Antek toroid PT for an 18w TMB build?
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Re: Antek toroid PT for an 18w TMB build?
One thing I'm still having issues with is that it will blow a fuse. Maybe 1 out of 100 times at startup. With the standby switch in standby position (no DC going to the filter capacitors) it will sometimes blow the 1A fuse.
A few days ago I went over everything with a fine-toothed comb looking for out of whack voltage readings, loose anything, etc. Couldn't find anything that didn't look normal. With my light bulb limiter it never blew a fuse. And 99% of the time it works fine without the light bulb limiter.
I suspect that it's the inrush current from the toroid power transformer.
Two questions...
I notice here on the modern schematics of the 18w it shows using a 2A fuse. Mojotone's instructions and kit use a 1A. Could that be partially the issue?
Also if I were to use a thermistor as Rob shows here (https://robrobinette.com/Generic_Tube_A ... nt_Limiter) I'm guessing that would prevent any issue from the toroid PT. Could I just put it between the LOAD terminal of the IEC plug and the fuse holder?
I think it's just the random current spike that needs to be dealt with.
A few days ago I went over everything with a fine-toothed comb looking for out of whack voltage readings, loose anything, etc. Couldn't find anything that didn't look normal. With my light bulb limiter it never blew a fuse. And 99% of the time it works fine without the light bulb limiter.
I suspect that it's the inrush current from the toroid power transformer.
Two questions...
I notice here on the modern schematics of the 18w it shows using a 2A fuse. Mojotone's instructions and kit use a 1A. Could that be partially the issue?
Also if I were to use a thermistor as Rob shows here (https://robrobinette.com/Generic_Tube_A ... nt_Limiter) I'm guessing that would prevent any issue from the toroid PT. Could I just put it between the LOAD terminal of the IEC plug and the fuse holder?
I think it's just the random current spike that needs to be dealt with.
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Re: Antek toroid PT for an 18w TMB build?
In the USA it's 2A, in the UK it's 1A. If you're on a 120VAC source, you need to use 2A.
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Re: Antek toroid PT for an 18w TMB build?
Thanks. I'm running on 120VAC. Hmm, I wonder why Mojotone is doing it like that? Just one more issue for builders of their stuff do deal with.JMPGuitars wrote: ↑Mon 06/13/22 5:54 amIn the USA it's 2A, in the UK it's 1A. If you're on a 120VAC source, you need to use 2A.
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Re: Antek toroid PT for an 18w TMB build?
After I first noticed the startup issue I hooked up my multimeter and set it to measure the MAX amp load when I flipped the mains switch on. Most of the time it would be below 1A or just above but there were a couple of times (which didn't blow the fuse) which spiked around 5 - 7A.
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Re: Antek toroid PT for an 18w TMB build?
Now that makes a lot more sense.
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Re: Antek toroid PT for an 18w TMB build?
That's why slow blow fuses are used. Make sure you don't get fast blow 2a fuses or you still may have a startup issue!!!joulupukki wrote: ↑Mon 06/13/22 7:17 amAfter I first noticed the startup issue I hooked up my multimeter and set it to measure the MAX amp load when I flipped the mains switch on. Most of the time it would be below 1A or just above but there were a couple of times (which didn't blow the fuse) which spiked around 5 - 7A.
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Re: Antek toroid PT for an 18w TMB build?
They are definitely slow blow fuses. The issue is inrush current with the toroid power transformer. I'm working at getting a thermistor to try that out and my guess it it should work great.Unit_1 wrote: ↑Tue 06/14/22 1:37 pmThat's why slow blow fuses are used. Make sure you don't get fast blow 2a fuses or you still may have a startup issue!!!joulupukki wrote: ↑Mon 06/13/22 7:17 amAfter I first noticed the startup issue I hooked up my multimeter and set it to measure the MAX amp load when I flipped the mains switch on. Most of the time it would be below 1A or just above but there were a couple of times (which didn't blow the fuse) which spiked around 5 - 7A.
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Re: Antek toroid PT for an 18w TMB build?
The two diodes protect the rectifier from excessive PIV. Many of the modern rectifier tubes don't seem to have as hard a vacuum as NOS, so this is a common failure mode.joulupukki wrote: ↑Sun 06/12/22 4:40 pmNot sure now actually. At some point I had read that these diodes could be used as current limiters. Not sure if that’s the case at all, but I guess for now they act as backups to the tube rectifier.zaphod_phil wrote: ↑Sun 06/12/22 3:26 pmHow would those 1N4007s help?joulupukki wrote: ↑Mon 06/06/22 12:28 am
I’ll probably also use two 1N4007 diodes before it hits the plate pins on the 6CA4 rectifier as current limiters.
Jack
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