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Old 17th August 2006, 09:59 AM   #11
jarthel is offline jarthel  Australia
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Quote:
Originally posted by ray_moth
Some ideas:

Using TV damper diode tubes, either as "full wave" rectifiers with a CT secondary or as one half of a bridge together with fast-recovery SS diodes in the other half, gives you both a slow start and low PS noise. Either of these arrangements will delay B+ for about 30 seconds and the amp tubes will be well warmed up by then. TV dampers are favoured by quite a few designers and I've never heard of any adverse effects due to applying B+ late.
examples of tv damper diode tubes?

Quote:
Originally posted by ray_moth

The use of a negative temperature coefficient resistor (thermistor) in the primary of the power tranny can help minimize initial current surges at switch-on.
when using thermistor, must it come before the slo-blo fuse or after the fuse? if before the fuse, do I even a slo-blo since the turn-on current flow would be controlled.

Thank you for the help
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Old 17th August 2006, 11:36 AM   #12
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I use 6D22S made by Svetlana but there are other (NOS) tubes, which are not too expensive. These are all rugged, single thermionic diode tubes that take quite a heavy heater current. They have isolated 6.3v heaters and can usually withstand 500-600v heater-cathode voltage, so they can use the same heater supply as other tubes in the amp.

As for the fuse, it should be the first thing in the AC line, so it should come before the on/off switch and the thermistor. I'd think slow-blow would probably be unnecessary, as you say.
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Old 17th August 2006, 11:43 AM   #13
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Quote:
Originally posted by jarthel


examples of tv damper diode tubes?


Click the image to open in full size.

I used 6AX4GTB's in my last amp. Seems I get 20 to 30 seconds before B+ hits. Plus they look cool while running

dg
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Old 17th August 2006, 01:33 PM   #14
jarthel is offline jarthel  Australia
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thanks for the help.

I guess I don't need a slow turn-on heater suppy.
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Old 17th August 2006, 01:41 PM   #15
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This is what I'm using in two of my actual projects. This heater supply/reg is taking about 12 sec to reach its set point. Take not it is a 12V version. You easily change the LM317 resistors to set it to 6V.
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Old 17th August 2006, 01:47 PM   #16
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This is the AC input of the equipment. Not shown, first the fuse, then the Power ON switch, then the In-Rush current limiter CL60, the the power transfo.

The heater transfo is connected directly there (Lines going down) and start ramp up immediatly. The filament supply is used to supply a small timer, in this case a simple 555. Then after some delay, it turns on RLY1 to activate the HV supply.

By choosing the 555 delay, you can start the HV after the HTR is fully turn on.

Simple and working quite well. Just to make sure that you choose a relay with contacts strong enough to absorb the HV transfo start-up current. The contacts also need to be rated for 120V in this case.

Have fun.
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