Hi,
I have just finished my new valve amp and I am now aware that there is a large inrush current.
Here the HT is connected to a GZ34 and then CLC, and the filament supplies a Rod Coleman regulator.
The question I have is, can I just add a thermistor straight after the plug (as shown above), and if so, can someone tell me exactly which thermistor I should use?
Thank you so much - I feel very old to be a noob, but hey ho.
Thanks again
Bass
I have just finished my new valve amp and I am now aware that there is a large inrush current.
Here the HT is connected to a GZ34 and then CLC, and the filament supplies a Rod Coleman regulator.
The question I have is, can I just add a thermistor straight after the plug (as shown above), and if so, can someone tell me exactly which thermistor I should use?
Thank you so much - I feel very old to be a noob, but hey ho.
Thanks again
Bass
Only if the inrush is too high, usually tube circuits doesn't require such a limiting current devices.
Search in the literature thousands of circuits of the tube b&w tv sets and no one I saw using those devices. Here when young, a Wells Garner circuit has been working for around 30 years and lacks any kind of current limiting. Only a 1Amper fuse in the primary of the power transformer.
Search in the literature thousands of circuits of the tube b&w tv sets and no one I saw using those devices. Here when young, a Wells Garner circuit has been working for around 30 years and lacks any kind of current limiting. Only a 1Amper fuse in the primary of the power transformer.
I think the culprit is the second transformer as the gz34 takes care of its own current. The second transformer is about 0.2 amps but I think the inrush is around 3 amps. I am going to try a CL-60 on the second one and see if that reduces the current.
If you amplifier uses a rectifier tube, then there is no inrush problem to worry about because the tube's slow turn on time eliminates that, 5U4's included. If the amp has S. S. diodes for the rectifiers, then some inrush limiting is needed. A PTC thermistor or a timed relay shorting out an inrush current limiting resistor are the usual fixes.
400VA of transformers may result in occasional current peaks of 50A or more, mostly for the first 1/2 cycle, depending on the phase of the AC at turn-on and the amount and direction of any remnant magnetism in the core from its last shutdown. Your lights will flicker, you'll hear a thump, your 3A fuse will blow! An inrush limiter (CL-60 is good for 5A continuous) and a slow-blow fuse of 1.5 times the actual current will take care of this. Transformers of a few hundred VA have enough DC resistance that this isn't a problem; transformers of 500VA and up will do this, even with no load. And charging a 40 uF to 400V takes about 3 Joules of energy; 50A (half-sine) x 240V x 10 ms = 60 Joules, so this dwarfs the power supply inrush, though it only occurs perhaps one of twenty turn-ons.
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What does 'aware' mean? Why do you think you need a 'solution' - is something failing ....?
Thank you all for your patience. I have learnt that the GZ34 will mean that the first transformer should not have a big inrush current, whilst the second that drives the heater regulator should also not cause one. I was using a fast blow fuse which I now understand to be the wrong choice, so I have some slow-blow fuses on their way.
Thank you all for your time
Thank you all for your time
Enjoy.
Tube circuits don't need usually fast blow fuses because there is always a normal initial pike current because: 1- heaters are cold and their resistance is low, 2- transformer is demagnetized and 3- (eventually with ss rectifiers or short heating time of the vacuum rectifier like 5U4) must charge the filter caps.
In the Langford-Smith book "Radiotron" is a large paragraph dedicated to this item. I humbly suggest you to search it in the web and read it.
Tube circuits don't need usually fast blow fuses because there is always a normal initial pike current because: 1- heaters are cold and their resistance is low, 2- transformer is demagnetized and 3- (eventually with ss rectifiers or short heating time of the vacuum rectifier like 5U4) must charge the filter caps.
In the Langford-Smith book "Radiotron" is a large paragraph dedicated to this item. I humbly suggest you to search it in the web and read it.
Basically he suggests the then-new slow-blow fuses. He points to an article with specific constructions, but already the Standards had evolved, and we no longer really care how they make it slow.
PRR; I agree about that sciences had advanced. But as the sir is talking about an old fashioned set using tube rectification (this isn't a criticism because I like it too over ss one) and the book is printed in 1999 (almost my copy), things are time-comparable and compatible, so I am sure that those concepts are still usefull.
Perhaps just after the secondary : 30R carbon resistor on each AC rail to act as soft start and in rush current limiter ? I see some use also small R value in serie before the primary ?
Thermistor and slow fuse are too much slow when switching on the amp to take care of the Tube span life (wall grid don't care about tubes and see a cold low impedance path as said above?) ?
Thermistor and slow fuse are too much slow when switching on the amp to take care of the Tube span life (wall grid don't care about tubes and see a cold low impedance path as said above?) ?
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I'm not sure what you mean by this. Is this a question about tube service life, and related to if a thermistor and/or a slow fuse are used?
Heaters are usually limited by the max transformer current.
This is fine so long as the transformer isnt grossly over rated.
This is fine so long as the transformer isnt grossly over rated.
Damn....
Thanks.... that means my toiroid which is 7v 2A is overated for the heater of a 6dj8 6.3V 365 mA IIRC. I have to read as I never took care of current limitation in power supplies with SS. First tube try for me...quite new.
Thanks.... that means my toiroid which is 7v 2A is overated for the heater of a 6dj8 6.3V 365 mA IIRC. I have to read as I never took care of current limitation in power supplies with SS. First tube try for me...quite new.