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Old 21st March 2005, 10:44 PM   #1
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Default Hey Planet_10 (and others)

When this was posted I recall Planet_10 showing interest. It also caught my eye as I had suitable trannies lying about. Thought it would make a nice little bedroom or workshop amp.

http://www.diyaudio.com/forums/showt...739#post552739

Knocked it up last weekend with mods as below:
1) My power supply was a bit high so I cathode biased the output - individual 390R cathode resistors bypassed by 470uF/50V Blackgate standards.
2) 20% Ultralinear Taps connected via 150R screen resistors
3) 1K balance pot between the input triodes cathodes with wiper fed by a 1.2mA ring of 2 BC547B current source
4) No global feedback (Zout = 3.2 Ohms)
5) Did'nt have the separate 13V winding so just rectified the heater winding to give approx -7V for the current source supply.

Note: I could have (but did'nt) voltage doubled the heater supply and then used fixed bias on the outputs (about -11V required with V+ = 310V for 28mA idle) using NOS Philips 6GW8 (ECL86).

Sound is quite lovely. <10Hz to 35kHz -3dB points at 1Watt which given the quality of the trannies I had was amazing. (Ex an old Heatkit, originally driven by 6BM8s with 250V rails). The shunt feedback is doing a great job. Output a clipping 10.5 Watts.

A good "newbies" project.

Cheers,
Ian
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Old 22nd March 2005, 01:10 PM   #2
Yvesm is offline Yvesm  France
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Default Re: Hey Planet_10 (and others)

Quote:
Originally posted by gingertube
When this was posted I recall Planet_10 showing interest. It also caught my eye as I had suitable trannies lying about. Thought it would make a nice little bedroom or workshop amp.
. . .
3) 1K balance pot between the input triodes cathodes with wiper fed by a 1.2mA ring of 2 BC547B current source

Could you detail how you build the current source ?
Quote:
4) No global feedback (Zout = 3.2 Ohms)
5) Did'nt have the separate 13V winding so just rectified the heater winding to give approx -7V for the current source supply.

Note: I could have (but did'nt) voltage doubled the heater supply and then used fixed bias on the outputs (about -11V required with V+ = 310V for 28mA idle) using NOS Philips 6GW8 (ECL86).

Sound is quite lovely. <10Hz to 35kHz -3dB points at 1Watt which given the quality of the trannies I had was amazing. (Ex an old Heatkit, originally driven by 6BM8s with 250V rails). The shunt feedback is doing a great job. Output a clipping 10.5 Watts.

A good "newbies" project.

Cheers,
Ian
I'm glad you like it
Mine looks like that :
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Old 22nd March 2005, 01:34 PM   #3
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Nice amp Yves You wound the transformers and made the end bells yourself ?
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Old 22nd March 2005, 05:55 PM   #4
Yvesm is offline Yvesm  France
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Hi Tekko !

Quote:
Originally posted by Tekko
Nice amp Yves You wound the transformers and made the end bells yourself ?
Nope, I just wound, I'm a poor metal worker but it happens that i'd the opportunity to have the chassis, drilled and bent as well as those bells. Just that size !
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Old 22nd March 2005, 06:39 PM   #5
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Hum ok.
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Old 23rd March 2005, 01:11 PM   #6
SY is offline SY  United States
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Gingertube's CS drawing:
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Old 23rd March 2005, 07:01 PM   #7
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Cool.

I salvaged iron for mine last week (and put up a 2nd set on eBay)

Click the image to open in full size.

Probably going to go with Russian "6BM8s" -- thet should just be coming out of cryo now,

I was going to order up some IXYS CCS chips & try those (1st on the front-end and then maybe on the output stage)

dave
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Old 23rd March 2005, 07:47 PM   #8
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That thing looks like it will induce loads of crosstalk btween channels.
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Old 23rd March 2005, 08:07 PM   #9
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Quote:
Originally posted by Tekko
That thing looks like it will induce loads of crosstalk btween channels.
Never thot of that, in a set of PP OPTs how serious would this actually be?

All the Nordmende OPTs come like that... it is convienient for mounting... i'm also going to be using paired sets to do some SE parafeed amps. They are very well made.

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Old 24th March 2005, 04:09 AM   #10
grataku is offline grataku  United States
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Not very serious Dave.
1) As you say DC flux is null in a PP and the AC is not that great either.
2) Distance between the cores is not that different than what Yves 's got.
3) Engineers at nordmende know a thing or two about electronics.
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