Looking for a replacement power transformer for a UE-100

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Ciardhubhan

Member
Joined
Apr 30, 2006
Messages
22
Location
Montreal
Fired her up today and I heard a vibrating noise from the unit, knew something was up and then the look of death as I saw her one orange eye grow dimmer and dimmer till finally, gone...  :-\

Does anybody happen to know of a suitable replacement power transformer for the UE-100, the older tubed model? I just tested the primary and it's open, for sure... I think I saw an ebay auction once with a set of UE-100s with replaced power transformers- hoping there's a direct drop-in replacement out there (or anybody with a spare unit for parts?)

Thanks in advance for anybody's help.. truly a heartbreaking day...
 
Nope, no drop-in replacements out there, it's far too complicated for that - you'll need to have a new one made to specs, I'm afraid...

Other option would be to assemble the right voltages from a number of off-the-shelf transformers working together, but that may not fit in the chassis.

Jakob E.
 
Hi Jakob,

Thanks for getting back to me, I really appreciate it. I thought that it would pretty much come to that, a custom job. That being said, I looked over the schematic and for the life of me, I can't figure out what the voltage/current values are for each secondary. I've tried backtracking from the rectifier codes but that hasn't led far, and at best would be a guestimate. How would you normally be able to figure something like that out?

kleinundhummelpowertransformer.jpg
 

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rather, what i meant to say was that as a last resort, i plan to back track the voltages by checking the capacitor ratings after the diode rectifiers... (the topmost one is already listed as 30V/40V, and given that the rectifier code says B30... I assume that it's meant for a 30V output + the ripple... and then guestimate that back to the winding voltage..

so say 30V smooth dc backtracks to rectified full wave dc rms of 30V / 1.4 = 21.4V DC and adding back 1.4V for the bridge rectifier = 22.8VAC RMS at the secondary winding?

is this about right or is there a more precise way to go about backtracking the secondary voltages... I'm not sure how to get the current rating though of the secondaries...
 
Don't do that! The topmost voltage is filaments, so I guess the correct output is probably 12.6Vdc, so the xfmr must be ca. 9-10Vac. It's almost impossible to calculate, because the actual voltage depends on the DC resistance of the secondary, which is some kind of an unknown. I believe the designers at K+H had to prototype several transformers before getting the right one. For the rest, the plate voltages are more tolerant. I guess the second voltage is ca 200-250Vdc and the 3rd and 4th are bipolar 2x 100-150Vdc.
 
You know that K & H are still in business? I wouldn't count on it but maybe they still have replacements or are able to help in some way. Sending a mail woulnd't be amiss..

Chris

 
I have recently serviced a pair of those, Voltage at the secondaris are:
12.6, 280, 92V, 92V.  for the current:  4A for the filament , then 100mA for the rest, should be enough.

Mik.
 
Thanks for all the great advice guys, I really appreciate it!

mik, thanks for the values you gave on those voltages- that really clears up a lot of things... based on the 12.6V you quoted for the filament voltage, you measured after the smoothing capacitors (after capacitor CN29 at the top of the diagram)? in other words, those are all DC voltages, not the AC coming straight off the transformer windings?

in other words, for me to order a custom trannie (say from edcor), i'd still need to backtrack somehow (or work with the transformer manufacturer) to get the true VAC RMS values of the windings themselves, factoring in the DC resistance of the secondary, as abbey road mentioned? or perhaps just say that i need a secondary that produces 4A of 12.6VDC after smoothing and the transformer manufacturer should be able to figure it out?

chris, thanks for the good point- looks like i will be trying to contact K & H just in case they've got spare parts or any other info before trying to mess with guessing a design for a replacement transformer...
 
Ciardhubhan said:
or perhaps just say that i need a secondary that produces 4A of 12.6VDC after smoothing and the transformer manufacturer should be able to figure it out?
I wouldn't count on a transformer winder to calculate that. I believe the rectifiers are selenium, not silicon, they are not easy to model. I think you should start with 12.6Vac, as mik has measured, and be ready to insert a low value resistor if the resulting DC voltage is too high. Anyway filaments are designed to withstand continuous 10% overvoltage.
I would start the unit with a Variac.
 
hi guys,

mik, thanks again for confirming with me on the voltage values, it certainly changes the gameplan a lot, and abbey road, thanks for the additional advice about adding a resistor in series just in case... i suppose though, if 12.6VAC was what was measured, then maybe the filament voltage was meant to be a bit higher after all in this design? i guess the only way to confirm is to literally measure the DC voltage that is supposed to appear after the smoothing cap on a functional unit... as you say though, a bit over shouldn't be too bad.

the only question mark at this point is for the 12.6VAC/4A winding, basically the effect of the dc resistance of the secondary of the original transformer/transformer that will replace it. given the high current, i suppose it would really be the only winding that would be affected significantly by dc resistance voltage drop...

so at the present moment, the consensus is to order a custom transformer that's 12.6VAC/4A, 280VAC/100mA, 92VAC/100mA and 92VAC/100mA?

how many ohms could the dc resistance be of the secondary for a modern power transformer that can put out 4A? say you tolerate +/- 1VAC (which seems to be quite a lot actually), that means the secondary has to be 0.25ohms or less...don't know if that's considered reasonable or to be expected..but surely a winder must factor that into the design given the specification is for 4A output...

 
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