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The cheap and easy way that a lot of guys use is a reversed
filament transformer, feed 6.3 into the 12.6 winding and get
about 60 volts out ... the tiniest of transformers will work.

TomMcNally wrote:The cheap and easy way that a lot of guys use is a reversed
filament transformer, feed 6.3 into the 12.6 winding and get
about 60 volts out ... the tiniest of transformers will work.

Tom, you just made my day!!! That's a great trick and I appreciate being clued in.

I don't know about you, but when I look at solving a problem I always seem to think in terms that are way to complicated rather than innovative. I hope it's not too late to retrain the way at least a few of my synapses fire....

I hope you have a good day as well,

Chris

TomMcNally wrote:The cheap and easy way that a lot of guys use is a reversed
filament transformer, feed 6.3 into the 12.6 winding and get
about 60 volts out ... the tiniest of transformers will work.

Would you use one or two, i.e. is it desirable to have one each per channel?

Chris

I would say if you are trying to keep the amps independent,
then use two ... there are some tiny ones out there.

TomMcNally wrote:I would say if you are trying to keep the amps independent,
then use two ... there are some tiny ones out there.

Perfect, thanks. Tiny is good 8-)

Chris

These small trannies work great and they are the smallest I've ever found for providing bias.

http://www.mouser.com/Search/ProductDetail.aspx?R=41FG100virtualkey21980000virtualkey41FG100

mesherm wrote:These small trannies work great and they are the smallest I've ever found for providing bias.

Thanks for the link! I checked Mouser and found some 1" by 1" PCB epoxy potted jobbies, but they cost twice as much. Can't beat the deal you sent me...the order will be placed tomorrow.

Have a good Memorial Day,

Regards,

Chris

Has anyone else noticed that the copies of the original Dynaco Mark III's all seem to be missing quite a few caps in the parts list?

Just curious about what's up with that if anybody knows.

Chris

Has anyone else noticed that the copies of the original Dynaco Mark III's all seem to be missing quite a few caps in the parts list?

Are the missing parts on the driver board?
If its like the ST-70, the driver board came preassembled so they didn't list the parts on it in the parts list.

mesherm wrote:Are the missing parts on the driver board?
If its like the ST-70, the driver board came preassembled so they didn't list the parts on it in the parts list.

Thanks, mystery solved.

I'm creating a computer schematic of my integrated amp from scratch to better understand where everything will connect and what it does. That's when I noticed my BOM didn't make sense.

Had I read the Mark 3 assembly instructions, I might have noticed.

Yep, RTFM.

8-)

Chris

Hi all,

When the wife leaves town for a few days, progress can be achieved almost without interruption: A few pics:

http://www.lagunatechnics.com/images/tubeaudio/chassis_01.jpg
http://www.lagunatechnics.com/images/tubeaudio/chassis_02.jpg
http://www.lagunatechnics.com/images/tubeaudio/chassis_03.jpg
http://www.lagunatechnics.com/images/tubeaudio/chassis_04.jpg

I do have a couple of questions:

1. Current limiters. I always assumed something like a CL-90 2A would be placed behind the on/off switch in series with the primary PT winding.
I recently read a post on another forum where someone said:

"To slow things down a little, insert a NTC inrush current limiting thermistor from GE/Thermometrics between the rectifier and the PSU filter."

Does anyone have any advice about this? Also, does the CL-90 2A sound like a reasonable value for a dual Mark III powered by a single toroid?

2. Grounding. Please check me on this. The green wire from the AC line supply will be bolted to the aluminum chassis plate. The same bolt will connect to the B- (Chassis Ground) on both SDS Cap boards. The same bolt will connect to a ground bus that radiates to maybe six star points, all interconnected via heavy gauge solid copper wire (maybe #12).

I know it sounds a bit complicated, but the whole wiring scheme looks a bit to complex to use a single star ground. Ideas, critique, laugther?

Seriously, I'll start soldering soon. Any review/suggestions at this time would be very, very welcome.

Cheers,

Chris