Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on December 14, 2012, 09:53:49 am

Title: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: kagliostro on December 14, 2012, 09:53:49 am

Initially the guy told he want to convert the TSA15H

http://www.ibanez.com/Electronics/model-TSA15H
 (http://www.ibanez.com/Electronics/model-TSA15H)

in a 6G3

with only a channel and no vibrato

but the PT and OT didn't seems adequate

the TSA15H amp is rated for 15W and the 6G3 for 22W

the PT of the 6G3 requires 333v of AC (375v B+)

the Ibanez TSA15H PT specs are as follow

0-250v AC (350v DC if SS rectify and a SAG resistor can be used)
0-12v AC
0-13v AC
0-32v (for Bias)

So he has think to mod the Ibanez in a 6G2 whose request (as PT) seems more similar to the original circuit

Modded 6g3
http://www.el34world.com/Forum/index.php?action=dlattach;topic=7161.0;attach=9618;image (http://www.el34world.com/Forum/index.php?action=dlattach;topic=7161.0;attach=9618;image)

Regular 6g3
http://www.el34world.com/charts/Schematics/files/fender/DELUXE_6G3.pdf (http://www.el34world.com/charts/Schematics/files/fender/DELUXE_6G3.pdf)

6g2
http://www.el34world.com/charts/Schematics/files/fender/princeton_6g2_schem.pdf (http://www.el34world.com/charts/Schematics/files/fender/princeton_6g2_schem.pdf)

Please can you report your opinion ?

Many Thanks

K

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: sluckey on December 14, 2012, 11:33:38 am

I think that PT will be OK for a 6G2 even with the trem circuit. You'll have to modify the bias circuit to work with a bridge rectifier if you can't get enough from that bias winding (see my amp scrapbook). Or easier, just convert to cathode bias for output tubes. It also appears you'll need to run filaments in a series/parallel configuration, ie, two 12AX7s series across 12VAC, same for two 6V6s.

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: kagliostro on December 14, 2012, 01:46:59 pm

Thanks Steve

I agree, the 6g2 seems better starting from the TSA15H

and, yes, the 32v winding for bias may be inadequate (I must try)

about the schematic to be used are you thinking to the JCM900 schematic present on your scrap book ?

the right voltage of the filament windings are 0-12v and 6.3v-0-6.3v, no 0-13v winding

the 12v is rectified and stabilized and supplies the screamer circuit and the preamp tubes

the 12.6v CT winding supplies the final tubes

Grazie

Franco

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: sluckey on December 14, 2012, 02:06:15 pm

Quote

about the schematic to be used are you thinking to the JCM900 schematic present on your scrap book ?

Well, you could do that. But since you have a 32-0VAC winding, just put a bridge on that. That 32VAC secondary will give -45Vdc. Look at the bias circuit in my scrapbook that's labeled "Separate bias winding and full wave bridge".

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: kagliostro on December 14, 2012, 03:52:58 pm

Oh, I remember that schematic !

EDIT: with 250v AC and 350v DC as the amp requires 315v for B+, do you think that the requested drop resistor will act also as a good SAG resistor ?

Many thanks Steve

Franco

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: sluckey on December 14, 2012, 04:11:58 pm

I guess so. 6V6s will also be very happy using 350Vdc.

Title: Re: Ibanez TSA15H conversion to 6G3 without trem or 6g2 ?
Post by: kagliostro on December 14, 2012, 04:45:55 pm

OK, may be no resistor or a resistor paralleled by a bypass switch as to have a SAG/NO-SAG effect

Thanks

Franco