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Edcor Universal Power Transformer for Tubelab SE

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I am having Edcor build a power transformer for the Tubelab SE. They don't currently have one with the correct HT winding that also has a CT 6.3V winding and a 5V @3A winding (I want the option to use a 5U4*).

I am adding a pair of taps to the HT winding that will allow me to run either around 300V or 400V B+ so that the amp will take full advantage of 45s or 300Bs. Since the input stage uses a CCS, it seems like being able to switch back and forth when switching tubes should work fine with an amp like this. Obviously, making this an actual switch falls under the same category of "oops" as putting a switch on the heater supply, but that is always an option.

Here are the specs:

330-260-0-260-330 @ 175mA
6.3V CT @ 3A
5V @ 3A

They quoted me $57.98 (plus the setup fee for me), which seems fairly reasonable. Is anyone else interested in a design like this? Obviously, you still have to compromise on the OPT impedance, but I don't mind losing a little power with 300Bs seeing 5k.

I'm done with Hammond.

Russ
 
I got the sales order today. Should take 3-4 weeks. Note the new part number is:

XPWR131

It is wrong in the post above! If you order one I would double-check the specs with them because they gave me the other part number over the phone yesterday.

FYI, bumping the 6.3 to 4A only added $4 to the cost. To go to 6A to try to cover 2A3s and some of the $beaucoup 300Bs would have required a larger bobbin and a bigger core, so the cost would have gone up more significantly. She said it would be "doable" on a single transformer, though.

I figured that the majority of folks that would want to build a "more universal" Tubelab SE using one of these would probably be looking at more of the reasonably-priced 300Bs.
 
Today I've discovered a weak point of an Edcor transformer...
 

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I just got the notification that the transformer has shipped. I'll post test results once it gets here.

Good timing too, as a friend of mine has loaned be a pair of Chinese 300BS tubes (the crazy globe ones with mesh screens) to try. He's got WEs now.... Prolly gonna pick up a pair of the "cheap" Shuguang 300B-98s before they go up in price more.

Russ
 
Good timing too, as a friend of mine has loaned be a pair of Chinese 300BS tube

I finally got to the warehouse to retrieve another pair of tubes for you to try. I need to go to the post office tomorrow to mail my taxes, I will send them as well.

Did you drop it or something?

There was another thread detailing the treatment of Wavebourns amp by Fedex
 
Here it is.

tubelab-se-testing-edcor-45.jpg


Wire coloring leaves a few things to be desired, but it seems to work as expected.

edcor-xpwr131.jpg


Voltages came in a bit high, even under load. The top row is the Tubelab SE in "45 mode", with about 25mA per tube. Meters are reading: 660VAC winding, 520VAC winding, B+ at the filter cap. Bottom row is in "300B mode", running Shuguang 300Bs (not mine) at about 28mA per tube. First two meters got swapped: 520VAC winding, 660VAC winding, B+.

tubelab-se-testing-edcor-bplus.jpg


The B+ in "45 mode" is a bit higher than I was hoping, but it is within range of what a lot of folks run it at. I'm using a Hammond choke that measures about 82 ohms, so some series resistance there would help bring it down for anyone concerned (or one could use the 6H Triad choke which is 150 ohms). I'd say the B+ in "300B mode" is right where it should be.

I've run the amp for an hour or so with the 300Bs and the transformer is only slightly warm. I'll let it go for a few more hours to let is heat soak. It does have a slight mechanical buzz, which is a little sad, but it's not too bad.

I had to put a fan on it because the tiny temporary heatsink on the heater regulator is not enough. It keeps tripping the thermal protection. The heater windings are where they ought to be. A tad on the high side, but not too bad.
 
Wavebourn said:
Design of bells is toyish. Period.

Buying Edcor transformers you need to consider ordering of mounting hardware somewhere else.

i would agree about the mounting flange. The bells are fairly thin sheet metal and the tabs are stamped right into it. You can bend them with your fingers. I would not expect them to survive shipment anywhere mounted by them. I meant to ask them if they offered bells for flat-mounting them.
 
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