Hi guys,
I've been watching all the hubbub about tubes so I found a couple of pieces to learn about and enjoy. If this is the wrong forum and should be in Tube Audio, just let me know please. I have a Magnavox console model 1ST268 that is in great shape, plays (although after warming up volume goes hi&lo). The amp has numbers 406426 ink stamped, and 636750 8 stamped into the chassis. It uses a 6EU7, 2 6BQ5's, and a 6CA4. Where can I find service manuals or schematics to help me figure out just how this works?
The other piece I have is a Motorola phono model number SK14M. I'd give a tube rundown but the back is still on it. Thanks a million folks, now if I can only understand why these electrons go here, I'll consider myself a genius:D Bob

The Motorola (listed as Quasar) is in Sams Photofact folder #453-9. I don't have that one, sorry. The Maggie I couldn't find at all... I did find model CT268, and I'll see if I have that one... and if it's close.

Check out the thread over in tube audio bout the Magnavox EL84 SE amps. It's mostly about restored ones, but they're the same type as yours. They say it's in Photofact 535-9 if that helps you, Tom.

Replacing the electrolytics and paper caps you should have a good set. A place to start would be a good cleaning of the chassis. Also use electronic cleaner on the tube pins and while wet work them in and out of the sockets several times. Use cleaner on all the controls and work them back and forth: that will probably stop the intermittent volume. It's often caused by iffy tube pin contact or oxidized controls.

Reece

Many thanks guys, I really appreciate the info. I intend on replacing the electrolytics in the Maggie to start with. I put an Ohmmeter across the smallest value in the multisection can and found the lowest value 30Mfd~25VDC is a dead short. Don't know if that would cause my issue or not but I bet it doesn't help it. This amp has Sprague caps in a few spots and I wonder what they are (elec, nonpolarized,...) They look like large horsepills, dark brown with an orange ring about one end. I figure they must have been replacements at one time or another.
Is there a better specific cap to replace the smaller value in the multisection? If the rest of the caps ohm out OK, should I replace them also with electrolytics of matching value and just cut the leads to them? Sorry for so many questions but I can research over and over and I'm still not sure, and I don't want to let the magic smoke out either LOL. Bob

The 30 MFD at 25 v cap section is the in the cathode circuit of the output tubes...it should be paralleled by a 100-200 ohm or so resistor. If this cap is shorted you will have no bias voltage on output tubes, causing them to overheat.

If this cap looks bad, you need to replace the entire can...you can install a terminal strip and use modern electrolytic capacitors, making sure polarity is correct. If one cap in this can is bad, the others likely are too or will shortly go bad.

The other caps in the set are paper caps, non-polarized. I always like to replace all of these, you can replace them with Mylar or Orange Drop caps of equivalent value and equal or higher voltage rating. These old paper caps can have excessive leakage (DC resistance), intermittent opens, or shorts.

Yes, replace all the electrolytics. They are cheap, and good insurance. If the can is topside chassis mount, leave it there for looks and disconnect all the leads underneath. You may need a terminal strip under the chassis to connect the new individual caps.

Stay close to the original value of the electrolytic in the output stage; ditto the one closest to the rectifier. You can go with a higher capacity than original for the final filter for less hum. Use voltage ratings same as original or next rating larger.

Reece

Thanks again guys for all of the tips. I will search for all of these capacitors, get them ordered, and then be back with more questions. Bob

BTW, the Motorola has been playing on and off for a few days. It is different than SS but I can't put my hand on it yet. It's probably the 501s that it's hooked to, huh???

Does anyone know what the value of a Motorola SK14M could be. The radio and turntable don't work because of a blown tube. The lights all come on, and the speakers work fine. Is there a market for these things, or I am just holding on to a big piece of junk?

Which tube is out? tube #? tubes are mostly still available, on the internet. if its not an expensive one, might be worth a try, just to see what it does.