Adding heater transformer to my 6b4g amp. help a noob please. - diyAudio
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Old 21st October 2012, 06:54 PM   #1
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Default Adding heater transformer to my 6b4g amp. help a noob please.

hi, I would like to have some guidance concerning adding separate transformers for my 6b4g amp. the schematic is attached.

I was told to fix that in my amp:
The output tubes are 6.3V heater types, directly heated.

There are a number of effects in directly heated tubes, that mean AC heating derived problem increase by the square of the Voltage.

So while AC heating the 2A3 at 2.5V can work okay especially in a PP Amp, the problems are >20dB greater with 6B4 type valves.

The sonic problems from AC include a warm, but muddy and not very detailed sound, often lacking subjective dynamics.

One solution would be to change the heaters to DC (not straightforward, bad DC on directly heater tubes sounds even worse than bad AC, but in different ways).


'' a heater transformer I would use a hammond 166ms (5vct 3A) for a each tube. the reason to stray away from 6.3V is less tube noise on the plate and better gain characteristics over the life of the tube.''

can anyone tell me if I should go on with the mod using the hammon 166 ms?
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Old 21st October 2012, 08:19 PM   #2
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What you need is a couple of Rod Coleman's filament boards. He supplies them as kits - see "26 pre amp" thread for example. You'll need a DC supply about 5v higher than 6.3v to feed the boards, so looking at 12v DC. Have no fear of DC not being as good as AC - with Rod's boards you'll get great sound and it'll be quiet too. His boards are very popular and also good value. He supplies full instructions.
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Old 21st October 2012, 08:36 PM   #3
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so rob coleman filaments board will replace the need for hommond transformers?
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Old 21st October 2012, 09:22 PM   #4
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Rod Coleman's boards are current regulators - you have to supply them with 12v DC so you will need something like transformers with 9v secondaries, schottky diodes and about 20,000uf in capacitors per tube.
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Old 21st October 2012, 09:47 PM   #5
rhone is offline rhone  Australia
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Hi Murphy,
I made a DIY 6B4G push-pull amp using Allen Wright's PP2C input stage. It uses plain old AC on the filaments and it is not warm, muddy or lacking in dynamics, quite the opposite. And with my 90dB sensitivity speakers it is decently quiet - no hum can be heard from the listening position.
Now I'm sure a sophisticated regulated supply like the RC one would be an improvement but it's not a REQUIREMENT to get acceptable sound. And it does add significant complexity to the amp: you need two extra transformers, basic rectification/filtering and then the regulating boards themselves. Do you have the space to accommodate all this? I don't, unfortunately.
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Old 21st October 2012, 10:15 PM   #6
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Well, like rhone I actually use AC with my PP 6B4G amp. A low value pot across the filaments is pretty good at nulling the noise.
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Old 22nd October 2012, 01:24 AM   #7
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Quote:
Originally Posted by rhone View Post
Hi Murphy,
I made a DIY 6B4G push-pull amp using Allen Wright's PP2C input stage. It uses plain old AC on the filaments and it is not warm, muddy or lacking in dynamics, quite the opposite. And with my 90dB sensitivity speakers it is decently quiet - no hum can be heard from the listening position.
Now I'm sure a sophisticated regulated supply like the RC one would be an improvement but it's not a REQUIREMENT to get acceptable sound. And it does add significant complexity to the amp: you need two extra transformers, basic rectification/filtering and then the regulating boards themselves. Do you have the space to accommodate all this? I don't, unfortunately.
oh, I didnt thought about that.
here you can see a picture
Mono 6B4G tube amp and Preamp - Canuck Audio Mart
that would be tight I think...

Last edited by murphythecat8; 22nd October 2012 at 01:29 AM.
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Old 22nd October 2012, 01:50 AM   #8
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You could also use these heater boards , Greg is on your side of the boarder and would save some shipping .
Classic Valve Design - Original and Legacy Design PCB's
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Old 22nd October 2012, 07:49 AM   #9
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Quote:
Originally Posted by battradio View Post
You could also use these heater boards , Greg is on your side of the boarder and would save some shipping .
Classic Valve Design - Original and Legacy Design PCB's
That's pretty basic - it would work as a DC option but there are much more sophisticated options than LM317 when it comes to directly heated tubes like DHTs, which is what you're talking about here. Even a LM1084/5/6 as current reg is a small step up, as was used in the Ronan Reg. Rod Coleman's filament regulators are a seriously sophisticated ultra low noise design which has been regularly improved and refined since 2004. They contain 5 active devices as well as a lot of passive components, and also have fine user adjustment of current/voltage with a pot - very handy for getting it right with different tubes and their variations in strength. And they're far from expensive for what they are, plus have full documentation and backup. I'm just one of hundreds of happy users.

As regards space in the chassis, Rod's regs are pretty tiny but do require heatsinks. the size of these depends on the tube being heated. 6B4G is 1 amp so that is calling for a medium size sink. And you need space for the power supply - one supply for each tube. A lot of us use outboard supplies with simple connectors like 4 pin XLRs.

If you're not too fussy about noise, stick to AC and a humpot. But even so you need separate AC supplies to each tube.

Last edited by andyjevans; 22nd October 2012 at 07:57 AM.
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Old 22nd October 2012, 12:26 PM   #10
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ok thanks a lot andy. I'm not to fussy about the noise, so it will be a humpot. which one, can you point me to one?
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