Forums - SE84UFO problem

jmac7

Verified Member

Posts: 14

SE84UFO problem
04/07/24 at 18:10:49

Hi,everyone. I seem to be having a problem? with my SE84UFO amp. I have had it for a while and I haven't tried EL-84 tubes. Yesterday,I put in a set of Radiotechnique EL-84L NOS from the 1960's. when I powered it up,there was little volume,almost none. I checked everything and put the stock tubes back in and all was good again. I also have a set of NOS EL-84 RCA tubes from the 60's. so I installed them. Again, I had very low volume. Distorted and unlistenable. So, I reinstalled a pair of new Sovtek EL-84's. Again all was fine. It seems that all of my NOS tubes don't work. I checked all of my El-84's on my tube checker all were very good. Anyone have any ideas? Am I doing something wrong? I flipped the bias switch and it had no effect, so I am at a loss.

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CAJames

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"I've run every
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Posts: 2120

Re: SE84UFO problem
Reply #1 - 04/07/24 at 22:40:32

Hum. I personally have not had good results from EL84 tubes, but not in the way you describe. The volume was perfectly normal, the sound just wasn't very good compared to other options. What you describe sounds like bad tubes to me, or tubes that are not actually EL84s. And there is no trick to using them, if your Sovteks work OK then it is hard to imagine the problem is you or the amp.

What "tube checker" are you using? And is it possible it is out of calibration? I guess one other idea, which is a long shot, is how do the tube pins look? If they are dark and/or corroded that could be an issue (although it seems highly unlikely that all those tubes suffer in the same way). But you could try hitting the pins with very fine grit sandpaper to clean them up.

Again JMO/YMMV and all that, but I wouldn't pay NOS prices for "heritage" EL84s when you can get 6P15P-EV or -ER tubes for considerably less and they sound better.

Also, and again strictly FWIW, there are many threads about UFO power tubes and specifically EL84 vs. 6P15P. For example:

https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1649456236

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[FOOBAR2000 | Jay's CDT2 MRK3] -> Denafrips Terminator 2 + Gaia
Sumiko Pearwood -> Mapleknoll Athena -> Luxman SUT -> Mapletree Phono 3E
STR-1002 -> Woo WA22 -> 2x UFO25s, balanced monos
Omega SAM , Hifiman Arya, Audeze LCD-XC

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jmac7 Verified Member Posts: 14	Re: SE84UFO problem Reply #2 - 04/08/24 at 12:42:42 Hi. I am using a Hickok 533 tube checker that has been calibrated recently. The tubes are definitely El-84. I have had them for several years. Some I got from a very reputable seller and and the pins are clean. Thanks for the info. I might give decware techs a call.
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CAJames Seasoned Member "I've run every red light on memory lane." Posts: 2120	Re: SE84UFO problem Reply #3 - 04/08/24 at 15:58:49 One other long shot idea that occurred to me is trying a different rectifier. Maybe your current rectifier has a problem with those EL84s. Good luck regardless, if you find a problem I'm curious what it was.
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jmac7

Verified Member

Posts: 14

Re: SE84UFO problem
Reply #4 - 04/09/24 at 17:17:41

Hello, again. I just talked to Steve and he said that some NOS EL-84 tubes have a different pin out from the new ones and that they won't work. He said that I could send it back to him and there is a mod that they do to the amp, that he can undo and the older tubes will work. I would never have thought that all EL-84's weren't the same. Jim

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Sean Seasoned Member Posts: 348	Re: SE84UFO problem Reply #5 - 04/09/24 at 17:43:11 Sounds like the Christmas comes early/hazen grid mod he is talking about. Do a search, it doesn’t come up much lately but a few years ago there were lots of posts about it.
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CAJames

Seasoned Member

"I've run every
red light on memory
lane."

Posts: 2120

Re: SE84UFO problem
Reply #6 - 04/09/24 at 18:03:15

Quote:

Posted by: jmac7 Posted on: Today at 09:17:41

Hello, again. I just talked to Steve and he said that some NOS EL-84 tubes have a different pin out from the new ones and that they won't work.

Very interesting. After a little googling I found this:

https://www.kcanostubes.com/content/modern-el84-amps-and-nos-el84s

I guess it explains why your tubes test OK, because there is likely no connection to pin 1 when testing.

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[FOOBAR2000 | Jay's CDT2 MRK3] -> Denafrips Terminator 2 + Gaia
Sumiko Pearwood -> Mapleknoll Athena -> Luxman SUT -> Mapletree Phono 3E
STR-1002 -> Woo WA22 -> 2x UFO25s, balanced monos
Omega SAM , Hifiman Arya, Audeze LCD-XC

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jmac7 Verified Member Posts: 14	Re: SE84UFO problem Reply #7 - 04/09/24 at 19:32:26 That's very interesting info. Thanks !!
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