Peerless K-049-D Mic Input XFMR

CJ

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here we go again, this time a new-in box Peerless,  +8dBm  500 to 60 K grid, lungs are still recovering from the black tar UTC and the Maxson before that, praying for wax this time,  :eek:  urgent care center right down the street, COPD,

don't know where it is used, don't care. all i know is that it is gonna get hacked.

could be a sleeper cousin to the famous K-241-D  which people strap for MC carts,

 

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CJ

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500 ohm primary inductance at 20 Hz,

looks like the core is done at about 1.6 volts rms,
 

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CJ

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here is 500 ohm primary inductance vs frequency at 1 v-rms in, flux too much at 10 Hz,
 

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CJ

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xfmr will not come out of the Al can, we have some spare cans made of steel, so we rip and tear to get that thing out,  had some black goop holding it in,
 

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CJ

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good deal, wax instead of the goop, wax drips of clean at low temps,

 

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CJ

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the Eagle has landed...
 

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CJ

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the core was taped up with some cloth, the wax melted right off and the lams come out easy, which is good as these are probably Supemendur, and we want to save those,
 

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CJ

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kind o a surprise here, the I bars are regular steel, they probably ran out of Nickel I bars, or they were trying to make a hybrid core to take a bit more signal,
 

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CJ

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primary winds on the outside,
 

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CJ

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#32 is a piece o cake to unwind,  47 turn partial layer on outside,
 

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CJ

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Peerless likes to put color codes inside their coils, probably denotes insl. thickness,
 

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CJ

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pretty straight forward coil, no bi-fi primary like the K-241-D, regular EI lams instead of EE lams, sq stk instead of 3/4 like the 241-D, no interleaving of winds, pretty good alloy coming in with a perm o 42,000 even with the steel I bars,

still have to unwind and count the 6,000 turns of #42,  :'(   

we could rewind this with the split bi-fi primary like the K-241-D and probably pickup another 20 K in freq response,

here is what we have so far>

 

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CJ

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sand the cut sheet that came in the box how cool is that?
 

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rackmonkey

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There's disagreement on max level between the 1950 catalog/cut sheet and later catalogs from '53 onward. Cut sheet and 1950 catalog show 0 dBm. Later catalogs show +8 dBm. It's probably the same situation as UTC A series iron, where early catalogs show +7 dBm and later catalogs show +15 dBm for several models. Maybe they went with higher steel content in the core later? Anyway, the 0 dBm max was the thing that kept me from using this as a line input for any of the compressors/limiters I've built. 

1950 catalog entry:

rAD62pkl.jpg


BT
 

PRR

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> looks like the core is done at about 1.6 volts rms,

Cut-sheet says "0dB" but that means 6mW in 500 Ohms (lagging behind VU standard of 1939).

Their 0dB is 1.732V. Which is exactly equal to your 1.6V plus <1dB marketing dept fudge.

> Cut sheet and 1950 catalog show 0 dBm. Later catalogs show +8 dBm.

No, to 1950 not dBm but 0dB, in reference to the *older* 6mW/500r spec.

There is 7dB difference based on Voltage. 7.78dB based on power. (But nobody went-through 500r systems to make them true 600r systems.) +/- the usual fudges, this fully accounts for the 0 vs 8 difference in ratings.

The real limit is that this is a To Grid transformer with 1:10(?) step-up. How much juice can you apply to a 6J7/1620 grid? 3V peak will slam it. This is 0.3V peak 0.2V RMS at the primary. You would certainly have pads to drop +8VU telco level to -18dB (re 6mW) at the primary.
 

rackmonkey

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Thanks for setting me straight on that, PRR. I knew that there were conventions prior to dBm, but I didn't realize dBm came into use by reputable manufacturers that late.  I always thought dB was useful only in relative terms and didn't have a circuit reference (which I also assume was codified by the 1939 standard you cite?) Never realized it had any other meaning.
 

CJ

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we could stretch the bobbin and wind this with an extra 1/4" of 29M6 steel to get the level up to K241D specs, and a bit more,
 

CJ

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ok here is the print for this guy>

 

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