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Old 10th November 2011, 12:09 AM   #101
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One thing I would like if possible is to have through hole headers for input and output so it could be possible to stack on another board in addition to the connectors you are using. Do you think this would be possible? Either way I am very interested.

Thanks,
Chris
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Old 10th November 2011, 02:28 AM   #102
tomchr is offline tomchr  United States
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If you're driving multiple boards by the same input voltage, you could run some solid core wire between the boards. The connectors I use are through-hole.

Note that the filaments supplied by each transformer winding will need to be at the same potential. So if some filaments in the amp are required to float at different potentials (to avoid breaking down the filament-cathode interface for example), they will need to be supplied by separate transformer windings. Hence, they won't be able to share Vin -- or even ground.

In case of directly heated tubes, you'll need one regulator per tube. Just like you need one transformer winding per tube. If one end of the filament is connected to ground for all the tubes you're driving, you could run them on the same Vin but using separate regulators.

Does this make sense?

Do NOT run regulators in parallel to get higher output current. Use the LM22679 for up to 5 A output current. If you need more current because you have many filaments in parallel, separate them out on multiple supplies. If you need more than 5 A out, you'll need a different regulator.

~Tom
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Last edited by tomchr; 10th November 2011 at 02:31 AM.
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Old 10th November 2011, 03:40 AM   #103
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Because you're working with some high-impedance components (tubes), I'm not going to recommend you to use a switching power supply for filaments unless you're going to build a very good filter pack and place some shields - grounded.
By the way, why do you try to use a regulator? the tubes are already designed to work with a.c.
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Old 10th November 2011, 05:09 AM   #104
tomchr is offline tomchr  United States
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Quote:
Originally Posted by pelikanu View Post
Because you're working with some high-impedance components (tubes), I'm not going to recommend you to use a switching power supply for filaments unless you're going to build a very good filter pack and place some shields - grounded.
By the way, why do you try to use a regulator? the tubes are already designed to work with a.c.
I don't like the intermodulation products that AC heating causes. Hence, my desire for DC heaters.

I've already implemented and tested switchmode supplies for tube heaters. They work well. See my arguments in Post #1 and my 300B Switchmode Supply thread.

~Tom
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Old 10th November 2011, 07:48 PM   #105
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Quote:
Originally Posted by tomchr View Post
In case of directly heated tubes, you'll need one regulator per tube. Just like you need one transformer winding per tube. If one end of the filament is connected to ground for all the tubes you're driving, you could run them on the same Vin but using separate regulators.
Why couldn't you run two DH filaments in parallel if both 'grounds' are connected and it doesn't exceed the current limit?
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Old 11th November 2011, 12:39 AM   #106
TheGimp is offline TheGimp  United States
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Because you just tied the two cathodes together.
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Old 11th November 2011, 03:16 AM   #107
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I haven't used a directly heated tube yet, but I tie indirectly heated tube cathodes together all the time. It works fine as long as they are supposed to be tied together. What am I missing?
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Old 11th November 2011, 03:21 AM   #108
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This supply could be approximated by an ideal battery. If both negative terminals of two identical batteries are tied together and they are driving equal loads, what does it matter if I replace the two batteries with one that is twice as big and connect it to two loads at once? The load is going to be anchored to the same reference and at the same output voltage and the supply is ideally zero output impedance...
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Old 11th November 2011, 03:24 AM   #109
TheGimp is offline TheGimp  United States
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If you intend to tie both cathodes together then this is fine.There are very few topologies where this is acceptable. Two output tubes - not, PP output Yes, LTP-not, Multiple gain stages - not...
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Old 11th November 2011, 04:20 AM   #110
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If you intend to tie both cathodes together then this is fine.There are very few topologies where this is acceptable. Two output tubes - not, PP output Yes, LTP-not, Multiple gain stages - not...
I'm really still not on the same page with you on this. I can think of ways to make all four of these work. In most designs, it doesn't work because cathode bias is frequently used. You can't share supplies because there is no common point to hang these supplies since each tube needs to develop its own voltage to bias itself (excluding shared cathode resistors, of course).

Specifically, Tom stated that "In case of directly heated tubes, you'll need one regulator per tube. Just like you need one transformer winding per tube. If one end of the filament is connected to ground for all the tubes you're driving, you could run them on the same Vin but using separate regulators."

If one end of the filament is connected to ground for all the tubes I'm driving(they are not cathode biased with individual cathode resistors), and they are equal filament voltage, and the regulator can put out the current, what exactly is stopping me from doing this? I know I just tied them together, but why is that a bad thing since I was going to tie them to the same place, ground, individually anyway?
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