropper resistors / voltage dividers etc ??
Thanks
Can I live with this, or would I still need dropper resistors / voltage dividers etc ??
Thanks
The resistors are a good idea, they will also lower inrush current.
This is most extensive paper on DHT life and filament operation Im aware of.
Techniques to Extend the Service Life of High Power Vacuum Tubes.
This is most extensive paper on DHT life and filament operation Im aware of.
Techniques to Extend the Service Life of High Power Vacuum Tubes.
Hi Camotecue,
I would expect emission to be greatly reduced at 3.7V, depending on load current perhaps cathode stripping will occur due to low filament temperature.
More to the point the performance of that rectifier will be quite poor, I would expect a relatively high internal drop and high internal resistance.
It really needs to be fixed..
I have encountered one instance where arcing sometimes occured during warm up in a 5U4 (1KV per plate - not my design! LOL) and the culprit was low filament voltage due to a series resistor in the filament circuit. Removed resistor, no more arcing, but finally due to my discomfort with a 5U4 with 2KV between the plates I replaced that 5U4 with a 5R4...
I would expect emission to be greatly reduced at 3.7V, depending on load current perhaps cathode stripping will occur due to low filament temperature.
More to the point the performance of that rectifier will be quite poor, I would expect a relatively high internal drop and high internal resistance.
It really needs to be fixed..
I have encountered one instance where arcing sometimes occured during warm up in a 5U4 (1KV per plate - not my design! LOL) and the culprit was low filament voltage due to a series resistor in the filament circuit. Removed resistor, no more arcing, but finally due to my discomfort with a 5U4 with 2KV between the plates I replaced that 5U4 with a 5R4...
follow up, ..
i decided to use both filament transformers with a 0.47 ohm / 5W wired into each one . That brought the voltage across the DHT right down to 2.5 V
Thanks for the help
As an aside, my SE 6BQ5 -> 46 now makes music . Just have a little hum left that the hum pots haven't been able to resolve. Look for pics and more more questions in a different thread.
i decided to use both filament transformers with a 0.47 ohm / 5W wired into each one . That brought the voltage across the DHT right down to 2.5 V
Thanks for the help
As an aside, my SE 6BQ5 -> 46 now makes music . Just have a little hum left that the hum pots haven't been able to resolve. Look for pics and more more questions in a different thread.
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