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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 5:31 am 
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john8750 wrote:
I really don't care for any startup sequence either.
I would like to take care of the 300b life span.

What do you mean exactly John?
I thought you were building a startup timer. Now you've decided not to?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 6:11 am 
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john8750 wrote:
Thanks again Men. I will make that dummy load, Peter.
My PS caps are 500volt 105c. B+ should be around 435.
I really don't care for any startup sequence either. I would like to
take care of the 300b life span.
I think the only thing you can do that might affect life span wound be to limit the startup inrush filament current with, say, an NTC thermistor but I question it's necessity since the filament transformer should already somewhat limit surge current due to it's winding DCR. There will still be a surge but each transformer simply isn't able to provide, say, 6 amps at 5V. The voltage will droop until the current comes down. (I believe the reports of 'blown filaments' you may have heard of were due to being powered by regulated DC, which fights to maintain the voltage regardless of current draw and will result in a much larger surge.)

500 V caps are, of course, fine when it's operating (at 435V) but they have to withstand the initial voltage surge too. 500V caps are usually surge rated (when they specify) for 1.1 times operating or 50V over max. That comes to 550 V and at 564 V you're a bit over the surge rating but things usually have a 'safety margin' so they'll probably hold. I'd feel better with 600 V caps, though.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 6:19 am 
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Pbpix wrote:
Flipperhome wrote:
.

You: "Yes it can mean on/off. A momentary contact can be used to "toggle" or change state. Latching is something else"

Me: "For heaven's sake. Stop muddying the waters. ..
OMG... stop splitting ... already split hairs.

Yes.. what I said is exactly correct... both in tone and meaning. And I was not "blaming" john.

The problem Flip is not the words or what John did ...
The problem is in the way YOU seem to always want to find fault or blame and worse is that you seem to enjoy making sharp-tone accusations which are abrasive and frankly offensive....
I'm sorry if my saying "Stop muddying the waters" offended you. From now on I'll try to remember and use your example of courteous, polite, repartee "You are flat-out WRONG buddy!"


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 6:25 am 
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Flipperhome wrote:
I'm sorry if my saying "Stop muddying the waters" offended you. From now on I'll try to remember and use your example of courteous, polite, repartee "You are flat-out WRONG buddy!"

It's just the tone of always seeking blame that's offensive.

Image

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 4:51 pm 
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Pbpix wrote:
john8750 wrote:
I really don't care for any startup sequence either.
I would like to take care of the 300b life span.

What do you mean exactly John?
I thought you were building a startup timer. Now you've decided not to?



Haven't decided yet. The startup timer circuit board is wired and ready. I have read that an ac filament with a soft start will prolong the 300b filament life. And a delayed B+, after tubes are heated is desirable. Some use a separate power switch.
I will mount the board anyway. Connect it, maybe. I need to finish this project.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 4:53 pm 
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Pbpix wrote:
Flipperhome wrote:
I'm sorry if my saying "Stop muddying the waters" offended you. From now on I'll try to remember and use your example of courteous, polite, repartee "You are flat-out WRONG buddy!"

It's just the tone of always seeking blame that's offensive.

Image



That's what we need guys. Two very important Men IMHO 8)

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 9:46 pm 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
I really don't care for any startup sequence either.
I would like to take care of the 300b life span.

What do you mean exactly John?
I thought you were building a startup timer. Now you've decided not to?



Haven't decided yet. The startup timer circuit board is wired and ready. I have read that an ac filament with a soft start will prolong the 300b filament life. And a delayed B+, after tubes are heated is desirable. Some use a separate power switch.
I will mount the board anyway. Connect it, maybe. I need to finish this project.

I've used the CL-90 thermistor (inrush current limiter) with excellent success in AA5 radios.
I placed it in series with the 120v AC input line
It starts out cold as high resistance of 120 ohms and after 20-30 seconds or so it drops to 1.18 ohms when hot. It can handle up to 16 amps of current.
Here's a list of all of them showing the cold and hot resistance.
https://www.digikey.com/products/en/cir ... l/151?v=45
Image
.

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Last edited by Pbpix on Dec Sat 02, 2017 7:24 am, edited 1 time in total.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Fri 01, 2017 10:12 pm 
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Wire one of the outlets in a metal outlet strip with a CL-90 to test.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 02, 2017 5:09 am 
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Thanks again guys. I got a little cold, not feeling well. I do like the thermistor idea.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sat 02, 2017 10:50 pm 
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I can get the 600volt caps. Will be powering up with full load soon. I will check B+ immediately. If over 435volt, maybe should need some resistance before rectifier?

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 03, 2017 1:27 am 
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john8750 wrote:
I can get the 600volt caps. Will be powering up with full load soon. I will check B+ immediately. If over 435volt, maybe should need some resistance before rectifier?
See if it get's to 550 V. It may not since the filaments in the 300Bs and rectifier will heat at about the same rate. That's your surge limit, not 435 V. Then see if it settles to 435 V +- 20%. Remember, the 12SL7 heater will take some more time to warn up during which the 300B bias current will be higher than once it settles in.

Series resistance won't help the turn on surge voltage, if that's what you're asking, because there's no current draw to cause a drop in voltage.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 03, 2017 1:34 am 
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John:
By way of comparison check out the power supply in the 6V6 amp.
With no built-in special device-delays, just normal power up functions;.. initially the B+ goes upward of 340 volts or so and then as the filaments heat up and the tubes start drawing current the B+ drops to about 295 v.
This all takes about 15-20 seconds.
No harm.. and normal tube operation.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 03, 2017 3:29 am 
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Pbpix wrote:
John:
By way of comparison check out the power supply in the 6V6 amp.
With no built-in special device-delays, just normal power up functions;.. initially the B+ goes upward of 340 volts or so and then as the filaments heat up and the tubes start drawing current the B+ drops to about 295 v.
This all takes about 15-20 seconds.
No harm.. and normal tube operation.



I get it now Peter. I just didn't like the b+ over 500volts. My filter caps are 500volt.
Flip explained that with a load, B+ could start about 450volts. And a very brief overvoltage
of 550 wont hurt.
I just need to wire the inputs, then ready for the test. Will connect my shop test speakers.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Sun 03, 2017 3:34 am 
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Flipperhome wrote:
john8750 wrote:
I can get the 600volt caps. Will be powering up with full load soon. I will check B+ immediately. If over 435volt, maybe should need some resistance before rectifier?
See if it get's to 550 V. It may not since the filaments in the 300Bs and rectifier will heat at about the same rate. That's your surge limit, not 435 V. Then see if it settles to 435 V +- 20%. Remember, the 12SL7 heater will take some more time to warn up during which the 300B bias current will be higher than once it settles in.

Series resistance won't help the turn on surge voltage, if that's what you're asking, because there's no current draw to cause a drop in voltage.



Then we are almost ready for the big test. I am a little worried about hum.
My wife says if I don't like the hum, teach it how to whistle.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Mon 04, 2017 6:21 pm 
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Flipperhome wrote:
john8750 wrote:
I can get the 600volt caps. Will be powering up with full load soon. I will check B+ immediately. If over 435volt, maybe should need some resistance before rectifier?
See if it get's to 550 V. It may not since the filaments in the 300Bs and rectifier will heat at about the same rate. That's your surge limit, not 435 V. Then see if it settles to 435 V +- 20%. Remember, the 12SL7 heater will take some more time to warn up during which the 300B bias current will be higher than once it settles in.

Series resistance won't help the turn on surge voltage, if that's what you're asking, because there's no current draw to cause a drop in voltage.



What would help limit the startup surge? I thought that the thermistor controls surge by starting with a high resistance.
Almost ready for the big test. :wink:

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 12:38 am 
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john8750 wrote:
Flipperhome wrote:
john8750 wrote:
I can get the 600volt caps. Will be powering up with full load soon. I will check B+ immediately. If over 435volt, maybe should need some resistance before rectifier?
See if it get's to 550 V. It may not since the filaments in the 300Bs and rectifier will heat at about the same rate. That's your surge limit, not 435 V. Then see if it settles to 435 V +- 20%. Remember, the 12SL7 heater will take some more time to warn up during which the 300B bias current will be higher than once it settles in.

Series resistance won't help the turn on surge voltage, if that's what you're asking, because there's no current draw to cause a drop in voltage.



What would help limit the startup surge? I thought that the thermistor controls surge by starting with a high resistance.
Almost ready for the big test. :wink:

If the filaments is the danger for surge .. there is current draw from the moment you turn on the filament transformers. So a thermister in that current path will reduce surge. Either on the primary or secondary side I'd guess.

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 2:00 am 
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john8750 wrote:
Flipperhome wrote:
See if it get's to 550 V. It may not since the filaments in the 300Bs and rectifier will heat at about the same rate. That's your surge limit, not 435 V. Then see if it settles to 435 V +- 20%. Remember, the 12SL7 heater will take some more time to warn up during which the 300B bias current will be higher than once it settles in.

Series resistance won't help the turn on surge voltage, if that's what you're asking, because there's no current draw to cause a drop in voltage.

What would help limit the startup surge? I thought that the thermistor controls surge by starting with a high resistance.
Almost ready for the big test. :wink:
Different source and types of surge, one is current (the filaments) and the other is voltage (B+).

When first turned on the filaments are cold and, so, have a lower resistance than when warmed up. That causes it to pull more current than when operating and 'surge' till warmed up. So a thermistor, which has, essentially, the reverse characteristics will limit the current surge.

The problem with B+ voltage surge is there isn't any current draw at first, which is what causes the surge to begin with. You can't use a resistor's IR drop to cut it down because there isn't any I. The simplest and safest solution is to just use components that can handle the surge.


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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 8:03 am 
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https://www.ebay.com/itm/Mean-Well-DCW0 ... 2749.l2648

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 8:07 am 
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https://www.ebay.com/itm/12W-LED-Strip- ... 2749.l2648

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 Post subject: Re: A new 300B amp project
PostPosted: Dec Tue 05, 2017 5:01 pm 
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Thank you Men. I am getting the picture here.
I noticed that some guys test this amp firstly with a lower AC supply, say 24volts.
Then measure for voltages of 20%. Is this a good thing to do?

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