The Steel Guitar Forum

I dicided 9 months ago to replace my old 72 Twin Reverb through a brand new one. It's this edition with color caramel ordered from England.
My old on is super quiet while the new one has a considerable hiss. Tried everything without succes. Is it possible to eliminate the hiss?

Why on earth would you "replace" a 1972 Fender Twin Reverb with one of the new "Fender-in-name-only" pieces of junk?? Your "old" one is MUCH MUCH better than new!!!

What Steve said.

If it ain't broke, don't fix it!!

Sigi Meissner wrote:I dicided 9 months ago to replace my old 72 Twin Reverb through a brand new one. It's this edition with color caramel ordered from England.
My old on is super quiet while the new one has a considerable hiss. Tried everything without succes. Is it possible to eliminate the hiss?

While I agree with the other comments, check the tubes for the hiss problem. Might be V6 in the preamp if it isn't the power tubes.

Buying a new tube amp these days comes with possible problematic "new" tubes.


The new tubes tend to suck...

Did You contact the supplier? It should still be under warranty.

My Son (in Australia) had exactly the same problem here...it went back to the dealer for warranty repair....ended up a replacement amp....yours is the fourth one I've heard about...

Peter

Might be V6 in the preamp if it isn't the power tubes.

Power tubes do not "hiss".

Excessive hiss in a new amp is a warranty issue, period. If it's louder than your vintage TR it could be a preamp tube, a defective plate resistor, a defective capacitor, a printed circuit board problem - there are a bunch of possibilities, all covered under warranty.

Fender owns Groove Tubes and loads new amps with mid-quality tubes; many gigging players that buy "reissues" replace all the tubes immediately to improve the tone (replacing power tubes requires checking the bias at minimum, which means a tech visit unless you are equipped to do it yourself).

But like others I'm baffled as to the reason for buying a cheaply-made "sort of" reissue when you own a far more reliable and easy-to-service vintage TR. If there are problems with your vintage amp they should be easy to solve by a competent tech.

That design is one of the most bulletproof ever made. Properly maintained, Fender's amps based on the same general circuit are probably the most reliable (and inexpensive to use) hand-wired amps around.

Jim Sliff wrote:

Might be V6 in the preamp if it isn't the power tubes.

Power tubes do not "hiss".

There have been reports of swapping power tubes to eliminate a hissing problem.

High gain tube amps may hiss when cranked as nature of the beast.

The OP wasn't clear exactly what was going on, whether the amp is still under warranty or not, or under what circumstance the hiss occurs.

But yes these reissues are hissing as reported by others and some experience it months in after taking possession of the amp.

If under warranty, it's easier to let the dealer deal with it if they are so inclined.

Groove Tubes are re-labels of tubes made outside of conus.

Send the re-issue back for a refund. Take your 72 in for a complete checkup/service. Put the money you saved back in your pocket. Hiss problem solved!

The problem is probably in the tremolo. In Fenders that are imported to Europe the photocell is replaced with little circuit board full of very small smd-components and it is quite noisy. The reason for substitute is that the original photocell contains kadmium. Good news is that in the main circuit board there is a place for the original component and your amp tech can change it.

There have been reports of swapping power tubes to eliminate a hissing problem.

High gain tube amps may hiss when cranked as nature of the beast.

I would love to read the reality behind those reports. "Swapping" power tubes between sockets doe snot take any out of the circuit or eliminate any electronic function. Swapping "preamp" tubes - sometimes, especially if a "preamp" tube is swapped with a same-type tremolo oscillator (a non-audio tube) that is lower in hiss. Or a "quieter" tube is swapped into a lower-gain position - both being used in actual audio stages.

And high-gain amps hiss, yes - and the "gain" is created in the *multi-stage preamp* - NOT power amp.

I got a whole batch of 12AT7s free one time. Every one of them had a pronounced hiss when used in the reverb driver of a twin. Oh well at least the price was right.

My amp tec changed one of the pream tubes. The hiss reduced drasticly. Thnx for your helpful comments

Sigi Meissner wrote:My amp tec changed one of the pream tubes. The hiss reduced drasticly. Thnx for your helpful comments

Well thats good news but it doesn't describe the fix.

A 12AX7 (7025) has a gain factor of 100, the highest of the bunch. A replacement tube can have slightly less gain so the hiss would indeed drop.

A 5751 has a gain factor of around 70, so replacing the 12AX7 with one of these would decrease the hiss just by the natural gain reduction of the tube by around 25 or 30 %.

a 12AT7 has a gain factor of around 60 , making it even less than a 5751. Swap that 12AX7 with one of these and certainly the hiss will drop as well.


If the original 12AX7 had the highest gain of any of the replacements than the hiss would be reduced because the overall gain of the signal going to the power tubes is reduced. A really good tech should tell us WHY he replaced the tube and if there was a difference in gain factors. You do this with a scope and multimeter.

A noisy tube is not the same as a weaker tube.

Many players pull 12AX7's on the front end and replace them with 12AT7's to purposely reduce the preamp gain. Some say it improves overall headroom, maybe it does maybe it doesn't. To me it appears that it just reduces the gain of the amp. IF the amp is designed with tubes X,Y + Z, those are the tubes I use.


As stated above, if an amp HISSES, sure it is very possible that a tube is causing it, but it is also possible that it has nothing to do with tubes. Changing a tube with a lessor gain factor gives the appearance of fixing the hiss but in all practicality the same amount of hiss is still present, but now at a lower gain level so it sounds like it is fixed.