1973 Magnavox. One dead channel.

[budwich]

Re: 1973 Magnavox. One dead channel.

how are you physically determining what pins are what? maybe you are looking at the "bodies" wrong?

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

I made a video: https://www.youtube.com/watch?v=p5KATw6cG-g

If I did something wrong, I am willing to accept my fate To triple check I used the Magnavox's board, since it has C,B,E labeled for each.

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

looks like you're doing it right, the only exception is that we don't see how the probes are plugged into your fluke

If you can return them to your local dealer, demonstrate it to them that something's fishy. If you can't return them I'd assume the markings are wrong and install them as you identified them as NPN or PNP.

It's a good thing you checked first instead of soldering them in and frying stuff!

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

looks like you're doing it right, the only exception is that we don't see how the probes are plugged into your fluke

If you can return them to your local dealer, demonstrate it to them that something's fishy. If you can't return them I'd assume the markings are wrong and install them as you identified them as NPN or PNP.

It's a good thing you checked first instead of soldering them in and frying stuff!

The Fluke has the red lead plugged in at "Volt, Ohms, Diode". Black to "com." You can see it for a split second at the start of the video, but I also tested it with that Proster.

The place I bought them from were very friendly on the phone, but shipping would be as much as the parts.

What do you all think? Roll the dice and run them for what they tested as? I could always order another set.. but then I gotta wait for them..

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Your call. Depending on how much I paid for them and how much it'd cost to refund them, I would use them if I had no fear of completely destroying them. Else the devices aren't what they seem to be, and who knows what's under the lids, some overdriven 2N2222 die... well doubt that, but it makes one wonder...

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

Your call. Depending on how much I paid for them and how much it'd cost to refund them, I would use them if I had no fear of completely destroying them. Else the devices aren't what they seem to be, and who knows what's under the lids, some overdriven 2N2222 die... well doubt that, but it makes one wonder...

I don't mind if the new parts burn up, I just don't want to cook anything else in the amp.

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

There's always a chance to release the magic smoke, but if you got your pnp and npn in the right slots you're more likely than not at least come up with something that sort of works...

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

On Mouser is a MJ2955G and 2N3055G made by onsemi. Yay/Nay?

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Those should be OEM parts, unlike NTE which may have simply bought MJ2955 and 2N3055, rubbed off the markings, painted NTE219 and NTE130 on them, and jacked up the price...

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

Those should be OEM parts, unlike NTE which may have simply bought MJ2955 and 2N3055, rubbed off the markings, painted NTE219 and NTE130 on them, and jacked up the price...

I wasn't sure if the G at the end meant anything, the specs are spot on tho..

I got the NTEs for the same price, that's why I was happy to find them in sets.. but I should have known better...

So, I also need the caps for the speaker crossovers, it has a 8mfd 25v. By the look of it, it seems to be a non-polarized with the leads out either end, but it doesn't seem to be a common value.. parts sites always point me to the really little Radial Polyesters..

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Appears 2N3055's are on the downward trend, was kind of doubting they'd be making these anymore, it's an ancient part... and NOS is eventually the only way like vacuum tubes. Or chinese/russian clones, like vacuum tubes...

The G series is lead free. Probably don't need to worry about it.

Same way with axial capacitors - since they are of large, nonstandard sizes they can't be machine placed and nobody wants to make them anymore. You'll have to deal with the radial or NOS units.

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

.
Same way with axial capacitors - since they are of large, nonstandard sizes they can't be machine placed and nobody wants to make them anymore. You'll have to deal with the radial or NOS units.

I don't mind if its the exact shape or whatever, I just wasn't sure what I can use as a replacement. For example, the current cap for the crossover is a rather large electrolytic, but could I use a gum drop capacitor of the same value, or a film? I also read that since its 10%, I could use something like a 6.x mfd instead of a 8?

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

yes you can generally use a plastic, paper, or ceramic cap in their place. You shouldn't use tolerance as a way to skirt matching capacitances however, these aren't storing charge (well they are...) but rather to build filters and you need to be exact for filters. Paralleling units is the only way to go. A 3.3uF + 4.7uF should work.

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

yes you can generally use a plastic, paper, or ceramic cap in their place. You shouldn't use tolerance as a way to skirt matching capacitances however, these aren't storing charge (well they are...) but rather to build filters and you need to be exact for filters. Paralleling units is the only way to go. A 3.3uF + 4.7uF should work.

I ordered some Nichicon UDBs. Set of 2x 6.8s and 2x 3.3s and 2x 4.7 I'll try both ways a try. "Designed specifically for crossover networks in Hi-Fi sound systems." Good enough for my neighborhood..

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Using the smaller 6.8uF will shift your cutoff frequencies. Again me, as a non audiophile, I probably can't tell the difference. However it clearly will change how things sound.

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

Using the smaller 6.8uF will shift your cutoff frequencies. Again me, as a non audiophile, I probably can't tell the difference. However it clearly will change how things sound.

I figured that will allow me to adjust it to stock, then see what it sounds like going up or down a bit.

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Curious what was the WPC rating for this amplifier?

Was comparing to this other integrated radio/amplifier I repaired, it uses TO-220 transistors. Supposedly only 15 or 20WPC or so. One of the transistors was fried to a crisp "again" (I saw that it had been reworked before, poorly.

The funny thing is that I swapped the fried transistor with a transistor I chose randomly from my junk box. Well, it wasn't totally random - I knew it was the correct NPN polarity but I couldn't find any details about the particular transistor so I just took a shot in the dark and luckily it worked. After adjusting the bias on the transistor I really couldn't tell if it was sounding weird or not. Seems to work just fine now.

Not sure how it fried but judging by the heat damage some of the plastic took, the old transistor got mighty toasty.

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

I have been told this is a 50 watt model. So I would think that means 25/25?

[eccerr0r]

Re: 1973 Magnavox. One dead channel.

Don't know, possible. Should be more than what my TO-220s can handle, TO-220s usually limit at around 80W or so before they hit thermal resistance limits of the package. TO-3's can dump more heat, from the 115W 2N3055 and 150W for 2N3771... Note these heat dissipation numbers have nothing to do with WPC but some data could be inferred.

[JunkForLess]

Re: 1973 Magnavox. One dead channel.

The new transistors test correctly.