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Post subject: JJ 5751
Posted: Tue Mar 17, 2015 6:08 am
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If you are looking for a slightly warmer tone, with decreased mu factor, this tube maybe worth a try. Has a similar tone to the good GE 5751 dual mica tubes of the 1960's. Good price, too.

Gonna test the Brimar CV4035 and the Raytheon 5755 later this week. Will post my opinions.


http://www.amazon.com/JJ-5751-PREAMP-VA ... B008ELWYH4


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Post subject: Re: JJ 5751
Posted: Tue Mar 17, 2015 9:30 pm
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I really like the JJ 5751, and have found a place for it in several amps, it works very well in V1. I even used two of them in my new Ibanez TSA30H, V1 and V2. I have compared it to many other 5751, modern and NOS, in many amps, and the JJ seems to be a winner in every amp.

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Post subject: Re: JJ 5751
Posted: Tue Mar 17, 2015 9:54 pm
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Looks like these reduce the input level making the amp quieter by about 30%.

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The gain factor of a tube simply measures how much it amplifies the input signal. For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain. Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up. Many guitar amp users (particularly harmonica players) like to reduce the gain to get a different sound or calm the amp down to prevent feedback.


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Post subject: Re: JJ 5751
Posted: Wed Mar 18, 2015 1:55 am
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On a related note, the JJ 5751 in the V2 position of my Ibanez, did not like the tube shield for some strange reason. No problem using the tube shield for V1 with the same tube. When I put the tube shield onto V2 it would make this loud, raspy, distorted sound when playing, but worked just fine without the shield. It wasn't the tube, I tried several, including the one that was in V1, and all worked fine in V1, but it was the V2 position and this particular amp. Maybe it has something to do with the direct coupling of the preamp tube halves, and the shield had some sort of capacitive affect on the tube....... :?: No other tubes that I tried had a problem with the tube shield being installed.

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Post subject: Re: JJ 5751
Posted: Wed Mar 18, 2015 2:00 am
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Nikola Tesla wrote:
....Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up...


Let's not start that nonsense again. :roll: The output section does NOT work harder when using lower gain preamp tubes. The output section amplifies what it is fed, and if you feed it less gain, it will amplify less. Turning up the volume to compensate for the lower gain preamp tubes, only allows the output to work as equally as it did before, not harder.

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Post subject: Re: JJ 5751
Posted: Wed Mar 18, 2015 6:58 am
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shimmilou wrote:
On a related note, the JJ 5751 in the V2 position of my Ibanez, did not like the tube shield for some strange reason. No problem using the tube shield for V1 with the same tube. When I put the tube shield onto V2 it would make this loud, raspy, distorted sound when playing, but worked just fine without the shield. It wasn't the tube, I tried several, including the one that was in V1, and all worked fine in V1, but it was the V2 position and this particular amp. Maybe it has something to do with the direct coupling of the preamp tube halves, and the shield had some sort of capacitive affect on the tube....... :?: No other tubes that I tried had a problem with the tube shield being installed.



Shimmi, try this. Touch the shield on V2. Does the added capacitance of your hand change the distortion's tone? Maybe, even eliminate it? If it does, you prolly are getting capacitance-coupled interference.


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Post subject: Re: JJ 5751
Posted: Wed Mar 18, 2015 5:37 pm
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I'll try that. No problem using the amp without one shield though.

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Post subject: Re: JJ 5751
Posted: Fri Mar 20, 2015 12:35 pm
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shimmilou wrote:
Nikola Tesla wrote:
....Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up...


Let's not start that nonsense again. :roll: The output section does NOT work harder when using lower gain preamp tubes. The output section amplifies what it is fed, and if you feed it less gain, it will amplify less. Turning up the volume to compensate for the lower gain preamp tubes, only allows the output to work as equally as it did before, not harder.


:lol: +1 Even I know it doesn't work that way. It works no harder or easier. What amazes me is I can build amps only knowing enough to be dangerous. Anyway I just installed a JJ 5751in my 5e3 in V1 and really like it. Really quiet tube too.

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Post subject: Re: JJ 5751
Posted: Fri Mar 20, 2015 4:03 pm
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63supro wrote:
shimmilou wrote:
Nikola Tesla wrote:
....Not only will this make the amp quieter, but it can also alter the sound by making the power section work harder when you turn it up...


Let's not start that nonsense again. :roll: The output section does NOT work harder when using lower gain preamp tubes. The output section amplifies what it is fed, and if you feed it less gain, it will amplify less. Turning up the volume to compensate for the lower gain preamp tubes, only allows the output to work as equally as it did before, not harder.


:lol: +1 Even I know it doesn't work that way. It works no harder or easier. What amazes me is I can build amps only knowing enough to be dangerous. Anyway I just installed a JJ 5751in my 5e3 in V1 and really like it. Really quiet tube too.



Dunno, I'm not competent in the field, looks like these guys are talking BS .. :evil:
http://www.thetubestore.com/Resources/G ... ain-Factor



:shock:


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Post subject: Re: JJ 5751
Posted: Fri Mar 20, 2015 4:43 pm
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Dunno, I'm not competent in the field, looks like these guys are talking BS .. :evil:

http://www.thetubestore.com/Resources/G ... ain-Factor



:shock:


Whomever wrote that for The Tube Store is not correct. The power potential of the output section is independent of the gain stage. No matter what input signal, this output stage will make a certain about of watts. Character of the wattage is dependent on the power source, Class type, feedback control, and output tubes. If fed a clean signal from the gain stage, the output section will make, say 30 watts. If fed a dirty signal, 30 watts.


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Post subject: Re: JJ 5751
Posted: Fri Mar 20, 2015 4:49 pm
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Yes, complete BS. :wink:

They have great customer service, they sell great tubes, but they have a few bits of nonsense on their site.

If it helps, I'll explain a little more. The preamp section basically controls the current through the output section, regulating how much current the output section actually puts out. If you turn down the preamp (volume or lower gain tubes), then the output section puts out less, accordingly. So, if you use lower gain tubes, lowering the output, then turn up the volume to compensate, the output is right back to where it was before with higher gain tubes and lower volume. Except that now the output is cleaner as it is not being fed a high gain signal that could achieve breakup easier. The higher the gain, the more easily a tube can be pushed to the point of breakup.

If you think of tubes as valves, and the preamp valves as the control for the output valves, it might be easier to envision how turning down the gain of the preamp will lower the "flow" of current through the output valves. The preamp section, with a lower amount of flow, will limit the total amount of flow available to the output section. If you lower the amount of available flow to the output tubes, then the output tubes can't possibly "work harder", even if you raise the volume to compensate.

When using lower gain preamp tubes, the sound, or the amount of breakup, is altered, to a cleaner sound, due to less gain, pushing the output less.

With any amplifier, less in equals less out. The only way to make the output tubes "work harder" is to push them more with more input, such as using higher gain preamp tubes, or a hotter guitar signal such as higher gain pups like hum-buckers.

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Post subject: Re: JJ 5751
Posted: Tue Apr 07, 2015 6:26 pm
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Beemer, thank you for pointing this out about JJ5751.

I have swapped numerous V2 tubes in my SR, some of them were fine, but yesterday at the gig I found that the 5751 is exactly what my SR needed. Warm tone, with beautiful creamy distortion, especially for riffs.

I was also able to go to Vol 5 with this tube (previously not more than 4), as indeed the amp sounded a bit quieter. Super Reverbs can be loud :mrgreen: .... this tube is the perfect match for the amp!

Cheers mate! :D


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Post subject: Re: JJ 5751
Posted: Wed Apr 08, 2015 7:14 am
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Nikola,

The black plate Raytheon 5755 with adapter is also a nice choice. A bit more complex harmonics than the JJ 5751. Richer bass.

The JJ 5751 does "loosen-up" with use. Well made tube that needs long break-in. Never gets the rich bass-mid harmonics that all Raytheon tubes seem to have from the get-go. At least, in my amps.


Here's the link to that tube (plus adapter).


http://www.partsconnexion.com/NOS-79368.html


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Post subject: Re: JJ 5751
Posted: Wed Apr 08, 2015 6:02 pm
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I may try one of Rayateon 5755 as well, but this JJ is just fine for my SR.

Would you know what tube is this, as it sounds pretty sweet in my other Black Face amp?!?

Image


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Post subject: Re: JJ 5751
Posted: Wed Apr 08, 2015 6:23 pm
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That is an RCA 7025. One of the best 12AX7 sub-types ever made. It has a low noise, spiral wound heater wiring. IME, this tube lasts forever.


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