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PostPosted: 28 Jun 2009, 01:39 
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Those who bought the Altronics phase splitter and the Edcor "all in" iron -- anyone able to modify Pete Millett's chassis PDF? Otherwise I'll wait until I get mine in, take actual physical measurements, and ask Pete Millett for advice.


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PostPosted: 28 Jun 2009, 12:18 
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Hi Dusty,
There are dimensions on the Edcor site but I am not able to produce a proper scaled / dimensional drawing. Note, you will also want to nail down choke model for the layout.

It might be best waiting for the parts to arrive. I'm not sure what will be the best way to mount the phase splitting transformer. I am thinking of mounting it to the PCB - any thoughts on this?
Cheers, Gio

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PostPosted: 30 Jun 2009, 03:51 
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Received my Edcors yesterday. Man, they are something to look at. I originally thought I would paint them a color different from the "Edcor" blue, but I am rethinking that because the finish is so good. No drips, no runs, no errors. And the shade of blue is really nice. I'm going to go ahead and plan my chassis color to coordinate with it. Consequently, I'm reconsidering my plan to buy Hammond enclosed chokes to mount next to these beauties. Doubt that I could match the color, so under the chassis chokes may be in order.

Now to find some time.

Cheers, Greg


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PostPosted: 01 Jul 2009, 07:39 
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Gio wrote:
I'm not sure what will be the best way to mount the phase splitting transformer. I am thinking of mounting it to the PCB - any thoughts on this?
Unfortunately, not. Received the Edcors (agreed -- they're hot! -- will definitely want to display them proudly), will wait for the Altronics at least.

Thoughts on the choke? Yeah, me neither.


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PostPosted: 01 Jul 2009, 11:27 
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So I started looking into the choke. I suppose the default is something like a Hammond (193J?), but I saw Pete Millett mention James on his page, so I looked around for James, but didn't find a whole lot. One vendor -- tctubes -- responded thusly:
Quote:
Yes, they do make very nice chokes as well. There's quite a variety available. Physically smaller ones have the cylindrical shape to them just like the 6113 transformers we have on the site (sold out at the moment but more on the way). There is a 5H 200ma one like that.

Then there are larger chokes that are physically similar to the 6123 transformers. The ones between 5-10H are rated as follows:
10H (250ma) 86 ohms
10H (200ma) 97 ohms
7H (300ma) 60 ohms
5H (350ma) 40 ohms

I'm not really sure what the prices are, they do change with volume. There's a smallish price break at 10 units and then a larger one at 50. At ten or less, the only advantage we really get is sharing the shipping and wire transfer fees. So far, I've always shipped via surface as its roughly 1/3 of air. These are transformers after all.

I have some interest myself in getting some chokes and the value range you are describing works for me so if you can pull together some folks on your end we might be able to make this work out reasonably well for all of us.

Once you pick a value you like, I'll inquire on prices.
I'm kind of a newb at this -- which of the first two would we prefer? I'm thinking each of us are going to want two each, so I only have to get four other people to be interested enough to want to pursue this. So, here are some pics to show how nice they look: tctubes link octave electronics link. Pete Millett also seems to think they are good quality at a reasonable price. So anyone else interested?


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PostPosted: 01 Jul 2009, 18:57 
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I found out that the beautiful Edcor blue is powdercoat, not paint. So I couldn't have painted over the end bells if I had wanted. I bought a pair of the Hammond 193J chokes, and now I have a dilemma of how to get those cheap looking Hammond end bells to live up to the Edcor standard. They are really crummy looking. I guess I'll have to get creative. I recently saw a tube amp for sale that used the Edcor blue iron, and the chassis was painted a lighter powder blue. It looked great. Maybe contrasting colors like that would look nice.


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PostPosted: 01 Jul 2009, 21:51 
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Hi guys, my plan was to get a open Hammond choke and put it on the underside of the enclosure. You can get also get an enclosed Hammond choke, but they only come in black.

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PostPosted: 02 Jul 2009, 18:06 
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Black is fine, it goes with anything. 8-) If I get the James, I will get black.

So everyone else is getting the Hammond? Anyone not getting the Hammond? I'll give it another week and a half, since a lot of people are out right now. It may be that I won't even need to get 4 more people who are interested in the James. Maybe 3, 2 each?


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PostPosted: 02 Jul 2009, 19:37 
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I've considered the open bracket chokes, as well. I may go with that rather than mount the 193Js and then wish I didn't have them next to the Edcors. I'm really wanting to finish this amp in fine fashion. My thoughts right now are a pair of monoblock chassis, long from front to back, something in the 16-17" range, and half that, or about 8-8 1/2" across the width. I want at least 4" height to give the under pcb components plenty of room. A 10H choke will take up some space, and my electrolytic caps are pretty tall. Don't want to go through another build like my KT88 SET, where everything was so crammed together.

Cheers, Greg


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PostPosted: 03 Jul 2009, 06:25 
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Pertaining to this choke discussion, can we determine exactly what the current draw is of this UniAmp circuit, and then know what the capability of the choke needs to be?

The recommendation I've seen is 5-10H, but nothing more specific. I was thinking the 193J specs were ideal, but now that I'm considering an open bracket, the choices are more limited on higher current draw.

After reading the following from Aiken Amps, I'm thinking that the selection is more crucial than I have thought before. It specifically is about guitar amps, but the same selection process would apply here for us.

Quoting Aiken Amps;
Quote:
How to select a choke:

Chokes are typically rated in terms of max DC current, DC resistance, inductance, and a voltage rating, which is the max safe voltage that can be applied between the coil and the frame (which is usually grounded).

DC current
If you are using a choke-input filter (not likely, unless you are trying to convert a class AB amp to true class A and need the lower voltage, or if you are designing an amp from scratch and want better supply regulation), the choke must be capable of handling the entire current of the output tubes as well as the preamp section. Note that this doesn't mean just the bias current of the output tubes, but the peak current at full output. This usually requires a choke about the size of a standard 30W-50W output transformer, since the choke must have an air gap (just like a single-ended OT) to avoid core saturation due to the offset DC current flowing through it, and the choke also must have a low DC resistance, to avoid dropping too much voltage across it, which will lower the output voltage and worsen the load regulation. This combination of low DCR, air gap, and high inductance (more on that later...) usually results in a substantial sized choke. To calculate the required current rating, add up the full power output tube plate currents, screen currents, and the preamp supply currents, and add in a factor for margin. For a 50W amp, this may be 250mA or so.

If, on the other hand, you are selecting a choke for a capacitor input supply (such as the typical Marshall or Fender design), then the requirements are relaxed quite a bit. The purpose of the choke in these type supplies is not for filtering and voltage regulation, but just for filtering the DC supply to the screen grids of the output tubes and the preamp section. The screens typically take around 5-10mA each, and the preamp tubes draw about 1-2mA or so (for the typical 12AX7; 12AT7's are usually biased for around ten times that). This means that you can get by with a much smaller choke, and, in addition, the preamp supply current doesn't vary that much, so you can get by with a higher DC resistance, which means smaller wire can be used to wind the choke, which means higher inductance for a given size core. Just add up the current requirements of the screens and preamp tubes, and add a bit more for margin. For a 50W amp, a typical value might be 50-60mA.


DC resistance
For a typical choke input supply, you need a choke with no more than 100-200 ohms or so DCR. A capacitor input supply typically might use a choke with a 250 ohm - 1K DCR. The higher the resistance, the more voltage drop and the poorer the regulation, but the cost will be lower.

Inductance
As for the inductance value, this depends on how much filtering you want. The inductance, in conjunction with the filter capacitance, forms a lowpass filter. The larger the inductor, the lower the cutoff frequency of the filter, and the better the rejection of the 120Hz (if full wave rectified) or 60Hz (if half wave rectified) AC component of the rectified DC. In general, the larger the better, within reason (larger inductances at low DC resistances mean larger chokes, which cost more money). Typically, 5-20 Henries is a good choice with the standard 32-50uF electrolytic capacitors. The inductance and capacitance values also determine the transient response of the supply, which means the tendency for the supply to overshoot or "ring" with damped oscillations whenever a current transient is applied (such as at startup or on a heavy current surge, such as a hard "E" chord at full power!).
End quote

Cheers, Greg


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