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Distortion on 1972 SVT Blueline with Ampeg 212AV

D

Dallyd31

Jun 22, 2005
521
90
Peterborough, Ontario
#1
Hey All !

My 1972 Blueline is running through a newer Ampeg 212AV. Sounds great, but when I run my Ric 4003 and get the amp volume up to about 10:00 is starts to distort, and at 11:00 its very fuzzy. Lots of cone movement and distortion. Wondering if this is about normal for an old SVT, there is an issue with the amp, or is the amp is just too much for the 212, even though it is rated for 600W
 
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#5
Sounds like an issue with your amp to me. An SVT by about 11 o clock should be getting a bit of drive, especially if you're playing hard or have a loud input signal. If it's completely fuzzed out you might have an issue somewhere in the preamp. Does this happen with both channels? Does the amp seem quieter than before? Does this happen with other cabs or basses?
 
#6
coreyfyfe said:
Sounds like an issue with your amp to me. An SVT by about 11 o clock should be getting a bit of drive, especially if you're playing hard or have a loud input signal. If it's completely fuzzed out you might have an issue somewhere in the preamp. Does this happen with both channels? Does the amp seem quieter than before? Does this happen with other cabs or basses?
Click to expand...
I know with mine I went back to the 810 with my SVT and it sounded much better with more headroom. So my 212 sat there for months without being touched.

Then about two months ago I plugged my old GK800Rb into the 212 and it sounds great. So I left like that and don't bother with the SVT anymore. It can live at 2 ohms with the two 810's
 
#7
Dallyd31 said:
Hey All !

My 1972 Blueline is running through a newer Ampeg 212AV. Sounds great, but when I run my Ric 4003 and get the amp volume up to about 10:00 is starts to distort, and at 11:00 its very fuzzy. Lots of cone movement and distortion. Wondering if this is about normal for an old SVT, there is an issue with the amp, or is the amp is just too much for the 212, even though it is rated for 600W
Click to expand...

I had to screw and glue a rattling cross beam inside my 212 AV. When it was loose , it sounded like distortion. The cab was damaged during shipping. Something to consider.
 
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#8
coreyfyfe said:
Sounds like an issue with your amp to me. An SVT by about 11 o clock should be getting a bit of drive, especially if you're playing hard or have a loud input signal. If it's completely fuzzed out you might have an issue somewhere in the preamp. Does this happen with both channels? Does the amp seem quieter than before? Does this happen with other cabs or basses?
Click to expand...

Yes, basically the same with both channels, and changes marginally with my P bass, but it is less hot than my Ric. As for less loud, I don't think so, I haven't really noticed. What would being quiter indicate ?
 
#10
10cc said:
I know with mine I went back to the 810 with my SVT and it sounded much better with more headroom. So my 212 sat there for months without being touched.

Then about two months ago I plugged my old GK800Rb into the 212 and it sounds great. So I left like that and don't bother with the SVT anymore. It can live at 2 ohms with the two 810's
Click to expand...

I had the opposite experience but my 8x10 is a flatback and I have a pair of the 112AV not the single 212. So maybe not perfectly comparable.
 
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#11
Dallyd31 said:
Yes, basically the same with both channels, and changes marginally with my P bass, but it is less hot than my Ric. As for less loud, I don't think so, I haven't really noticed. What would being quiter indicate ?
Click to expand...

If you noticed that the amp was quieter than usual across both channels I'd suspect worn tubes somewhere in the 6C4 to power amp area. I'd check the bias at the very least, as you can do that easily with a meter on these amps.
 
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#12
Normally a 600W cab is a good match for a 300W amp. How the EQ is set is important. Too much bass is like turning up the volume.

Some types of speaker cabinet distortion are good, others are not. If it's a mechanical sounding flubbing, you are hitting the excursion limit and damaging the speaker.

As Corey said, you have to ensure that the amp is healthy. Ideally, first test the amp wih another cab. Assuming it is the amp, given your comments, I would swap out the 12DW7 in the power amp (lower) chassis. If you don't have one, use a 12AX7 for the test, it won't hurt the amp. Next I would swap out the two 12BH7 tubes and check the bias.
 
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#16
Just went home for lunch. Changed the 6C4 tube as well as the 12BH7. So, essentially all new (NOS) tubes. No difference. Tried it with my Mesa410 cab ( although that is an 8 ohm cab). Same fuzzy at around 10:30 on the volume dial. Its not flubby, farting out sound. Its a distorted "fuzz". Sounds fantastic until you get to that point though.
 
#17
Dallyd31 said:
Just went home for lunch. Changed the 6C4 tube as well as the 12BH7. So, essentially all new (NOS) tubes. No difference. Tried it with my Mesa410 cab ( although that is an 8 ohm cab). Same fuzzy at around 10:30 on the volume dial. Its not flubby, farting out sound. Its a distorted "fuzz". Sounds fantastic until you get to that point though.
Click to expand...

I'm trying to think back to my SVT and how loud I could get it with the small cabs. I think this may have been taken the last time I used it, my EQ settings aren't far from what you described and I was running a rick 4001, but my volume is below 9 o'clock and I was loud enough for the stage, but I also use an overdrive and compressor always on for that band, so I'm not looking for clean headroom either. Knob position isn't exact, though with a pcb-mounted pot I wouldn't expect too much variability, but by about 11 o'clock on most of the old ampegs I'd expect at least some hair. It could just be that the amp doesn't do as much clean volume as you want.

RvX6ezv.jpg
 
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#18
The tubes were the first stage.

Some distortion at 11 is not unusual. Lots of fuzzy is not.

In case I missed it, are the power supply electrolytic caps original?

As these caps age, the amp will run out of headroom and distort sooner as you turn it up. Worst case, you hear an increase in line related (120Hz) hum. If the electrolytic power supply caps are original, they should be checked. A tech would inspect them for bulging and leaks, if all is well, then take dc voltage readings at each node in the power supply. This includes the big electrolytic in the preamp chassis. These readings would be compared to the reference values on the schematic. There are other tests that can be done.

I have never seen an original cap in an SVT from that era that was up to spec today. It is the nature of the products and how they were used in these amps. If they have issues, they should be changed.
 
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