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EHHA Rev A - Interest Thread - Page 9

post #121 of 1656
Quote:
Originally Posted by bada bing View Post

Unregulated DC off a bridge on a 12.6volt xformer tap yields about 16 volts dc. Wears out heater filaments unnecessarily fast.

 



You wouldn't be using a 12.6V tap, because this amp won't be using a 'tube' power transformer. The amp itself requires 30+30, so you would almost certainly have a separate heater transformer. You can precisely spec this transformer however you like, for whatever diodes you like.


 

Quote:
Originally Posted by bada bing View Post

Then there's the issue of line variations nationwide of about 10%. I suppose there's plenty of ways to skin the cat, but I personally would accept AC heaters or (preferably) use regulated DC.



How is line variation OK for AC heaters, but not unregulated DC?


Edited by Beefy - 8/19/10 at 3:02pm
post #122 of 1656

I must be missing something... why not just use something along the lines of a voltage reference + op-amp for the heaters?

(sort of like a dynalo PSU)

 

Adding another rectifier, regulator and associated components seems kind of waste and you could power it all from a single transformer.


Edited by MisterX - 8/19/10 at 4:58pm
post #123 of 1656

Heater current is 0.33A. That would be an awful lot of wasted power and heat to knock down from 30V to 12V, wouldn't it? Not to mention doubling the current on the main power supply and transformer.

 

[EDIT] I looked at the datasheet, and 6GM8 is 0.33A at 6.3V. I don't know why 12V was being talked about earlier. So regulation for each heater from a 30V rail would burn up 7.8W. That's pretty nutty!


Edited by Beefy - 8/19/10 at 5:35pm
post #124 of 1656
12.6 in series. One supply for both tubes.
post #125 of 1656
Thread Starter 

Good questions. MisterX were you thinking of just pulling from the rails? I'm not sure that you meant this, but it would burn a lot of wasted power. OTOH, we could consider a switching regulator (as in the CTH) which is much more efficient.

 

Beefy I designed a 12.6V supply because I thought you would only have one and you would put the tubes in series. It is easer to make a regulated supply at 12.6V than it is at 6.3V from off the shelf transformers. A 12.6V transformer yields a high enough DC that at 350mA the regulator won't drop out. And, to be sure, I figured we would use an LDO regulator. This is all, as you know, very common.

 

A simple rectified/filtered DC supply usually has problems with line regulation and almost always requires dropping resistors and yields a variable heater voltage depending on the line voltage. Whereas with a 12.6V regulated supply you get rock steady heater voltages.

 

This was my reasoning, but we're still designing so we can go wherever there is consensus. I was just thinking that if one board had the rail PS and other the heater PS you would get everything you need with just two snappable boards.

 

Edit: I see that jdklake's post squeezed in before mine.


Edited by runeight - 8/19/10 at 6:14pm
post #126 of 1656
Quote:
Originally Posted by Beefy View Post

 

[EDIT] I looked at the datasheet, and 6GM8 is 0.33A at 6.3V. I don't know why 12V was being talked about earlier. So regulation for each heater from a 30V rail would burn up 7.8W. That's pretty nutty!


The 6H30 draws 0.9A, if your keen for rolling you’d need to step it up even further! 

post #127 of 1656

using the 6H30 in this amp is a mistake. That tube isn't used in the proper operating point. The 6GM8s sound vastly superior in this amp.

post #128 of 1656

sachu, can you elaborate “proper operating point”?

 

... the 6H30 is listed under possible alternatives on Alex’s site.

post #129 of 1656

yeah..but the voltage and current on the plates is far too low and this tube is wasted..i mean it'll make music and all but is easily bested by the 6GM8.

post #130 of 1656
Thread Starter 

Gents, the 6922 and 6H30 are listed as alternatives because they can be used and will come to a functional operating point. But they are both operating at well below normal voltages. 6922 is probably closer to a respectable operating point, but neither is optimal.

 

6GM8 is the low voltage tube that fits the amp's design.

 

post #131 of 1656

Back on that heater supply thing, a discrete 6.2V regulator is not a lot of parts.

 

6.2v regulator

R1 represent the heater load.

 

Likely needs a cap on the output though.

post #132 of 1656

Won't we need heatsinks on the devices? 

post #133 of 1656

 

Quote:
 MisterX were you thinking of just pulling from the rails?

 

 

Yes, My bad. I had assumed a reference to the the Dyanlo PSU made that clear but in hindsight it's kind of the same as interpeting a PCB layout without a schematic.

 

Here's a link---->  

http://www.diamondstar.de/DynaloPSU544_schem_1024x.jpg

 

 

Edit: LOL @ the forum spell checker

post #134 of 1656
Thread Starter 
Quote:
Originally Posted by cobaltmute View Post

Back on that heater supply thing, a discrete 6.2V regulator is not a lot of parts.

 

6.2v regulator

R1 represent the heater load.

 

Likely needs a cap on the output though.


Yes, this would work. Essentially the opamp and the pass transistor are a very simple discrete equivalent of a standard linear regulator but using more parts. It would be easier, IMHO, to use an adjustable LDO regulator -- same number of parts in the end, but less circuit complexity because you only have three terminals to worry about.

 

In either case it will need a heatsink on either the pass BJT or the linear reg and a cap on the output.

post #135 of 1656

Any thoughts about the 6n27p in this amp?

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