Using a choke at the place of R21

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Using a choke at the place of R21

Postby kku » Tue Mar 05, 2013 11:04 pm

Just finished the 1626 version and it is smashing. If not using any DAC or pre, it does have a sweet sound signature. However, it hums louder than my GSG. My GSG is using 2 chokes. The GSG is super quiet, being the quietest amp I own, more quiet than a commercial push pull amp with toroid type PT.

I want to see if adding another choke to replace R21(=100 ohm) might lower the hum a bit or not. I have a Triad C 14x(150 ohm) choke sitting here. Would it be ok to do so?

http://www.mouser.com/ds/2/410/-14X-63818.pdf
User avatar
kku
 
Posts: 64
Joined: Mon Jul 25, 2011 5:30 pm

Re: Using a choke at the place of R21

Postby Shannon Parks » Wed Mar 06, 2013 6:35 am

Is it a stock Darling Clementine otherwise? That choke would be OK, and even the standard 1H would help a lot if the problem isn't elsewhere, say from the filament on the 12SL7.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: Using a choke at the place of R21

Postby EWBrown » Wed Mar 06, 2013 10:29 am

I've built several of these, with 1626, 12V6GTs and 6L6GCs, with no hum problems.

Make sure that the PC board has a grounding connection to the chassis, if this is missing, it can, and most likely will, hum.
The PC board mounting holes are not connected to the board's signal and power ground.

I've used the dual choke approach, it works very nicely!

HTH

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Re: Using a choke at the place of R21

Postby kku » Wed Mar 06, 2013 4:13 pm

Amp is 100% stock. I've rotated 3 different 12SL7s and 2 different pairs of 1626s, so hopefully tubes are not the cause(unless I have all 3 bad 12SL7s). The hum is not annoyingly bad, it's just not as quiet as my GSG. While soldering one of the 47uf cap, I remember it took longer than others and I'm sure the temperature got too hot. Perhaps it's that cap that is causing the hum. Let's see how 2nd choke helps.

Another note: 100% stock amp. Before adding another choke, I was just checking the voltages on amp and they are bit off compared to the voltage chart. NO input signal and all tubes in sockets. The AC voltage on 269EX red wires is 211VAC(200VAC on chart). Red wire on GXSE15 reads 259VDC and blue wire 255VDC(chart values are about 15VDC lower). Filament readings are 14.3VDC. Is this OK or I should get another 269EX.
User avatar
kku
 
Posts: 64
Joined: Mon Jul 25, 2011 5:30 pm

Re: Using a choke at the place of R21

Postby EWBrown » Wed Mar 06, 2013 8:37 pm

That looks aboutright, the 269EX was designed with a 115VAC primary, so with today's AC line voltages running about 120-123VAC, the secondary voltages will run a tad high, not to worry...


The 47 uF cap might have been overheated, but unless it was really "barbecued" it should not have gone bad from soldering.

Check the PC board to chassis grounding, and depending on the OPTs, there is a slight chance that they might be picking up the stray magnetic field from the power tranny, a simple test for this isto take out the 1626s and listen for a low 60Hz hum is present. The GXSE15s have end bells andalso should be adequately magnetically shielded.

I ran into this, several years ago, while pre-testing a design with a Hammond 261M series open-frame power trannie and two 125ESEs. The PT's magnetic field, in this case, radiated out to about 18 inches. The 269EX has end bells, and is properly (magnetically) shielded, so this should not be the case, under 99% of normal conditions.

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Re: Using a choke at the place of R21

Postby kku » Thu Mar 07, 2013 2:00 pm

PCB is grounded to chassis. The OTs are on other side of chassis so they are 10 inch away from the PT, so that no chance of interaction between PT-OTs. I built GSG the same way. It's not too bad, to hear hum on 1626 amp, I have to keep my ear closer than a foot from my 98 db speakers. But with GSG it is almost non-existent.

I'll take out 1626s and try your test anyway. And also still need to try adding another 150 ohm choke whenever I get chance.
User avatar
kku
 
Posts: 64
Joined: Mon Jul 25, 2011 5:30 pm

Re: Using a choke at the place of R21

Postby kku » Fri Mar 08, 2013 12:24 pm

Added Triad C-14x choke(150 ohm). The voltages at red and blue wires of OTs haven't dropped with the higher resistance of 150 ohm. The hum levels are as low as my GSG, undetectable on my 98 db speakers. Just a tiny amount of hum through 32 ohm headphones.

This is an excellent sounding amp. Over the time I plan to upgrade coupling caps, and all power caps to something like 400VDC speaker caps or just F&T.

14.3V on filaments = shorter life for tubes or not?
User avatar
kku
 
Posts: 64
Joined: Mon Jul 25, 2011 5:30 pm

Re: Using a choke at the place of R21

Postby Thermion » Sat Mar 09, 2013 7:58 am

kku asked if "14.3V on filaments = shorter life for tubes or not?"

IMHO the increased filament voltage will indeed shorten the life of the tubes. I am very sensitive to this in my own amplifiers. I typically run my vintage dynaco amplifiers through a variac to keep it under control. In my diytube amps, I use a dropping resistor in series with the filament winding.

JT
Thermion
 
Posts: 181
Joined: Mon Jul 07, 2003 6:04 pm
Location: Fisher, IL

Re: Using a choke at the place of R21

Postby Shannon Parks » Thu Mar 14, 2013 5:53 am

kku wrote:14.3V on filaments = shorter life for tubes or not?


Total heater current is 0.65A. Excess voltage is 14.3V - 12.6V = 1.7V.
So with V/I=R, we have:
1.7V / 0.65A = 2.6 ohms
And the power dissipation, P=IV, will be:
1.7V * 0.65A = 1.1W
So replace the jumper at R26 with a 2 or 3 ohm, 2W (or higher) resistor. You can also parallel two 5 ohm 1W (or higher) resistors.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: Using a choke at the place of R21

Postby kku » Mon Mar 25, 2013 2:31 pm

Thanks Shannon! Got a 3 ohm Mills resistor on its way. I always wondered why Tom McNally's amps had resistor in series with filaments. Now I know why. (lol)

Is there a way of slightly lowering the B+ by lowering value of caps in power supply?
User avatar
kku
 
Posts: 64
Joined: Mon Jul 25, 2011 5:30 pm


Return to clementine

Who is online

Users browsing this forum: No registered users and 9 guests