Magnavox model 1ST616 "Concerto" console stereo

[electra225]

This is the second-from-the-bottom in the Magnavox lineup that is in my collection. This stereo sold for around $300 when it was new, plus $30 for the Multiplex adapter, which this one has. The tube codes are the 31st week of 1961. The rectifier was built by RCA, the 6EU7's by Sylvania, the 6V6GT output tubes in Japan, I think by Siemens. The four little speakers are coded 137, Chicago Telephone Supply, week 35 of 1961. The 12" woofers are dated the 35th week of 1961 with a 270 EIA manufacturer's code. I don't have my EIA code documents located yet, so perhaps someone here had that information. This stereo has the 57 series tuner, the 70 series MPX, and the 88 series amp. It is a particularly robust performer for one of the 88 series amps. Nice strong, firm bass. The issue I had always had with this stereo, fairly typical of the 88 series amp, is getting the treble to be bright enough. I may have found part of the problem while I had the back off. Somebody (wonder who?) whomever took this thing down to the last board, did a wire by wire restoration, but did not replace the crossover caps. What would you bet that refreshing those caps would also return the treble response? Ron the Refinisher and I had this thing down to its bare bones, put 18 coats of hand-rubbed poly over shellac. This in 2017. It has worn well. Even though it is a five-knobber, this tuner is one of the better in my collection. It has FM-AFC which is a blessing with Magnavox tube tuners. The AM performance is a tad anemic, which I'll investigate while I had the back off. And some dusting wouldn't hurt, either.

[William]

It's a good looker, Greg. It has the same tuner look as my Symphony and I notice the Buick record. I have that record too.

Bill

[electra225]

Thanks, Bill. If I didn't have a Buick, I would not have that record. It's not really my kind of music. That stereo houses my collection of demonstration records. So I don't lose them.......

There are a couple RCA demonstration records with your name on them. I believe one of them might be appropriate for your Home Theater that belonged to your parents.

[William]

Thanks, Greg, I'm looking forward to those records someday.

Bill

[hermitcrab]

Bill according to the chart I found... 270 is Quam-nichols company... here is a link to the chart
http://www.thevintagesound.com/ffg/eia-codes.html

[William]

Thanks, Elton!

Bill

[electra225]

Yes, thanks, Elton. I printed a copy.

[electra225]

I made some 16uf caps and installed them in this stereo. IT sounds lots better. I also found the balance switch was dirty. That is the second Magnavox stereo I have found a dirty balance control on. This one is ready for a CD changer.

[TC Chris]

I made some 16uf caps and installed them in this stereo.

Made some caps? I paused and thought, maybe you mean you paired some electrolytics in reverse polarity to make a nonpolarized crossover cap? Or you restuffed a can to look good? Or you're turned that handsome shop into a capacitor factory?

Chris Campbell

[electra225]

Yes. I paired two 33uf electrolytic caps with the negatives tied together to create one 16.5uf non-polarized electrolytic crossover capacitor. Sorry for the confusion. I'm old and I was tired and my brain had stopped working an hour before I typed that statement.

[hermitcrab]

Forgive me if I am wrong , but aren't you suppose to tie the + to - and vice versa to create a non-polarized cap? tying the minuses together still makes it polarized ...

[electra225]

My understanding is that if you connect a capacitor with the positive of one connected to the negative of the other, you would double the value of the capacitors and you would still have a polarized capacitor, since one end of the assembly would be positive, one end would be negative, with the caps in series. If you connect the capacitors with like poles connected, such as negatives like I did, the capacitance of the assembly would be half the value of the individual caps. You would also have two positive ends exposed, these being like poles, there would only be one pole, the positive poles. I'm not sure I fully understand why they used non-polarized capacitors in crossover networks, but I'm sure somebody on here can explain that better than I can.

[hermitcrab]

My bad... I did not understand you had to use higher value caps in series to get the required capacitance... you are correct... I myself usually have a few of 8's and 16's non polarized on hand, I usually get a couple when I order from Digikey when I order electrolytics ...never hurts to have a few around. I was surprised to hear the difference after replacing with new caps... those cardboard crossover caps from the factory have dried up years ago ... it should be standard practice to replace crossovers caps on all restore projects

[electra225]

Probably pure laziness on my part. I reckon I figure if it is working, best not mess with it. The part you don't replace in a restoration will be the first one you replace when the project is done.

[Motorola minion]

That is similar to my 1960 with an AMP 175 I have and even with 8 speakers, tone control response could be better. Ill try upping the crossover capacitors!

[electra225]

The 88 series amps I own both have the condition of having really dull high ends. Crossover caps are critical with those amps. They have lots of bass, but the top end could be a tad brighter for my taste. I have to run the treble control full on. Now I can run it a tad under half with lots of bright highs. On the 93 series I run treble a tad over half. Their problem is they produce so much bass it overpowers the treble, so I run it a tad brighter and enjoy the sweet 93.......

In fairness, I run the bass full on with the 93......

[Firedome]

It may be all in my head but I've never heard any 6V6GT amp, and I've had a ton of different ones, that had the clear and clean hi-end response of any of the better 6BQ5 amps, of which I've also had many, thus I lean strongly towards 6BQ5 amp designs for that reason... perhaps it's an unfair prejudice on my part but it's there for sure. Has anyone else had that experience?

[electra225]

I don't know about ALL 6V6 amps, but that has been my experience with Magnavox 6V6 amps. My preference, from a mechanical standpoint is the 6V6 design. Many/most of the 6BQ5 amps drive the output tubes pretty hard. My experience has been that the 6V6 amps are not as finicky about setup as the 6BQ5 amps typically are. I agree that 6BQ5 amps typically have that certain "sweet" sound, missing in other designs, I realize this isn't very scientific.....

[hermitcrab]

There is a debate about this very subject on audiokarma... reading the posts there.... most agree the 6BQ5 has better midrange than the 6V6 and a little more output , but as stated they are being driven to the max ... I only have one unit with the PP 6V6 and it is the 3 channel motorola for the center bass. the stereo channels use the single 6BQ5.. it sounds OK the Bass is there but no way overwhelming ....

[electra225]

Magnavox runs the 6BQ5's at 350 volts on the plate, which is not as hard as some. I have heard of 400 volts on the plates of 6BQ5's. Magnavox drives the 6V6's at 295 volts in most cases on the 88 series amps. Other than the indescribable "sweet" sound of the 93 series, it is six of one and half dozen of the other as far as I'm concerned. And, in fairness, the 88 series amp typically powers cone speakers. With the exception of the Symphony with their six cone midrange and tweeters, the 93 series uses horns for tweeters. I have found more natural "brightness" with horns than with cone speakers in Magnavox applications.