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FDP Forum / Amp Mods, Repairs, and Projects / Reverb tube

Big Joe

USA

Oct 3rd, 2018 08:03 PM   Edit   Profile  

Does anyone have a preferred Reverb Tube or are they all basically the same unlike the differences we see in the V1 position with different tube brands.

Peegoo
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Stinks like hell

and the neighbors complain
Oct 3rd, 2018 08:53 PM   Edit   Profile  

The reverb driver and recovery tubes don’t have the marked effect on tone like V1 does. A good tube in spec is a good reverb tube.

Some will probably disagree with me, but this has been my experience.

Leftee
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VA

Oct 4th, 2018 03:24 AM   Edit   Profile  

Often they’re a current driver like a 12AT7. As long as they function inside the designed parameters, they do the job. I’ve not noticed any tonal nuances.

These days if I want to experient with different preamp tubes, it’s V1 only. I usually don’t mess with the rest if the amp is performing ok.

And, honestly, I don’t swap tubes much at all any more. If the amp sounds great, swapping tubes is really something my imagination hears better than my ears.

(This message was last edited by Leftee at 05:25 AM, Oct 4th, 2018)

Big Joe

USA

Oct 4th, 2018 06:24 AM   Edit   Profile  

What I suspected is the reverb tube, like a rectifier tube either works or it doesn’t. Although a reverb tube as in may case was working with degraded tone,cracking and a wining sound. Once a rectifier tube goes, you get nothing.
I asked the question, because I never had a reverb tube go. I usually only replace my power tubes every 2-3 years or so.
I must say that there is a difference in tone with new matched power tubes vs tired ones.

pdf64

UK

Oct 4th, 2018 10:13 AM   Edit   Profile  

Er, what amp are you referring to?
And which tube/s are you referring to as the 'reverb tube'?
Note that with regular BF / SF Fenders, there's a 12AT7 reverb driver tube and and 12AX7 triode section that acts as a reverb recovery gain stage.
The other section of that 12AX7 acts as gain recovery stage from the losses of the passive wet / dry mixer, ie it's in the main signal path.
Hence a naff / tired tube there could mess up the tone of the amp. But it's reasonable to expect a tube to last a long time in there, no need to replace preamp tubes unless your 'known good' spare (of the correct type) sounds better.
Which is something that's worth checking out once in a while, or when a problem is suspected.
Note that when replacing power tubes, to achieve consistent results between sets, it's beneficial to check the mains Vac, HT (B+) Vdc, and plate or cathode current of each plate tube.
I understand that it's common for the mains Vac in North America to be well over the nominal 120V, eg up to 129Vac. If that's the case in your area, I suggest the use of a BrownBox to reduce it to the correct level for the amp being used.

BbendFender
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American Patriot

About as ordinary as you can get.
Oct 4th, 2018 12:42 PM   Edit   Profile  

It's just a 12AT7. I wouldn't compare it to a rectifier tube. 12AT7's get weak.

willie

Too Near Atlanta GA

Amp Tech Emeritus
Oct 4th, 2018 01:44 PM   Edit   Profile  

Agree comparison to a rectifier is not a really accurate analogy...but we get the idea in mind. :)

I'd also pay close attention to what pdf64 stated in his explanation of the reverb circuit as he is on the money as usual. I have not in my experience seen a great deal of tube failure related to excessive mains AC voltage, though it is quite plausible that such could occur. The 12AT7 is the common reverb driver of choice in most Fender reverb amps because it's a tough cookie...But indeed, they do go soft especially due to the fact that they run at close to or over their spec'd rated plate voltages. I never suggest using cheap or poorly designed phase inverters or reverb drivers...they take a beating.

BTW, Measured line VAC in my shop is 127.5 Volts at 60 cycles (Hertz for you younger folks... :) )

Big Joe

USA

Oct 4th, 2018 01:53 PM   Edit   Profile  

I replaced the 12AT7 tube in my PRRI. I used a ECC1 tube I had and all is well now.

(This message was last edited by Big Joe at 03:54 PM, Oct 4th, 2018)

willie

Too Near Atlanta GA

Amp Tech Emeritus
Oct 4th, 2018 02:17 PM   Edit   Profile  

??? ECC81? That's a 12AT7... :)

w

Big Joe

USA

Oct 4th, 2018 03:12 PM   Edit   Profile  

12AT7 and an ECC1 are the same value tube. The 12AT7 was the Grove tube that went bad which I replaced with a JJ ECC1.

willie

Too Near Atlanta GA

Amp Tech Emeritus
Oct 4th, 2018 03:24 PM   Edit   Profile  

What I'm trying to tell you is that the tube you are referring to is an ECC81 not an ECC1 which I do not believe exists in the world of vacuum tubes. :-) Yes, the ECC81 and 12AT7 are the same.

w

Leftee
Contributing Member
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VA

Oct 4th, 2018 04:02 PM   Edit   Profile  

I swapped out the output tube in my DSL1 with a NOS ECC82.

That’s one better. (-;

Big Joe

USA

Oct 4th, 2018 05:22 PM   Edit   Profile  

Yes of course an ECC81.. just a typo.

(This message was last edited by Big Joe at 07:22 PM, Oct 4th, 2018)

willie

Too Near Atlanta GA

Amp Tech Emeritus
Oct 4th, 2018 07:15 PM   Edit   Profile  

Figured that was the case Joe....

The ECC82/12AU7 is also a good choice in many applications...

w

Big Joe

USA

Oct 5th, 2018 04:25 AM   Edit   Profile  

The main premise of my question is...Do any of these tube variations offer any difference to the sound or characteristics of the reverb .ie. tighter, boomy etc.

Leftee
Contributing Member
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VA

Oct 5th, 2018 08:40 AM   Edit   Profile  

It really depends on how/where they’re used in the circuit. That’s why I said I generally only swap V1 if I want to play “chase the tone dragon” with tube swaps. Next is the PI. I’ve done a fair bit of tube swaps with various amps and V1 has usually had the most profound effect. And often that is only a slight change. I’m talking the small tubes. Not output tubes. It’s a fun passtime. And, I’m sure other more knowlegable folks can add better insight. I’m just speaking from somewhat limited experience.

That is saying that all the tubes swapped are good tubes to begin with.

willie

Too Near Atlanta GA

Amp Tech Emeritus
Oct 5th, 2018 09:10 AM   Edit   Profile  

Again, as mentioned above....the 12AX7 reverb recovery amp stage most certainly can have a positive or detrimental effect on "tone" (that most subjective of things). The driver tube can make the reverb sound weak or even distorted if it is defective but beyond that it isn't a real factor in "tone". Of course, rectifier tubes are often said to be a factor based on their ability to either sag the voltage or stay stiffened during current loading...so there you go. :) It's all magic anyway...smoke and mirrors I say. :-)

willie

Big Joe

USA

Oct 5th, 2018 10:46 AM   Edit   Profile  

Thanks Willie you answered my question on the Reverb tube.

pdf64

UK

Oct 7th, 2018 12:00 PM   Edit   Profile  

Regarding the efficacy of tube rolling in a PRRI, note that it doesn't have a PI tube as such. Rather one V4 section is a cathodyne, the other is the trem oscillator.
A cathodyne operates under the constraint of 100% negative feedback, hence I don't see how any tonal contribution from the particular tube fitted could have much / any effect, as the entire gain of the tube is working to linearise the response and so negative that.

Hence I suspect that any functional 12AX7 in V4 will give a similar response / tone; does anyone's experience differ?

It's a very different scenario to V1, where the 2 sections operate without any negative feedback and additionally are arranged in cascade (thereby perhaps squaring the particular tube's tonal contribution).

PRRI schematic

(This message was last edited by pdf64 at 04:08 AM, Oct 8th, 2018)

FDP Forum / Amp Mods, Repairs, and Projects / Reverb tube




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