If I add a reasonable-inductance but enormous choke with very little DC resistance before the capacitor filters in the main B+ supply, it should be easier for the power transformer to deliver current thru more of the wall-supply cycle, but what is the end result for the resultant B+ voltage? Will it always drop? I guess I should model but what's the rule of thumb?
Look up any basic tutorial on power supplies and read the differences between capacitor input filter versus choke input filter. The cap input filter charges to peak, or about 1.414 times RMS voltage of the AC. The choke input filter will charge to about 0.9 times RMS.
Chokes
Chokes
An ideal choke input supply gives you a DC voltage equal to 2 sqrt(2)/pi of the secondary AC RMS voltage. This is 90.03%. The derivation requires calculus and trigonometry - the maths you learnt in school does have its uses!
So does building it and bunging a meter on it!
Enzo already said 'about 90%'
Thanks again Enzo, I remember reading that link from aikenamps.com before but apparently neither the math nor rule of thumb stuck in my brain. Unlike what Katie & dad posted, a CLC is still basically a capacitor input filter, and a choke input filter like I asked about has a choke immediately after the rectifier. But either way, I'm not talking about a small choke between B+ and grid supply & preamp either.
I'm cooking up another single-ended guitar amp and picking out a power transformer, and I have some very nice chokes. So I'm just deciding what to do with them, if anything.
I'm cooking up another single-ended guitar amp and picking out a power transformer, and I have some very nice chokes. So I'm just deciding what to do with them, if anything.
Thanks again Enzo, I remember reading that link from aikenamps.com before but apparently neither the math nor rule of thumb stuck in my brain. Unlike what Katie & dad posted, a CLC is still basically a capacitor input filter, and a choke input filter like I asked about has a choke immediately after the rectifier. But either way, I'm not talking about a small choke between B+ and grid supply & preamp either.
I'm cooking up another single-ended guitar amp and picking out a power transformer, and I have some very nice chokes. So I'm just deciding what to do with them, if anything.
Chokes were used historically to reduce hum, because decent sized capacitors weren't available, so there's little reason to use them these days - unless you're going for the extra distortion as the HT rails comes down lower?.
Some Info / Resources:
Page 11 of the Hammond Catalogue - print it and stick it on your wall
http://www.hammondmfg.com/pdf/5C08.pdf
Model your power supply (free download software):
PSUD2
This is RECOMMENDED - I use it a lot.
The addition of a choke has the capacity of spreading the conduction angle of power drawn from the transformer. This reduces peak currents, diode switching stress etc and reduces the noise reflected back through the transformer into other windings. This can help reduce noise problems with bias supplies and heater supplies.
Cheers,
Ian
Duncan Amps also has a tone stack simulator software - worth a look while you are there.
Cheers,
Ian
Page 11 of the Hammond Catalogue - print it and stick it on your wall
http://www.hammondmfg.com/pdf/5C08.pdf
Model your power supply (free download software):
PSUD2
This is RECOMMENDED - I use it a lot.
The addition of a choke has the capacity of spreading the conduction angle of power drawn from the transformer. This reduces peak currents, diode switching stress etc and reduces the noise reflected back through the transformer into other windings. This can help reduce noise problems with bias supplies and heater supplies.
Cheers,
Ian
Duncan Amps also has a tone stack simulator software - worth a look while you are there.
Cheers,
Ian
I'm considering taking apart both Champs this winter and making a guitar reverb and a guitar power amp.
I'm thinking maybe I'll take the parts from the old cheap Champ clone and make a tube reverb. The 37 watt power transformer will work fine for 3 12AX7, and the little output transformer will make a nice reverb driver if I chose the tank carefully.
Then I'll take the parts from the Uber-Champ and make a single-ended power amp that's very adjustable. That larger 47-watt power transformer has plenty of filament current to run even a KT120 or KT150, or overdrive a 6V6 for dirty. This will use the 15-watt output transformer from the Uber-Champ.
I have several tube guitar preamps.
I'm thinking maybe I'll take the parts from the old cheap Champ clone and make a tube reverb. The 37 watt power transformer will work fine for 3 12AX7, and the little output transformer will make a nice reverb driver if I chose the tank carefully.
Then I'll take the parts from the Uber-Champ and make a single-ended power amp that's very adjustable. That larger 47-watt power transformer has plenty of filament current to run even a KT120 or KT150, or overdrive a 6V6 for dirty. This will use the 15-watt output transformer from the Uber-Champ.
I have several tube guitar preamps.
so there's little reason to use them these days
Except they massively reduce the amount of rectifier "hash" - especially if you're using silicon rectifiers
Except they massively reduce the amount of rectifier "hash" - especially if you're using silicon rectifiers
I've never heard any 'hash' from silicon rectifiers, either with or without a choke - although if it's something that you worry about?, fit 1000pF capacitors across each rectifier diode.
Chokes were there because you couldn't get decent size electrolytics, and you can of course now.
Those who ignore history
That is not just oversimplifying the situation: it is misleading.
To quote from 1995
Date: 1995/06/18 Newsgroups: rec.audio.tech Henry A. Pasternack
The differences are (as outlined earlier in this thread)
Overbeck, W. P. "Critical inductance and control rectifiers." Proceedings of the IRE 27, no. 10 (1939): 655-659
M. G. Scroggie a.k.a. 'Cathode Ray': Wireless World, December, 1957.
There is a third style used occasionally in radio - see Input Choke & Resonant Choke Power Supplies for RF Linear Amplifiers by Tony IØJX & Pesa IKØHIT
Chokes were there because you couldn't get decent size electrolytics, and you can of course now.
That is not just oversimplifying the situation: it is misleading.
To quote from 1995
Long article on power supply design."Choke-input filters are the butt of derision by modern engineers who have little experience with them and do not understand their many advantages."
Date: 1995/06/18 Newsgroups: rec.audio.tech Henry A. Pasternack
The differences are (as outlined earlier in this thread)
The addition of a choke has the capacity of spreading the conduction angle of power drawn from the transformer. This reduces peak currents, diode switching stress etc and reduces the noise reflected back through the transformer into other windings. This can help reduce noise problems with bias supplies and heater supplies.
Overbeck, W. P. "Critical inductance and control rectifiers." Proceedings of the IRE 27, no. 10 (1939): 655-659
"the choke-input filter is considered superior because it lowers peak current requirements for the rectifier tubes, it improves the form factor of the current pulses through the rectifier tubes and plate transformer, it provides better regulation to load at the output of the rectifier, and it aids in balancing the currents through the tubes."
M. G. Scroggie a.k.a. 'Cathode Ray': Wireless World, December, 1957.
"The capacitor-input system gives bad regulation "
There is a third style used occasionally in radio - see Input Choke & Resonant Choke Power Supplies for RF Linear Amplifiers by Tony IØJX & Pesa IKØHIT
That is not just oversimplifying the situation: it is misleading.
You can find websites to support any point of view
But it's even LESS important here in instrument amps, where people are using valves specifically for their lower quality, and designing circuits to further lower it.
The use of a PSU choke is there to make the supply 'collapse' more easily and further distort the sound - and is a perfectly valid reason for using one.
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