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Old 3rd June 2009, 05:51 PM   #11
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Quote:
Originally posted by rknize


560 ohm should be a good middle-ground. I run my EL34s like this with 460V B+. The 6L6 I run a little hotter at 470 ohms. At least two builds recently have been able to get their 6L6s to glow with the 560 ohm. If I remember correctly, they were both Chinese 6L6s, not 6L6GCs. My JJ 6L6GCs don't start to glow until I crank them with about 340 ohms on the cathodes.

I just popped my EL34's back in last night, and I was kind of surprised when I couldn't turn the volume up past 1/2 way with out the speakers breaking up. I'm probably going to try and put in a selectable resistor setup.

I have Chinese 6L6GC's that glow - visible red plates with the lights on... they were really cheap so I'm not super worried, but thats not quite right either.
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Old 3rd June 2009, 06:08 PM   #12
rknize is offline rknize  United States
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Hmm...sounds like the tube was up against one of the rails. Did you have them in UL mode? Most of my output tubes will break-up at high volume in UL mode. This is compounded when there is no CFB. In triode, they are pretty clean up to about 85% where they start going into cutout (blue glow in the tube flashes off). Pushed a little harder is when the distortion becomes audible to me.

Maybe measure the cathode-to-grid voltage at idle?
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Old 4th June 2009, 03:02 AM   #13
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I feel like I'm thread jacking!

sorry skipper - I'll continue this in my original thread (after this post :P )

yes Russ it was in UL mode, no feedback. After switching in Cath feedback I can turn up the volume... I think I was just surprised that this tube (EL34) was so different.

My initial build was with transendar OPTs that don't have a UL tap, and I don't think I tried all of the various options with the '34 when I received the massive Edcor's.

back to you skipper
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Old 16th June 2009, 12:17 AM   #14
skipper is offline skipper  United States
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Hey Guys,

I've received 90% of my parts and I have started to assemble my board. I am still waiting for my coupling caps, I think they arrive tomorrow. I am going to get it up and running first before I start adding extra stuff like the adjustable cathode resistors. Below is a list of my build. The tubes I ordered were12AT7 and 5AR4 but I was sent the GZ34 and a CC81, are they the same.

Thanks for all the help so far.

skipper

Edcor XSE25-8-5K OPT.
Edcor xpwr059
Hammond 193H choke
Auricap coupling caps .22uf 600V
6L6GC (chineese)
GZ34 JJ
CC81 JJ
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Old 16th June 2009, 12:50 AM   #15
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Quote:
The tubes I ordered were12AT7 and 5AR4 but I was sent the GZ34 and a CC81, are they the same.
The ECC81 and GZ34 are the same as the 12AT7 and 5AR4 respectively. Those are just the European designations for those particular tubes.

Cheers and happy building!

James
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Old 16th June 2009, 01:32 AM   #16
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you can use the TDSL web site to check for tube compatibility.

TDSL
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Old 16th June 2009, 07:47 AM   #17
skipper is offline skipper  United States
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Default can someone compare their wiring

Hi,
The Edcor PWR transformer I am using has these values:

Edcor xpwr059
375-0-375 , 175 mA 50V .05A 6.3V CT 6A 5V CT 3A

Its wiring color is different than what is in the simple se wiring instructions. This is how I am wiring it. Can anyone who's used the XPWR059 comment on wiring this to the board.

2x brown wires 5V (2.5V each one) - T1-YEL terminals
5V CT white/brown wire not used.

2x Yellow wires 6.3V (3.15V each one) - T1-GRN terminals
6.3V CT white/yellow wire not used.

2x Red wires 750V (375V each one) - T1-RED terminals
750V CT BLK/RED wire to T1-RED-YEL

2x Grey wires 50V and Common, not used.

Per the lable that came with the Trans.

120 Volt Primary: Connect the two primary windings in parrallel.
Black adn Green connected together
Black/White and Green/White connected together.

Does that sound about right, I suppose it does not mater which wire is connect to the fuse? What is the 750V CT used for?

Thanks,
skipper
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Old 16th June 2009, 03:08 PM   #18
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looks right, but I don't have that transformer.

Some people have a preference on fusing the hot side, but I don't believe that there is an electrical reason to do so. Break the loop and no current flows...

Re: grounding the 750v center tap. Thats a good question. If I had to guess I'd say that it provides the return path to the rectified B+ voltage. It's not like the heater windings where the return is obvious...
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Old 16th June 2009, 04:00 PM   #19
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Put the fuse on the hot side of the mains, it's safer. That way if the fuse blows, there is no mains power in the amp. If it's on the neutral side and blows, there is still mains power inside the amp.

For devices with CE, UL, CSA safety approval, the hot side has to be fused, and with medical devices, both sides have to be fused. That's why most IEC power entry modules have two fuses. Arguably, with two fuses you could end up with live mains inside the unit if the neutral fuse blows and the hot fuse is still intact.
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Old 16th June 2009, 04:40 PM   #20
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Also, if there is a short from hot to earth ground on the primary side somewhere (like the power switch), a fuse on the neutral won't even blow!
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