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Old 21st January 2009, 02:48 AM   #21
anatech is offline anatech  Canada
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Hi dsavitsk,
They will not get UL, ULC or CSA approval in that case. Avoid.
Quote:
Oh, also, I called Amveco and the primaries are would bifilar, meaning that the only insulation from your primary to your secondary is the enamel on the wire.
Are you sure it's not simply the primaries that are not bifilar wound? I can't see them winding the secondaries with the primaries. I also don't think it's possible as the secondaries probably are wound with a heavier wire.

-Chris
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Old 21st January 2009, 04:46 AM   #22
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Quote:
Originally posted by anatech
Are you sure it's not simply the primaries that are not bifilar wound? I can't see them winding the secondaries with the primaries. I also don't think it's possible as the secondaries probably are wound with a heavier wire.
It is just the primaries, but what isn't shown in the schematic is that Poinz is using the second primary in series with the secondaries for the HT supply.

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Old 21st January 2009, 05:01 AM   #23
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Listen, anatech, I am not hypothesizing.  As long as I was using the 6AQ5, I was fighting microphonics.  Testing, selecting, rejecting!  I have in the box some 50% of this type unusable in this circuit for this reason. Like trying to make diff-amps out of 5965s, I just got tired of that shirt.  I hope they turn out good for something, maybe outputs.

By all means, do as you think best.  Somebody just above advised me to find a nice lo mu triode.  I did.  The 6T4 gives me the sonics and image I got out of the original 6SN7 circuit, with four times the drive, more moderate gain, and street cred.

Unh!

Poinz
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Old 21st January 2009, 09:53 AM   #24
Stuey is offline Stuey  Australia
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Quote:
Originally posted by Poindexter
6T4s are very available.  You're just not going to find them at boutique vendors (at least not yet :^).  You got to ask your bulk vendors, those guys with warehouses full of old orphan teevee tubes.  They'll tell you, 'Heck yah, how many you want?'.  Get at least a dozen; twenty or thirty is better (if they want over a couple bucks each for quantity, tell 'em to be reasonable), so you can test up and match.  You'll have enough for the rest of your natural life for the price of a good NOS 6SN7. I got 170 of them from Jack at The Tube Center, all RCAs in clean boxes, for $2.50 each.

Aloha,

Poinz
Yep, I was thinking of vendors with TV tubes. I'll just have to find them - a bit rare over here!

Cheers Poinz; do you NEED to match tubes? I wouldn't have a clue how! (yet)

Cheers

Dumb A** Stuey
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Old 21st January 2009, 07:34 PM   #25
anatech is offline anatech  Canada
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Hi Poinz,
Hey, cool down.

You made a general statement that I supported for your tube choice. I just pointed out that you couldn't extend that to all cylindrical plate structures.

Using an output tube for a signal application may get you into the realm of microphonics. As I pointed out, these tubes are the final active devices in the chain. No more gain after these. Therefore, microphonics are not really that important a characteristic for these.

Now, what do you have a problem with? Show me one place where I disagreed with you please.

-Chris
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Old 21st January 2009, 07:53 PM   #26
anatech is offline anatech  Canada
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Hi dsavitsk,
Quote:
but what isn't shown in the schematic is that Poinz is using the second primary in series with the secondaries for the HT supply.
Ahhh, that makes sense then. Thank you.

In a case like this, the manufacturer may void warranty. The transformer is not safe to use in this configuration. I'm still worried that the isolation is way below what it should be. Not unless they hipot the primary to case normally with normal ratings. Then I can really see the rating of 500V between primary windings.

Hi Stu,
Quote:
do you NEED to match tubes?
No. Matching tubes is done when using them in push pull and / or parallel. This is done to make sure both tubes share current (in parallel) and to ensure each half of the waveform is amplified equally (in push pull).

-Chris
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Old 22nd January 2009, 02:39 AM   #27
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I ain't hot.  Sorry if you picked that up.  I was dealing to the present circumstance, not the general case.  I am a developmental guy, not a theorist.

I would in fact submit that microphonics are a problem anywhere, at least in my experience.  The 6AQ5s were in fact being used in an 'output' capacity here, although you are quite correct that there is a power amplifier following.  I was wondering if the effect was not noticed in power output duty, perhaps partially because the original circuits that used it would probably have had substantial global NFB nulling a lot of it out.  In modern purist audio, we place demands on component parts that they would not have had in mass-market audio in the late tube days.

Still, microphonics are never a positive influence on the sound, and many of those 6AQs were the most microphonic tubes I have seen.

Aloha,

Poinz
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Old 22nd January 2009, 06:32 PM   #28
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On a related note, I have found a transformer for this circuit that should work admirably and not require any, ah, creative hooking up.

It is the Antek AN-0232

25VA, 2×32V secondary, should yield more like 68V in series at our 7W draw.  Fullwave doubler, there's ~140Vdc for our delectation.

Eleven bucks, and John'll ship two or three of them for $10!

Poinz is a happy camper.

P
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Old 22nd January 2009, 08:39 PM   #29
anatech is offline anatech  Canada
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Hi Poinz,
No Problem.

The point I was making was that not only is this tube the last step in the amplifying chain, but it also has an output transformer that is a step down device. Couple that with the normal use in a single, full range speaker and any microphonics will not be noticed. In the Heathkit EA-2, these are used in push-pull. I have never heard any microphonics from here either.

So that is the normal, intended use of these tubes. They don't need to be free from microphonics as something like a normal signal tube might be. This would be similar to any other power output type tube, although these were intended for low powered economy use.

-Chris
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