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SurfGuitar101 Forums » Gear »

Permalink 6g15 reissue rebuild questions!

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I bet you're right since there is plenty of space. I'll see how difficult it is and make sure it will fit. All good points that you bring up.

Progess?!

Got a head start on my board as components are arriving. Waiting on some stragglers, so I'll have to do some de-soldering. I have to make headway when I can.

image

image

image

image

I just had practice today with my Weber reverb kit. In order to get the sound that I wanted out of it I still had to use a clean boost but MANNNN it's so much reverb and it helps sustain the notes so well. It took me 4 months and 3 amp tech friends for me to get it done. I'll never build an amp again, but it's still a great unit. But you seem to know what you're doing more than I do!

Get wet and loud wit... Abomionable Showmen FB Showmen Twitter

hmmm... I don't know about that. Luckily my Dad is an engineer. Of course, he looked at my plans and laughed about how out of date the whole thing was. "Get with the times!" he said.

I hope it all works out. I'm new at this. Got the 'lectrolitics soldered up tonight. This weekend I will be emptying the chassis.

Some new photos.

Rectifier:

Main board:

Electrolytics:

Cool, very "vintagey looking" Yes

Thanks. That's the plan. (especially those "vintagey" Aerovox caps. I'm keeping my fingers crossed that it will sound as vintagey as it looks.

Last edited: Feb 25, 2012 13:14:28

A word on how to set up the grounding in your amp before you mount the circuit boards in the chassis.

Grounding become critically important where you have different amps strung together, by connecting signal cables. You really want to eliminate as many ground loops in the ground return network as possible, in order to simplify the ground return.

The main cause of hum from grounding is where you get micro-rises in ground potential between different ground return points. We like to think the ground potential is the same potential everywhere. But in fact it isn't. The earth (being the gigantic capacitor that it is) constantly has varying rises and falls in ground potential (- that cause havoc with power supplies the world over). Similarly the ground returns in amplifiers exhibit ground potential rises and falls at different points (albeit that these are microcosmic compared to the earths ground potential differences).

Furthermore, although we like to think of filter caps as functioning to perfectly shunt all AC from the power rail to ground return, the reality is that all e-caps have some ESR which results in a tendency for 'microwobble' AC at the ground end.

In addition, because each bit of wire is an inductor with its own micro-resistance, then in a situation where you have different AC voltages between different ground return points, which are strung randomly together by lengths of wire that you call your 'ground bus', this can induce random AC interactions between different ground potentials from other ground return points (on which - for example - sensitive pre-amp filter cap grounds may be 'resting'). The result is that you can get the more sensitive parts of the ground return circuit merely 'riding on top of' this micro-wobble AC, thereby reflecting this AC back through the filter cap and into the supply rail (and thence into the signal path, where it manifests as hum).

Here are some links to some articles on grounding which you may find thought-provoking before you continue assembling the SAR unit.

Link to a superb article on grounding my Merlin Blencowe (The Valve Wizard)

http://valvewizard2.webs.com/Grounding.pdf

The gist of this article is that if you keep ground returns from each respective part of the circuit going to the same ground return point as the filter cap that is supplying those respective parts of the circuit, this greatly reduces the possibility of micro-wobble AC from one part of the ground return 'cross-infecting' the ground return at another part of the circuit. This is more critical in a stand alone reverb where you are connecting it to another amp.

I routinely build my amps using this type of grounding and they have a really really uber quiet noise floor.

Here is another brief (albeit excellent) article (this time by by R.G. Keen) on how to set up grounding:

http://music-electronics-forum.com/attachments/10929d1284360823-star-grounding-amps.pdf

FWIW I have found this method to be really invaluable in doing the grounding for SARs that I build, because it reduces the number of ground return points, and keeps the really critical high-current ground returns together.

Just sayin'.

He who dies with the most tubes... wins

Surf Daddies

Last edited: Feb 25, 2012 17:49:46

Thanks again tubeswell. I'll certainly read those articles and try to get my head around it all. Grounding is one of those things that is still very mysterious to me. There was another mention of star grounding on another forum I have been posting on where Tavo of "Nocturne" fame and Billy Zoom of "X" debate the benefits of this scheme in a properly grounded SAR.

They start talking about it on post #15.

Okay... well I walked to home depot on my lunch break. Bought a pair of snips and a sheet of zinc. measured, clipped, and folded it (using my desk drawer at the office) in 10 minutes.

Cost less than any available "doghouse" and I get to keep the snips!

So, I'm getting close to taking out the current guts. A few questions...

Seems to me that by looking at the schematic for the reissue and the original unit, the choke has two black wires. Does it matter which side the choke wires come from? Or is it not an issue which way it is fed from the rectifier board?

Same question for the heaters. Are both green wires from the transformer interchangeable? Can I send either one to the tip of the pilot and then just send that wire to the 2/3-4/3-4 and the other to the 7/9/9 pins?

Everything else is pretty clear, but the transformer wires are a bit confusing due to the duplicate colors. I'll be clearly marking the current connections with labels once I clip the plug ends and I'll send those to the same connections as on the RI.

For example CP-8 from the PT goes to the AC switch and CP-3 goes to the fuse. (these are the two black wires from the PT)

BUT!!!!
CP-11 and CP-12 (the two RED wires from the PT) seem to be interchangeable?

image

Last edited: Mar 01, 2012 11:24:38

jbennett wrote:

Seems to me that by looking at the schematic for the
reissue and the original unit, the choke has two black
wires. Does it matter which side the choke wires come
from? Or is it not an issue which way it is fed from
the rectifier board?

Choke leads are interchangeable

jbennett wrote:

Same question for the heaters. Are both green wires
from the transformer interchangeable? Can I send either
one to the tip of the pilot and then just send that
wire to the 2/3-4/3-4 and the other to the 7/9/9 pins?

Yes

jbennett wrote:

Everything else is pretty clear, but the transformer
wires are a bit confusing due to the duplicate colors.
I'll be clearly marking the current connections with
labels once I clip the plug ends and I'll send those to
the same connections as on the RI.

For example CP-8 from the PT goes to the AC switch and
CP-3 goes to the fuse. (these are the two black wires
from the PT)

These are the primary winding leads

jbennett wrote:

BUT!!!!
CP-11 and CP-12 (the two RED wires from the PT) seem to
be interchangeable?

That's correct

He who dies with the most tubes... wins

Surf Daddies

T! Thanks again. Glad my schematic reading was correct. On the original unit there are two black "primary windings" on the PT. On the reissue unit there is a black and white wire. The black runs to the fuse while the white goes to the switch. I was in error when I said they were both black in my previous post.

You can see the unit here:

image

Another issue, since I'm using a three prong power cord. The old schematic doesn't say what wire goes where from the power cord. So, am I right that the black wire will connect to the fuse, while the white wire goes to the switch? (and green to the chassis ground-nut)

It would make sense to me the other way around, to send the live wire to the switch rather than the fuse.

Note: the reissue uses a different switch that takes both wires from the power cord and then, when ON sends one to the transformer and one to the fuse.

Last edited: Mar 01, 2012 16:08:43

jbennett wrote:

Another issue, since I'm using a three prong power
cord. The old schematic doesn't say what wire goes
where from the power cord. So, am I right that the
black wire will connect to the fuse, while the white
wire goes to the switch? (and green to the chassis
ground-nut)

Yes the ground lead needs a good terminal clip attached to its own dedicated chassis mounting bolt, which you should secure with a locking-type nut.

For the primary winding, one lead goes straight to the neutral/return wire of the mains cord.

It is best practice for the active/phase mains wire to go the fuse, then the mains switch, then to the other end of the PT primary. In doing this, the active wire from the mains cord should connect to the 'bottom'* solder terminal of the fuse holder. The ring/'top' terminal of the fuse holder goes to the mains switch, and thence to the other end of the primary winding.

*If you mount the active wire on the ring terminal of the fuse holder, you risk electrocution when the fuse holder cap is removed with the amp plugged into a live mains outlet (because the ring terminal on most fuse holders is a direct connection to the metal flange on the end of the opened/uncovered fuse holder).

He who dies with the most tubes... wins

Surf Daddies

Last edited: Mar 01, 2012 23:45:49

Okay. So you are describing the Weber 5g15 power cord wiring. Will the original fender wiring not work? Or is one better than the other.

In the old fender plan the switch bridges the connection of the neutral wire with one of the primary wires (black). So that primary to the PT must be attached to the other primary (white) inside the PT. And hence...POWER.
I guess I could just check for a zero reading on my meter from both primaries to answer that mystery.

Thanks again. As for the ground, I'll be reusing the existing ground mount nut. It is it's own secure bold on the chassis in green, clearly labeled.

On the AC side it is - according to my knowledge - unimportant which lead you interrupt with the switch. The circuit is open no matter where.
besides that it is more the contemporary way to switch both leads comming from the PT.
So you´ll never have a live lead behind the switch when switched off.

here comes the WEST SAMOA SURFER LEAGUE

I figured it must not matter much since many schematics, old and new, don't label neutral/ground on the AC wires.

don´t mix up neutral and ground!
there is a difference: http://en.wikipedia.org/wiki/Neutral_wire.
i would call the AC wires life and neutral and the grounding wire, which is always green/yellow ground.

here comes the WEST SAMOA SURFER LEAGUE

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