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Building a scratch version of Dave Gillespie's 8600 mod

just depends on your drawing convention. Some things don't use the "hops" and use dots to indicate connection, other things use "hops" and any cross without one is a junction. So long as its consistent its not a big deal.
 
I've been working on my schematic. I probably could fill in a few more values for voltages. But, I believe this to be pretty close to complete. Does this all look reasonable? It's all essentially directly from the DGSE1 schematic, with the addition of the ground breaker, CSS, and the use of silicon diodes for rectification.

I can't seem to get an image out of Kicad, so unfortunately, I made a pdf instead.

Thanks!
 

Attachments

I just did a crappy screen grab for discussion.

Don't forget to throw a virtual center with two resistors across the 6.3V filament winding and attach the center to one of the 6BQ5 cathodes.
EDIT: OK- I see them, but they do not go in series with the heaters. The two resistors go across the winding and the center to the cathode.

What is with the 120 ohm in series with the bypass capacitor across the current source? I don't think a rumble filter in this way is necessary- The 8600 and most output stages have the cathodes at an AC ground. If you really need a rumble filter on an amplifier with heavy negative feedback it will have to be a passive high pass filter at the input, outside of the feedback loop. Don't forget the zobel (.1uF and 47 ohm) are directly across the speaker output terminals. I don't remember what power and output transformers you are using on this- I'll have to go back through and look.

You might also through a 0.01uF "X1" rated safety cap across the primary winding- suppresses noise from power line and eliminates any switch pop.

If you really need the series power dropping resistor, you can always add another bypass cap at the diode/resistor junction for yet another stage of filtering, that is free, and retains the higher peak voltage out of the rectifier. (I did something like that in my Fat Daddio (schematic attached))


1785537668234.png
 

Attachments

  • Fat_Daddio_SE_Schematic_Final.jpg
    Fat_Daddio_SE_Schematic_Final.jpg
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Last edited:
wparks said:
I just did a crappy screen grab for discussion.

Don't forget to throw a virtual center with two resistors across the 6.3V filament winding and attach the center to one of the 6BQ5 cathodes.
EDIT: OK- I see them, but they do not go in series with the heaters. The two resistors go across the winding and the center to the cathode.

What is with the 120 ohm in series with the bypass capacitor across the current source? I don't think a rumble filter in this way is necessary- The 8600 and most output stages have the cathodes at an AC ground. If you really need a rumble filter on an amplifier with heavy negative feedback it will have to be a passive high pass filter at the input, outside of the feedback loop. Don't forget the zobel (.1uF and 47 ohm) are directly across the speaker output terminals. I don't remember what power and output transformers you are using on this- I'll have to go back through and look.

You might also through a 0.01uF "X1" rated safety cap across the primary winding- suppresses noise from power line and eliminates any switch pop.

If you really need the series power dropping resistor, you can always add another bypass cap at the diode/resistor junction for yet another stage of filtering, that is free, and retains the higher peak voltage out of the rectifier. (I did something like that in my Fat Daddio (schematic attached))


View attachment 3810345
Click to expand...
This all makes sense. I'll revise tomorrow (if I get some time).

The outputs are from Matt. They're simplified versions of his higher end ones (5k only to 8 z only). They should be similar to his HiFi transformers, but were a bit cheaper.

That's helpful on the zobel. I copied it where it was on the original schematic, but have room to move it.

Thanks!
 
I realized that what you referred to as the rumble filter was not intended to be a rumble filter. It's a series resistor with the bias pot in your schematic. I put it on the wrong side of the ground.

Obviously that needs to go. With the lm317 ccs, is there no need for the bypass capacitor either?

Thanks!
 
wparks said:
Don't forget to throw a virtual center with two resistors across the 6.3V filament winding and attach the center to one of the 6BQ5 cathodes.
EDIT: OK- I see them, but they do not go in series with the heaters. The two resistors go across the winding and the center to the cathode.
Click to expand...
What is the point of that virtual center connected to a single cathode? What does it do?
 
It provides a DC elevation for the heaters to help prevent hum and/or cathode deterioration mainly in the small signal tubes and particularly when a cathode is at an elevated DC voltage like in a mu follower or a long tail pair that is direct coupled to the driver tube. Heaters and cathode form a weak diode between them if the cathode is at a higher DC voltage than the heater. The tube data sheets all show max plus and minus voltages for heater to cathode.

gadget73 just beat me to this but I'll post my reply too.
 
I'm almost done with my case work. A few hours on the dremel tomorrow (then some bondo and paint). I'll be back in the next week or so with pictures and questions.
 
scootsity5 said:
I'm almost done with my case work. A few hours on the dremel tomorrow (then some bondo and paint). I'll be back in the next week or so with pictures and questions.
Click to expand...
I painted last night. Need to sand and do some finishing work, then I'll be mounting components. I'm still alive!

I forgot to drill out for a power switch. . . . Oops. I'll make it work...
 
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