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Ampeg SVT Blueline 1969/70

G

Greg Evans

Dec 3, 2023
33
89
#1
I have had mine since 1972. Bought second hand in America and used heavily until 1984. It has been in storage ever since. Got it out for the first time last week and it is in very poor condition. Damp and general rot has taken its toll.

Is there anyone out there who could give me advice on beginning the restoration of this (my) pride and joy? Now living in the UK.
 
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#2
Probably a good idea to start with general cleaning.

You could try to recondition the capacitors by bringing the amp up slowly on a variac...but if it's been almost 40 years since the amp was powered up, I wouldn't hold my breath.

Of course, if it has not been converted to 220V, that needs to be done first. Setting the amp up for 220V may not be possible though, as the 69 schematic shows a single primary winding on the PT. So a step down transformer will be required...or you can have someone custom wind power transformer (PT). There are no off-the-shelf PTs for this amp if it is still set up for 6146 as the screen winding runs at a lower voltage than later 6550-based SVTs. I had Heyboer do a custom PT for my 69. The main reason I bought it was to see how the amp sounded with 6146s.

I would also check to make sure node-H has been built into the power supply. Without this update, the driver tubes can be pushed into blocking distortion. The bias for the output tubes runs through the second driver stage, so if blocking distortion occurs the output tubes loose bias and conduct full on...which leads to tube failure.

Here are posts that will point you to other useful threads and provide a lot technical materials you need:
https://www.talkbass.com/threads/nad-project-svt-blueline.1372524/#post-21974171
https://www.talkbass.com/threads/nad-project-svt-blueline.1372524/#post-21974251

Here is an image for the Power PC card showing the cuts for the reliability update. Don't think I included this in the posts linked above, but there is a gut shot of an amp with the mod clearly visible.
upload_2023-12-3_17-40-7.png
 
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#3
Thanks for the info Wasnex! I am in the cleaning stage, got it all apart and will post som pics today. Looks more like a 70/71 to me now that it’s apart.

once I’ve cleaned it I will have to find someone good here in the UK to start the electrical/electronic work. Are you aware of any UK techs on the forum?

thanks for the response. Greg
 
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#5
Greg Evans said:
Thanks for the info Wasnex! I am in the cleaning stage, got it all apart and will post som pics today. Looks more like a 70/71 to me now that it’s apart.

once I’ve cleaned it I will have to find someone good here in the UK to start the electrical/electronic work. Are you aware of any UK techs on the forum?

thanks for the response. Greg
Click to expand...

70-71...does this mean its set up for 6550? If it's 6550-based, the PT may have a dual primary, so it can be configured for 220-240V. Also the power PC card should have node H of the power supply already built in.

There are or were a few UK techs on TB. AFAIK, they don't generally get involved with SVT repair threads. I believe @Mr. Foxen still posts. His shop is Ampstack in Bristol. Maybe he can point you in the right direction.

If the amp has the original capacitors, you can look for date codes. If not, you can look for date codes on some of the pots...I think the bias pot have date codes on them, but you have to view codes on the inside of the chassis.
 
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#7
Wasnex said:
70-71...does this mean its set up for 6550? If it's 6550-based, the PT may have a dual primary, so it can be configured for 220-240V. Also the power PC card should have node H of the power supply already built in.

There are or were a few UK techs on TB. AFAIK, they don't generally get involved with SVT repair threads. I believe @Mr. Foxen still posts. His shop is Ampstack in Bristol. Maybe he can point you in the right direction.

If the amp has the original capacitors, you can look for date codes. If not, you can look for date codes on some of the pots...I think the bias pot have date codes on them, but you have to view codes on the inside of the chassis.
Click to expand...
 
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#12
crguti said:
Why would you keep an amp in storage for nearly 40 years?
Click to expand...

I don't want to make this personal or about anyone's lone decision, but this question does lead to a valid general point.

That is, this thing we call storage can be a bit of a self-deception about excess/disused belongings we can't allow ourselves to let go of to better homes or use somewhere else.

Storage in most cases is far from an archive or climate-controlled vault where things are preserved. "Storage" more often than not is more like a boneyard closet or garage where things go to rot that you gradually waste a steady flow of money year after year for "storage".

Electronics, art, and other goods in storage for 40+ years are a tedious, costly way to gradually degrade and break those things down before they go to the rubbish dump. It's not good for anyone but landlords and banks earning interest from mortgages. For everyone and everything else concerned it's just a waste. I think that's a shame.

Taking ownership--yeah I know, this topic bugs me. Semi-rant over.
 
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#16
Greg Evans said:
I have had mine since 1972. Bought second hand in America and used heavily until 1984. It has been in storage ever since. Got it out for the first time last week and it is in very poor condition. Damp and general rot has taken its toll.

Is there anyone out there who could give me advice on beginning the restoration of this (my) pride and joy? Now living in the UK.
Click to expand...

If it were mine, I'd take it to a qualified tech.
 
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#19
Greg Evans said:
Very helpful Wasnex. How can I spot the Node H built in or not?
Click to expand...

By reviewing the schematics and comparing to the power PC board. FYI Node H goes through R52
upload_2023-12-4_13-14-24.png

AFAIK the transition from 6146 to 6550 happened sometime in 1970.

Here are some additional file, my apologies if I have already provide some or all. Attached is a schematic for the 1970 power, 1977 service manual, and the 1969 Preamp. I provided the 69 preamp because the wiring in the umbilical that connects it to the power amp varies somewhat by era. There may be other minor differences as well.
upload_2023-12-4_13-21-18.jpeg


@beans-on-toast is a very good resource for old Ampeg tech material. He supplied quite a bit of what I have already provided.
 

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#20
Greg Evans said:
I agree! I have 3 others so time is not the issue. I can clean it up and make it ready to assess. Just need to find someone who will see it through with me.
Click to expand...


If you don't know what you are doing, cleaning may do more damage than good. The amp may very well be beyond economical repair. Refurbishments may be possible, but rather expensive. It's also possible the circuit boards disintegrate under a soldering iron. If it can't be rebuilt, there may be some valuable parts that can be salvaged.
 
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