Hey Planet_10 (and others)

gingertube · 21st March 2005, 10:44 PM

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

Yvesm · 22nd March 2005, 01:10 PM

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 :

Tekko · 22nd March 2005, 01:34 PM

Nice amp Yves

You wound the transformers and made the end bells yourself ?

Yvesm · 22nd March 2005, 05:55 PM

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 !

Tekko · 22nd March 2005, 06:39 PM

Hum ok.

SY · 23rd March 2005, 01:11 PM

Gingertube's CS drawing:

planet10 · 23rd March 2005, 07:01 PM

Cool.

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

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

Tekko · 23rd March 2005, 07:47 PM

That thing looks like it will induce loads of crosstalk btween channels.

planet10 · 23rd March 2005, 08:07 PM

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.

dave

grataku · 24th March 2005, 04:09 AM

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.

21st March 2005, 10:44 PM	#1
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	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

23rd March 2005, 07:01 PM	#7
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	Cool. I salvaged iron for mine last week (and put up a 2nd set on eBay) 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 __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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22nd March 2005, 01:34 PM	#3
Tekko diyAudio Member Join Date: Jan 2005	Nice amp Yves You wound the transformers and made the end bells yourself ?

22nd March 2005, 06:39 PM	#5
Tekko diyAudio Member Join Date: Jan 2005	Hum ok.

23rd March 2005, 07:47 PM	#8
Tekko diyAudio Member Join Date: Jan 2005	That thing looks like it will induce loads of crosstalk btween channels.

24th March 2005, 04:09 AM	#10
grataku diyAudio Member Join Date: Dec 2000 Location: -	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.