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 Post subject: 6EU7 tube
PostPosted: Mar Mon 01, 2010 6:41 pm 
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I'm wondering how many have equipment that uses this audio tube. I recall that it was developed expressly as a higher quality replacement for the 12AX7. The purpose was for better hum and noise characteristics in audio equipment. Today, the 12AX7 survives and is still in production, but the 6EU7 is obsoleete, yet readily available NOS.
I have one 1960's preamplifier that uses six of these tubes. The sound is great. I've never been able to run a comparison between this tube and the 12AX7, however.
So I'm wondering... Does anyone have equipment that uses the 6EU7? Or, has anyone ever converted a 12AX7 preamp, for instance, to 6EU7?
Note: Conversion is fairly simple IF the 12AX7 is being run with filaments paralleled and using 6 volt supply. Other than the filament, the tubes are essentially electronically identical.

Also, is anyone aware of vintage equipment that uses this tube?
The one item I know of is the Preamplifier I've had since new, a Heathkit AA-141-A My main beef, a small one, with this preamp is the lack of inputs.
Mark D.


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 Post subject:
PostPosted: Mar Mon 01, 2010 7:10 pm 
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The trouble with the 6EU7 was this. In fulfilling its stated purpose (reduced hum and noise), it was in direct competition with the 7025. And unlike the 6EU7, the 7025 was a direct substitute for the 12AX7 in ALL cases.

This put it at least two laps ahead of the 6EU7 in marketability. For example, owners of older 12AX7 gear could plug-and-play the new low-noise tubes. No time, bother and expense wasted on conversion.

Larry

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PostPosted: Mar Mon 01, 2010 9:47 pm 
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The 6EU7 was an effort by RCA to sell tubes , it made them and others had to buy the rights to make them , the patent on the 12AX7 had expired

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 Post subject:
PostPosted: Mar Mon 01, 2010 9:49 pm 
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BigBandsMan wrote:
The trouble with the 6EU7 was this. ...No time, bother and expense wasted on conversion.

Larry


Guess that pretty much sums it up! The basing is entirely different with the 6EU7 with the filament being pins 1 & 2. So that throws it out as a drop in sub. Another orphan is the 12DW7/7247. It is a dissimilar dual triode. One triode section a 12AU7 and the other triode section is a 12AX7. Scott used them in the high end tuner and I think that the EICO ST-70 amplifier used them as well. They can be expensive if the seller thinks he has something. Or, sometimes they slip through the cracks, just like the 6EU7...

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 Post subject:
PostPosted: Mar Mon 01, 2010 10:01 pm 
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Yes, the pinout was different with the 6EU7, but I never considered rewiring a tube socket to be a big deal. I can understand where the average "tube roller" wouldn't have a clue about that, though.

So now I understand why the 6EU7 doesn't see much use, but still, can anyone come up with other equipment that does use it? If not, that would tell me that total sales of this tube must have been like, maybe 11? :-) I've always been impressed with the life performance of the 6EU7, but it's probably not really much better than the better 12AX7's, although I have read a number of forum posts on various audio forums from people with hum trouble... Probably ground related, not tube, in most cases.

Mark D.


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PostPosted: Mar Mon 01, 2010 11:38 pm 
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Don, I have an old buddy who tears his hair out over 12DW7's. It seems that his favorite Ampeg amp uses those tubes, and he can't ever find enough spares to suit him.

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PostPosted: Mar Tue 02, 2010 1:00 am 
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Hi Guys, i do know that seeburg used this tube in a few of its late 50s early 60s amps as a preamp tube, the ay160 seeburg i know used 2 of them.

Gary


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 Post subject:
PostPosted: Mar Tue 02, 2010 2:40 am 
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Several of the Magnavox console amps used the 6EU7. Bogen used in in some of the Challenger series amps, maybe others. Stromberg used it in the ASR-220 amp, but no others I know of. I have some Mullard made ones, RCAs, maybe Sylvania?


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PostPosted: Mar Tue 02, 2010 2:45 am 
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VM used the 6EU7 in their 730 tape recorder, from around 1962.

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 Post subject:
PostPosted: Mar Tue 02, 2010 4:37 pm 
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I have 2 Heathkit AA151 integtated amps that use 6EU7's and I know that Magnavox used them too. Harry


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 Post subject:
PostPosted: Mar Tue 02, 2010 4:59 pm 
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My Gibson GA1RVT and VM 1450 amps use them. I've seen them in a couple of other pieces of audio gear.

-Steve W.


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 Post subject:
PostPosted: Mar Tue 02, 2010 5:54 pm 
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My Magnavox 9304 amp from an old console uses 2 6EU7's, as does a host of other Maggie amps.
Indeed they are becoming hard to find, but I've got a dozen or so of them (NOS) so my amp should keep going till I drop.

From what I know though, the difference between the 6EU7 and the 12AX7 isn't really that much, and in most cases the conversion is painless.

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 Post subject:
PostPosted: Mar Tue 02, 2010 11:23 pm 
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The 6EU7 was a very common tube in Gibson guitar amplifiers.I had several customers who requested I rewire the sockets to accept 12AX7s because the 6EU7 is getting hard to find.I never had a problem doing the modification.
Jim


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 Post subject:
PostPosted: Mar Wed 03, 2010 12:16 am 
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Listening to a Magnavox 9302 right now with a pair of 6EU7 tubes in it. The ones in this one are original, but tested fine. Thats one great thing about low level signal tubes, they don't really wear out.

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 Post subject: Re: 6EU7 tube
PostPosted: Sep Tue 25, 2018 3:39 am 
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RCA used the 6EU7 in many of their early 1960's console amplifiers. A typical amp was a pair of 6BQ5's, a 6EU7, a 6CA4 and a "high" output stereo cartridge. Remarkable thing was those amps for a 3 watt amp sounded terrific!


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 Post subject: Re:
PostPosted: Sep Tue 25, 2018 5:01 am 
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gadget73 wrote:
Listening to a Magnavox 9302 right now with a pair of 6EU7 tubes in it. The ones in this one are original, but tested fine. Thats one great thing about low level signal tubes, they don't really wear out.




Beg to differ on this. My Sherwood S5500II's phono preamp 12AX7/7025, took a dump and went noisy a few days ago. Lots of hum.


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 Post subject: Re: 6EU7 tube
PostPosted: Sep Tue 25, 2018 7:46 am 
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Artcurus,
Are you sure it isn't a filter or bypass cap gone bad?

Not to say they can't fail, but I have yet to see a low noise tube become the only source of hum.

Forgive me, because I do not know your level of experience with this subject matter, or from your perspective, ditto for you about me. :-) :D


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 Post subject: Re: 6EU7 tube
PostPosted: Sep Tue 25, 2018 1:54 pm 
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Location: Hawthorne, Ca
I have two Heathkit AA151 amplifiers that use 6EU7's. I've also serviced equipment from other manufacturers that also used 6EU7's, so I don't think the tube is really uncommon. Harry


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 Post subject: Re: 6EU7 tube
PostPosted: Sep Tue 25, 2018 2:37 pm 
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I suspect that you cannot buy these cheap anymore. People are always fishing around looking for the next sub for the expensive tubes or the next alternative. I bet you would pay as much as a 12AX7 at least, on ebay.


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 Post subject: Re: 6EU7 tube
PostPosted: Sep Wed 26, 2018 12:24 am 
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donhradio wrote:
Artcurus,
Are you sure it isn't a filter or bypass cap gone bad?

Not to say they can't fail, but I have yet to see a low noise tube become the only source of hum.

Forgive me, because I do not know your level of experience with this subject matter, or from your perspective, ditto for you about me. :-) :D


Dead positive, in fact, I myself replaced two original caps that SEVEN other techs somehow missed in the preamp section. Don't ask. The amp has been recapped/rebuilt. After I swapped the 12AX7, hum all but disappeared. The original tube has a heater/cathode short.

I have had to replace noisy 6AN8 in various equipment. (I have no love for this tube). Also 6EU7 and 7199. (Stromberg Carlson amp). I'm a mobile DJ and my main power amps use 6EU7 and a 12FQ7 (I think that's it), the 6eu7 has gone south on those at least once. Always fun right before a gig.

I also had a Telefunken 12AX7 in a Bogen FM stereo tube tuner that caused hum. took forever to find that one and that was a REAL surprise considering the brand.


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