Yes, it now has a broadcast receiving licence plate.
Remember These?
- Cressy Snr
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#286 Re: Remember These?
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- Mike H
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#287 Re: Remember These?
There's another couple of tricky aspects about fuses I forgot to mention. One is that the blow current is usually double the rated (printed) current. So your 500mA will need 1A to break them. Or thereabouts.
EXCEPT, when high ambient heat derates the fuse so if a fuse keeps blowing while it's supposed to be well within limits, it' because it's filament has been heated and weakened. Guess how I know.
Used to have this problem in enclosed chassis which are heated by transformers etc. The simple answer is double the rating. But then you wonder what the blow current actually is.
EXCEPT, when high ambient heat derates the fuse so if a fuse keeps blowing while it's supposed to be well within limits, it' because it's filament has been heated and weakened. Guess how I know.
Used to have this problem in enclosed chassis which are heated by transformers etc. The simple answer is double the rating. But then you wonder what the blow current actually is.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- Cressy Snr
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#288 Re: Remember These?
Thanks for that info Mike. I reckon any short or arcing will try to draw a lot more than one amp, so I would think the half amp rating is probably right for this application. So going by your info, at least I shouldn't get nuisance blowing.
Well I'm now bereft of amp.
It has now left the living room and is awaiting its time to be put into a box.
I think I've taken it as far as I can, so next time it appears it'll be the boxing up bit.
I've now got the computer back online, so I'll be in a better position to do the schematic before the weekend.
Meanwhile, there's Ray's build to watch.
Well I'm now bereft of amp.
It has now left the living room and is awaiting its time to be put into a box.
I think I've taken it as far as I can, so next time it appears it'll be the boxing up bit.
I've now got the computer back online, so I'll be in a better position to do the schematic before the weekend.
Meanwhile, there's Ray's build to watch.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#289 Re: Remember These?
Yep, fuses have a i squared t measure. A T fuse is rated to take 100% of its rated current for ever (though thats only the IEC rating, the UL rating is 75%), above that, its time and current that matters. THis graph shows that a T fuse will take 3 times its rated current for 1 second, and 2 times for 100 seconds. But there is also the repeated use characteristic, so the time will add up as the fuse weakens.
A T fuse will withstand 10 times its rated current as a inrush.
More info here
https://www.schurter.com/content/downlo ... ection.pdf
A T fuse will withstand 10 times its rated current as a inrush.
More info here
https://www.schurter.com/content/downlo ... ection.pdf
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#291 Re: Remember These?
Steve, to help with my peace of mind, can you label/number the pins for the 13E1 when you update your schematic. CheersCressy Snr wrote: ↑Wed Jan 02, 2019 3:47 pm I've now got the computer back online, so I'll be in a better position to do the schematic before the weekend.
Sorry, I couldn't resist!
- Cressy Snr
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#292 Re: Remember These?
Audio act schematic with pin numbers for 13E1:Ray P wrote: Steve, to help with my peace of mind, can you label/number the pins for the 13E1 when you update your schematic.
Cheers.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- izzy wizzy
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#293 Re: Remember These?
Probably not the time for a question like this but I'll ask anyway. Prolly covered previously tho I don't remember. Why is the driver biased with less current than the input?
- Cressy Snr
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#294 Re: Remember These?
I like the sound with it like that.izzy wizzy wrote: ↑Fri Jan 04, 2019 3:20 pm Probably not the time for a question like this but I'll ask anyway. Prolly covered previously tho I don't remember. Why is the driver biased with less current than the input?
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- IslandPink
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#295 Re: Remember These?
Good enough reason ; but actually they're almost the same, aren't they ?
Do you also need more grid-cathode headroom on the driver ? - is the drive level quite a lot, before feedback ?
Do you also need more grid-cathode headroom on the driver ? - is the drive level quite a lot, before feedback ?
"Once you find out ... the Circumstances ; then you can go out"
- Cressy Snr
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#296 Re: Remember These?
Yep the drive level has to be high before feedback. The drive level I have is the best compromise I could squeeze out of it, whilst keeping distortion down. There was a lot of wrangling and nudging things to get the amp to sound as good as it does.IslandPink wrote: ↑Fri Jan 04, 2019 5:09 pm Good enough reason ; but actually they're almost the same, aren't they ?
Do you also need more grid-cathode headroom on the driver ? - is the drive level quite a lot, before feedback ?
Wolfgang and me discussed this a lot if one cares to look back at the thread.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
- izzy wizzy
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#297 Re: Remember These?
Thanks.
Excellent. The 5687 is a great sounding valve.
Look forward to hearing it at Owston if you and it are going.
Cheers,
Stephen
#298 Re: Remember These?
Short question: WhyYep the drive level has to be high before feedback.
Secondary Question: Its normally gain that is needed, rather than the ability to swing voltages it wont be swinging. Feedback will reduce the voltage swing, so does it have to be there in the first place.
Longer Question: I would love to see what that amp works like by looking at the voltage level into the output valve with a load on the amp. I can only assume the grid and cathode move a long way apart, but it would be nice to see it
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- IslandPink
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#299 Re: Remember These?
Maybe I was getting confused with open-loop gain.
"Once you find out ... the Circumstances ; then you can go out"
- Cressy Snr
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#300 Re: Remember These?
I'm only going on what Bruce Rozenblit says, as I understand it, in his books with the OTLs in as projects.Nick wrote: ↑Fri Jan 04, 2019 8:13 pmShort question: WhyYep the drive level has to be high before feedback.
Secondary Question: Its normally gain that is needed, rather than the ability to swing voltages it wont be swinging. Feedback will reduce the voltage swing, so does it have to be there in the first place.
I don't seem to see all these nuanced terms that are obvious to others. I'm very, very literal and figure that you need more swing in the first place so that there is sufficient in reserve for the feedback to bring it back down again so the amp amplifies to the degree you want it to. For me voltage swing and gain are interchangeable (but apparently not) To the way I think, big swing resulting from tiny swing = high gain. Only slightly bigger swing from tiny swing = low gain. That's how I see it.
Sgt. Baker started talkin’ with a Bullhorn in his hand.