Anyone Using SED EL34s blowing tubes?

wrea398 · Post by **wrea398** » Sun Apr 10, 2011 9:38 pm

Hi guys.

I wondered if anyone has been having any issues with SED Winged C EL34s recently. First off, I bought a "matched set" from "Amplified Parts" (good price) and installed them cold. I had a few bias issues (resistors etc.) and couldn't get it dialed hot enough. After getting it close, I never saw the mV on PIN 8 get any higher than 37-38mV. I backed it off to 35.5mv. I know it was never too hot. Started playing for a few minutes, jacked the volume up to 5-6 and saw a flash of light and blew the HT fuse. Changed fuse, slowly turn it up and blew the fuse again at 5-6.

The bias formula has my tubes set to 37.8mV max for 70% and 32.4mv at 60%
Hottest tube was set to 35-36 and at that setting the lowest was 28.8 and the two others were 30-31. "So much for matched sets". I moved the tubes around and the heat followed the tube. Looks like a bad tube.

Just wondered if anyone experenced the same thing with SEDs recently.

axeman · Post by **axeman** » Sun Apr 10, 2011 11:15 pm

No bad experience with mine. Did you replace the SED with the old ones to trouble shoot? Actually 4 years ago when I built my first 69 1959 v7 flashed, but I replaced all the tubes with new ones without an incident. That was the only time since 1998.

robert · Post by **robert** » Mon Apr 11, 2011 3:32 am

Hi,

IMHO this tube tube in your tube set was simply of "bad quality".
This happens sometimes, regardless of the brand and manufacturer!
Send it back to your dealer for guarantee.

Regards

Robert

wrea398 · Post by **wrea398** » Mon Apr 11, 2011 10:28 am

Funny thing.... I inspected the tubes visually and noticed the bad one is made differently. The plates on 3 tubes are more towards the base and the 4th one has longer metal supports and the plates are noticeably higher in the tube. Wonder if this means anything (ie, quality control).

wrea398 · Post by **wrea398** » Mon Apr 11, 2011 10:33 am

I didnt have any old tubes as this build was new. I have some new tubes on the way. I ordered another SED quad and now I will have some extras incase I have another failure. I do know when rechecking my voltages, the higher heat from V7 followed the tube wherever I put it. All voltage are spot on. 452 at PIN 3, 450 at PIN 4 and 452 at PIN 6.

axeman wrote:No bad experience with mine. Did you replace the SED with the old ones to trouble shoot? Actually 4 years ago when I built my first 69 1959 v7 flashed, but I replaced all the tubes with new ones without an incident. That was the only time since 1998.

robert · Post by **robert** » Tue Apr 12, 2011 7:00 am

Hi wrea,

I wish you good luck! Please, report here, when you've got your new SED tubes.

My experience is:

SED EL34s (normally) are as rugged as the RFT EL34s- e.g. they both even can take 500V on the screens without having problems.

BTW: sadly, the RFT EL34s meanwhile are hard to get

Regards

Robert

wrea398 · Post by **wrea398** » Tue Apr 12, 2011 3:33 pm

Will do Robert. I think I may have gotten a lemon in the last quad. The highest voltages on my amp was 467 without tubes and 452 with tubes. I just played around yesterday with the bad one to confirm. It sparks inside the same tube no matter which socket its in. I sent it back this morning for a replacement. Havent installed my new quad yet. Saving it for the weekend. I will let you know Monday.

robert wrote:Hi wrea,

I wish you good luck! Please, report here, when you've got your new SED tubes.

My experience is:

SED EL34s (normally) are as rugged as the RFT EL34s- e.g. they both even can take 500V on the screens without having problems.

BTW: sadly, the RFT EL34s meanwhile are hard to get

Regards

Robert

wrea398 · Post by **wrea398** » Sat Apr 23, 2011 8:42 am

Yeah it was definately a tube. I tested all 4 on a BK707 and the bad one fluctuated from 100-120% very erratically when the other 3 held nice and steady. I tried it in the amp one more time with slow blow fuses and the tube popped the HT fuse again AND blew a filament this time around. It measures a total short on the meter now. Sent it back for a trade out. I installed some new JJs for now "they sound like crap" compared to the SEDs but they are hanging in there nicely. I have another new set of SEDs but I will wait on my replacement instead of using the new tubes. Just like you guys stated, sometimes there is a bad apple in the bunch. My main concern was if SEDs was going down in quality and if anyone had experienced anything lately. To me they still are the best sounding tubes I have had. Amplified Parts is working with me on a warranty trade out for a new tube. Thanks for all your input.

wrea398 · Post by **wrea398** » Mon Apr 25, 2011 2:24 pm

Tube replaced, amp is rockin...Looking for a cabinet for it and Im finished. So far so good. Biased right in at 35mV... sounds killer!!

robert wrote:Hi wrea,

I wish you good luck! Please, report here, when you've got your new SED tubes.

My experience is:

SED EL34s (normally) are as rugged as the RFT EL34s- e.g. they both even can take 500V on the screens without having problems.

BTW: sadly, the RFT EL34s meanwhile are hard to get

Regards

Robert

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Anyone Using SED EL34s blowing tubes?

Anyone Using SED EL34s blowing tubes?

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