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Old 25th April 2016, 03:42 AM   #1
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Default Filement voltage Tolerence?

TSE 300B amp. I built it in two chassis, separating the amp and the power supply. They are connected with a 36" cable. I may have some voltage drop over cable length. On 300B filaments I have 4.85 volts. But on the 5842's I only have 5.62 volts. The amp seems to be working, and sounding just fine. Any ill effects from low filament voltage? Thank you all.
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Old 25th April 2016, 09:47 AM   #2
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See page 2; http://www.tubebooks.org/tubedata/we300a_b.pdf
The filament should be within 10% of ratings otherwise damage may occur. Too cold = electron stripping, too hot = burnt out filament.
The 5842s should have 6v3 but 5v67 is as low as I would go. 4v5 is the minimum for your 300a or b, so that is OK.
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Old 25th April 2016, 03:17 PM   #3
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I used 16 gauge wire in my umbilical cable. I figures it would have less resistance then a smaller gauge wire, therefore less voltage drop. Was this wrong? Should a bigger or smaller gauge wire equal less voltage drop? Thank you all.
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Old 25th April 2016, 03:21 PM   #4
Mooly is offline Mooly  United Kingdom
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All things being equal, thicker cable = less drop.

Have you measured the AC voltage dropped along the cable ? Just measure end to end with it all working and double the result to account for the return side.
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Old 25th April 2016, 03:45 PM   #5
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When you say you separated the amp and the power supply, what exactly does that mean?

Putting the transformers on a separate chassis shouldn't cause any trouble ( other than additional cost and inconvenience ) . Putting the HV and bias rectifiers, filters, etc., on a separate chassis probably wouldn't cause you any trouble ( other than additional cost and inconvenience ) because the dc currents are low and you can adjust for the small variance with the amplifiers adjustments.

Putting the DC filament rectifiers, filters, regulators, etc., on a separate chassis is asking for trouble because of the high DC currents involved. You can't really adjust the DC filament regulator up, because, IIRC, it has a max output voltage of 5 volts - so no headroom. That was one of the issues I ran up against on the TSE 801 diversion.

You could consider moving the 6.3 volts AC to the main board, and do all your rectification, regulating, etc., on it, although I think 4.85 volts should be fine for your 300B. The 5842's are a little low - there is a dropping resistor on the board you can change, I think, that could take care of this. My 5842's run at 6.0 volts and they seem fine at that voltage.

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Last edited by w5jag; 25th April 2016 at 03:48 PM.
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Old 25th April 2016, 03:59 PM   #6
w5jag is online now w5jag  United States
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Quote:
Originally Posted by JonSnell Electronic View Post
See page 2; http://www.tubebooks.org/tubedata/we300a_b.pdf
The filament should be within 10% of ratings otherwise damage may occur. Too cold = electron stripping, too hot = burnt out filament.
The 5842s should have 6v3 but 5v67 is as low as I would go. 4v5 is the minimum for your 300a or b, so that is OK.
Western Electric didn't specify a tolerance that I could see on that datasheet.

When I was looking into this for my TSE 801 project, and I'll concede my "research" was admittedly casual, the tolerance rule of thumb, when not actually specified by a manufacturer, was plus or minus five percent, not plus or minus ten percent.

So, for a 300B 4.75 to 5.25 volts. He's okay there. For the 5842's ( they may have an actual spec - I haven't looked ) 5.985 volts - 6.615 volts. He's not Ok there, by that metric.

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Old 25th April 2016, 08:47 PM   #7
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There is one resistor in the 6.3 volt line to the 5842 filaments. R3, and it's 2.2 ohms. Any idea what to change it to? To up my voltage some? I don't need much. Thank you all.
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Old 26th April 2016, 07:42 AM   #8
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Its trial and error really. If you already have 2.2 ohms in series then that suggests you probably have around 0.6 volts dropped across it at the moment. So it seems you are down to pretty much shorting it out to bring the voltage up.

Try a 1 ohm to start (or just parallel your 2.2 with another 2.2) and see what that does.
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Old 26th April 2016, 03:33 PM   #9
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Originally Posted by Mooly View Post
... If you already have 2.2 ohms in series then that suggests you probably have around 0.6 volts dropped across it at the moment. So it seems you are down to pretty much shorting it out to bring the voltage up.
....
I agree

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Old 27th April 2016, 01:31 PM   #10
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I believe that resistor is there to drop some volts for the "hot" Hammond power transformers that tend to deliver too many volts. If your 6.3V is not coming in high, you can put a jumper here.
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