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Old 10th July 2005, 07:00 AM   #1
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Default 300b filament q, yes another one.

Just converted my 91 type amps (5z3+6sj7+300b) to Joe Roberts style heater supply from straight AC and I'm still not completely happy with the humm or overall sound. What's the best way to get good DC supply from 5vAC, I've been reading the other posts but am confused by the number of various methods. I am leaning towards diode bridge + CLC, will this give me a high enough voltage and can it sound better than AC? Any recommendations for parts, diode bridge and choke? I have enough room, is it better to go with a pre made bridge or make one up? Thanks.
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Old 10th July 2005, 09:58 AM   #2
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Did you try using 7805 voltage regulator?
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Old 10th July 2005, 10:45 AM   #3
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Quote:
Originally posted by Pentium100
Did you try using 7805 voltage regulator?

Hi

Allthough it does deliver pure DC, in my experience the LM7805 sounds dull. If you want the best transparancy, try current source heating.

For those not wanting to build one, look at

www.TentLabs.com

otherwise Google around for something to build yourself

succes
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Old 10th July 2005, 12:40 PM   #4
Previously: Kuei Yang Wang
 
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Default Re: 300b filament q, yes another one.

Konnichiwa,

Quote:
Originally posted by gtmcgar1
What's the best way to get good DC supply from 5vAC
Using a seperate transformer with more than 5VAC....

Here is why.

5V when rectified give at best 7V, but you need to subtract rectifier losses. When using Schottky diode bridges you loose at least 1V or a little above so your RMS Voltage will be closer to 5.5V (allowing for ripple) than 7V. Using normal rectifiers will drop out more voltage.

With no voltage overhead you have no option to regulate or filter, so you cannot do anything but rectifier & capacitor with possibly a low dcr (and invariably low inductance) choke or a simple resistor and another capacitor to filter a little more, non of which will give much filtering.

Use a few more volts and you can do some real filtering.

Sayonara
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Old 10th July 2005, 05:15 PM   #5
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I think I have room for a seperate fil transformer. Please help recommend what parts I need. If I use something around 8v would that be enough? Which schottky diodes work well, any input on choke type or specs? Thx for the help guys.
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Old 10th July 2005, 05:53 PM   #6
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by gtmcgar1
I think I have room for a seperate fil transformer. Please help recommend what parts I need. If I use something around 8v would that be enough? Which schottky diodes work well, any input on choke type or specs? Thx for the help guys.
Here the schematic of two Heater Circuits of mine (drawn as part of the whole amplifier):

Click the image to open in full size.

Click the image to open in full size.

Sayonara
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Old 12th July 2005, 06:10 AM   #7
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Thanks everyone for the help. I have a 6.3vct 2a fil tranny and the diodes. Any advice on cmc spec or where to get a hold of one. Also what exactly is hc-0.08, Thanks again for the help, I'm still new to this tube stuff.
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Old 12th July 2005, 08:31 AM   #8
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by gtmcgar1
Any advice on cmc spec or where to get a hold of one.
CMC = Common Mode Choke, you find them in every good electroinics catalogue. Years ago I butchered around 100 identical old 286 Compaq PC's (for work - destroy the HDD's before thrown out). Their Powersupplies yielded up many nice parts including very nice CMC's, I'm still using parts from that stash.

From Catalogues, look for the higher current, higher inductance ones.

Quote:
Originally posted by gtmcgar1
Also what exactly is hc-0.08
It is a heater choke I had Stevens & Billington design for me. I am not sure if it is still around, it did not seem to sell well so may have been dropped. The Spec was 80mH @ 50Hz and 1.5A DC current. Before you ask, the 2.9mH Items are generic 4 or 5A Toroidal items from the usual electronics catalogues, in my case RS-Components and Farnell for the UK, Mouser & Digikey aparently are the US equivalents, I would not know.

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