Ampeg SVT Blue Line question

[BKL5]

I find it helpful to carry a piece of ¾” ply or an oak board to use as a ramp. This allows you to slide it up and take some weight off while wrangling the cab or head in the rear door or the trunk.

Larger cabs like the 810 below and the right vehicle can be easier than a smaller cab.

Hi beans-on-toast,
Excellent video... and some good advice. Thanks!

 

[Wasnex]

I think the first ones were made for or at least used by The Rolling Stones in 1969,

6146s make a bit more power than 6550s but don't like the high screen current that occurs with hard clipping. Some people put bigger resistors on the screens to make the amps more reliable.

I have a Blueline with pots dated to 1968. Unfortunately it has an aftermarket PT that is spec'ed for the 350 volt screen supply used with the 6550 version of the amp. The original 6146 PT provided 220V for the screen supply. The 6146 is spec'ed for max of 250V on the screens, but a lot of radio types suggest the tubes are more reliable with screens limited to 200V. As 6146s also don't like high screen voltage, someone has modded my amp with a big series resistor and a bypass capacitor to drop the working voltage down to about 250V. Unfortunately if one of the tubes stops conducting this will cause the screen supply voltage to increase beyond spec. Another TalkBass member used a choke to solve this problem and was able to slightly increase the output power of his 6146 equipped amp. A choke is probably the best solution but a bit beyond my knowledge and motivation level. Next time I open the amp I will attempt to build a resistor ladder that will drop the screen voltage a bit more and make the supply more stable.

Also have Skunkworks SVT equipped with Sylvania 6550s. It sounds a bit different than the Blueline, but not much.

 

[bobyoung53]

6146s make a bit more power than 6550s but don't like the high screen current that occurs with hard clipping. Some people put bigger resistors on the screens to make the amps more reliable.

I have a Blueline with pots dated to 1968. Unfortunately it has an aftermarket PT that is spec'ed for the 350 volt screen supply used with the 6550 version of the amp. The original 6146 PT provided 220V for the screen supply. The 6146 is spec'ed for max of 250V on the screens, but a lot of radio types suggest the tubes are more reliable with screens limited to 200V. As 6146s also don't like high screen voltage, someone has modded my amp with a big series resistor and a bypass capacitor to drop the working voltage down to about 250V. Unfortunately if one of the tubes stops conducting this will cause the screen supply voltage to increase beyond spec. Another TalkBass member used a choke to solve this problem and was able to slightly increase the output power of his 6146 equipped amp. A choke is probably the best solution but a bit beyond my knowledge and motivation level. Next time I open the amp I will attempt to build a resistor ladder that will drop the screen voltage a bit more and make the supply more stable.

Also have Skunkworks SVT equipped with Sylvania 6550s. It sounds a bit different than the Blueline, but not much.

I had a skunkworks head (somewhere between #220-250 IIRC) some years ago, it had a little less output than my 70's 6550 heads, had a little less gain and was a little more sedate sounding, I modded it to put 12DW7's in it hoping to get that 70's sound but the sound didn't change nor the gain, 11-12 0'clock was about equal to 10 o'clock on a 70's head, all in all I like the 70's heads a lot better. I'd love to get my hands on a 6146 head, too bad about the power transformer.

 

[Wasnex]

I had a skunkworks head (somewhere between #220-250 IIRC) some years ago, it had a little less output than my 70's 6550 heads, had a little less gain and was a little more sedate sounding, I modded it to put 12DW7's in it hoping to get that 70's sound but the sound didn't change nor the gain, 11-12 0'clock was about equal to 10 o'clock on a 70's head, all in all I like the 70's heads a lot better. I'd love to get my hands on a 6146 head, too bad about the power transformer.

I think a lot of people would argue that your babies came from the best era. I would be surprised if you found another SVT you liked better.

I knew about the PT being replaced before I got the amp; I didn't worry about it because it's a very high quality transformer and most of the sound comes from the OT instead of the PT. I wouldn't have bought the amp if I knew the tech ordered the wrong transformer and installed it in the wrong orientation. He had to move the preamp forward 1/2 inch so it would clear the top of the PT. Unfortunately the close proximity of the preamp and the transformer induces a little extra hum. If not for the noise of the typical SVT fan, the hum would be totally unacceptable. You can barely hear it over the fan, so I don't worry about it too much.

I have a kit to remount the PT in the proper orientation but it is a very involved process that involves completely removing the PT from the amp, removing and replacing the transformer end caps and chassis mount, and finally reinstalling the PT in the amp. I could probably do this over a couple of days, but what a hassle!

The Skunk has less hum than any SVT I have come across. Volume wise I think the Skunk and the 6146 are pretty close, but the 6146 is definitely a bit more compressed. The compression could be because of the big resistor used to tame the screen voltage, or possibly it might need a complete cap job. Channel 1 gain is pretty similar between both amps. Both amps start to grind a bit around 10 o'clock and would be totally distorted by 12. The 6146 has significantly lower gain on channel 2. Due to the compression, I think the 6146 sounds slightly better for slap and the Skunk slightly better for finger style.

 

[bobyoung53]

I think a lot of people would argue that your babies came from the best era. I would be surprised if you found another SVT you liked better.

I knew about the PT being replaced before I got the amp; I didn't worry about it because it's a very high quality transformer and most of the sound comes from the OT instead of the PT. I wouldn't have bought the amp if I knew the tech ordered the wrong transformer and installed it in the wrong orientation. He had to move the preamp forward 1/2 inch so it would clear the top of the PT. Unfortunately the close proximity of the preamp and the transformer induces a little extra hum. If not for the noise of the typical SVT fan, the hum would be totally unacceptable. You can barely hear it over the fan, so I don't worry about it too much.

I have a kit to remount the PT in the proper orientation but it is a very involved process that involves completely removing the PT from the amp, removing and replacing the transformer end caps and chassis mount, and finally reinstalling the PT in the amp. I could probably do this over a couple of days, but what a hassle!

The Skunk has less hum than any SVT I have come across. Volume wise I think the Skunk and the 6146 are pretty close, but the 6146 is definitely a bit more compressed. The compression could be because of the big resistor used to tame the screen voltage, or possibly it might need a complete cap job. Channel 1 gain is pretty similar between both amps. Both amps start to grind a bit around 10 o'clock and would be totally distorted by 12. The 6146 has significantly lower gain on channel 2. Due to the compression, I think the 6146 sounds slightly better for slap and the Skunk slightly better for finger style.

I heard 6146 amps were usually louder than 6550 amps although Jimmy has one and says he can't tell the difference between his 1969 and his VR but I don't think he plays loud either. My skunkworks may not have been performing up to specs although it was pretty nice when I got it, was a leftover, bought it in 2000 from a music store who had been an Ampeg dealer.

 

[coreyfyfe]

I heard 6146 amps were usually louder than 6550 amps

I believe the issue is the difference between amps designed for 6550s and amps converted to 6550s. The 6550 schematics show a number of voltage differences and different PT part number. Aside from the 660-695 error (Bill Hughes has said this was a drafting carryover and it should be 660V on all versions) the screen voltage is 220 vs 350, plate voltage on the PI is 320 vs 380, plate voltage going to the preamp is 480 vs 485. The screen voltage is the important factor here, at least to the 6550s.

 

[JimmyM]

I heard 6146 amps were usually louder than 6550 amps although Jimmy has one and says he can't tell the difference between his 1969 and his VR but I don't think he plays loud either. My skunkworks may not have been performing up to secs although it was pretty nice when I got it, was a leftover, bought it in 2000 from a music store who had been an Ampeg dealer.

I've played them screaming loud in my house for hours at a time insanely ABing them and I stand by that comment.

EDIT: My newer SVT isn't a VR. It's a Heritage CL.

 

[Wasnex]

I heard 6146 amps were usually louder than 6550 amps although Jimmy has one and says he can't tell the difference between his 1969 and his VR but I don't think he plays loud either. My skunkworks may not have been performing up to secs although it was pretty nice when I got it, was a leftover, bought it in 2000 from a music store who had been an Ampeg dealer.

Based on the various posts I have read, healthy 6146 based amps generally make a bit more than 300 watts, healthy 6550 based amps usually a bit less than 300 watts. The difference in perceived loudness is pretty minimal. I don't have means of measuring mine, but volume wise, they slot right in between my 200 and 400 watt tubes amps.

Aside from a name engraved rather sketchily in the Skunkworks badge mine was mint when I bought it. The fact that one of the electrolytics shorted suggests the amp might not have been turned on for an extended time, possibly years.

I try to work all of my amps for a couple of hours every month to keep them healthy...it can be very challenging. I don't know if its my imagination, but they seem to sound better when played regularly.

 

[beans-on-toast]

I try to work all of my amps for a couple of hours every month to keep them healthy...it can be very challenging. I don't know if its my imagination, but they seem to sound better when played regularly.

They can sound better because using the amp will reform the capacitor insulation which breaks down when the amp sits unused.

I can see running your amps every month as being challenging as you said. I try to fire up my amps at least once every six months. Some people do it once a year.

 

[GreaserMatt]

The holy grail of early tube bass heads imho...