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An Idea Realized - The Philco Super 89 - Printable Version

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An Idea Realized - The Philco Super 89 - Ron Ramirez - 08-17-2008

For a long time now, many radio collectors have cursed the Model 89 and its autodyne oscillator circuit that, sometimes, only works when it wants to (or so it seems).

If you do not mind sacrificing authenticity, I have developed a modification that will permanently cure this trouble with your 89.

Just like the Super 71 I previously discussed here, it involves replacing the Type 36 tube and five-pin socket with a seven-pin socket and 6A7 tube.

The oscillator coil must also be rewound. Details are given in this thread about the Super 71.

A note of warning: Instead of winding 128 turns for the secondary, I strongly suggest you wind 150 turns instead. On my 89 project, it refused to align correctly until I added the extra turns. Once I did, however, it aligned right up to near perfection.

So, it works well on AM; how about the "police" band?

The 6A7 mod gives a vast improvement over the original Type 36 autodyne circuit on the "police" band. Have you ever noticed that on a conventional 89, that the sensitivity audibly drops when the "police" band is selected? Well, the 6A7 mod does not suffer this issue; it is just as sensitive on the "police" band as on AM.

Photos to follow later.

Let me know what you think. In my opinion, this is the production change Philco should have made in mid-1933 when the 6A7 tube became available, but didn't.

- Steve Davis - 08-17-2008

Ron, when I did the restoration on my model 19, I did have to rewind the feed back winding of the oscillator coil as is usually the case. I also baked it in the oven and sprayed it with lacquer and I have never had any trouble with the oscillator. But I am going to do the modification to improve the reliability (and hopefully the performance) of the radio. As far as authenticity, it doesn't matter because my radio isn't a perfect example anyway. Also Ron I would like to say thank you for putting this type of information out for the rest of us.
Steve

- Ron Ramirez - 08-20-2008

Here is a partial schematic showing the changes to the Philco 89 oscillator circuit.

[Image: http://www.philcoradio.com/images/phorum/osc_009.jpg]

- Ron Ramirez - 08-20-2008

Forgot to mention - Steve, you bring up a very good point. If you prefer to keep your 89 or 19 original, baking your set's oscillator coil in an oven at 175 to 200 degrees, for 30 minutes, is a must to drive out any residual moisture. Sealing the coil with lacquer after rewinding the tickler winding is also a must. And keep in mind you may have to drop that oscillator cathode resistor to 8.2K from the original 15K.

You should also bake the form before rewinding if you do perform this mod to your 89 or 19; and seal the coil with lacquer after rewinding.

- BDM - 08-21-2008

Now this is interesting. The Bionic Philco 89, or the $6(000,000) Philco radio Icon_mrgreen Good job Ron!

- Ron Ramirez - 08-21-2008

Heh, that's one way of looking at it. Thanks Brian! Icon_smile

Let's see...

I think the original basket case 89 cost me $15. Add in the cost of resistors and capacitors...speaker and tubes came from my private stash...and you have a total cost of maybe $30. Cost of labor involved in stripping, painting, reassembling...PRICELESS. Icon_lol

I really wonder why Philco did not make this change in 1933. Old man Skinner probably would not allow it - IF it were even suggested...even though those autodyne oscillator circuits in the 89 and 19 sets were giving problems even when the sets were new.

Just think...THIS could have been the 89 Code 123, instead of their changing the 89 mixer-oscillator to a Type 77 tube late in 1934 and retaining that autodyne circuit. Had they adopted the 6A7 instead, I believe we would not be hearing too many complaints about 89 and 19 sets these days.

Re: An Idea Realized - The Philco Super 89 - Ron Ramirez - 09-10-2008

A photo of my completed Super 89 chassis.
[Image: http://www.philcoradio.com/images/phorum/super89_023.jpg]

Re: An Idea Realized - The Philco Super 89 - Steve Davis - 09-10-2008

Ron, that's beautiful!

Re: An Idea Realized - The Philco Super 89 - Ron Ramirez - 09-10-2008

Thanks very much, Steve.

A lot of work went into that chassis...and the cabinet is not finished yet.

Re: An Idea Realized - The Philco Super 89 - Ron Ramirez - 09-12-2008

Philco 89 chassis before restoration:

[Image: http://www.philcoradio.com/images/phorum/super89_016.jpg]

Philco Super 89 chassis after restoration/modification:

[Image: http://www.philcoradio.com/images/phorum/super89_024.jpg]

Re: An Idea Realized - The Philco Super 89 - BDM - 09-12-2008

Hats off to ya Ron. That set would have made my rough parts shelf Icon_mrgreen

Re: An Idea Realized - The Philco Super 89 - Ron Ramirez - 09-12-2008

Thanks, Brian. Icon_smile

This is precisely why I chose this chassis as the "guinea pig" to perform the 6A7 mod - because it was in such rough shape.

Obviously, the power transformer is a replacement. The original was toasted.

The coils had their usual problems. And the oscillator coil was completely rewound anyway, to correspond to the Model 18 style oscillator circuit. I was really lucky in that both IF transformers were OK. The off-on-band switch responded well to a thorough cleaning.

And it was on this set that I finally managed to nail down the trick of rebuilding the electrolytic condensers so that they appear to be original, when looking at them from underneath.

Needless to say, I am quite proud of this chassis. I'll be even prouder, once I complete restoration of its cabinet, originally a Model 32B tombstone cabinet.

Re: An Idea Realized - The Philco Super 89 - BDM - 09-12-2008

That's actually a good point for anyone. If you want to cut your teeth on experimenting or modifications, or a new way to perform a restore. Use a parts chassis.

Re: An Idea Realized - The Philco Super 89 - DeckApe - 09-12-2008

Ron, THANK YOU for posting those pictures! Not only are they a wonderful study in "for the love of the game," but you've given me a great deal of hope for my rather rusty 40-190 chassis. I will get that radio talking to me!

Re: An Idea Realized - The Philco Super 89 - Ron Ramirez - 09-14-2008

Here is the 32B tombstone cabinet - the future home of the Super 89 chassis - in progress.

[Image: http://www.philcoradio.com/images/phorum/super89_010.jpg]

I've added a piece of quarter-round where one was missing above the front panel, and have also done a lot of gluing. Believe me, it looks a lot better in this photo than it really is. Still need to stabilize one of the grille cutouts, the one at center right where there is an obvious break. Also need to fill some cracks and defects, then sand down and refinish. I am going to try and save the finish on the front panel if I can.