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Ampeg SVT (old school) amp help - 60s/70s

sleepy_monkey

sleepy_monkey

Dec 20, 2007
4,169
199
Asheville, NC
#1
Hey team. So I’ve been out of the ‘playing out’ game for a long time. I’ve been a TBer for a really long time. I’m a home warrior now.

Yesterday I saw a deal on an old school Ampeg SVT and the squareback cabinet. I jumped on them.

The head doesn’t work…some burnt ceramic parts (maybe resistors..not sure) so I’ll need to find someone in western NC to sort that out. So first, does anyone know anyone?

Second…it needs all new tubes for the power section as they are missing. Any suggestions that will be ok for just playing at home?? I see the pricey options, but any full kits that won’t get crazy?

Third, any idea of the date? I can’t quite make out the full serial….but maybe someone can see something I don’t.

I’ll be replacing the grill cloth with the appropriate cloth and after that letting the mojo stay.
 

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#2
Style of the head is mid to late 70s.

The flatback cab is earlier, wouldn’t have been a matching pair from the factory, by the time that head design came out they had gone to tilt back cabs.

Use whatever power tubes your tech installs and will warranty. I have new sensor tung sols in mine, others prefer different brands.

Can’t help on NC local but I’m sure others will be along who can. Good luck. Should be a great sounding pair if you can get the power supply issues sorted out.
 
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#3
That looks like at least a '74 based on the real panel . . . No fan opening, 3 cord retention lugs, and it looks like the the manufacturer plate says Ampeg . . . A division of Magnavox. Also, it's a black-line graphic front panel.

There's a website that has year-by-year categorization which I'll look for.

Fluptops was the best source for old Ampeg parts, but I think he had a major fire a while back.
 
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#4
ELG60 said:
That looks like at least a '74 based on the real panel . . . No fan opening, 3 cord retention lugs, and it looks like the the manufacturer plate says Ampeg . . . A division of Magnavox. Also, it's a black-line graphic front panel.

There's a website that has year-by-year categorization which I'll look for.

Fluptops was the best source for old Ampeg parts, but I think he had a major fire a while back.
Click to expand...
Yes, I’ve been scouring Fliptops for the parts. Looks like they are back up and running. It has been a while since I’ve ordered from there, but always a great resource.
 
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#5
coreyfyfe said:
Style of the head is mid to late 70s.

The flatback cab is earlier, wouldn’t have been a matching pair from the factory, by the time that head design came out they had gone to tilt back cabs.

Use whatever power tubes your tech installs and will warranty. I have new sensor tung sols in mine, others prefer different brands.

Can’t help on NC local but I’m sure others will be along who can. Good luck. Should be a great sounding pair if you can get the power supply issues sorted out.
Click to expand...
Thanks for the info. Maybe I can find some used tubes and get this going on a budget. :)
 
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#7
sleepy_monkey said:
Thanks for the info. Maybe I can find some used tubes and get this going on a budget. :)
Click to expand...

Not really an amp where I would approach repairs with an “on a budget” mindset.

The damaged part there is R49 on the schematic, should be a 4.7k, 15W rated part on this era of amp. It looks like the repair has been half-assed already, given you’ve got two burned out cement block resistors there. This connects to the rectifier circuit and first power supply/filter cap node.

 
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#8
coreyfyfe said:
Not really an amp where I would approach repairs with an “on a budget” mindset.

The damaged part there is R49 on the schematic, should be a 4.7k, 15W rated part on this era of amp. It looks like the repair has been half-assed already, given you’ve got two burned out cement block resistors there. This connects to the rectifier circuit and first power supply/filter cap node.

Click to expand...
Thanks and definitely makes sense on just doing it right instead of on a budget.

I need to get this to someone that can get it straightened out. I’ve worked on vintage electronics…but with this I’m not sure what has been done (since you suggested someone else might have already done something). Is that R49 a ‘wear’ part or something else likely the issue and blew that?? Probably too much to determine based on just pics.
 
#9
A sextet if 6550s alone is going to run about $360. It's really important to get the amp sorted before new tubes are installed. The repairs may be relatively cheap or the amp may be a total money pit.

Here's my example. In 2013 I bought a 69 SVT for $1350 delivered. It was supposedly in good working order and had a new Mercury Mags power transformer. It arrived with a dead tube and the fan was non-op. The fan had simply come unplugged in shipping. The dead tube pulled a screen resistor. When I replaced the resistor I noticed the Power PC circuit car had seen a really hard life. Also there was a mod to drop the screen voltage because the new PT was not correct for the earlies SVTs. This mod greatly limited how much power the amp could produce.

The output tubes were mix and match. I bought a new matched set of 6146Ws and have slowly nursed the amp back to health. I installed major reliability update that should have been done in 1970. I gathered specs for a few years and then had Heyboer wind a proper PT. This allowed me to remove the screen circuit mod so the amp will make full power. So far I have spent almost $700 on just parts. I have done the work myself. IME usually when a tech works on your amp, the most expensive charge is labor by a long shot.

The amp sounds great and makes a lot of power. It does have a bit too much residual hum, but it's much better than when I received it. My belief is the mid control inductor is is the likely the primary source of the hum. The following is from the SVT II service manual.

1746897911595.png


Original mid control inductors are pretty much unobtanium. I believe Mercury Mags offers a proper replacement but it's pretty expensive.
 
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#10
sleepy_monkey said:
Thanks and definitely makes sense on just doing it right instead of on a budget.

I need to get this to someone that can get it straightened out. I’ve worked on vintage electronics…but with this I’m not sure what has been done (since you suggested someone else might have already done something). Is that R49 a ‘wear’ part or something else likely the issue and blew that?? Probably too much to determine based on just pics.
Click to expand...
Doing it right does not mean getting the most expensive NOS tubes you can find, by the way. A couple you can only get NOS but they’re not very expensive.
 
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#13
sleepy_monkey said:
Got it. Any that you would recommend that won’t break the bank? I see what is on the Fliptops site and a few others. Again, this isn’t going to be a gigged setup….basement rig…lol.
Click to expand...
Gigging or sitting in a basement: the circuit doesn’t care.
Poorly done/ partial / inept repairs will cost MORE when other parts burn up.
 
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#17
Whatever you do, don’t power it up. You said that you have electronics experience. Make sure that the electrolytic capacitors are fully discharged and have zero voltage across them. If you feel comfortable doing so, before sending it out, it would help to carefully clean it up. Use pharmacy isopropyl alcohol (IPA) with Q-tips and cotton makeup removing pads. This is a time consuming process and can save on tech time.
 
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#18
coreyfyfe said:
Style of the head is mid to late 70s.

The flatback cab is earlier, wouldn’t have been a matching pair from the factory, by the time that head design came out they had gone to tilt back cabs.

Use whatever power tubes your tech installs and will warranty. I have new sensor tung sols in mine, others prefer different brands.

Can’t help on NC local but I’m sure others will be along who can. Good luck. Should be a great sounding pair if you can get the power supply issues sorted out.
Click to expand...
Take it to Todd Sharpe in Nashville. A couple hours drive, but his shop is as good as it gets for nice amps.
 
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