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Old 23rd April 2012, 03:56 PM   #1
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Default Newbie Looking for Replacement OPTS Motorola Console Amp

Hello to All

I found a Motorola 3 ch ECL82 PP console (perhaps record player) amp and power supply. Fascinating bugger. But at my experience level just about anything is fascinating to me.

Anyway, this little guy has separate preamp-amp-power supply, all joined together with cables. Can't seem to find a chassis no.

Well, it has one larger OT and two of the tinniest OTs I've ever seen on tube gear. I think the larger OT is for bass, other two for high freq.

Anyway,One of the smaller OTs has taps yanked off so it needs to be replaced.

I want to use this setup to run a couple of little JBL Control-1 speakers with my television.

My question is: can I replace the tiny OTs with slightly larger ones. I don't have the experience to be able calculate the needs of this amp so it would be visual assessment as to fit?

I've been unsuccessful in finding documentation or even a model no. for this amp but within my readings I've gleaned that two of the ECL82's are Mono PP for bass and the other two ECL82's are Stereo SE for high freq.

I'd just like to say, I may be self-educated but I know better than to take the voltages in this unit for granted. I cut the old two lead power cord off and it will be a long time before it is ever powered up.

Thanks for all of your consideration,

Doug Y.
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Old 23rd April 2012, 04:32 PM   #2
kevinkr is offline kevinkr  United States
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Hopefully you don't mind if I edit the title of your thread? From the title I had no clue at all as to the question you were asking and I doubt you will get any answers.


I'd also post some pictures of the amplifier in question.

Yes replacing the output transformers with something better (Look at Edcor) is possible and would probably result in better performance. At the same time you should replace all of the electrolytic and coupling capacitors and check resistors for large changes in value.

I suspect this is a bit beyond you at the moment, so I recommend you start by reading the newbie and safety threads here.
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Old 23rd April 2012, 04:37 PM   #3
kevinkr is offline kevinkr  United States
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Edited thread title.
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Old 23rd April 2012, 05:33 PM   #4
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After you read the high voltage safety stuff, read this Vintage Magnavox tube amp about purchasing and replacing the electrolytic capacitors. My posts to that in particular.
As far as selecting an output transformer, first (I think that is what Kevin means by OPTS) you select the lowest frequency you will want to hear. Then you find out what impedance your speaker is (usually 8 or 4 ohms). Then you need to know the input "impedance" of the transformer. I believe you do that by looking at the output tubes ( the tall ones usually, in pairs) to find out what plate resistor they have. If you don't know which of the output tube pins is the plate resistor, look at the datasheets on triodeelectronics.com. The pin numbers are usually on the socket. The resistor color code to read the value is on wikipedia if you don't know.
Although, here in Indiana the opportunity to get another console record player or 15 W PA amp comes pretty often if you visit the charity resale shops. That would be the cheapest way to get the transformer. However, the PA ones won't have much low frequency capability since that was more expensive than a tinny voice only transformer.
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Old 23rd April 2012, 05:36 PM   #5
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Comet,

Definitely heed Kevin's remarks about newcomer and safety threads.

The power transformer from the "beast" should be quite adequate at feeding a 2 channel amp that plays full range. Again, Kevin gave you the "skinny" with regards to O/P "iron", as Edcor definitely offers suitable stuff.

The 6BM8/ECL82 is a nice tube and Russian specimens are available for replacements.

I'm going to contact Jeff Yourison. He has all the notes on a LOW cost SE 6BM8 project based on a Mullard original. 2 WPC is all you get, but they are nice watts. Hopefully, that's enough for the speakers you have in mind.
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Last edited by Eli Duttman; 23rd April 2012 at 05:37 PM. Reason: grammar
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Old 23rd April 2012, 06:58 PM   #6
rmyauck is offline rmyauck  Canada
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On OPT with leads yanked off it may be worth a try to unwrap insulation to find leads and reattach Hopefully most likely will be ripped out of outer coil & you have the other OPT for color of leads and location etc.

Randy
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Old 23rd April 2012, 10:25 PM   #7
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Hey Folks

Thanks for all of your response.

Kevin. . .of course I don't mind editing if it makes things clearer. Thanks. Changing out components and checking resistance I can do. I'm pretty good a soldering. (for a beginner). Right now the OT issue is preeminent.

I'll certainly try and upload some images. The only capture device I have is my webcam. I'll see what develops!

As to safety. . .like I said I have snipped the old two lead power cord so there is no powering the unit. I've had it for at least 10yrs and it hasn't been plugged in. I hope the capacitors are bled but just to be sure I will short the contacts but there is a lot to do before we are near that point. I'm working on a carcass now.

Here's part of the deal Indianajo. . .There is no way that I'm going to grasp the concept and application of theorem. All the theory is gradually sinking in but at this point I have no sense of what 1 ohm of resistance amounts to. That comes with exposure. I have spent a career in the machine shop and it takes a bit of time before concepts can be visualized by this head. I'm inclined to approach this project in a reverse engineering fashion. I'd like to look at similar amps of similar layout and match components by scale, so to speak. These OTs are tiny.
. . .and thanks, I'll make the contact you suggested for the parts that I'll need.

rmyauch. . . there are visible wires where there might have been a connection and I could probably tap into those but I'm tempted to replace the OT with a unit maybe 20% larger than what is there.

. . .and Mr. Duttman, It is a very strange layout considering the symmetry of the tube layout but to consider that two of the PP output tubes serve a larger bass transformer. Then the other two tubes are SE for stereo high frequency. Kind of a bi-amp in one chassis. But I'm not sure that this is the case. That's why I need a schematic.

First thing I need to do is get an image uploaded.

Thanks everyone.
DY
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Old 23rd April 2012, 11:05 PM   #8
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Quote:
Kind of a bi-amp in one chassis.
They used a "subwoofer/satellite" setup. Sum the bass (such as it is) to mono. It was done to save money and increase profit. If the purchaser got any benefit, it was entirely accidental.
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Old 23rd April 2012, 11:18 PM   #9
rmyauck is offline rmyauck  Canada
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If you keep the amp as is the stock small one may work nicely, but firstly as you mentioned you'll have to figure out if the small ones are PP or SE. Just thought it's worth a try just to get you going then maybe upgrade later.

This thread may help:

Motorola 3 channel Tube Amp from Console

Schematics:

http://techpreservation.dyndns.org/

Randy

Last edited by rmyauck; 23rd April 2012 at 11:38 PM.
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Old 23rd April 2012, 11:47 PM   #10
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That Motorola 3 Ch amp is probably real close. Mine is smaller. It must have been out of a record player.
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