dropping resistor for line voltage

10/15/2011 10:21:28 AMBrian

I am restoring my EICO 324 and would like to keep the AC line voltage within the unit close to what was originally intended. If my line voltage is approx. 124v can I put a resistor in the unit's ac line just before the switch? What resistance value and wattage would be recommended?

10/15/2011 10:37:20 AMNorm Leal

Brian

Yes you can add series resistance in the AC line but there are things to consider. How much voltage do you want to drop? What current is drawn by EICO 324? A resistor will get warm so where are you going to mount it?

If a unit draws 1 amp and you want to drop 10 volts need a 10 Ohm resistor. This resistor will dissipate 10 watts.

Divide voltage you want to drop by current drawn and it will give resistance. Voltage times current gives wattage.

Norm

10/15/2011 12:59:26 PMBill G.

:Brian
:
: Yes you can add series resistance in the AC line but there are things to consider. How much voltage do you want to drop? What current is drawn by EICO 324? A resistor will get warm so where are you going to mount it?
:
: If a unit draws 1 amp and you want to drop 10 volts need a 10 Ohm resistor. This resistor will dissipate 10 watts.
:
: Divide voltage you want to drop by current drawn and it will give resistance. Voltage times current gives wattage.
:
:Norm
:
::I am restoring my EICO 324 and would like to keep the AC line voltage within the unit close to what was originally intended. If my line voltage is approx. 124v can I put a resistor in the unit's ac line just before the switch? What resistance value and wattage would be recommended?
::
:
:
Norm is right.
More explicitly, R = V/I, where R is the resistance you need in the resistor, V is the voltage you want to reduce and I is the current draw of the device.
Then you need P = V * I, where P is the required power rating of the resistor. V and I are the same.

Putting an AC current meter across the turned off on/off switch will turn the unit on and give you the current draw, I, that you need for the equations above.

Best Regards,
Bill Grimm

10/15/2011 3:10:19 PMDan

:I am restoring my EICO 324 and would like to keep the AC line voltage within the unit close to what was originally intended. If my line voltage is approx. 124v can I put a resistor in the unit's ac line just before the switch? What resistance value and wattage would be recommended?
:---------------------
I don't think 124VAC would affect the performance of an Eico 324 very much, if at all. The power transformer isolates the line, and the 115v. secondary is only half-wave rectified. (There's also a 6.3v. tap for the tube heaters, which would make a slightly higher AC line negligible). Slightly higher secondary voltage won't really affect the signal quality or characteristics. I just re-capped my Eico 324 - - probably the best thing you could do for it! If you're dealing with a significant voltage problem, you could always run it in series with a variac. (My household voltage varies between 118 - 125, depending on the time of day. Never had any problems.)

10/15/2011 3:20:00 PMPeter G. Balazsy

Hi Brian:
You probably won't have any adverse problems with your unit using it with today's slightly higher line voltage.

If you don't want to deal with the heat from a big hot resistor, there are other ideas.

So if you feel you really still want to drop 10% off the incoming line you can easily do that with a 120/12volt filament transformer used as a "bucking" transformer. You can build it right into the same box if you have room.

Another idea is to use a Variac adjustable power transformer (set to 110vac or whatever you'd like) on your bench that feeds a dedicated power strip that you can plug your Eico into.

10/15/2011 4:38:13 PMBrian

I guess my biggest concern over a higher AC voltage was a surge in B voltage that would exceed the electrolytics. Also, my unit has no resistor preceeding the diode as well.

Hi Brian:
:You probably won't have any adverse problems with your unit using it with today's slightly higher line voltage.
:
:If you don't want to deal with the heat from a big hot resistor, there are other ideas.
:
:So if you feel you really still want to drop 10% off the incoming line you can easily do that with a 120/12volt filament transformer used as a "bucking" transformer. You can build it right into the same box if you have room.
:
:Another idea is to use a Variac adjustable power transformer (set to 110vac or whatever you'd like) on your bench that feeds a dedicated power strip that you can plug your Eico into.
:

10/15/2011 5:02:36 PMDan

:I guess my biggest concern over a higher AC voltage was a surge in B voltage that would exceed the electrolytics. Also, my unit has no resistor preceeding the diode as well.
--------------------------------------------

Brian - - the "B" voltage should be 125v after the rectifier. It then passes through R1 (2.2k) with a 20 uf electrolytic on either side = 110v output. Those caps are rated at 150V, but in all honesty, I would highly recommend replacing them before using this old generator! I won't even attempt to power up anything over 40 years old without recapping it - - cheap insurance. My rule of thumb - - replace ALL caps (except ceramic & micas) before powerup. I recapped my "new" Eico 324 a couple weeks ago, and it only cost about $7.50 total - - - with 450v electrolytics and 600v. mylars. After 45 years of working with vintage electronics, I've come to know first hand what damage a shorted cap can do (and they really STINK when they blow!) Just my .02 worth. . . .

10/15/2011 6:37:34 PMPeter G. Balazsy

Dan:
Brian did say he was restoring the unit. I assume that he intended to replace all the paper caps as well as the 20uf 150vdc electrolytics.
Your conservative advice is definitely wise Dan, however I'm quite sure that new replacement electrolytic caps of 22uf or so rated for 160vdc will most likely be perfectly fine for the future life of this unit.

10/15/2011 7:11:37 PMEdd

Sir Brian. . .

Transposed from your earliest other dupe thread

With due consideration of the units manuals specs, do you even want to do that?

" POWER REQUIREMENTS: 105-125 Volts AC, 50/60 cps ; drain 15 watts "

The median of the spec would be 115VAC input.

Two or 3 options:

However if being my task to do, I would be using a 6.3 VAC or 12.6 VAC filament transformer.

That unit gets its primary wired across the AC line thru the switch, then its separate
6.3 VAC /12.6 VAC secondary winding is wired series opposing with the primary winding of the
units original power transformer, so the the end result is an actual decrease of the primary applied
voltage by that 6.3 VAC /or / 12VAC amount.

If you accidentally have the filament transformers winding installed series adding, you wil be having the
transformer putting out either 6.3 VAC or 12.6 VAC TOO MUCH, so reverse its secondary windings leads.

Since the primary current on the power transformer is merely ~125 ma, a dinky filament transformer
with the puny spec of only 500 ma on its secondary winding would still be overkill.

The end effect being as if you were using either 117VAC or 112VAC line voltage input.

Option two would be to use a series power resistor inline with the original power transformer primary.

Use a 10 0hm 5 watt power resistor (overkill) to do the brunt of the power dissipation work and then shunt across it with a lower wattage
resistor to be able to then " fine tune" in the voltage to your desired 115 VAC equivalent input voltage.

That trimming resistors ballpark value is 27 ohms at 1 watt.

The last option was the use of a series capacitor in the line, and since we are dealing with but a mere 1 watt of
power needing to be dissipated . . . . is it even worth the consideration ?

73's de Edd

The things that come to those that wait, just may be the few things left by those who got there FIRST.

:Dan:
:Brian did say he was restoring the unit. I assume that he intended to replace all the paper caps as well as the 20uf 150vdc electrolytics.
:Your conservative advice is definitely wise Dan, however I'm quite sure that new replacement electrolytic caps of 22uf or so rated for 160vdc will most likely be perfectly fine for the future life of this unit.
:

10/16/2011 12:00:48 AMPeter G. Balazsy

EDD:
Wouldn't a series "dropper" capacitor be a problem feeding a transformer?

My experience has that L/C combo oscillating wildly.

So I don't use a dropper cap feeding a transformer.

10/15/2011 7:42:02 PMDan

Peter- completely agree with you. The reason that I stock 450V electrolytics is because they only cost about $.50 more than 160v, and I can use them in virtually all the old stuff I work on. Keeps inventory down, and I have to re-order less often. But I'm a lazy cuss. . . . . !

10/16/2011 6:17:54 PMBill G.

Just my .02 worth. . . .
:
Hi Dan,
Is that your 0.02uF worth?
Standard value.

All the Best,

Bill

10/17/2011 1:18:03 PMDoug Criner

Brian: Your main concern is overstressing the two 20-uF electrolytic filter caps (C3a and C3b)? The originals were rated 150V (but according to the schematic, the first cap, C3a, sees only 150V at nominal conditions). The closest modern cap rating is 22uF, 160V, so assuming you're replacing the caps, that will give you an addtional 6% margin. Or, you could go whole-hog, and buy a 250-V or 450-V cap for C3a).

As far as worrying about a "surge" in B+ plate voltage, I can't visualize that happening (that's what C1 and C2 are for). And, I wouldn't be at all worried about there not being a resistor ahead of the diode - evidently, EICO wasn't either

10/17/2011 1:20:56 PMDoug Criner

Correction: the shematic shows only 125V across C3a, not 150. Sorry.

10/17/2011 1:26:04 PMClifton

Doug,

Perhaps a CL-90 might ease his mind as far as the surge?

Clifton

:Brian: Your main concern is overstressing the two 20-uF electrolytic filter caps (C3a and C3b)? The originals were rated 150V (but according to the schematic, the first cap, C3a, sees only 150V at nominal conditions). The closest modern cap rating is 22uF, 160V, so assuming you're replacing the caps, that will give you an addtional 6% margin. Or, you could go whole-hog, and buy a 250-V or 450-V cap for C3a).
:
:As far as worrying about a "surge" in B+ plate voltage, I can't visualize that happening (that's what C1 and C2 are for). And, I wouldn't be at all worried about there not being a resistor ahead of the diode - evidently, EICO wasn't either
:

10/17/2011 5:40:38 PMDoug Criner

Clifton - I think a CL-90 inrush limiter is always a nice idea. I tend to intstall one in each antique radio I repair.

A CL-90 will limit the initial turn-on inrush CURRENT charging the filter caps, save wear and tear on a vacuum-tube rectifier (but this EICO 324 uses a solid-state diode), delay full power to the tube heaters, and MAYBE reduce the risk of cathode stripping. And, after the CL-90 is warmed up, it will still drop the line voltage a volt or two, which is nice. But I don't think a CL-90 will reduce any line VOLTAGE surges or reduce stress on the filter caps (except for that volt or two that a CL-90 drops at steady-state).

10/18/2011 1:20:12 PMClifton

Doug,

I didn't say, but meant initial turn on surge. Perhaps MOVs could be used across the primary of the power transformer.

Clifton

:Clifton - I think a CL-90 inrush limiter is always a nice idea. I tend to intstall one in each antique radio I repair.
:
:A CL-90 will limit the initial turn-on inrush CURRENT charging the filter caps, save wear and tear on a vacuum-tube rectifier (but this EICO 324 uses a solid-state diode), delay full power to the tube heaters, and MAYBE reduce the risk of cathode stripping. And, after the CL-90 is warmed up, it will still drop the line voltage a volt or two, which is nice. But I don't think a CL-90 will reduce any line VOLTAGE surges or reduce stress on the filter caps (except for that volt or two that a CL-90 drops at steady-state).
: