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Last night I measured My lowest Hum level ...

99.10.84.237
Posted on November 7, 2020 at 19:50:34
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003





Yes my All DHT, All AC Heated 26-26 DC coupled 45 Stereo SET amp,
A month ago my Fluke 87 meter read 0.38mvAC at left side speaker
post and right side read 0.27mvAC .

After doing a little tweaking . My leftside reads 0.23mvAC and the
right side now reads 0.16mvAC.

The hum from this amp is now barely audible, This is all thru
Altec GPA 604 woofer in a MLTL cabinets and a seperate JBLdriver and
horn , with modified Altec Passive crossover .

This is all DHT on the cheap !

Have fun
Willie

 

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    ...
Under load or open termingals?, posted on November 8, 2020 at 06:06:28
Ivan303
Audiophile

Posts: 48887
Location: Cadiere d'azur FRANCE - Santa Fe, NM
Joined: February 26, 2001

also with open input or loaded input?


First they came for the dumb-asses
And I did not speak out
Because I was not a dumb-ass

 

RE: Under load or open termingals? under load ...., posted on November 8, 2020 at 10:35:59
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

not open ..

Willie

 

RE: Last night I measured My lowest Hum level ..., posted on November 8, 2020 at 12:03:15
91derlust
Audiophile

Posts: 1101
Joined: December 25, 2014
 That is some nice low hum for AC filaments on DHTs, 3 stages no less!

Curious to know how you achieved that Willie.

Cheers.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

 

RE: outstanding work ..., posted on November 9, 2020 at 14:21:57
deathtube 667
 MLP for the win !!!

Way to go, sir.

DT 667

 

RE: Last night I measured My lowest Hum level ..., posted on November 9, 2020 at 16:56:26
Stuben
Audiophile

Posts: 669
Location: Guber Ohio
Joined: December 30, 2005
 Lipo Batteries? :)

Good job. How many turns are on your pots?

Stuben

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 9, 2020 at 17:11:25
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003
 As we all know those 26's are pretty power hungry little tubes.
I just could not find a good SS heater to meet my demands,cause To have enough gain for my DHT final stage, one
26 wouldn't cut it.

So (2) 26's coupled together would give enough gain for the final stage. Plus I could tie the filament heaters
together for some good ole Humbucking effect .

I started with a Hammond 2.5volt AC 6.0amp power
transformer then (2) 10watt small value resistors off each
leg of the tranny then a nice inline AC line filter.

Of course you have to find the right value resistors to
bring your voltage down to 1.50AC ...

Then it's just a matter of finding a good location to mount
each one in a spot in your amp for the lowest AC Hum.

I've been using this setup for over a year now and I love it.
A simple solution for my complex problem..

Have fun!
Willie

 

RE: Last night I measured My lowest Hum level ..., posted on November 9, 2020 at 17:14:25
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

IIRC.... single turn

Willie

 

RE: Last night I measured My lowest Hum level ..., posted on November 9, 2020 at 19:50:21
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003
100 Ohm !

 

so it is time to take the next challenge--mesh 26..., posted on November 10, 2020 at 07:25:55
bouncy ball
Audiophile

Posts: 1221
Location: British Columbia
Joined: July 26, 2003
 OK, just kidding.

That is one hack of the job to get the hum level down.

I bet it is one sweet sounding amp. I also much prefer DC couple.

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 10, 2020 at 12:56:13
Tre'
Industry Professional

Posts: 17297
Location: So. Cal.
Joined: February 9, 2002
 "So (2) 26's coupled together would give enough gain for the final stage. Plus I could tie the filament heaters
together for some good ole Humbucking effect."

The input stage's cathode is tied to the drive stage's cathode?

are these tubes fix biased or cathode biased?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 10, 2020 at 14:11:34
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003

The (2) 26's are Cathode biased..

Willie

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 10, 2020 at 15:37:45
Tre'
Industry Professional

Posts: 17297
Location: So. Cal.
Joined: February 9, 2002
 If the filaments are tied together then the cathodes of those two tubes are tied together and both tubes have the same cathode bias voltage.

Is the cathode resistor bypassed with a capacitor?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 10, 2020 at 19:20:28
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003
Yup !


Willie

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 11, 2020 at 06:36:07
Tre'
Industry Professional

Posts: 17297
Location: So. Cal.
Joined: February 9, 2002
 Cool. Interesting.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: outstanding work ... No ...., posted on November 11, 2020 at 18:51:49
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003
...... Thank You I mean Yes Thank you !


Willie

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 17, 2020 at 05:24:29
RPMac
Audiophile

Posts: 377
Location: So. Mississippi
Joined: January 3, 2005
 Interested in the Humbucking effect. Would like to see your schematic, but understand if you don't want to post it here.

 

Thanks for the info! nt., posted on November 19, 2020 at 02:59:28
91derlust
Audiophile

Posts: 1101
Joined: December 25, 2014
 .
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 22, 2020 at 20:02:58
drummerwill
Audiophile

Posts: 965
Location: St Louis Mo.
Joined: January 7, 2003
 Check out the archives , I posted the entire Schematics
awhile back.

If you can't find it, I'll dig them out and repost them again
soon ! I don't mind Sharing.

Willie

 

Found it, thanks. Nt, posted on November 23, 2020 at 04:18:11
RPMac
Audiophile

Posts: 377
Location: So. Mississippi
Joined: January 3, 2005
 Nt

 

RE: Last night I measured My lowest Hum level ... Wasn't that hard ,,,,, posted on November 23, 2020 at 04:35:54
RPMac
Audiophile

Posts: 377
Location: So. Mississippi
Joined: January 3, 2005
 Ver. 6.0 your latest?

 

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