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calling all tube amp experts (ampeg B-15R question)

Doc Halo

Doc Halo

Musician, heal thyself.
Oct 10, 2004
347
220
Nashville, Tennessee
#1
So I bought an Ampeg B-15R from another TBer a few weeks back. I really love it, but I have a couple of of questions about they way that it performs. To wit:

1. In the last few days, when I switch out of standby mode (after giving the tubes several minutes to warm up), the amp emits a wash of white noise--sort of like waves breaking over the beach--for about 10 to 15 seconds. Once the noise dissipates, the amp is perfectly silent and functions normally. Any clues what might be causing this?

2. I've noticed that while the transformer on the right hand-side gets warm to the touch with normal use, the transformer on the left-hand side never gets warm at all. Is this normal?

After years of solid-state and hybrid amps, I've really been bitten by the tube bug. Any insights would be greatly appreciated. Thanks!
 
#4
My SWAG on the startup noise would be that some component (could be a tube, a capacitor, a resistor, or something else) is beginning to fail. When the voltage first hits the circuit, that component makes noise. Then as it warms up, the component starts working normally and the noise goes away. The first and easiest test would be to change out the tubes one at a time, letting the amp cool off in between tube swaps, and see if you can identify the culprit. If that doesn’t work, you’ll have to give it to a tech for proper troubleshooting. If you’re not gigging with the amp, you might be able to live with that noise for quite awhile before anything actually fails.

Guys coming from the solid state world tend to resist the idea of buying a spare set of tubes, but it’s a useful thing to have around. If you’re performing with the amp, spare tubes are mandatory.
 
#5
Thanks for the replies, guys. RickenBoogie, you're right--it's a terrific little rig.

main_sale said:
I don't have your white noise problem but my transformer on the right also gets warm to the touch. I consider that to be normal. The white noise, not so much.
Click to expand...

I expected both transformers to get warm--what I thought was odd was that the right one did, and the left one didn't. If yours does the same, then I guess it is normal.

Fletcher Munson said:
My SWAG on the startup noise would be that some component (could be a tube, a capacitor, a resistor, or something else) is beginning to fail. When the voltage first hits the circuit, that component makes noise. Then as it warms up, the component starts working normally and the noise goes away. The first and easiest test would be to change out the tubes one at a time, letting the amp cool off in between tube swaps, and see if you can identify the culprit. If that doesn’t work, you’ll have to give it to a tech for proper troubleshooting. If you’re not gigging with the amp, you might be able to live with that noise for quite awhile before anything actually fails.

Guys coming from the solid state world tend to resist the idea of buying a spare set of tubes, but it’s a useful thing to have around. If you’re performing with the amp, spare tubes are mandatory.
Click to expand...

Your SWAG sounds entirely plausible to me. On the other hand, both times that I powered up the amp this morning, the noise wasn't there, so now I don't know what to think. :confused:

I appreciate the advice about the spare tubes as well. I expect to do at least some performing with this amp, and I've also recently purchased one of the last of the SLM-era SVT-CLs and an early SVT-II Pro for other applications. I have a feeling I'm going to become fairly used to having plenty of extra tubes around the house. :)
 
#6
The right transformer is the power transformer, so it would make sense that it would be warmer than the output transformer, considering if it's in satndby, the OT isn't being used.
 
#8
Hi.

If the amount and/or duration of white noise is changing depending of the time the amp has been off the likely cause is any of the electrolytic capacitors. Main filter caps would be the first I'd check. When they age, the storing capacity is reduced and they tend to lose the "silent start" feature.

For me, that's perfectly normal in an old tube amp. I've used amps with all kinds of starting noises for years with no additional problems. One reason has been that the availability of caps has been piss-poor for decades over here, so nowadays I probably wouldn't just use the amp, but replace the cap(s).

If the noise is always there no matter how long the amp has been off, and the duration stays the same, I'd suspect a carbon resistor in a RC circuit.

In any case, I see the starting noise more like a feature than a fault in a vintage (tube) amp.

As for the spare tubes, have as many pre-amp tubes with You as you like, those can usually be replaced if they blow while on a gig. Carrying power tubes isn't necessary or feasible if You don't have the equipment to replace a few other components in the circuit on the road too ;).

Regards
Sam
 
#9
T-Bird said:
Hi.

If the amount and/or duration of white noise is changing depending of the time the amp has been off the likely cause is any of the electrolytic capacitors. Main filter caps would be the first I'd check. When they age, the storing capacity is reduced and they tend to lose the "silent start" feature.

For me, that's perfectly normal in an old tube amp. I've used amps with all kinds of starting noises for years with no additional problems. One reason has been that the availability of caps has been piss-poor for decades over here, so nowadays I probably wouldn't just use the amp, but replace the cap(s).

If the noise is always there no matter how long the amp has been off, and the duration stays the same, I'd suspect a carbon resistor in a RC circuit.

In any case, I see the starting noise more like a feature than a fault in a vintage (tube) amp.

As for the spare tubes, have as many pre-amp tubes with You as you like, those can usually be replaced if they blow while on a gig. Carrying power tubes isn't necessary or feasible if You don't have the equipment to replace a few other components in the circuit on the road too ;).

Regards
Sam
Click to expand...

Hey Sam,

Thanks for the highly informative post. One of the electrolytic capacitors could certainly be the source of the noise. I hadn't used the amp for about two weeks when the noise appeared the day before yesterday. In contrast, I played the amp quite a bit yesterday, and it was silent each time I switched out of standby.

I also appreciate the idea that the noise, whatever its source, is part of what makes a tube amp a tube amp. My initiation into the tribe proceeds apace. . . :cool:
 
#11
Hi weary hobo.

You're welcome.

Sounds like the caps are showing their age then. Sounds also like there's quite a few "hours" on them left if they are silent after being off for a day or so.

MAMMOTHvolume said:
transformers shouldn't be getting warm its a sign that there not big enough for the amp ;o
Click to expand...

Transformers are usually just as big as what gets the job done barely and that's too small in the engineering viewpoint.

BUT...

Tube amps draw quite an idle current even if class AB like in this instance, and obviously the full power if class A. The transformer losses heat the transformer more or less. Much more than in a class AB SS circuit in any case.

If the transformer gets hot to touch, then there's a problem. The amp would in most cases cease to function well before that though.

Regards
Sam
 

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