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Tube Newb Question....12AX7 and 12AX7A

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Craig I find your no bs perspective very refreshing. I'm a transplanted Michigander who learned to solder with Dad on a LK-72 and a LT-111 which I still have but not operational. We purchased the kits from that funky electronics store next to the hobby shop in downtown Flint in the mid sixties. Would love to buy you a Flint Coney some time. Take good care.

Funny you mention Coney's... During the summer tourist months we have a Coney stand on the Lake down the street. Really awesome people own and run it. They offer both Detroit and Flint Coney's! They even serve the curve (I bet you know what that means) LOL!! Come on up for a visit some time and bring the LK-72- LT110.... it is a 110 is it not?

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Since this discussion is back to swapping triodes with different characteristics, a way to achieve a workable situation is to "contact bias" the tube- i.e. grounding the cathode and using a very large, say 10 megohm, grid resistor. Although some consider this technique "non-audiophile," the results are quite fabulous; in fact, the distortion for a given plate voltage is often a bit lower than when the tube is self biased with a cathode resistor/capacitor. In the shop we often did this for people who insisted on having the flexibility of swapping 12AX7s, 12AT7s, 12AU7s, etc. The nice thing about this method is that the tube bias adjusts itself as the tube ages. Virtually all of the vintage triodes were actually designed to allow this method of use. Bass response is phenomenal as it is not limited by the often undersized cathode bypass cap. In summary, it's an easy modification to do for those with experience in working under the chassis; and, it's easy to change back if the results are not as desired.

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Mark,

You proved it once again....you missed your calling in life. You should of been a Electronics Professor. Very clear, concise way of proving my point. Thanks for taking the time. It really makes me miss the early days when you spent so many hours helping me understand what is going on inside these circuits... I have no idea where I'd be in this business without your help back then. You made it so easy and enjoyable to learn!

Craig

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This is a great thread, informative and educational. I know very little about the inner workings of the tube world and this info has helped alot. I still know nothing relative to the rest of you, thank to all that have contributed.

Tom

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This is a great thread, informative and educational. I know very little about the inner workings of the tube world and this info has helped alot. I still know nothing relative to the rest of you, thank to all that have contributed.

Tom

Ditto.

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Thanks for all the input guys.

Finally got around to talking to Jolida today (great customer service, by the way) and they confirmed that it is indeed safe to replace the stock 12AX7A with a standard 12AX7 in the JD100 cdp.

Now I've got some Mullard, Amperex and Telefunken's to have some fun with. [:D]

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The long plate Mullards won. [Y]

Smooth, lush and detailed. It was fun flip-flopping tubes between the HH Scott 222c and the Jolida cdp. Telefunken smooth plates in the 222c and Mullard long plates in the Jolida. Sweet sounds. [:D]

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There may also be slight differences in inter-electrode capacitance, I would not mix and match them, but as a matched set they should be interchangable. In the shop we used to select tubes based on microphonics (gently tapping the tube with the eraser end of a pencil to determine if it could be heard in the speaker) more than anything else.

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In the shop we used to select tubes based on microphonics (gently tapping the tube with the eraser end of a pencil to determine if it could be heard in the speaker) more than anything else.

Gee, that sounds like something that I would have said!!!

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Bought a jjecc803s  after reading ( researching ) about its fine qualitys. Real disappointment, waste of money. I've tried various tubes, more or less the same.

I wonder are we mugs, tube rolling? It's making someone rich.

question, in electronics don't they improve, resistors, capacitors, inductors, transformers, etc over time, so why make reissue ( old design of valves ) yes they can improve these tubes don't they use computers to design products?

or is it just easy money.

I might go back to ic chip reproduction of music.

Now this will boil someone's blood. The best valve I've heard was made by the 

AFFORDABLEVALVE COMPANY the quality of his amp was very good for the price,

COME BACK AFFORDABLEVALVE VALVE COMPANY, LIM YOUR AMPS ARE CHAMPS.he may have boiled someone's BUT HIS AMPS SAYS IT ALL.

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17 hours ago, Hopeton williams said:

Bought a jjecc803s  after reading ( researching ) about its fine qualitys. Real disappointment, waste of money. I've tried various tubes, more or less the same.

I wonder are we mugs, tube rolling? It's making someone rich.

question, in electronics don't they improve, resistors, capacitors, inductors, transformers, etc over time, so why make reissue ( old design of valves ) yes they can improve these tubes

 

Well, tubes DO have a break-in period (of up to 300 hours, depending on the model... ) So they do get better over time. You can buy good tubes for under 10 dollars a piece, so I can't see why we'd be 'mugs'...

So my advice here: give your new tube (or tube amp) enough time to break in. Also: some tube amps need up to half an hour for heating up and giving optimal sound quality (even if broken-in).

 

That was my contribution in bringing this 10 year old thread back to life!

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I got a laugh out of this thread so thanks for bringing back from the dead. 

Only after many tube rolls and dollars spent do we slow down enough to find out why a well made tube amp is designed the way it is: The circuit is designed AROUND a specific tube. If you're system sounds better with a variant tube in place, this is usually an indicator of a problem elsewhere in your system.

 

At some point I installed a 6BL8 in my Dynaco in place of the 6GH8A it was designed around. It sounded better. When I finally fixed the excessive high frequency roll-off in my speakers, the 6GH8A sounded better again. That's just one example of several that reinforced this idea for me. 

Better made tubes adhere more faithfully to their design specs. That's why a Blackburn Mullard 12AX7 sound better than a new production 12AX7. The reason new production tubes aren't made better, even though they could be, is simple supply and demand. In the 50's and 60's they were making tens of millions of tubes for all industries. They had the headroom to build in quality. Today they make thousands exclusively for audio. There's not enough meat on the bone. 

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4 hours ago, ILI said:

Well, tubes DO have a break-in period (of up to 300 hours, depending on the model... ) So they do get better over time.

...

Also: some tube amps need up to half an hour for heating up and giving optimal sound quality (even if broken-in).

 

True, but in my now-faded-memory experience, the "upwards of 1/2 hour" and "upwards of 300 hours" neither elicit "night and day" differences.

 

The only good thing IMO that tubes provide over silicon is the glowing, pulsating plasma in the output tubes, but that might require some good weed to truly appreciate!

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Wow, cool to see this thread pop up after almost ten years!

The 222c was my first tube amp. Tried some others but the Scott tube integrated amps do it for me. I now have three 222c's. All restored. All awesome.

After trying several different tubes, what this amp was designed for works best. There are others that get the job done but none perform as well as NOS 12AX7's and 7189's.

Sent from my SM-G950U using Tapatalk

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Since this thread was unearthed...

 

I saw folks mentioning using a 5751 for 12AX7.  Is that really a good idea and what’s the expected result? 

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2 minutes ago, xoundmind said:

Since this thread was unearthed...

 

I saw folks mentioning using a 5751 for 12AX7.  Is that really a good idea and what’s the expected result? 

5751 has 30% less gain than a 12AX7.  Definitely not recommended for a phono stage.  However, some of the good 5751, such as RCA blackplate, can be less noisy and microphonic than a comparable 12AX7.

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3 hours ago, jimjimbo said:

5751 has 30% less gain than a 12AX7.  Definitely not recommended for a phono stage.  However, some of the good 5751, such as RCA blackplate, can be less noisy and microphonic than a comparable 12AX7.

I used 5751's instead of 12ax7's for years in my phono stage. A little less volume, but a lot quieter.

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8 minutes ago, kevinmi said:

I used 5751's instead of 12ax7's for years in my phono stage. A little less volume, but a lot quieter.


 

Any discernible tone difference? 

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Just now, xoundmind said:

 

Any discernible tone difference? 

I really don't think there is much difference, but I went from vintage GE 5 star 5751's to vintage Amperex 12ax7's, so there might be some difference. It's been about a year since I did the swap.

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