The tale of the '65 PRRI and the Chinese tube

SerpentRuss

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I mostly post on the amp building section of the forum but this is a better spot for this particular story. This is not a '57 corvette in a barn for $200 story, but probably as close as my son will ever get.

He's 19 and has been on the hunt for a tube combo with spring reverb for a while. Nothing particular, just looking. Since I'm already working on a project for him and he knows how long it takes me to get anything built, he's been checking out Facebook marketplace, Craigslist, used at GC, etc., for something he can afford. So he texts me a couple of days ago, the boy is deathly allergic to speaking on the phone, and asks if $350 dollars is a fair price for a Princeton Reverb Reissue that's not working. I text back, "probably, it depends". So he wants me to go look at it and I can't get free. I ask him if the amp cabinet looks good in the photos and he says it does, so I tell him, go ahead, roll the dice, and buy it.

So a couple hours later he's bought the thing for $200 dollars! Here is the deal. An old man, "like you dad", meets him in the local Lowe's Food parking lot with said amp and needs help setting it out of the car. Old man, says amp plays, but doesn't sound right. He thinks it "needs a tube" and since he bought it cheap at an estate sale, he'll sell it to my enthusiastic son for $200 dollars, slightly more than he paid for it. He likes my boy, probably because he doesn't know how bad he was at loading the dishwasher or keeping his room clean when he lived at home.

My son says the amp plays pretty well, but has no life and can't be forced to break up at all. He says you can dime it, and it plays clean. I tell him to drop it off at the house and I'll look at it.

So last night I play the thing. He's right, it get's loud but stays clean and it sounds about as lifeless as a beached jellyfish. So I decide to pull the works and get voltages. The amp is pristine, not one tear on the Tolex, certainly a bedroom or studio dweller in it's previous life. It still has the Fender feature card tucked under the handle like it's just been unboxed, I kid you not. So I start pulling tubes so I don't bust them when I set out the guts. First tube is a JJ, 12AY7!

So I pull the rest of the preamp tubes and they are the original Groove Tube trash, all with the correct values, two 12AX7s and one 12AT7. So I pop them back in and I happen to have a EH 7025 within arms reach to put in V1. I fire it up, and gentleman, the amp is fixed. A previous owner, obviously not Old Man, neutered the amp for some personal reason.

So I call my son, I like to make him practice speaking every once in a while, and tell him to come get the amp. He comes over and I explain what was wrong and we start talking about gain and the 12Ax7 family of tubes. To my amazement, he is actually paying attention. The back cover is still off so I decide we should roll some tubes and see which sounds best, kind of a father-son bonding experience. We try a JJ ECC803S, JJ ECC83S, JJ 5751, NOS GE 12AT7, the afore mentioned EH 7025, and a tube simply marked China 12AX7.

I think the 5751 is the hands down winner. He likes the unbranded Chinese tube. This tube is in my stash because he bought a budget mic preamp about a year ago and said the reviews said the preamp was good, the tube was not, so I swapped it out for him with some NOS 12AX7 I had.

I have to admit, to my "old man" ears, the Chinese tube isn't at the bottom of the pack. It's his amp, and so I'm willing to part with the now priceless Chinese tube just to make him happy. That's the kind of dad I am.

I'm still waiting to for my own $200, '57 corvette moment. It better hurry up, I'm not getting any younger.
 
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Wildcard_35

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Nice! That's a great find. It's also good you're helping your son practice talking on the phone every now and then. As a kid, talking on the phone came naturally, but it took a little bit to be comfortable with "business talk" on the phone, and explaining what it was I was trying to communicate. It's an important skill for any adult to have, especially if you need to go full-on Karen and "ask to speak to the manager" for a redress of grievances!
 

darkwaters

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I can completely understand why someone would have a substituted a 12ay7 tube for 12ax7. I frequently do that with my amps (including my PRRI) to give me a more controllable, cleaner range of volume and more headroom. In my case, I play clean and avoid overdrive/distortion. Different strokes.
 

SerpentRuss

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I can completely understand why someone would have a substituted a 12ay7 tube for 12ax7. I frequently do that with my amps (including my PRRI) to give me a more controllable, cleaner range of volume and more headroom. In my case, I play clean and avoid overdrive/distortion. Different strokes.
Oh, I definitely know why the previous owner did it and respect everyone's choice for how they set up their own amp.

Of the tubes we rolled I thought the 5751 was the choice and it has a max gain of 70, so it tamed the PRRI quite a bit compared to the 100µ choices. In the Princeton Reverb, the two stages of V1 that bracket the tone stack are really the only gain stages in the amp, the cathodyne PI doesn't give you any gain at all. Putting a 40µ 12ay7 in V1 makes a significant difference, putting the PRRI in almost a bedroom amp category. To my ear there was a bit of sparkle lost too and my ears don't hear sparkle all that well anymore.

Interestingly to me was how dead the 7025 sounded, plenty of gain, but no sparkle. Maybe the 7025 is just really neutral, not adding or subtracting anything.

Like you said, different strokes for different folks.
 

darkwaters

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I was getting some noise from the reverb/tremolo in my PRRI and someone here mentioned putting a 7025 in V4. Worked like a charm.
 

Dacious

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Chinese Shuguang tubes which have the metal backwards 'E' mica spacer get a bad wrap - but they're one of two current production AX7s that will live in the cathodyne phase inverter or cathode follower preamp of amps like the Tweed Deluxe, various Marshalls and Mesas and Oranges. The other is the JJ 12AX7. A lot of these amps feature a cathode follower either in eq recovery or effects loop even with the loop bypassed.

Mesa fits their amps with JJs and Marshall with Marshall-branded Shuguangs. You also find Shuguang and Ruby branded 7025, 12AX7A and 12AX7B which I think they find by sorting them. They're Shuguang tubes. I find they're great first stage tubes for crunchy amps and I always keep them on hand for reverb drivers, eq recovery and so on.

I often find amps where the seller is selling them cheap because 'someone' retubed then with all EHX or 'Mullard' or other New Sensor Russian tubes. The amp cuts out with a fizzle at about 20 minutes when the grid overheats. Then after a few minutes' cooling it'll run for another 15 minutes before crapping out again. Vox Nighttrain 15s, I've bought numerous secondhand - V2A is a cathodyne eq recovery and V2b is a cathodyne pi so either triode can stop the amp.

Marshall, Vox, Orange, Mesa, some Tweed Fender and Princeton/Reverb are all amps this can affect. I think Mesa actually voices their amps brighter to cater for dark JJ tubes

In my Orange Rocker 32, V2 is the clean channel preamp. I like an old Sovtek 12AX7LPS in this position - it's a bit smoother, warmer and sparkiler. Orange used a Ruby 12AX7A in V1 (dirt preamp) like V2 and it works great for gritty drive.
 
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