[AffeX]

Quote:

Originally Posted by AffeX /img/forum/go_quote.gif Thank you for noticing this Ferrari. I also wondered if the 12V would be too much, as you earlier suggested 2x9V. So from your post I read this: 1. I can run both s22 and heater psu from same torroid without compromising sound quality - otherwise I'm sure you would have said so 2. As 12V AC rectified gives 16-17V DC, then 6V AC rectified might give me 7-8V DC. So why don't I just use the 2x6V secondary as they are? I was afraid, 2x6V AC wouldn't be enough to give me 2x6,3V DC as I believe the rule of thumb says, AC supply larger than DC needed.

Would be very big help for me if someone had a final conclusion on this, so I can get on with my amp, one way or the other. Anyone? Ferrari, maybe?

 

[digger945]

Quote:

Originally Posted by AffeX /img/forum/go_quote.gif Would be very big help for me if someone had a final conclusion on this, so I can get on with my amp, one way or the other. Anyone? Ferrari, maybe?

It depends on what transformer you're going to use and what voltage you decide on.
Do you already have a transformer, and if so what voltage and how many primary/secondaries(or a part #)

 

[AffeX]

ok digger945, I'll post a resume, saving you the scrolling

Quote:

Originally Posted by AffeX /img/forum/go_quote.gif I'm planning this NT-LN 250.30-6 (250VA/2x30v/2x6V) shielded audio torroid from THEL for my balanced EHHA build. My idea is to use 2x30V as is for the s22 psu, and from same torroid connect the 2x6V in series to provide 12V for this power regulator a dual LT1063 power regulator, suggested by Ferrari for powering tube heaters. I will connect the two sides of this power regulator in parallel to the 12V, and set output to 6,3V. Any comments on this would be most welcome. In particular I'd like to know, if it affects sound quality to pull both amp power and heater power from same torroid?

Quote:

Originally Posted by Ferrari /img/forum/go_quote.gif It's not a very good idea to use 12V secondary voltage to make 6.3V DC. The heatsink will get unnecessary hot, even without load. Remember that the voltage after the rectifier bridge is ~16V - 17V.

Quote:

Originally Posted by AffeX /img/forum/go_quote.gif Thank you for noticing this Ferrari. I also wondered if the 12V would be too much, as you earlier suggested 2x9V. So from your post I read this: 1. I can run both s22 and heater psu from same torroid without compromising sound quality - otherwise I'm sure you would have said so 2. As 12V AC rectified gives 16-17V DC, then 6V AC rectified might give me 7-8V DC. So why don't I just use the 2x6V secondary as they are? I was afraid, 2x6V AC wouldn't be enough to give me 2x6,3V DC as I believe the rule of thumb says, AC supply larger than DC needed.

 

[digger945]

I have already looked back and read all or your posts.
Give me a minute to translate the specs for your NT-LN 250.30-6.
It says 250VA and 3.5A.
Let me see what I can figure out.
You are probably going to get quicker answers from Ferrari though.

 

[digger945]

No indication as to how the current is divided between the 30v and 6v secondaries.
Perhaps you would be better off looking at a transformer that is rated at 6.3v with a load on it.
The one you are looking at, the NT-LN 250.30-6 has a +7% rating with no load(ohne Last/Leerlauf?), so I assume the given voltages of 30v and 6v are the loaded specs.

Not only does Duc speak the language, he probably has the correct part for you and one that is close to you as well.

Let me look back to his EHHA built and see if I can tell what transformer he used.

EDIT I must say that 250VA is kind of overkill for this amp, even in balanced fashion. I run 2 amp boards on one 80VA transformer no problem. You can figure a safe estimate of ~7VA per tube to cover all possible tubes including the 6H30.

 

[dBel84]

I had a quick look at the THEL site (my German is dodgy at best) , it looks like you can run each set of windings at current ratings that should not exceed 50% of the specified voltage. I read the 7% variation as loaded - unloaded so the output should be pretty close to spec'd loaded or unloaded.

The LT1083 should be able to regulate ( it has a min 6.5V input requirement ) and current draw will be a fraction of what is needed. I have to agree that 250VA is overkill but if you have already bought, so be it.

..dB

 

[Ferrari]

I have to agree that the NT-LN 250.30-6 transformer from Thel is a bit overkill for the EHHA, especially when using it for a headphone amp. Output voltage at no load (Leerlauf spannung) of this type transformer is +7% higher than the specs, thus 32.1V and 6.42V secondary voltage respectively.

As digger945 and dBel84 already said, if you already bought this transformer, just use it.

Personally I have used an 80VA / 2x9V toroidal (Eur 10 from local discount store) for the heater circuit for my balanced EHHA.

 

[AffeX]

I really appreciate your comments, you are very helpful digger945 and dBel84!
I have not bought the transformer yet. Looked at this transformer because it's supposed to be 'audio grade', shielded etc
I know 160VA would be more than enough for the amp, but they have no 160VA/30V versions of this quality. The s22 kits at GlassJar are limited to 100VA max, and that seemed too little. So I need a different transformer anyway, and figured I could save some space (and money) by using only one transformer for both heater and amps.
I want it all in one enclosure, so the shielded transformer to avoid noise/humming seemed like a good idea.
You are both right, the 30V is min. loaded, and +7% can be expected unloaded, but what is said about the 50% is, that if eg only one of the 30V outputs is used, it can deliver as much as 3.5 + 50% = 5.25A.
I figure that I need 1-1.5A for tube heating 4x6GM8 and about the same for 4xEHHA.
I'm sure 250VA is enough for both amp and heaters.
My only worries, except spending money on a total overkill, is that 2x6V won't be enough for the LT1083 power regulator, even though the specs on the Ebay site, says 5-25V AC
I might just have to try it out or search for similar housed transformers with two secondaries.

Edit: Just noticed Ferrari already posted - thanx Ferrari. Following your suggestion though, I would need two transformers each about 8-10 cm wide.

 

[tonearm]

You might want to go the dual transformer route. Separate one for the heaters so you can fire them up first using a delay circuit.

Apex Jr has 160VA Avel Lindberg transformer (with dual primaries for 230volt operation) that are suitable for the HV section of the EHHA for about 22$ a piece. He could easily ship it to Europe via USPS small flat rate box for another 12.50$.

 

[Ferrari]

Quote:

Originally Posted by AffeX /img/forum/go_quote.gif ... My only worries, except spending money on a total overkill, is that 2x6V won't be enough for the LT1083 power regulator, even though the specs on the Ebay site, says 5-25V AC ...

... to get 3V ... 20V DC out.

 

[AffeX]

Quote:

Originally Posted by tonearm /img/forum/go_quote.gif You might want to go the dual transformer route. Separate one for the heaters so you can fire them up first using a delay circuit. Apex Jr has 160VA Avel Lindberg transformer (with dual primaries for 230volt operation) that are suitable for the HV section of the EHHA for about 22$ a piece. He could easily ship it to Europe via USPS small flat rate box for another 12.50$.

So $35 total but to get it through danish customs would probably add about 50% and I would need dual transformers as you mention. The THEL 250V would easily be a better option, as it's cheaper all in all, shielded, better quality than Avel Lindberg I believe, and I would only need space for one.
About the delay circuit, I thought of just switching on the transformer with one switch allowing 6V to heat the tubes but delaying the 30V output for a minute using this device also powered from the 2x6V output.

 

[AffeX]

Quote:

Originally Posted by Ferrari /img/forum/go_quote.gif ... to get 3V ... 20V DC out.

Yeah, I see the hinted voltage drop. So 6V AC may only give me 4.5-5V DC and my plan suck. 6V AC is too low and using the 6V output in series to get 12V is too much for the LT1083. I guess it was too 'perfect' to be a true success.

But thanx to all of you for working this through with me.

 

[digger945]

I have used heater voltages from 5.8v to 7v for 6.3v tubes and I really don't see much difference. No difference at all in sound to me.
I will be looking for something that I think you could use. Do you ever shop ebay? Have you decided if you want to use a seperate transformer and off the shelf PS for the heaters? This info will help when looking for stuff online(if you haven't already purchased the PS unit).

 

[ujamerstand]

Why not just breadboard a regulator? You can add a voltage follower using something like MJE3055 to a LM7812 to provide all the current you'll need. Its a cheap solution too. Instead of spending 30 bucks a regulator, you can spend around 10 bucks for 2 12V regulators, and spend that extra 50 bucks on something else.

 

[AffeX]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif I have used heater voltages from 5.8v to 7v for 6.3v tubes and I really don't see much difference. No difference at all in sound to me. I will be looking for something that I think you could use. Do you ever shop ebay? Have you decided if you want to use a seperate transformer and off the shelf PS for the heaters? This info will help when looking for stuff online(if you haven't already purchased the PS unit).

I already paid and ordered, the LT1083 based dual psu from Ebay, that Ferrari suggested. I believe it's a good circuit, and it can provide the current, should I ever roll the tubes and try 6H30. Best alternative would probably be a couple of Avel L. transformers, 160VA/2x30V for the s22 and 80VA/2x9V for the heater psu. I know that's straight forward, but I'd loose the other benefits of the THEL trafo; the space saving and the shielding.

I may just go the dual transformer route, as tonearm suggested - or use the 6VAC for heating as is. But I know I would hate doing that because of the risk of AC noise.