SS Rectified Get*Set*Go

[ecir38]

ed B, do you think there would be a audible differance between using standard or fast recovery in this application? I am asking because I could make a couple of them and roll them to see what I like best.

[EWBrown]

The fast recovery (uF4007 or uF5408) diodes are less likely to generate noise or a "buzz" on the B+ supply. MUR4100s may also be good (4A @ 1000V)

There is another approach, though I've not tested it, connect a 10 ohm 5W WW resistor in series between each "hot" lead of the power trannie's HV secondary and its associated diode rectifier, and then connect one 0.001 uF, 1600V (or greater) disk ceramic cap across the secondary, and a second similar cap between the two diodes' anodes. This results in what is known as a rapid reverse spike recovery filter (RRFSR) , and should work.

The simple version of this is to connect the 0.001 uF 1600V disk ceramic caps across each rectifier diode. Not as effective, it is "old school" approach.

I'd go with the uF diodes (or schottky diodes) first, there is less circuit complexity to mess around with...

Try one of each, and see what sounds best (if there is even any discernable difference).

/ed B in NH

[ecir38]

Thanks, I will throw this in on my next order and give it a try.

[SDS-PAGE]

It's good to see you're having fun with the amp, Brad. -Min Yellow_Light_Colorz_PDT_16

[77seriesIII]

I'd go with two uF4007s or uF5408s, two 100-220 uF / 450 V caps, and use the choke that is already in place, just disconnect it from its two barrier strip connections, and connect it between the + end of the two added external caps.

Connect a 50 ohm (or higher value) 2W resistor to the two barrier strip locations where the choke was connected. Since the 6SL7 by iteslf draws very litle current, a larger resistor could be used, anything 100 ohms to 1K (or even higher) , the actual current consumed by the 6SL7 is around 1.2 mA total. A 1K resistor is going to offer a 1.2 VDC drop, so it is rather insignificant. The idea is to get about 150VDC "resting" voltage at the plates of the 6SL7.

HTH

/ed B in NH

Ed

I am putting the above together today and was wondering where do the 220-uF/450V caps go in the circuit? Are they a replacement? I re-read the section on the 5408 and am comfortable with their placement, but not so much so with the caps. Does it go Choke then Caps(+) then Terminal block, negative side of cap?

Thanks

Erick

[EWBrown]

For the "external" caps and SS rectifiers, the two HV AC secondary leads would connect to the SS rectifier anodes, thetwo cathodes connect together and go to the cap-choke-cap (AKA CLC) filter.

The circuitry is pretty much conventional, the negative side of thh two caps connect together, then go back to the PC board "zero" volts connection. The "new" B+ voltage then connects to the two OPT "B+" leads, this is probably best done off the PC board, rather than using the existing two-point barrier strip, this also eliminates any PCB surgery, and allows for going back to the original design at a later date if so desired. .

What this does is to feed the two power tubes with SS rectification, which offers higher DC voltage and current handling capability, but leaves the 6SL7 on the original tube rectifier. It also allows better isolation between the driver and the PA stage B+ lines.

The 6AX5 now handles very low current, just a mA or two, and actually it could be replaced with a 6X5 which is a pin-compatible drop-in replacement.

It may sound a bit complicated, just draw the diagram out first on paper first, and it should become apparent.

HTH

/ed B in NH

[77seriesIII]

Ed,

Thanks and now a clarifying question. for the CLC ties into J5, right? Do I use pin 1 or 2, am guessing pin 2 but want to make sure before I fire it up and hear the PFFTT noise.

Erick

[EWBrown]

Dopey me... I'll have to go back a few steps and see what / where J5 is... Yellow_Light_Colorz_PDT_09 Where the original choke connections were, just install a 50-200 ohm, 1W resistor across the two terminals. With the VA's diminutive current consumption, the voltage drop is going to be quite small, so the actual resistance value isn't too important here.

I'd connect the SS-rectified CLC B+ straight to the OPTs' B+ leads and leave it off the PCB connections altogether, as it would otherwise get back into the other on-board circuitry.

I know, a picture is worth a thousand words, but I don't have a reasonable way to trnaslate a hand drawing to something that a computer can digest and post here...
With the company "transition" our network connections and e-mailing are just a wee bit wonky at present, and the nice multifunction cpier which can generate PDF files and then e-mail them is not on line, and won't be for another few weeks. That was the greatest thing for getting hand drawn diagrams into computer-usable formats with very little effort...

/ed B in NH

[77seriesIII]

Ed,

Cool! I remembered reading about the resistor across the choke points after you posted it again...reading not just a skill anymore I think we were able to draw it out from your written instructions. I'll see if I can create a PDF of that over the weekend and post it here.

Ok...three of us looked at the schematic and we are scratching our heads on where the zero voltage point is at, the place where you recommend connecting the caps to. I was being courageous and mentioned that it was any 0v point as designated on the voltage chart within the build instructions but had the "beat down" from the technical aspect of the build group. For example: on V1, the 6SL7 it could be pin 1 or 4. Am I right or is there another 0v point that I should use or one you would recommend?

Thanks for the help... the board is done, well almost. I missed a few resistors and am waiting on the 220uF 450v caps, should be tomorrow. After that, a few tests and my first DIY amp will be done...hopefully no magic smoke escapes or mirrors break.

A dear close friend took the picture of my Dad and I building the GSG Amp as a father/son project:

http://www.jpgmag.com/photos/399574

Take care and I hope the New Year brings all your desires!

[Shannon Parks]

Nice photo!

[TomMcNally]

the g*s*g becomes art ! very cool

[EWBrown]

When building any amp project, or working on my vehicles, there are many times that I wish I had four hands Yellow_Light_Colorz_PDT_06

though I dunno about using a butane-fired soldering iron on a PCB. OK, I've done it once or twice, but that was a long time ago, on a planet very very far away Yellow_Light_Colorz_PDT_04 Yellow_Light_Colorz_PDT_08

Re the GSG ground / zero volts point.

The four-place barrier strip, on which the two outer terminals #1 and #4 connect to the power trannie secondary HV leads. Positions #2 and #3 are the best ground point to use, this should avoid any weird current loops. With a bit of creativity, two ring or spade lugs can fit under one screw, or two wires can crimp into one (blue sleeve) lug.

/ed B in NH

[77seriesIII]

Thanks guys on the photo comments I'll pass them on to my better half!

Ed thanks for that last bit of detail. On the butane torch...Dad wasnt too sure of it but I have many years on butane soldering irons. the Army issued us battery operated ones...POS things never even got hot enough to warm your hands before the batteries drained. After seeing one of my crew chiefs with one I always flew with one to do quick repairs, and ended up doing all my aviation repairs with it. It is adjustable so that helps.

[EWBrown]

I've used the gas-fired soldering irons on emergency vehicle wiring repairs (I don't believe in the alleged sanctity of a crimped on connection) and on some older heavy-duty PCBs in a pinch, when the normal electric iron wasn't available. However the torch does look good in the photo, perhaps the CCD or film registers the IR component better than the human eye. Besides, not having a power cord dangling over everything makes for much nicer aesthetics!

The battery operated irons were OK for very fine gage wire and quick touch-ups, and that's about all. The newer "cold heat" irons have possibilities, but I've not yet used one on a decent project. They eat up AA cells about as fast as Ted Kennedy can pound down a fifth of scotch... Yellow_Light_Colorz_PDT_09

The way the "cold heat" irons work is that they don't heat the tip, they heat up the actual connection, which then can melt solder. They are also good at blowing fine PCB etches, and ascertaining that 1Amp fuses WERE good... :o Yellow_Light_Colorz_PDT_08

/ed B in NH

[hembrook]

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