trying to understand differences in Ampeg 300W tube amps...

[Swiss Frank]

So it looks like Ampeg has (prices from Musician's Friend):

• SVT Heritage 50th anniversary $2700
• SVT-CL Heritage $2400
• SVT-VR Vintage reissue $2200
• SVT-CL Classic $1800
• SVT-2 Pro (I'm looking at one used for $600)

These all seem to have 6x6550 power stages and 3-tone-plus-mid-freq tone controls.

I see the SVT Heritage has two separate channels with different historical voicings. The others have slightly more or fewer tone variations. (Oddly, the cheapo SVT-2 Pro has the full graphic EQ, a lot more control than the others.) I'm not concerned with the graphics and historical switches, and I'm tempted to think that their new amps probably wouldn't have changed the historical circuits too much except for if the old circuits actually needed some changes to deal with 5-strings, popping, fretless, etc.

My special concern is that the SVT-2 is said by some to be especially noisy. Why would it be noisier than the other circuits? Can someone point to specific aspects of the design of the SVT-2 Pro that would make it lower fidelity?

 

[basscooker]

You should be happy with any of them, new. The used 2-pro is easily serviced by any qualified tech, provided it hasn't been altered too much.

At that level of gear, with all-tube SVTs you really can't get the "wrong" one.

 

[JimmyM]

You should be happy with any of them, new. The used 2-pro is easily serviced by any qualified tech, provided it hasn't been altered too much.

At that level of gear, with all-tube SVTs you really can't get the "wrong" one.

Correct. One can nitpick about gain/master vs single volume with two channels, but at the end of the day they're all SVT's.

 

[greengoblin]

You can also add to the list, the SVT II Non-pro. More of a traditional circuit compared to all of the others. Some say/think it is the truest form (tone wise) of an SVT compared to the original SVT Blueline. Although many say they can all sound similar.

My understanding, I could be off/wrong (feel free to correct me and I will edit). The SVT CL and SVT VR and SVT 2 Pro all use the same power section. The difference comes in the preamps. The SVT 2 Pro and SVT VR use (5) preamps tubes, (3 x 12AX7, 2 x 12AU7). I havent looked at the schemes to see if the preamps are the same. The SVT CL uses a preamp with (2) 12ax7's. The SVT II non-pro uses preamp with (2 x 12ax7's, 1 12au7).

All use a set of (6) 6550's for power tubes.

The SVT II Non Pro and SVT 2 Pro add an additional EQ section that can be turned off.

From my understanding, the SVT CL and SVT Heritage CL are the same with the exception that the Heritage series are assembled in the US by Hodgie (and maybe others).

I don't have any info on the newest addition from the Yamaha group.

 

[Jim C]

They all sound pretty similar to me too.
The used market for CL's, 2 pro's and 2 Non Pro's is bargain time these days
I would not buy one that does not make any sound as this can get pricey
If it works well, it's probably a safe buy on the used market

 

[coreyfyfe]

You can also add to the list, the SVT II Non-pro. More of a traditional circuit compared to all of the others. Some say/think it is the truest form (tone wise) of an SVT compared to the original SVT Blueline. Although many say they can all sound similar.

The II non-pro was basically channel 1 of the vintage circuit plus a graphic EQ. The vintage amps and II non pro have a few additional gain stages. There's a cathode follower buffer stage on V1 before the boost switches, in the vintage amps this was the AU7 half of the 12DW7, in the later 70s amps and the II non pro it's the second half of the 12AX7. There are also extra tube stages around the midrange control. The CL simplifies this circuit a bit, instead of three tubes across that channel they use two tubes.

My understanding, I could be off/wrong (feel free to correct me and I will edit). The SVT CL and SVT VR and SVT 2 Pro all use the same power section. The difference comes in the preamps. The SVT 2 Pro and SVT VR use (5) preamps tubes, (3 x 12AX7, 2 x 12AU7). I havent looked at the schemes to see if the preamps are the same. The SVT CL uses a preamp with (2) 12ax7's. The SVT II non-pro uses preamp with (2 x 12ax7's, 1 12au7).

Yeah the power amps are basically the same, the schematics for the CL are usually labeled as the 2 pro despite a few changes. The II Pro and VR have more options on the balanced out (level, pre/post) that the CL amps don't have. Circuitwise though they're all pretty much the same. Compared to the vintage amps the 12BH7s are replaced with 12AU7 and the 12DW7 with a 12AX7.

From my understanding, the SVT CL and SVT Heritage CL are the same with the exception that the Heritage series are assembled in the US by Hodgie (and maybe others).

The heritage uses the same design but with update/upgraded circuit boards, premium tubes, the nicer tube clamps, and they're assembled/tested in the US. The new 50th anniversary model is basically a heritage version of the VR with some tweaks on the second channel.

 

[Wasnex]

So it looks like Ampeg has (prices from Musician's Friend):

• SVT Heritage 50th anniversary $2700
• SVT-CL Heritage $2400
• SVT-VR Vintage reissue $2200
• SVT-CL Classic $1800
• SVT-2 Pro (I'm looking at one used for $600)

These all seem to have 6x6550 power stages and 3-tone-plus-mid-freq tone controls.

I see the SVT Heritage has two separate channels with different historical voicings. The others have slightly more or fewer tone variations. (Oddly, the cheapo SVT-2 Pro has the full graphic EQ, a lot more control than the others.) I'm not concerned with the graphics and historical switches, and I'm tempted to think that their new amps probably wouldn't have changed the historical circuits too much except for if the old circuits actually needed some changes to deal with 5-strings, popping, fretless, etc.

My special concern is that the SVT-2 is said by some to be especially noisy. Why would it be noisier than the other circuits? Can someone point to specific aspects of the design of the SVT-2 Pro that would make it lower fidelity?

Functionally the 50th AV and VR are very similar. They have two channels with input gain, but no master volume. Channel two is revoiced a bit on the 50th AV, but it still has the same exact controls as the VR. These amps are functionally like vintage SVTs but the preamp circuitry is quite a bit different; I'll explain why below.

The Heritage and Classic CL are bassically the same circuit. One channel with gain and master volume. If you crank of the master, the tone and response is very similar to channel one of the 50th AV or the VR. If you want preamp driver, turn the master down.

Functionally, the power amps are all pretty much equivalent but there are some minor differences in the phase inverter and driver circuits.


Here is how the 50th AV and VR preamp differs from vintage SVT:

The vintage SVTs used three types of tubes in the preamp. 12DW7, 12AX7, and 6C4. The 12DW7 and 12AX7 are dual triode tubes. The 6C4 has one triode. The triodes in a 12AX7 are identical and have a gain factor of about 100. The triodes in a 12DW7 tubes are dissimilar. One triode is like a 12AX7, and the other is like a 12AU7, which has a gain factor of about 20. 12AU7 is also a dual triode tube with identical sections. A 6C4 is basically half of a 12AU7.

The SVT VR has the same functionality as a vintage SVT, but it does not use the same signal path. In a vintage amp, the signal flows in channel 1 sequentially through the two triodes in V1, then the two triodes in V3, and finally the two triodes in V4. V2 is the 12AX7 used for Channel 2.

In the SVT VR the signal in channel 1 flows in and out of various 12AX7 and 12AU7 tubes. Here's the order: V1a, V2b, V2a, V3b, V3a, V4b.

Since the VR uses three 12AX7s and two 12AU7s, ten triodes are available, but only 9 are used, just like the vintage amps. The unused triode is V1b. V5a and V5b make up the gain stages of channel 2, and V4a fills the role of the 6C4.

My belief is the 50th AV uses the same signal path as the VR, but some component values are modified to change the voicing of channel 2. Until a schematic is published, this is supposition.

 

[Wisebass]

at the end of the day they're all SVT's.

Even early in the morning they are loud enough!


Wise(b)ass

 

[foal30]

Functionally the 50th AV and VR are very similar. They have two channels with input gain, but no master volume. Channel two is revoiced a bit on the 50th AV, but it still has the same exact controls as the VR. These amps are functionally like vintage SVTs but the preamp circuitry is quite a bit different; I'll explain why below.

The Heritage and Classic CL are bassically the same circuit. One channel with gain and master volume. If you crank of the master, the tone and response is very similar to channel one of the 50th AV or the VR. If you want preamp driver, turn the master down.

Functionally, the power amps are all pretty much equivalent but there are some minor differences in the phase inverter and driver circuits.


Here is how the 50th AV and VR preamp differs from vintage SVT:

The vintage SVTs used three types of tubes in the preamp. 12DW7, 12AX7, and 6C4. The 12DW7 and 12AX7 are dual triode tubes. The 6C4 has one triode. The triodes in a 12AX7 are identical and have a gain factor of about 100. The triodes in a 12DW7 tubes are dissimilar. One triode is like a 12AX7, and the other is like a 12AU7, which has a gain factor of about 20. 12AU7 is also a dual triode tube with identical sections. A 6C4 is basically half of a 12AU7.

The SVT VR has the same functionality as a vintage SVT, but it does not use the same signal path. In a vintage amp, the signal flows in channel 1 sequentially through the two triodes in V1, then the two triodes in V3, and finally the two triodes in V4. V2 is the 12AX7 used for Channel 2.

In the SVT VR the signal in channel 1 flows in and out of various 12AX7 and 12AU7 tubes. Here's the order: V1a, V2b, V2a, V3b, V3a, V4b.

Since the VR uses three 12AX7s and two 12AU7s, ten triodes are available, but only 9 are used, just like the vintage amps. The unused triode is V1b. V5a and V5b make up the gain stages of channel 2, and V4a fills the role of the 6C4.

My belief is the 50th AV uses the same signal path as the VR, but some component values are modified to change the voicing of channel 2. Until a schematic is published, this is supposition.

I'm officially putting you in the PassinWind, Mr Foxen grade of "Mothers who know their poopie".

 

[Wasnex]

I'm officially putting you in the PassinWind, Mr Foxen grade of "Mothers who know their poopie".

I am a mere Padawan compared to the great masters.