7189's vs EL84's

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bigblues
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Post by bigblues »

7189's have a max plate diss. of 13.2 watts. EL84's have a max pd of 12 watts. Wouldn't the 7189's be good in a non-adjustable bias amp, like a Fender Blues Jr. , that runs around 14 watts pd ?
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Post by solow1977 »

where do i buy a pair of 7189?
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Post by zaphod_phil »

Actually 7189s only have a dissipation rating of 12W like a regular EL84, but are designed to take higher voltages. 7189A's are the ones rated for 13.2W dissipation. You also need to be careful with those, as they have a slightly different pin configuration than EL84s.
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Re: 7189's vs EL84's

Post by zaphod_phil »

mojohand wrote:
Fri 03/18/05 11:34 pm
Would using a good matched pair of NOS 7189's (like maybe Sylvania blackplates, or Amperex, or GE) provide any improvement in an amp that normally uses EL84s?

I've read these make a good upgrade in lo watt (15 to 20 watt) amps using EL84s
I know this is an old thread, but I really need to say that people shouldn’t waste their good money on matched power tubes. I once bought a pair, when I didn’t know better, and the amp sounded somewhat sterile compared to when I used a non-matched pair. Matched tubes are really only needed for hi-fi, not guitar amps. Non-matched tubes help generate nice, warm sounding even-order harmonics. The great legendary guitar amp companies of the past also didn't use matched tubes, and just put in tubes as they pulled them out the box.

Here's what really blew my mind, I once used a couple of random Russian-made 6V6 tubes in a prototype of a commercial amp build. They were just in my tube stash and were even dated several years apart from each other. However, the amp worked flawlessly and sounded excellent!

7189 tubes are a very good substitute for EL84s, even though they are actually beam tetrodes, while EL84s are true power pentodes. 7189s and 7189As are like rugged EL84s and are therefore typically used in heavy-duty applications like organ amplifiers. Note that the 7189A version has a different pinout. Unfortunately, I’ve never had the chance to A/B test 7189s against EL84s for tone.
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Re: 7189's vs EL84's

Post by geoff 1965 »

interesting point about the matched tubes ZP,the output transformer also play's a part i.e. my hammond 1750PA has unequal resistance on the primary so even if i fit an exactly matched pair of tubes there is a difference of about 1/2 watt dissipation between them when biased.
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Re: 7189's vs EL84's

Post by zaphod_phil »

Yes, that's a very good point Geoff! And we also shouldn't forget that the PI might not be perfectly balanced either. Needless to say,I prefer some imbalance in a PI, like the Marshall 18W has :)
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Re: 7189's vs EL84's

Post by JMPGuitars »

On the flip side of that, the definition of matched tubes is loose. Some people consider 5% variance matched, while others consider as much as 20% (sometimes more??) as matched.

Then there's the fact that most matched tubes aren't actually matched. Matching transconductance (a common method of matching) isn't nearly as accurate as matching with a curve tracer, and probably nobody selling tubes uses a curve tracer.

I do usually get matched tubes, but the matching I bother with is free (and as I mentioned above, usually meaningless). So whether matched or not, they're probably not. Or maybe they are. Who knows (just kidding, I know, I have a curve tracer). 😉

If you take two random tubes that weren't matched to begin with, and install them in an amp, they might be matched. You'd have to test them to know.

Now what I think is a waste of money is overpriced NOS tubes. If you don't have a really good tube tester, or a curve tracer, then chances are you're getting ripped off (and even if the tubes are good, do they reeeeeeeally sound better?). This isn't an issue of simply matching as much as it is in tube performance, and life expectancy. People love paying for mojo though. 🤷

The only way we could really test this theory of matched vs. not matched is to curve trace tubes, and make sure at least 2 are well matched, and a 3rd is not matched within at least 20 or 30%. Then we could swap one of the tubes and do a real A/B comparison.
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Re: 7189's vs EL84's

Post by zaphod_phil »

JMPGuitars wrote:
Wed 03/18/20 5:52 pm
I do usually get matched tubes, but the matching I bother with is free (and as I mentioned above, usually meaningless).
But if it's not the meaningless kind, it will probably degrade the tone of your amp, as I found out for myself. That was a real waste of the extra $$ I paid.
JMPGuitars wrote:
Wed 03/18/20 5:52 pm
If you take two random tubes that weren't matched to begin with, and install them in an amp, they might be matched. You'd have to test them to know.
If they're matched, they will usually give a bit less hum than a non-matched pair. I've actually done that - ie found a pair of approximately matched tubes in a bulk lot by choosing pairs that gave least hum in an amp :)
JMPGuitars wrote:
Wed 03/18/20 5:52 pm
Now what I think is a waste of money is overpriced NOS tubes. If you don't have a really good tube tester, or a curve tracer, then chances are you're getting ripped off (and even if the tubes are good, do they reeeeeeeally sound better?).
If they're genuine Mullards, they probably will sound better, but not just because they're old. Mullard's quality control was simply phenomenal.
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Re: 7189's vs EL84's

Post by JMPGuitars »

zaphod_phil wrote:
Wed 03/18/20 6:44 pm
But if it's not the meaningless kind, it will probably degrade the tone of your amp, as I found out for myself. That was a real waste of the extra $$ I paid.
I'd like to test this scientifically(ish). Maybe I'll put some effort into it at some point. ;)

zaphod_phil wrote:
Wed 03/18/20 6:44 pm
If they're genuine Mullards, they probably will sound better, but not just because they're old. Mullard's quality control was simply phenomenal.
Sure, Mullard was a great brand, and I like the new production stuff too. But the question is, does the NOS Mullard sound like it's worth $200 instead of under $20 per tube? Is it really 10 times better?? I doubt it. I know it certainly isn't worth it to me. Now if somebody gave me a NOS set as a gift, I guess I wouldn't be upset. :lol:
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