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SurfGuitar101 Forums » Gear »

Permalink NOS Tubes and Fender Reverb Units

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I know there are some older threads about this, but figured I'd start a fresh discussion as I'm currently going through this. I'm messing around with NOS tubes in my 62' Fender Reverb unit. Bought a couple of overpriced RCA 6k6s to swap out with the unlabeled tube that came with it when I purchased it. I noticed an immediate increase in the focus of the reverb: it added depth but with more room before the notes become "washed out," you might say. Replaced a modern 12at7 with a vintage RCA, noticed less noise...not sure if it was that big of a difference. I also picked up a few vintage Mullard 12at7s to try. I swapped out another Russian EH 12ax7 that was in the unit with a vintage RCA...didn't notice a real difference. Going to try a Mullard in there too once it arrives.

Any thoughts people have on these units and tubes would be appreciated. Just trying to milk the most tone and usability I can get out of this thing.

Hopefully we'll get a lively discussion going on NOS vs current production stuff. I've also experimented with all kinds of tubes in my Reverb Units and other vintage Fender amps. I've formed a few opinions, along with some favorite tube types. It would seem that, more often than not, Fender gear from the '60's came with RCA tubes, and later the etched glass GE stuff. (BUT, just like with speakers, it's whatever they could get a good deal on in bulk). The notable exceptions are the Tung Sol 5881 power tubes that were OEM in lots of late 50's early '60's amps, and the RCA labeled Mullard GZ-34/5AR4 rectifiers found in several of the combo amps. Back to your Reverb: the 12AT7 probably won't affect the tone much, so I use pretty much anything, new or old. After throwing about six different 6K6's in mine, all NOS USA stock, I ended up putting back the funky orig RCA with a zillion hours on it. I just liked it better. (I'm definitely NOT an expert, but my impression is that Reverbs don't run at as high voltages as the amps do, and the tubes tend to last forever). As far as 12AX7's go, my all time favorite, in any application, are the Amperex made in Holland Bugle Boys. Some guys like their Mullards, some their Telefunkens, and nothing wrong with RCA's, but I've found the Amperexes to be just about perfect in whatever I've put them in. Along with everything else vintage and NOS, they've gotten stupid expensive, but don't be afraid to try a couple of used/good ones.

On a related note, any feedback on the recent production Tung Sol re-issues?

Last edited: May 15, 2018 23:53:49

Replacing the 6K6 with a vintage RCA was definitely the biggest bang for the buck so far for me.

Blackbox wrote:

Replacing the 6K6 with a vintage RCA was definitely the biggest bang for the buck so far for me.

Same here. RCA 6K6

I recently swapped a vintage Tung-Sol 6K6GT into my reissue to eliminate the overdriving that the 6V6GT was causing and it worked like a charm. Beyond that, I think the nuances of tone from a reverb unit are lost on me. It changes the dry tone so extremely anyway that the little differences between tubes don't add up to much, to my ear.

I freely admit don’t know much about this, but I am interested. Are you guys rebiasing everytime you change a tube? Don’t you need fancy stuff to figure out the output of each tube? And then tweak something weird inside the amp? Or is that not a big deal with preamp tubes vs. power tubes?

I ask because I’ve thought about changing the power tubes but I don’t wanna wait two weeks for the amp dude to rebias just to hear if there’s a difference. I also admit I have done zero research!

Dan Izen

Last edited: May 16, 2018 08:16:59

You only need to bias power tubes, and then only in certain circuits (most Fender amps would be included here).

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I haven't been doing any sort of rebias when switching out the 6k6.

The Fender Reverb is cathode-biased. Swap away.

Ah! Copy that thanks for the info!

After going through a bunch, settled on the RCA 6k6, a Mullard 12at7 and a Telefunken 12ax7. I tried a Mullard 12ax7 but it was a bit too aggression. The Telefunken seemed cleaner and tighter.

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