Question For SVT Blue Line Experts

BassScum · #1 12-15-2010, 12:56 PM

I have an SVT Blue Line which I dated to be 1970 (according to the pot date codes) and it has 6146 power tubes but doesn't have the relay socket so I figure early 1970. A previous owner converted the 12DW7 tubes to 12AX7's. I want to go back and install the 12DW7 tubes as originally designed. I 'm aware of the R6,R7,R25 changes on the pre amp, but what about the 1, 12DW7 on the power amp? Is it necessary to change the values there and if so which resistors are affected there?

Also my unpainted tube chassis doesn't have a data plate on the back. I've noticed others from various web sites without it as well. Did the earlier non painted versions not have the data plates or is mine missing?

okcrum · #2 12-15-2010, 01:34 PM

I believe all the component changes were on the preamp board, and only the tube swap was done on the power amp.

This looks like the mod here, at least for the preamp.

You can check yours against the original schematics here.

BassScum · #3 12-15-2010, 01:48 PM

Thanks, Okrum. When I get home I'll check the circuit for the power amp 12DW7 and compare it to the schematic.

But... Does anyone have any info on the data plate that I asked about in my original post?

coreyfyfe · #4 12-15-2010, 02:22 PM

What do you mean by data plate?

Do you mean the this?:

If so it should be attached separately over the metal grill (using the same set of screws that hold the grill in place). Since they are removable yours may have been lost. Fliptops sells a replacement, but they are cut to the specs of 68-69 SVTs which are apparently slightly different than later models, so make sure your holes will line up.

http://www.fliptops.net/catalog/prod...roducts_id=884

Otherwise, I'm not sure what you mean, the back of mine is blank too....

beans-on-toast · #5 12-15-2010, 03:01 PM

The 12DW7 to 12AX7 mod was normally just done in the pre-amp. In the power amp, you could just plug a 12AX7 in place of the 12DW7 without any changes. As okcrum stated.

It is still possible that someone changed some of the resistors in your power amp. The only way to tell would be to have to look.

On the power amp, the correct 12DW7 values are:
R6=15K (brown, green, orange),
R7=1M (brown, black, green) ,
R8=1K (brown, black, red),
R9=10K brown, black, orange).

6jase5 · #6 12-18-2010, 01:23 PM

JohnK and JimmyM are great resources for blue line SVT info. I have one as well, but I just play and I'm useless with tech info.

JimmyM · #7 12-18-2010, 02:05 PM

i'm useless with tech info too, jase. i just know the basic history.