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Ampeg SVT-CL

RASHOSS

RASHOSS

Supporting Member
Jan 21, 2011
310
97
Oak View, CA
www.youtube.com
#1
At sound check last night I was peeking into the back of the head and noticed that 1 of the 3 smaller tubes (preamp tubes?) was not lit up. Does this typically mean it's "blown"?

I had all of the tubes changed about 10 years ago. Do other SVT-CL users change these tubes on a "regular" basis, or just keep pushing em until they pop? Is there any way to KNOW when they NEED to be changed?
 
#6
RASHOSS said:
Then, per Johnk's reply, does the tube not being lit up mean ANYTHING? Is the brightness of the tube a reflection of how well it's working?
Click to expand...

No, some brand's designs "hide" the heater filament so they wind up not "appearing" to glow as much. If it doesn't glow at all then it will be dead as the heater warms the cathode, the cathode then emits electrons. The heater can glow and the cathode not emit electrons (the tube won't function).
 
#7
RASHOSS said:
At sound check last night I was peeking into the back of the head and noticed that 1 of the 3 smaller tubes (preamp tubes?) was not lit up. Does this typically mean it's "blown"?

I had all of the tubes changed about 10 years ago. Do other SVT-CL users change these tubes on a "regular" basis, or just keep pushing em until they pop? Is there any way to KNOW when they NEED to be changed?
Click to expand...

TEN years ago?LMAO......:ninja:
 
#8
Lol. My tubes were last changed in 83. I was -3

Here are the tubes in my 72 svt
63e67c23.jpg
 
#11
Ya, tubes can last years. Even newer ones you should still get a good few years out of them. It's a little more of a crapshoot with them, but they've gotten a lot more reliable these days.
 
#12
This is what the SVT-CL User's Manual says about changing tubes.

Changing the Tubes

Tubes wear out in direct proportion to how often and how hard you play the amplifier. Power tubes should be checked at least once a year - more frequently if you use the amplifier nearly every day. When power tubes wear out, the amplifier will begin to grow weak, lack punch, fade up and down, or lose highs and lows. Power tubes work together in a push/pull configuration and should all be replaced at the same time with matched or balanced tubes. Your dealer can recommend the best replacement tubes for your amplifier. Preamp tubes aren’t worked as hard as power tubes and typically last longer. When a preamp tube wears out, the amplifier may squeal, get noisy, lose gain and sensitivity, or just quit working. A service center can determine which tube(s) may need replacing.

If the amp is used regularly, the tube bias should be checked about once a year as it the characteristics can change with use. Setting the bias will optimize performance. Also, if you can not set the bias properly, this is an indication that the power tubes need to be changed.

For a gigging amp, having a tech check out the amp on a regular basis is a good thing. Don't just bring it in when it is sick.
 
#13
B-o-T.........

I gave the people who wrote that interesting bit of near-misinformation a ration of trashin about it......

I'd advise ignoring it...... tubes last as long as they last...... it depends on a host of factors, most of which you won't know.

And "tube testers" are, in most cases, going to give bad answers. The best tube tester is the equipment. if it works right and sounds right, it IS right.

If not, a tube is the easiest fix, and they DO have a "wear-out" mechanism, so yes, they decline in "emission" over time. "Time" can be pretty long........

The VR manual is FAR more reasonable......

The Nature Of Tubes: Why (And When) To Replace Them:
Tubes are made up of a number of fragile mechanical components that are vacuum-sealed in a glass envelope or bubble. The tube's
longevity is based on a number of factors which include how hard and often the amplifier is played, vibration from the speakers, road travel,
repeated set up and tear down, etc.
Any time you notice a change in your amplifier's performance, check the tubes first.
If it's been a while since the tubes were replaced and the sound from your amplifier lacks punch, fades in and out, loses highs or lows or
produces unusual sounds, the power tubes probably need to be replaced. If your amplifier squeals, makes noise, loses gain, starts to hum,
lacks "sensitivity", or feels as if it is working against you, the preamplifier tubes may need to be replaced.
The power tubes are subjected to considerably more stress than the preamplifier tubes. Consequently, they almost always fail/degrade first.
If deteriorating power tubes aren't replaced they will ultimately fail. Depending on the failure mode, they may even cause severe damage to
the audio output transformer and/or other components in the amplifier. Replacing the tubes before they fail completely has the potential to
save you time, money and unwanted trouble. Since power tubes work together in an amplifier, it is crucial that they (if there is more than
one) be replaced by a matched set. If you're on the road a lot, we recommend that you carry a spare matched set of replacement power
tubes and their associated driver tubes.
 
#16
Jerrold Tiers said:
B-o-T.........

I gave the people who wrote that interesting bit of near-misinformation a ration of trashin about it.... tubes last as long as they last......
Click to expand...

Jerrold,

Yes, the VR guideline is somewhat more helpful. It is good for an owner to have some guidelines. I suppose that manufacturers want to cover themselves to some extent. It must be the tubes, not the amp.

I always chuckle when I read these sort of things. I have some tubes in an organ pre-amp that have been in regular service since the late 1930's. They seem to be holding up fine but I have a couple of spare sets just in case. Who knows, some owner in the distant future may need them. :p


David
 
#17
I replaced all the tubes in my CL after it was only seven years old, at the recommendation of a "tech" who claimed he tested them and found two of the power tubes bad. The end result was worth it, even though replacing them didn't solve the initial problem (it was the standby circuit violently crapping out). Out came the Sovteks, and in went JJ pres and Winged "C" power tubes, and I immediately noticed it's tone more resembled the vintage SVTs I had owned in the past. Preamp tubes can be fun to try out and swap around, as I also tried different GT and Mesa brands, but found the JJs sounded best.
 

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