NAD/Project SVT Blueline

[greengoblin]

Picked up a project for my workbench, my holy grail of bass amps, a Blueline SVT. Looking over this head, I can see it has had some hands in it for different things. A few solder traces have pulled up, a few changed caps and some missing parts. This thing is definitely a project that will have me busy for some time.
After inspecting everything, the head case and tolex are in excellent shape for it's age. The faceplate is in great shape and does not look like a repo. The preamp looks like it is all there and has all the tubes that I havent pulled yet. The chassis is not painted and it used to have 6146 tubes as the holes and grommets are still present. The serial on the unpainted chassis is 005223, the hand written number on the chassis is either "01" or "61". Im thinking 61... The preamp is marked "46" so, if I am not mistaken, they originally would match?

I am sure I will have a lot of questions. Such as:
Did these amps come with a tube cover over V6, V7 and V8?
Does anyone have a spare backplate they want to sell? Fliptops is out and it is the one piece I am missing.
The grille cloth looks odd to me, so I am thinking it may not be original?

Will keep you guys posted as I go with more pics and info. Going to redo this and keep as much as possible original. Focus on testing and replacing the missing tube socket for now.

Sorry for the crappy first pic.

 

[Wasnex]

Picked up a project for my workbench, my holy grail of bass amps, a Blueline SVT. Looking over this head, I can see it has had some hands in it for different things. A few solder traces have pulled up, a few changed caps and some missing parts. This thing is definitely a project that will have me busy for some time.
After inspecting everything, the head case and tolex are in excellent shape for it's age. The faceplate is in great shape and does not look like a repo. The preamp looks like it is all there and has all the tubes that I havent pulled yet. The chassis is not painted and it used to have 6146 tubes as the holes and grommets are still present. The serial on the unpainted chassis is 005223, the hand written number on the chassis is either "01" or "61". Im thinking 61... The preamp is marked "46" so, if I am not mistaken, they originally would match?

I am sure I will have a lot of questions. Such as:
Did these amps come with a tube cover over V6, V7 and V8?
Does anyone have a spare backplate they want to sell? Fliptops is out and it is the one piece I am missing.
The grille cloth looks odd to me, so I am thinking it may not be original?

Will keep you guys posted as I go with more pics and info. Going to redo this and keep as much as possible original. Focus on testing and replacing the missing tube socket for now.

Sorry for the crappy first pic.

By V6, 7, 8 I assume you mean the PI and driver tubes. No tube shields on these.

Up in the preamp, all tubes have shield except V5.

FYI I also have an 87 Skunkworks SVT. None of the preamp tubes are shielded and it has less hum than any SVT I have ever played.

Some recent thread you might find interesting...all Bluelines but later versions running 6550s if I remember correctly.
NAD/new nightstand day, my very 1st SVT!!!
NAD - SVT for me!
1970 Ampeg SVT blue face 6550's power amp issue

Once you get the amp up you'll want to see if Node H has been built into the power. I recently did this on my 69.

Here's a redacted post from one of the other threads.

The early bluelines with the 6146 tubes used a different power PC board. These boards are fairly easy to recognize because the original amps did not have power supply node H. In 1970, there was a factory mod that cut traces and added a capacitor and resistor to form node H.

Here is an image that shows the cuts required to add node H on the original board.
View attachment 3182351


Here is what the full mod looks like. I circled the cuts and bridged traces. You can also see the added resistor and capacitor.
View attachment 3182353

I'll add a few more files here; just click the thumbnails. Review the schematics and you'll notice some circles on the power amp schematics that are intended to draw your attention to the mod to install Node H.


No thumbnails for the service manuals. Be aware that Power PC board in the early bluelines does not match the diagram in the service manuals, since Node H was not built into the board.

I look forward to helping you get this beast going...it's not totally altruistic. Would love to get power supply readings for Nodes A, D, E.

I bought NOS JAN6146W from 6146 Tubes - Tubes - Transmitting, Audio, Misc.

Schematic says
A 660V
D -150V
E 220V

I believe real world readings are closer to
A 695V
D -183V
E 230V

 

[Wasnex]

If you need to build in Node H.

I sketched out this diagram while back. The blackline is the factory trace that connects to Node B of the power supply viewed from the bottom of the amp. You need to make three cuts so Node B is isolated from the driver tubes. Then build a bridge from Node B to R50. Next build a bridge between the cut trace connected to R14 and R15. I made the connection for Node H at the bridge to R15. Take your time and double check your work before making cuts. I used a fairly heavy chrome paper clip for the bridges.



If needed, you can order a capacitor kit from Fliptops. Capacitor Kits

My amp was still running most of the original caps from 1969 and most of them were way out of spec. I recapped the amp using the 6550 capacitor scheme. I ordered new 100/40uf twist locks from Hayseed Hamfest | Life's Too Short for Restuffing Can Capacitors.


I wired R52 to form Node H on one of the multi section capacitors and just ran a wire to the board.


6550 power amp schematic in case you want to use the capacitor scheme.


Let me know if I made any mistakes in the diagrams or if they are confusing.

 

[greengoblin]

By V6, 7, 8 I assume you mean the PI and driver tubes. No tube shields on these.

Up in the preamp, all tubes have shield except V5.

FYI I also have an 87 Skunkworks SVT. None of the preamp tubes are shielded and it has less hum than any SVT I have ever played.

Once you get the amp up you'll want to see if Node H has been built into the power. I recently did this on my 69.

Here's a redacted post from one of the other threads.

I bought NOS JAN6146W from 6146 Tubes - Tubes - Transmitting, Audio, Misc.

Schematic says
A 660V
D -150V
E 220V

I believe real world readings are closer to
A 695V
D -183V
E 230V

Thank you for all of the info!! Yes, everything in the pre has shields with the exception of the 6c4 which is a Groove Tube. And yes, the PI and driver tube cover. is what I was referring to. Wasnt sure if that was an old model feature or new. Havent decided what to do for the power tubes yet. May go 6550's, but it would be cool to go back to 6146. We'll see..

When I rebuilt my 1970 V4b project, I had found ohm readings for the transformers to check them before powering them up. Havent been able to find similar specs for the SVT yet. Showed something like 60 ohms per pair on the output tranny.

Would be nice to have a Skunkworks as well! May look for a II non pro next...

 

[Wasnex]

Thank you for all of the info!! Yes, everything in the pre has shields with the exception of the 6c4 which is a Groove Tube. And yes, the PI and driver tube cover. is what I was referring to. Wasnt sure if that was an old model feature or new. Havent decided what to do for the power tubes yet. May go 6550's, but it would be cool to go back to 6146. We'll see..

When I rebuilt my 1970 V4b project, I had found ohm readings for the transformers to check them before powering them up. Havent been able to find similar specs for the SVT yet. Showed something like 60 ohms per pair on the output tranny.

Would be nice to have a Skunkworks as well! May look for a II non pro next...

There should be a plate that screws to the top of the chassis to cover the Power PC board. The PI and drivers tubes stick up through the plate. No tube shields. The plate mainly keeps dust out and also keeps curious fingers away from harm.

A different Power Transformer is required to properly run 6550s. Node E (Screen Supply) for the 6146 equipped amps runs around at 220V per the schematics. On the later 6550 equipped amps, Node E runs around 350V. I didn't learn about the transformer change until after I bought my 69...unfortunately it has a very expensive replacement PT with the wrong screen taps.

If you decide to convert to 6550s, I would consider trading PTs if yours is good...but I think you would be better off running 6146s. Hopefully you can get yours up and running, share the power supply voltages, and then I will get a company to custom wind me a proper new PT.

 

[Wasnex]

The grill cloth on your amp is definitely not original. Unfortunately vendor supplies were depleted awhile back. Mojotone offers some options that would probably look a bit nicer.

[Invalid or Expired Link Removed]

 

[beans-on-toast]

The cabinet is a ‘69, I can tell be the sharpness of the top edge.

Definitely a lot of work, depending on how far you want to take it.

You can start by doing some homework here:

Ampeg SVT Blueline Club, 68 to early 70's.

 

[greengoblin]

If you need to build in Node H.

I sketched out this diagram while back. The blackline is the factory trace that connects to Node B of the power supply viewed from the bottom of the amp. You need to make three cuts so Node B is isolated from the driver tubes. Then build a bridge from Node B to R50. Next build a bridge between the cut trace connected to R14 and R15. I made the connection for Node H at the bridge to R15. Take your time and double check your work before making cuts. I used a fairly heavy chrome paper clip for the bridges.

View attachment 3209610

If needed, you can order a capacitor kit from Fliptops. Capacitor Kits

My amp was still running most of the original caps from 1969 and most of them were way out of spec. I recapped the amp using the 6550 capacitor scheme. I ordered new 100/40uf twist locks from Hayseed Hamfest | Life's Too Short for Restuffing Can Capacitors.


I wired R52 to form Node H on one of the multi section capacitors and just ran a wire to the board.
View attachment 3209612

6550 power amp schematic in case you want to use the capacitor scheme.
View attachment 3209617

Let me know if I made any mistakes in the diagrams or if they are confusing.

Sweet, thank you. Will have to check these out next time I sit down with it.. Just gathering a list of some items I will need so I can get to a point of being able to power up.

There should be a plate that screws to the top of the chassis to cover the Power PC board. The PI and drivers tubes stick up through the plate. No tube shields. The plate mainly keeps dust out and also keeps curious fingers away from harm.

A different Power Transformer is required to properly run 6550s. Node E (Screen Supply) for the 6146 equipped amps runs around at 220V per the schematics. On the later 6550 equipped amps, Node E runs around 350V. I didn't learn about the transformer change until after I bought my 69...unfortunately it has a very expensive replacement PT with the wrong screen taps.

If you decide to convert to 6550s, I would consider trading PTs if yours is good...but I think you would be better off running 6146s. Hopefully you can get yours up and running, share the power supply voltages, and then I will get a company to custom wind me a proper new PT.

There are clutch screws for the plate and I picked up a plate from Fliptops on my last order. Need to place another though as I am missing a ton of nuts and screws.

Didnt realize about the different power tranny for 6550's. THought I read where there werent changes and Ampeg hadnt made changes for the swap, but it could be internet mis-information. If it is a major change for 6550;s, I will definitely be going original. My V4b I could swap with some resistor upgrades that I was changing anyhow. So it was easy in that amp.

The grill cloth on your amp is definitely not original. Unfortunately vendor supplies were depleted awhile back. Mojotone offers some options that would probably look a bit nicer.

[Invalid or Expired Link Removed]

Well I am actually lucky, as I do have a roll of Ampeg grille cloth. Originally bought it to swap out the grille on my v4 cab, but decided not to swap it. Thought it was from Fliptops, but I bought it from Antique Electronic Supply. So I am covered there. Luckily I kept it in the closet all these years.

The cabinet is a ‘69, I can tell be the sharpness of the top edge.

Definitely a lot of work, depending on how far you want to take it.

You can start by doing some homework here:

Ampeg SVT Blueline Club, 68 to early 70's.

Thanks Beans! I read that post even before I had a Blueline just to get more familiar with them. Now I have even more reason to go back over all of the details. And yes, wait til you see the internal pics, I have a very long road ahead of me. But, I like a good challenge and I would rather spend quality time repairing this than to see it go in a dumpster... With my V4b build I went a little nuts on the rebuild. Seeing how I had even less parts for it I didnt feels to keep it original as much. But with this thing, I am going to keep as much as I can original.

The serial number on the chassis dictates a very early build, but seems to be even way before the serial dating I see posted being 005223. The seller thought maybe it was a very early build before production or a prototype. However two post on the chassis date 1970... Hmmm...

 

[greengoblin]

New pics.. Sorry, they are from my cell phone. I have the rear mesh grille/fan, but not the black back plate.

 

[JimmyM]

Believe it or not, I am told the original lot of 69's did not have a backplate. This after I bought one from Fliptops

 

[Wasnex]

New pics.. Sorry, they are from my cell phone. I have the rear mesh grille/fan, but not the black back plate.

The early amps may not have had a back plate. IMHO, it's purely cosmetic and unnecessary. I have seen some amps with the chassis labeled with a sharpie.

Seems odd that all the plate connectors have been removed. I wonder if a previous tech already converted the amp to 6550s. The traces on your Power PC boards looks pretty decent and it appears Node H has been added.

I was reviewing the specs for the 6146B versus 6146Ws last night.

The 69 SVT is spec'ed for Bs. Not a lot of NOS Bs available, but you can buy new Shuguangs.

6146B have 35W max plate dissipation. There is confusion on whether 6146W is 35W or 25W. Some claim that W's made after a certain time around 1964-65 were 6146B spec, and earlier tubes are 6146A spec. 6146W Information:. Others claim all 6146Ws are just ruggedized 6146As, which makes them a 25W tube.

The only datasheets I have found is for the RCA and Mazda 6146W. The RCA datasheet appears to be dated 9-65 and indicates 25W max plate dissipation (ICAS). Invalid Link Removed. The Mazda data sheet also indicates 25W Invalid Link Removed.

The commonly available 6146Ws are GEs and Philips ECG. I can't find datasheets for either. If these tubes have 25W plate dissipation ratings, following the factory bias procedures (assuming plate voltage ~690V) puts them at about 70% dissipation, which is probably fine. The question then becomes how well they stand up to abuse.

 

[Wasnex]

There are clutch screws for the plate and I picked up a plate from Fliptops on my last order. Need to place another though as I am missing a ton of nuts and screws.

When I did the cap job, I replaced all the rusty clutch screws with philips from my local hardware store. The amp is not a museum piece, so I am not concerned with keeping the hardware original.

 

[greengoblin]

Believe it or not, I am told the original lot of 69's did not have a backplate. This after I bought one from Fliptops

I was too late and they are all sold out. But I have seen that some may not have had a plate. The headbox has screw holes for one so there may have been one added at some point. Not a huge priority for me and if it didnt have one, that is cool too. Wont affect the tone! haha The super early chassis number has me somewhat confused comparing it to the date code sites.

The early amps may not have had a back plate. IMHO, it's purely cosmetic and unnecessary. I have seen some amps with the chassis labeled with a sharpie.

Seems odd that all the plate connectors have been removed. I wonder if a previous tech already converted the amp to 6550s. The traces on your Power PC boards looks pretty decent and it appears Node H has been added.

I was reviewing the specs for the 6146B versus 6146Ws last night.

The 69 SVT is spec'ed for Bs. Not a lot of NOS Bs available, but you can buy new Shuguangs.

6146B have 35W max plate dissipation. There is confusion on whether 6146W is 35W or 25W. Some claim that W's made after a certain time around 1964-65 were 6146B spec, and earlier tubes are 6146A spec. 6146W Information:. Others claim all 6146Ws are just ruggedized 6146As, which makes them a 25W tube.

The only datasheets I have found is for the RCA and Mazda 6146W. The RCA datasheet appears to be dated 9-65 and indicates 25W max plate dissipation (ICAS). Invalid Link Removed. The Mazda data sheet also indicates 25W Invalid Link Removed.

The commonly available 6146Ws are GEs and Philips ECG. I can't find datasheets for either. If these tubes have 25W plate dissipation ratings, following the factory bias procedures (assuming plate voltage ~690V) puts them at about 70% dissipation, which is probably fine. The question then becomes how well they stand up to abuse.

Yeah, I started reading some posts on the 6146B's and W's. Leaning on brings it back that way, but will have to review the boards closely to see what has been done so far. I really only pulled it for pics and havent touched it since. But at least my first box of Fliptop stuff came.. Well, minus the back plate as they were out.

When I did the cap job, I replaced all the rusty clutch screws with philips from my local hardware store. The amp is not a museum so I am not concerned with keeping the hardware original.

Very true. Most of mine have been retained so I will keep them for now. Although my clutch head screw driver is a hair too big for the ones on my V4b.

 

[Wasnex]

Yeah, I started reading some posts on the 6146B's and W's. Leaning on brings it back that way, but will have to review the boards closely to see what has been done so far. I really only pulled it for pics and havent touched it since. But at least my first box of Fliptop stuff came.. Well, minus the back plate as they were out.

In reviewing the gut shot photo, it appears the tube sockets have been rewired for 6550s. Note there appears to be thick black wires connecting pin 3 to the plate connections on the Power PC board.

 

[JimmyM]

I was too late and they are all sold out. But I have seen that some may not have had a plate. The headbox has screw holes for one so there may have been one added at some point. Not a huge priority for me and if it didnt have one, that is cool too. Wont affect the tone! haha The super early chassis number has me somewhat confused comparing it to the date code sites.

Well it's an unpainted chassis so it's very early for sure. Mine has screw holes for the backplate, too, although the chassis number was long gone and the labels for the stuff on the back has been written over a few times. But I talked to the previous owner once, and he confirmed it was a super early one.

 

[beans-on-toast]

Look in the power amp chassis for a pot date code starting with 137 followed by year and week of the year on the hum balance pot. There are also codes on the bias and balance pots.

 

[greengoblin]

Look in the power amp chassis for a pot date code starting with 137 followed by year and week of the year on the hum balance pot. There are also codes on the bias and balance pots.

Yeah, so far the two pots I could get to are from 1970. What year did they start painting the chassis? Also, the tag was still inside for the initials of who built the amp originally. Two marked "S.K" and one marked "D.B. - 18".

 

[JimmyM]

Yeah, so far the two pots I could get to are from 1970. What year did they start painting the chassis? Also, the tag was still inside for the initials of who built the amp originally. Two marked "S.K" and one marked "D.B. - 18".

Best I can tell is it was sometime in 1970 for the painted chassis.

 

[beans-on-toast]

Yeah, so far the two pots I could get to are from 1970. What year did they start painting the chassis? Also, the tag was still inside for the initials of who built the amp originally. Two marked "S.K" and one marked "D.B. - 18".

Ampeg always overlapped, there is no clear changover date. As Jimmy said, some time in 1970.

To refine, check the date codes on the other pots and the cement block resistors in the power amp. If the can caps are original they also have a date code. The earliest cabs had Lord isolation mounts, there is a date on those as well.

 

[greengoblin]

Best I can tell is it was sometime in 1970 for the painted chassis.

So then it could be a '70 model as the bias pots list the 35th week of 1970, 1377035. Was hoping it to be older, but really am just ecstatic to actually have one!

The balance pot looks to have been changed at some point as it looks like it is from '83. 380C2 100-5 19-8337

Ampeg always overlapped, there is no clear changover date. As Jimmy said, some time in 1970.

To refine, check the date codes on the other pots and the cement block resistors in the power amp. If the can caps are original they also have a date code. The earliest cabs had Lord isolation mounts, there is a date on those as well.

Looks like the caps list 1970 as well and one resistor lists 12-69.

Still seems like a strange serial number for a '70 head.. But with all of the changes that have been done to this thing, who knows its true history.. Will get some date codes off the preamp pots as well, maybe today.