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6SN7 mod for ST - 70

TX_Tube

TX_Tube

Active Member
I know there are a few dozen modifications that can be made to these amps, so I would like to narrow it down to the 6SN7 mod. The ST - 70 in this project is an original piece, with the taller, cloth wire power transformer in it. To start things off, a new upgraded Triad Xformer will be going in, along with new PS board. The most important part of any amp, is the power supply and the 6SN7s do draw some current, so a new PS is in order. You have got to have enough amperage flowing to the tubes, so they can reach their optimum performance level. Should allow for a lot of bass in the amp also.

The VTA 6SN7 board will be the board chosen for the rebuild. VTA has always offered up well designed products in the past, so there should be no problem there. Hopefully a few members here in the Forum have preformed this mod already and if so, I would like to her their opinions on their 6SN7 mod project. TIA
 
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Erhard Audio offers a mod with the same Mullard designed circuit for the 6SN7 driver board, but it also includes a new solid state power supply integrated into the circuit board. It is available on ebay or directly from the Erhard web site. The price of the combined board is about what it costs to add a separate power supply to the VTA board.
If you check out his website, there is also some information concerning what size power transformer is recommended.
I found his customer support to be first class.
 
I built a VTA ST-70, but used the 12AU7 board. I did try adaptors and used 6SN7's. I really didn't notice much if any difference between the 12AU7's and 6SN7's. The 12BH7 I am using in the center voltage gain socket does sound better to my ears though.
 
Thanks Pablodeux and Lavane for your input. I was checking around and it looks like the Triode upgrade boards allows for a lot of flexibility for the tube rollers that are out there. The EF86 board allows for a whole host of tubes to be used in the phase inverter spot, so it might be a better choice for the upgrade. A question for Lavane, is the EF86 board the 1 you chose to use in your ST70 upgrade project? TIA
 
TX_Tube said:
Thanks Pablodeux and Lavane for your input. I was checking around and it looks like the Triode upgrade boards allows for a lot of flexibility for the tube rollers that are out there. The EF86 board allows for a whole host of tubes to be used in the phase inverter spot, so it might be a better choice for the upgrade. A question for Lavane, is the EF86 board the 1 you chose to use in your ST70 upgrade project? TIA
Click to expand...
The VTA board allows for 12AU7 variants, 12BH7's, E80CC's, and ECC99's.
Kegger suggested the E80CC for the center socket. I used it for awhile.
 
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