A further note here would be to never, ever turn on old electronics and "see what happens." A much better idea is to use a variac and slowly bring up the voltage over many hours, which re-shapes and reforms old electrolytics.
An even better solution is to completely replace all electrolytics before the item at hand is even turned on.
An EV1144 was my first amplifier - my dad rescued it out of a dumpster (busted) for me, along with a KLH 18 tuner (still good) and some Atlec 10" two-way speakers (busted). The system was aparently a victim of the "turn it up to 11" syndrome. The outputs and drivers were blown in the 1144, and the woofers were fried on the speakers. I managed to beg some replacement germanium output transistors from Bendix, and I used HEP replacements for the driver transistors. McGee Radio sold me the replacement drivers for the speakers.
The innards of the amp got eventually gutted and replaced with circuits based on the old Motorola power Darlington audio amp application note, using the heat sinks from the original output amplifiers. The improvement was enormous.The amplifier eventually dissolved in a welter of modifications and guttings for parts. I still have the power transformer sitting around somewhere. I never was terribly impressed with the schematic, especially the preamp section, which used a dodgy bias scheme requiring selected parts.
The innards of the amp got eventually gutted and replaced with circuits based on the old Motorola power Darlington audio amp application note, using the heat sinks from the original output amplifiers. The improvement was enormous.The amplifier eventually dissolved in a welter of modifications and guttings for parts. I still have the power transformer sitting around somewhere. I never was terribly impressed with the schematic, especially the preamp section, which used a dodgy bias scheme requiring selected parts.
Well, if u use old electronics often, the electrolytics can last for many, many years with no problems. It's kinda like letting a car sit up for years without being used. Don't use it, and the fuel lines will gum up, the gas will be bad, etc. The only difference is that if it's power-supply eletrolytics, and u turn it on and they fail -- which is a very good possibility here, I might add! -- then you're probably going to take out a lot of components, like the power transformer, etc.
And may the Lord help ya if u take out an old gold/silver-wound audio transformer
.Randy
That sounds great. Also, does that thing have a grounded, three-prong power cord? A lot of old electronics from that era didn't have them, and should one of the primary bypass caps let loose (short), you're going to have 120 VAC on the chasis. Personally, I'd replace those caps no matter what and add the proper cord.
Another quick and easy mod (while ur at it) is to replace the #47 lamps and the like with a bright LED. If you're a purist, then by all means use an original lamp, but it is nice to refurbish an old piece of electronics and not have to worry about trying to find those lamps in another 10 years
.Oh. BTW (by the way), since u did turn the thing on, you can also tell if the supply caps need to be replaced (if you know the piece electronics well) if you noticed a significant increase in hum. Almost a sure sign that the supply caps are bad, although it could be that a bypass cap in the supply is leaking or about to let loose, and this is not a good situation, to say the least! (Read: you're about to have 120 VAC on the chasis.)
It is important to also note here that there are a few other causes of hum in amplifiers, with the first one being something known as common-mode hum. Basically, a portion of the output signal finds it way back to the power supply, this signal is rectified in the supply bridge, travels along the supply rail, and winds up in the amplification chain. This situation is easily solvable in the design phase of the amplifier, yet a lot of manufactures balk at the cost of adding such amenities to their circuits. That is, 50-cent parts really start to add up, especially when they take into account that they'll be building 100,000 units and such. It is also important to note here that such bypassing will be a sure sign of a quality amplifier, but good luck finding such circuitry in anything other than the amps you'll see on sites like this. You can do these things in one-off amplifiers, which is why you'll see circuitry for some the best amplifiers in the world on sites such as this, dickl.
Another form of amplifier hum comes from improper placement of the audio transformer. Basically, inductors love induce their voltages and increase the size of their electromagnetic fields -- they live for it
-- and should u place the coils close to each other in either a series or parallel setup, they'll gladly establish a new, larger field, with both coils now acting as one. Unfortunately, what this does is take power-supply induced, 60-Hz hum from the power transformer and inductively couple it to the audio transformer, and what you wind up with is 60-Hz hum on the outputs. This can usually be solved by rotating the audio transformer 90 degrees from the supply transformer and keeping it a good distance away from the supply transformer.Unfortunately, if this wasn't done in the design phase of the amp, good luck trying to remove the hum!
Anywho, should you run across an amplifier like this, I'd suggest that you strip the thing and rebuild it on a new chasis. I'm not kidding here. There are few things you can do to get rid of this problem, other than trying to install shields that look like crap and seldom work or by adding a 2nd chasis and moving the audio transformer WAY over there, but that usually involves moving all other kinds of electronics with it too, so you might as well strip the thing and start over. (Note: it's reasons like this that proper layout is paramount in electronic design.) If you haven't spent 3-4 days on proper layout (I'm serious), go back and do more of it!
Well, that's about all I have to say, at the moment. Sorry about the diatribe/tome
, dickl, but I just wanted to make sure you understand what you're dealing with here, my friend!Thanks for the long answer. I will install a new power cord.....good idea there. Also I thought of putting in LED as all the bulbs are burnt. Tell me more about putting LEDs in here. I tried to get a voltage reading from the bulb wires and all 3 are at 3 volts AC. The selector switch is supposed to power them 1 at a time according to the diagram.
Do you have some experience with this model? Or are you just reading the diagram?
I am trying to figure out what LEDs to use.
Do you have some experience with this model? Or are you just reading the diagram?
I am trying to figure out what LEDs to use.
Okay. Will do
.No. I don't have any experience with that make and model. What I do have is a lot of experience restoring old amateur radio equipment and broadcast-band radios from the 30's, 40's, 50's, and 60's.
Unfortunately, I just looked up the 3V bright LED's, and the damn things are outrageously expensive in single-lot purchase
. So, on second thought, you're are probably better off replacing the 3V lamps, in your situation.To answer the question, though: if this were a 6 or 12VAC bulb, I would find the common-point power rail of that circuit, filter the AC, and apply a DC voltage to the switch, and that would select the LED through a series current-limiting resistor, with the opposite end of the LED at ground. Call the resistor 1.5K ohms at 1/2 watt, for sake of discussion. There are many sites out there that show u how to do this and calculate the resistor for your needs, btw.
Hope this helps,
Randy
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Oh...one other thing that I forgot here. In some situations, there might not be a good solution, and it really depends on the overall layout of the piece of gear at hand. LED's are infamous for generating broadband noise, and a good circuit will always include RF-bypass components to get rid of this problem (known as "RF hash."). But even then, sometimes there is still nothing that can be done to remove the noise. Like I said, it depends on the circuit. Personally, I just try it out and see what gives. If I can't get rid of it, I go back to the bulbs .
Randy
.Randy
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Led replacements Results for Based LED Miniature Lamps
Transistors Germaniun Transistor Selector Guide
Transistors Germaniun Transistor Selector Guide
Thanks a ton for looking this up, Simon. I'm sure it will help dickl a ton.
Nice to know there is finally a direct bulb replacement for those lamps.
Will save me a bunch of time with my next restoration
.Thanks man,
Randy
Transistors for EV1144
I have a EV1144 ( not EV1144A) and when got it at a flea market I found all little transistors out.
Only power germanium devices where ok.
I changed them with BC 550 ( or if you prefer you can put 2N2222).
Main caps were ok, but I had to change all others caps in the circuit.
At the end the amp worked fine.
If you have the schematic of EV1144 (not EV1144A) please let me know.
regards
tunedguy57
I have a EV1144 ( not EV1144A) and when got it at a flea market I found all little transistors out.
Only power germanium devices where ok.
I changed them with BC 550 ( or if you prefer you can put 2N2222).
Main caps were ok, but I had to change all others caps in the circuit.
At the end the amp worked fine.
If you have the schematic of EV1144 (not EV1144A) please let me know.
regards
tunedguy57
Only thing that I have is the manual on the 1144a http://archives.telex.com/archives/EV/Amplifiers/Service Manual/EV 1144A Service Data.pdf
I did get my ESR meter in a couple of days ago and pretty quickly found a 5MFD 15v cap in the input from preamp to main amp open. I have just ordered some caps and should have them in a few days. The same cap for the other channel checks out OK......so I will start with this cap and see what happens after replacement.
I did get my ESR meter in a couple of days ago and pretty quickly found a 5MFD 15v cap in the input from preamp to main amp open. I have just ordered some caps and should have them in a few days. The same cap for the other channel checks out OK......so I will start with this cap and see what happens after replacement.
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