Ampeg Reverberocket r12r

[Gadefejer]

I have this tube amp from 90's, which has a problem with rather high static noice/hiss but only on the clean channel and regardless inputsignal and level settings.

Very annoying as the clean channel was the whole reason for buying it long ago and even more as I now want to play at low levels. I'm not sure if it has always had this kind of bad sideeffect or my ears have become very sensitive by time. The fact is that it has never been to any service and has spend most of it's life packed away.

I'm ignorant with electronics but have tried to tap a little on the tubes without being able to hear any kind of change. Service around here cost almost same as what I spent from new, so the outlook is to sell it for very little or fix it with advice from knowledge people.

[Chuck H]

Hiss is generally a thermal noise byproduct of resistance. It's made worse by high gain settings because wave form compression brings all the frequencies to the same level. If your using pedals, be sure your hiss isn't being caused by the pedals by trying your rig with another amp.

Your amp is a re issue. I'm not familiar with that amp, but if it's like so many other reissue amps Ampeg may have used little 1/4 watt resistors wherever they thought they could get away with it. Sometimes changing some of these resistors can help with hiss. Sometimes it seems the ground scheme in these reissue amps has problems too. A popular mod is to rebuild reissue amps with similar to original parts on similar to original eyelet or turret boards. This often brings these amps closer to the performance of the originals.

[Gadefejer]

Thanks. I’m not using any pedals and adjusting the gain on the amp has no influence on the hiss/noise.

Yes, it’s a re issue. Technical specifications does not make sense for me, but I find a little here.
http://www.ampeg.com/pdf/R-12R.PDF

What I would be able to do myself could be to change a tube, but I understand it’s not likely that it’s the problem.

PS If I dare to throw more money after the amp, should I then ask the shop to adjust the bias and how many hours would be a fair deal?

[Tom Phillips]

My first recommendation is that you find someone or a store with another R12R reissue that you can compare to your amp. We cannot tell how bad your noise is from a description of the sound since everyone has different perception. If you find that other amps of your same model sound better to your ears then you know that yours can be improved. If they are all just as bad to your ears then you will know that it is probably not worth trying to improve your amp.

Does the reverb control affect the noise?

As you already said, you can try changing the tubes. Or you could just swap positions of the three small tubes. These are the pre-amp tubes and the stock type used is 12AX7 for all three. If the noise changes then we can work on isolating the noisy tube.

It doesn't sound right to me that your local shop wants about as much as the value of the amp to troubleshoot a problem like this. Hopefully you can find another shop. A good tech will know what to do to get an amp sounding correct within the limits of the original design. If you ask a tech to do specific things then you may end up paying for work that was not needed. I am not in favor of specifically asking a shop to do specific procedures such as “adjust the bias.” In this case you want the shop to reduce the clean channel background noise. If the tech says that he knows that your amp should be quieter and is qualified to fix it then you will decide if you trust him and are willing to pay the quoted price. If the amp is already benched for service then a bias adjustment is no big deal and I would consider it part of the checkout and tuneup and make the adjustment if it was needed.

[Gadefejer]

I have googled through many video reviews with the Ampeg R12R reissue and not heard or read other people mention this kind of hiss. If I do a recording with a usb mic it’s very obvious to hear (I guess for everybody with normal hearing) before I start to play and it's not a static noise coming from the mic.

I have tried to adjust all the buttons incl. the reverb from lowest to highest but nothing have impact on the hiss. Another but weaker kind of hiss adds at maximum volume, but I guess it’s normal to get a little hiss when it’s turned all the way up.

I’m purely ignorant with electronics and it may be funny to you, but what has kept me from trying to switch around with the tubes, was that I recently saw a video when I searched the web for a solution. A guy with special knowledge said it was dangerous for amateurs to try to fix tube amps. Even to switch tubes when the power was not connected. Don’t do anything unless you know what you are doing etc., so this has kept me from switching around. I found it hard to believe but being ignorant I didn’t felt like playing with high power.

I live in north Europe which is fairly expensive compared to other countries and as I recall I paid about 900 dollars for the amp back in the 90’s. A local professional looking shop state a price for new tubes and adjusting bias for another Ampeg (SVT m/6550) at 850 dollars. I can probably find cheaper shops ones but moving it around to get a better offer will very soon eat the difference as taxies also know how much to charge.

[Tom Phillips]

A local professional looking shop state a price for new tubes and adjusting bias for another Ampeg (SVT m/6550) at 850 dollars.

The Ampeg SVT is one of the most expensive amps to re-tube. Don't use that as a comparison for service pricing on other Ampeg models.
I suggest that you ask your local shop for an estimate to work on your exact amp for the specific problem that you have.
Regards,
Tom

[Gadefejer]

Thanks. I will try that. And if you can say it's safe enough for a fool to switch around with the tubes when power is not connected I will probably dare this before.

[Chuck H]

The danger of moving tubes in an amp that's unplugged is that if you accidentally touch the insert pins when they're still in the sockets you can come into contact with high voltage. I've NEVER heard of this happening. But it's safe to assume it can.

If the problem hiss is so loud that the natural amp hiss (when you turn the amp up) isn't as loud, you almost certainly have a problem. It may be a bad tube or a bad ground lead. It shouldn't be too hard to fix. Unless you've had it in for a diagnosis/estimate you can't know what it will cost.