Will This possibly work? - Page 2

dr._sleep · 12th August 2005, 12:46 AM

The shafts for the pots would be mounted through the top of the chassis.

The feedback circuit is voiced to control linearity at any point in it's adjustment window. There is a control for each channel that allows you to fine tune the feedback on the fly for any given recording, although the most common use is to find that magic spot where the amp becomes synergistic with a given set of speakers and then leave it there.

Perhaps a novel way to apply NFB.

dr._sleep

Trout · 12th August 2005, 01:37 AM

Quote:

Originally posted by planet10

No

That is no simplier than the RH84. And the RH84 feedback is much more local.

In our experience, the global feedback pentode wired amp (as per your map) doesn't work as well as the same amp triode wired with no feedback, and that doesn't sound as good as wired RH-style. The RH also has twice the power as the triode version.

dave

I Like This one the best, Not as many extra parts and now I can proceed without trying to find another spot to mount more pots.

I have got everything mounted already, Power supplies built, Filaments wired Ect. Now I will move on to the actual circuitry as you posted.
Thanks for all the help, I should have pictures tomorrow as I am moving at a good pace.

Its FINALLY cooled down here and we even got a little rain. My lawns in terrible condition (dead/dormant) as we have been in severe drought for 2 months now.
But it should be weeks before I will have to stop tinkering to mow haha.

Once again,, Thanks!!
Gene

Eli Duttman · 12th August 2005, 01:39 AM

There is an elegant solution to the NFB issue, but the "iron" is costly. Use O/P trafos with 20% cathode feedback tertiary windings. The "finals" will be LINEAR and the damping factor will be good. The drive voltage requirements for the "finals" is high.

Trout · 13th August 2005, 04:11 AM

Quote:

Originally posted by planet10

No

That is no simplier than the RH84. And the RH84 feedback is much more local.

In our experience, the global feedback pentode wired amp (as per your map) doesn't work as well as the same amp triode wired with no feedback, and that doesn't sound as good as wired RH-style. The RH also has twice the power as the triode version.

dave

Dave, I have this wired up, Now I have a few questions.
#1 Expected output would be 4-5W ?
#2 Input source should be from? Portable CD Player? or Line out from say my laptop or Tape player?

I have powered it up, Its Hum Free and nothings smoking which is always a good sign, It appears to be just about right, I did put in my poorest condition tubes as to no risk any of my NOS stuff.
Gene

planet10 · 13th August 2005, 04:28 AM

Quote:

Originally posted by Trout
#1 Expected output would be 4-5W ?

Yes

Quote:

#2 Input source should be from Line out from say my laptop or Tape player?

Yes.

dave

amperex · 13th August 2005, 11:13 PM

Find two old vintage Hammond quad 6V6 amps on eBay with the 6J5 tube, not the newer versions. The PP audio transformer can be used for SE up to 8-watts without core saturation issues and it has that important cathode winding. These trannys have a following at AA.

Use the power transformers & two chokes for a killer LCLC power supply. Change that stock 5U4 for a Sylvania 5R4GYB smooth black plate to get the voltage down to a reasonble level. Radio Daze in NY has the somewhat rare NOS 5R4 for $13 each.

amperex · 13th August 2005, 11:21 PM

the regulated screen is a great idea. I would use a gas tube regulator shunted with a .1 uF cap to remoce braodband noise and feed that to a 10HY or so 500 ohm choke and use a 20uF poly cap to bypass the screen.

Trout · 15th August 2005, 02:15 AM

OK,
I Missed Something or at least maybe my parts are. At best I am getting about 1/2w maybe less output.

Very Very clean sound, just not enough of it. I havent had a chance to run the voltmeter around it since its been built, So as soon as time allows, I will get that info.

The OPTs are magnavox salvaged originally EL84 SE, The PT was from same unit.

Gene

Trout · 15th August 2005, 02:38 PM

Update,

Sounds Great! Found the output issue was actually a source issue.

I do get a very very low level hum, Not even noticable even at very low settings while cd plays. I suspect easily cureable .

Very Impressive sound quality though far better than the donor the transformers were extracted from.
Its A Keeper!!

Gene

planet10 · 15th August 2005, 07:22 PM

Quote:

Originally posted by Trout
Its A Keeper!!

pictures?

12th August 2005, 01:39 AM	#13
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	There is an elegant solution to the NFB issue, but the "iron" is costly. Use O/P trafos with 20% cathode feedback tertiary windings. The "finals" will be LINEAR and the damping factor will be good. The drive voltage requirements for the "finals" is high. __________________ Eli D.

13th August 2005, 11:13 PM	#16
amperex diyAudio Member Join Date: Feb 2005 Location: MI	Audio tranny solution as mentioned...... Find two old vintage Hammond quad 6V6 amps on eBay with the 6J5 tube, not the newer versions. The PP audio transformer can be used for SE up to 8-watts without core saturation issues and it has that important cathode winding. These trannys have a following at AA. Use the power transformers & two chokes for a killer LCLC power supply. Change that stock 5U4 for a Sylvania 5R4GYB smooth black plate to get the voltage down to a reasonble level. Radio Daze in NY has the somewhat rare NOS 5R4 for $13 each.

13th August 2005, 11:21 PM	#17
amperex diyAudio Member Join Date: Feb 2005 Location: MI	I forgot...... the regulated screen is a great idea. I would use a gas tube regulator shunted with a .1 uF cap to remoce braodband noise and feed that to a 10HY or so 500 ohm choke and use a 20uF poly cap to bypass the screen.

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12th August 2005, 12:46 AM	#11
dr._sleep diyAudio Member Join Date: Jul 2005 Location: southern us	The shafts for the pots would be mounted through the top of the chassis. The feedback circuit is voiced to control linearity at any point in it's adjustment window. There is a control for each channel that allows you to fine tune the feedback on the fly for any given recording, although the most common use is to find that magic spot where the amp becomes synergistic with a given set of speakers and then leave it there. Perhaps a novel way to apply NFB. dr._sleep

15th August 2005, 02:15 AM	#18
Trout diyAudio Member Join Date: Nov 2004 Location: Midwest Madman	OK, I Missed Something or at least maybe my parts are. At best I am getting about 1/2w maybe less output. Very Very clean sound, just not enough of it. I havent had a chance to run the voltmeter around it since its been built, So as soon as time allows, I will get that info. The OPTs are magnavox salvaged originally EL84 SE, The PT was from same unit. Gene

15th August 2005, 02:38 PM	#19
Trout diyAudio Member Join Date: Nov 2004 Location: Midwest Madman	Update, Sounds Great! Found the output issue was actually a source issue. I do get a very very low level hum, Not even noticable even at very low settings while cd plays. I suspect easily cureable . Very Impressive sound quality though far better than the donor the transformers were extracted from. Its A Keeper!! Gene

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