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Post subject: Tubes 101...please.
Posted: Sat Jul 30, 2011 9:06 pm
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Ok amp gurus...I need a little bit of education here. I have been planning to pick up some new tubes for my amp (Jet City JCA2112RC) to have around in the event that a tube goes out. So before I waste my hard earned money, I have a few questions.

First:
I have heard that different preamp tubes can make a difference in tone, can anyone suggest a good 12AX7 or compatible tube that will help take some of the edge off of this very bright amp?

Second:
What are everyone's favorite tubes for both pre/power? (12AX7 and EL84)

Third:
When my amp is at full tilt (gain and master both all the way up) it begins feeding back. It is a shrill feedback, almost like when a microphone feeds back, this happens whether the guitar is plugged in or not, and even if the volume on the guitar is all the way off.
Is this a sign that the tubes may be getting close to due for a change?

Ok...I suppose that's all the questions I have for now, I may have more later.

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Post subject: Re: Tubes 101...please.
Posted: Sat Jul 30, 2011 9:54 pm
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Current 12AX7 I like, that has warm mids and is rolled off on the top is the Mullard Reissued 12AX7. Caution, they are long plates, so buy them from someone who tests for microphony. Same goes for the Sovtek 12AX7LPS. Which has good mids.

Favorite 12AX7 of all time? For warm mids the 1960's Mullard Blackburn ECC83. For extended range the German made Valvo or Siemens E83CC. Pure clarity has to be the Telefunken smooth plate ECC83. US brands of the 1950-60 are all pretty good. Sylvania having a bit cleaner top end than the warmer RCA. Triple mica 5751 are also great tubes. As is the windmill getter Raytheon 5751. Raytheon 12AX7A is another nice tube. Even, the Matsushita made ones. Or the Japanese 12AX7 of the early 1970's that used Mullard dies. Tungsram ECC83 of the 1980 are also good tubes.

For EL84, I currently have a good sized batch of Russian Reflector made 1980's 6pi14pi-EV (also known as Sovtek EL84M). For British tone--- hard to beat a good 1960's Mullard or Philips Miniwatt EL84. RCA and Sylvania also made some great EL84 and the Holy 7189A. Tungsram EL84 of the 1980's are also great tube. Dark, powerful tone.

Thirdly, you prolly have a borderline microphonic tube. It will start to feedback at lower volume ranges as the guts get looser and looser. Subbing out, should find the culprit. But, unless you play at full tilt, the microphony can add a bit of sparkle to the tone. Most tubes (esp gain stage) have a bit of microphonic character. Sometimes, putting a dead quiet tube in this stage can also deaden the tone.


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Post subject: Re: Tubes 101...please.
Posted: Sat Jul 30, 2011 10:12 pm
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BMW2002Ti wrote:
Current 12AX7 I like, that has warm mids and is rolled off on the top is the Mullard Reissued 12AX7. Caution, they are long plates, so buy them from someone who tests for microphony. Same goes for the Sovtek 12AX7LPS. Which has good mids.

Favorite 12AX7 of all time? For warm mids the 1960's Mullard Blackburn ECC83. For extended range the German made Valvo or Siemens E83CC. Pure clarity has to be the Telefunken smooth plate ECC83. US brands of the 1950-60 are all pretty good. Sylvania having a bit cleaner top end than the warmer RCA. Triple mica 5751 are also great tubes. As is the windmill getter Raytheon 5751. Raytheon 12AX7A is another nice tube. Even, the Matsushita made ones. Or the Japanese 12AX7 of the early 1970's that used Mullard dies. Tungsram ECC83 of the 1980 are also good tubes.

For EL84, I currently have a good sized batch of Russian Reflector made 1980's 6pi14pi-EV (also known as Sovtek EL84M). For British tone--- hard to beat a good 1960's Mullard or Philips Miniwatt EL84. RCA and Sylvania also made some great EL84 and the Holy 7189A. Tungsram EL84 of the 1980's are also great tube. Dark, powerful tone.

Thirdly, you prolly have a borderline microphonic tube. It will start to feedback at lower volume ranges as the guts get looser and looser. Subbing out, should find the culprit. But, unless you play at full tilt, the microphony can add a bit of sparkle to the tone. Most tubes (esp gain stage) have a bit of microphonic character. Sometimes, putting a dead quiet tube in this stage can also deaden the tone.


Thanks for the suggestions BMW!

On the feedback issue...It has gotten 'slightly' worse, and while before it only happened at full tilt, I notice it happening with the master down to about 7 (9 being max on this amp) now, so I think I may just need to pick up some tubes and switch them out.

Anyone else with any suggestions?
Also, any opinions on Electro Harmonix preamp tubes (12AX7EH)? I've read some good reviews on them online today, thinking I may go that route for preamp if they're pretty good.
They also make an EL84 (EL84EH) that has good reviews across the board. I have read the most positive reviews when it comes to JJ Electronics' EL84 tubes.

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Post subject: Re: Tubes 101...please.
Posted: Sat Jul 30, 2011 10:19 pm
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EH are good tubes. One caution about JJ power and rectifier tubes. Get them from someone who will test them in an amp setting (not just a tube tester----which run at much lower plate voltages and cathode currents than amps), if possible. Their QA has dropped notoriously, in the last few years.

As for EL84... Sovtek EL84M, if you can find them.


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Post subject: Re: Tubes 101...please.
Posted: Sat Jul 30, 2011 11:07 pm
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BMW2002Ti wrote:
As for EL84... Sovtek EL84M, if you can find them.


I have also heard good things about Sovtek. Thanks once again.

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 12:56 am
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Try a JAN-Phillips 5751 in V-1

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 12:59 am
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Sorry Chet, I'm a technical dunce when it comes to tube amps. I deduce that V1 = Valve 1; would that be correct?

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 1:07 am
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TimDrakeMusic wrote:
Sorry Chet, I'm a technical dunce when it comes to tube amps. I deduce that V1 = Valve 1; would that be correct?



Tim
V-1 is usually the pre-amp tube all the way on the right side farthest away from the transformer.

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 1:11 am
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CAFeathers wrote:
Try a JAN-Phillips 5751 in V-1


You beat me to it, Chet.

8)

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 1:14 am
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Retroverbial wrote:
CAFeathers wrote:
Try a JAN-Phillips 5751 in V-1


You beat me to it, Chet.

8)

Arjay


Great minds think alike?

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 1:18 am
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Indeed!

8)

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 1:25 am
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CAFeathers wrote:
TimDrakeMusic wrote:
Sorry Chet, I'm a technical dunce when it comes to tube amps. I deduce that V1 = Valve 1; would that be correct?



Tim
V-1 is usually the pre-amp tube all the way on the right side farthest away from the transformer.


Right on, Thanks Chet. So, 5751 in V-1, then two 'standard' 12AX7 V-2/V-3? I had read a few different things online where people were mixing and matching preamp tubes. I figured I'd come here for my education. At least here I know who knows what they're talking about.

I suppose that any advice from Chet and Arjay, is pretty solid.

I believe I'll go with the JAN Philips in V-1, try out the EH12AX7s in V-2 and V-3. And I'l probably go with the EH EL84s also. Thanks guys!

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Post subject: Re: Tubes 101...please.
Posted: Sun Jul 31, 2011 4:45 am
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TimDrakeMusic wrote:
CAFeathers wrote:
TimDrakeMusic wrote:
Sorry Chet, I'm a technical dunce when it comes to tube amps. I deduce that V1 = Valve 1; would that be correct?



Tim
V-1 is usually the pre-amp tube all the way on the right side farthest away from the transformer.


Right on, Thanks Chet. So, 5751 in V-1, then two 'standard' 12AX7 V-2/V-3? I had read a few different things online where people were mixing and matching preamp tubes. I figured I'd come here for my education. At least here I know who knows what they're talking about.

I suppose that any advice from Chet and Arjay, is pretty solid.

I believe I'll go with the JAN Philips in V-1, try out the EH12AX7s in V-2 and V-3. And I'l probably go with the EH EL84s also. Thanks guys!



That is correct. Keep us up to date.

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Post subject: Re: Tubes 101...please.
Posted: Tue Aug 02, 2011 4:57 pm
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Just did a quick bit of reading on the JAN Philips 5751. I read that this tube will have about 70% of the gain of a typical 12AX7. That is fine by me, as my amp has very little headroom (breakup at about 2.5 of 9). My new question is...will replacing only the V-1 tube have that drastic of a difference or should I expect only a slight difference only using the 5751 in V-1?

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Post subject: Re: Tubes 101...please.
Posted: Tue Aug 02, 2011 5:10 pm
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The total gain in a stage is only partially dependent on the "mu" (70 versus 100) of the tube in that stage. Voltage, bias setup, feedback, coupling parameters all play a role. You may not get a dramatic change in drive. All systems are amp/tube/setup/feedback (local & global) dependent. You are just gotta need to try it out to find out for your amp.


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