Cheers all,
First thanks to VTA team for a great kit. Second thanks to Ian for his list of tips.
We did the build, and the following mods.
1.Redesigned to single point isolated ground.
2.Built 650uf 900V second SCM.
3.Installed heat sink on LM334.
4.Upgraded to Mulford coupling caps.
5.Added AB-Q-m-125 board.
6.Swapped power switch with RCA jack locations.
7.Added parasitic suppressors 1.4uH 20 turns on 2W 47ohm carbon resistor to grid(s) and plate.
8.Added Furman line conditioner.
9.Bias reference set to 0.45V (45ma) per tube.
10. 2 coats Red basecoat, 2 coats clear on transformer shells.
11. 1m copper tape wrapped around laminates and outside of windings of chokes, HV and output transformers, tied to chassis not signal ground.
12.Chassis and signal ground are isolated and fault protected.
13.Installed time delay on HV.
14.Changed Hv time delay to 17 sec consistent with AB-Q-M-125 sequencing.
Result is very clean, and very very quiet amp. Much larger SCM provides much better transient response due to much larger charge pool.
The speakers are GSG 15" roundover cabinents, JBL D130F (37hz), JBL LE85 (500hz), Altec 511B, Fostek T-90A and Dayton 500,5000 three way crossover. All 8 ohms.
For those who remember JBL compared to all other speakers are front row seats perspective. Very little power is required to drive these as opposed to todays speakers. You hear every scratch, pop, back ground noise, and the music. Compared to some excellent studio monitors which you can not hear this stuff due to low sensitivity. The 125 RMS capacity insures no sag in response. And amp is never straining to keep up. Clear, crisp, tight and transparent sound in the tradition of JBL.
Could not be happier. Later this week both birch boxes will be shot with 2 coats clear coat with Kandy Apple Red tint, then 8 more coats of clear, back, bottom and inside port satin black base coat with 1 coat of clear.
https://i.servimg.com/u/f72/20/41/94/21/img_2011.jpg
https://i.servimg.com/u/f72/20/41/94/21/img_2010.jpg
John Birdlebough
Chief Engineer (Retired)
First thanks to VTA team for a great kit. Second thanks to Ian for his list of tips.
We did the build, and the following mods.
1.Redesigned to single point isolated ground.
2.Built 650uf 900V second SCM.
3.Installed heat sink on LM334.
4.Upgraded to Mulford coupling caps.
5.Added AB-Q-m-125 board.
6.Swapped power switch with RCA jack locations.
7.Added parasitic suppressors 1.4uH 20 turns on 2W 47ohm carbon resistor to grid(s) and plate.
8.Added Furman line conditioner.
9.Bias reference set to 0.45V (45ma) per tube.
10. 2 coats Red basecoat, 2 coats clear on transformer shells.
11. 1m copper tape wrapped around laminates and outside of windings of chokes, HV and output transformers, tied to chassis not signal ground.
12.Chassis and signal ground are isolated and fault protected.
13.Installed time delay on HV.
14.Changed Hv time delay to 17 sec consistent with AB-Q-M-125 sequencing.
Result is very clean, and very very quiet amp. Much larger SCM provides much better transient response due to much larger charge pool.
The speakers are GSG 15" roundover cabinents, JBL D130F (37hz), JBL LE85 (500hz), Altec 511B, Fostek T-90A and Dayton 500,5000 three way crossover. All 8 ohms.
For those who remember JBL compared to all other speakers are front row seats perspective. Very little power is required to drive these as opposed to todays speakers. You hear every scratch, pop, back ground noise, and the music. Compared to some excellent studio monitors which you can not hear this stuff due to low sensitivity. The 125 RMS capacity insures no sag in response. And amp is never straining to keep up. Clear, crisp, tight and transparent sound in the tradition of JBL.
Could not be happier. Later this week both birch boxes will be shot with 2 coats clear coat with Kandy Apple Red tint, then 8 more coats of clear, back, bottom and inside port satin black base coat with 1 coat of clear.
https://i.servimg.com/u/f72/20/41/94/21/img_2011.jpg
https://i.servimg.com/u/f72/20/41/94/21/img_2010.jpg
John Birdlebough
Chief Engineer (Retired)
