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 on: Today at 07:49:24 PM 
Started by KL7OF - Last post by KB2WIG


"   What a terrible thing to have lost one's mind. Or not to have a mind at all. How true that is.  "

                                                                                                                                                   D. Quayle


 on: Today at 07:45:03 PM 
Started by WA4WAX - Last post by WBear2GCR
Really 400 watts to drive the grids??
Seems to me that you only will draw probably less than 10 watts??
Seems like excess core...?

 on: Today at 04:58:43 PM 
Started by KL7OF - Last post by WD8BIL
Truth for the weak minded!

 on: Today at 11:00:39 AM 
Started by w9jsw - Last post by KD6VXI
I've been away from the house the last two weeks....  But, got home and my board is there.

Thanks a million.  One of these days I might get some time to out it together and transplant into the Viking!


 on: Today at 09:16:11 AM 
Started by WB1GCM - Last post by Steve - K4HX
Some info at the link below (may be dated in some cases):


 on: Today at 01:09:21 AM 
Started by WA4WAX - Last post by Opcom
I've used a 5W/70V one for a 600 Ohm match (690 Ohms) by putting a 4 Ohm speaker on the 8 Ohm tap. Transformer rating at best would be 1.25W for the same frequency response. There are a bunch of rules of thumb on these things but always best to check actual performance before making it permanent.

Off-label use of these transformers is something I've had a little hands-on experience with. The video shows the right way to use them as a matching transformer sans DC and the math looks OK but it should be clarified on that 5W unit he's showing, for which the diagram was drawn, that if the 2.5W tap is selected as the CT then the start is the common tap and the finish is the 0.62W tap @ 8000 Ohms (8K CT). If the start is the common and the CT is the 1.25W tap then the finish is the 0.31W tap at 16K Ohms (16K CT). These statements are only correct when the 'speaker' side has the stated load of 4, 8, or 16 Ohms, properly attached.

I totally agree about 'no DC at all' on these things, but would temper that by stating 'no unbalanced DC at all'.

So, the following is just opinion, but it's suported with a lot of experimentation and actual use. Those little transformers and their large cousins are very good step-up from speaker-ish impedances to grids, as long as DC through any winding is negligible. They can give excellent performance close to 'hi-fi for communication work' if the unit has a wattage 4-8 times higher than the power level present. This is because they have small cores that don't handle bass well, but this mostly applies to older units which are usually specified for around 70Hz low frequency.

It is super-easy to drive AB2 6146 grids with a 7W/70VCT unit, and the frequency response was much better than it would have been at the 7W rating. 6146's take only 200mW to drive so they sounded beautiful. Anyway, it was tube power amp in a vehicle and didn't cost like a Milbert.

In the case of grid drive, it is only important to provide the low-Z winding with the voltage needed to be transformed, by the turns ratio, to the secondary voltage wanted for the grid to grid drive. The low Z source could have any reasonabl;e internal impedance as long as the voltage demanded by the turns ratio put across the low-z side and has good regulation and does not exceed the voltage for the transformer tap impedance corresponsing to the transformer's wattage rating.

There are much higher quality and higher power ones available from Edcor than the usual 50 year old ones in our junkboxes. Their respose goes to 40Hz at full power according to Edcor. I use a 400W one to drive 3-500Z grids. Only a 100W one is needed for 20Hz audio response (25W peak drive) but ya know.. I didn't want the driver transformer to be the frequency-limiting factor at all. The 400W one puts any transformer problems far outside the audio bandwidth limits in use. But again this is all just my opinion.

I want to share my experiences with Edcor line matching transformers for off-label uses because it has been really good. These are newer and better audio quality that those shown in the video and I think the best available for a reasonable cost. I suppose that modern audio distribution systems are subject to better expectations, so Edcor supplies appropriate parts.

The Edcor WA series is for low-z drive to a high Z load. They can be ordered with a 140/70V (140VCT) winding and choice of a 4 or 8 Ohn mwinding, so there is the high voltage center tapped side and the low impedance side.

Edcor WA series https://www.edcorusa.com/ampoutput#/specFilters=122m!#-!824

The attachment is my cheat sheet for doing the experiments with several Edcor models. I have used the 30, 120, 240, and 400W ones.

 on: Yesterday at 11:12:27 PM 
Started by KL7OF - Last post by W7TFO
Only you can prevent forest bears.


 on: Yesterday at 11:06:48 PM 
Started by KL7OF - Last post by W7TFO
You know where to go for that sort of stuff, Steve...:-).


 on: Yesterday at 08:36:28 PM 
Started by WA4WAX - Last post by ka1tdq
Timmy has a nice write-up on the subject:


Personally though, I get ideas visiting gentlemen's clubs.

(the ones with the girly-girls. I mean, naked girls)


 on: Yesterday at 08:28:01 PM 
Started by w9jsw - Last post by w8khk
My second board arrived this afternoon.  Beautiful work...  Thanks, John!

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