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 Post subject: Re: 6EM7 power amp
PostPosted: 25 Nov 2011, 23:51 
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Joined: 19 Nov 2011, 19:48
Posts: 7
Suncalc wrote:
All the Hammond universal SE transformers (p/n 125xSE) are limited to 100Hz-15kHz response.


Within -1 dB.
That's a pretty tight standard. Not sure I'd consider that "limited to," exactly. Certainly there are transformers with better specs, that much is true.

Remember this, though: with a typical first-order -6dB/octave slope, -1dB is found one octave beyond the -3dB point. In other words, assuming a first-order high-pass filter response at the lower end and a first-order low-pass filter response at the upper end, the -3dB bandwidth equivalent to the spec quoted above would be 50 Hz to 30kHz, -3dB.

I'm not saying that that's so amazingly great, mind you, just that you may not always be comparing apples to apples depending on how other manufacturers present their specs. If someone says "Bandwidth is 20 Hz to 70 KHz," that's meaningless without a dB element in the given spec. If it's NOT given, the assumption is that it's -3dB, but that's an engineering department assumption - it's not always observed in the marketing department, and I suppose it could even be worse than -3dB if they thought no one was really looking.

EDIT: Looks like at least one testing experiment supports the Edcor recommendation: http://www.tubelab.com/BudgetOPT.htm
Pretty impressive!


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 Post subject: Re: 6EM7 power amp
PostPosted: 26 Nov 2011, 07:29 
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Joined: 06 Jun 2008, 18:23
Posts: 5301
Location: Australia
Matt: Yes I decided earlier today that I would stay with the Edcors. For the mono-blocks I may be spanning the build over three small cast Al chassis. One will have 1 X power filter, 2 X power trannnies, 2 X rec tubes and 2 X small chokes and 2 X filter networks.

The other two chassis will have OPTS and 6EM7. Just early thoughts.

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 Post subject: Re: 6EM7 power amp
PostPosted: 26 Nov 2011, 12:16 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
I'll also recommend the Edcors over the Hammond universal OPTs. Another problem with Hammond is that they have been moving production from North America to Asia. Take a look at this thread about Hammond transformers made in China.

Cheers

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 Post subject: Re: 6EM7 power amp
PostPosted: 28 Nov 2011, 16:01 
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Joined: 14 Feb 2010, 13:13
Posts: 711
Location: Lisbon, Portugal
Oh dear...

Asia is about to swallow the world!

Hammond, such a prestigeous brand!

Cheers,
Miguel


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 Post subject: Re: 6EM7 power amp
PostPosted: 28 Nov 2011, 16:58 
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Location: Australia
In the electronics store I work in 95% of what we sell is made in China. We have a huge failer rate across all items sold. Some are DOA. A small amount of items from Korea and Taiwan, they are better made and rarely fail.

I hope this does not spell the end of Hammond. Though expensive and possibly not the very best OPTs etc. they are of good and reliable standard.

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 Post subject: Re: 6EM7 power amp
PostPosted: 06 Dec 2011, 07:06 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
I now have the main parts to build the PS chassis for Paris Trios (three chassis form of Paris). Here are a few outlays. Yes I know the power trannies are upside down. I like the layout where the trannies are off-set with the tubes in a line (layout_I). The Hammond 5H chokes fit easily inside the chassis. Two XLR plugs on the back will feed 12VDC and 250VDC to each amp chassis which carries an OPT and 6EM7.
Attachment:
Layout_I.jpg
Attachment:
Layout_II.jpg
Attachment:
Layout_III.jpg


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 Post subject: Re: 6EM7 power amp
PostPosted: 06 Dec 2011, 16:23 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
tubegeek wrote:
Suncalc wrote:
All the Hammond universal SE transformers (p/n 125xSE) are limited to 100Hz-15kHz response.


Within -1 dB.
That's a pretty tight standard. Not sure I'd consider that "limited to," exactly. Certainly there are transformers with better specs, that much is true.

Remember this, though: with a typical first-order -6dB/octave slope, -1dB is found one octave beyond the -3dB point. In other words, assuming a first-order high-pass filter response at the lower end and a first-order low-pass filter response at the upper end, the -3dB bandwidth equivalent to the spec quoted above would be 50 Hz to 30kHz, -3dB.

I'm not saying that that's so amazingly great, mind you, just that you may not always be comparing apples to apples depending on how other manufacturers present their specs. If someone says "Bandwidth is 20 Hz to 70 KHz," that's meaningless without a dB element in the given spec. If it's NOT given, the assumption is that it's -3dB, but that's an engineering department assumption - it's not always observed in the marketing department, and I suppose it could even be worse than -3dB if they thought no one was really looking.

EDIT: Looks like at least one testing experiment supports the Edcor recommendation: http://www.tubelab.com/BudgetOPT.htm
Pretty impressive!

Just had a chance to look at the link in this thread (thanks tubegeek). It is very informative and though it is one man's opinion based on his testing and test methods it is a darn good guide and makes you (me) think about OPTs a little harder. When building tube amps the OPT is very important and must be given serious consideration. I think this site drives that home. All should take a look.

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 Post subject: Re: 6EM7 power amp
PostPosted: 06 Dec 2011, 19:36 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hey Mark,
Be sure to look into the voltage ratings of the XLR connectors. They may not be rated for 250VDC.

What sort of connectors are others using for high voltage? :?:

I like layout three. The tubes seem protected by the transformers. Try maximize distance so you don't get excessive heat build-up.

Cheers

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 Post subject: Re: 6EM7 power amp
PostPosted: 06 Dec 2011, 22:36 
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Joined: 23 Jul 2010, 17:03
Posts: 54
Location: North Carolina,USA
I always use 8 pin octal sockets and plugs.Im not shure of there ratings but I've seen old Organ tube amps use them and I think the original Dynaco's used them.It gives you 8 pins to work with so the way I do it is Heater+on pin #1,HT- on pin #4,HT+ on pin #6,and heater- on pin #8.This gives you an empty space between active pins so you could double up if you had any dought.This is also my method for 6 volt heat only.If I ever get around to building anthing that requires 12V heat i would use different pins.Im not shure if there is a standard for this or where I got it from but I always do it the same way and have had no problems...David

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 Post subject: Re: 6EM7 power amp
PostPosted: 07 Dec 2011, 13:24 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Blackriver - an 8 pin tubes socket sounds great. Do you have a link for plugs that fit a standard socket?

Cheers

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