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Model 80 Compact alignment - Printable Version

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Model 80 Compact alignment - barshnik - 06-25-2013

Found this locally for a reasonable price. Things seem to have been mostly untouched, both chassis and cabinet. Keith and I are planning to leave the cabinet un-refinished (except for grill cloth, which is not original).

Keith has redone the bakelite cap blocks, all other caps, and most of the resistors.

Having problems aligning - we've seen both 450 and 460 kHz mentioned as the IF freq, but it refuses to want to hear the signal generator at anything other than about 250 kHz. It does get stations on the very high end of the band, nothing below about 1000 kHz.

Any ideas what we can try? Keith, chime in as I may not have properly described the alignment issues you are having.

John F

[Image: http://wl.filegenie.com/~yowboy/80cfrontr.JPG]

RE: Model 80 Compact alignment - keithw - 06-25-2013

Hello all,

Here is the rundown. While waiting for parts I swept the RF, LO and IF tuned circuits. Normally I can thet the allignment about 90% this way. On this radio the IF is published as both 450 and 460 khz. As found the IF on this one could not be tuned there. The caps simply would not go low enough in value. About the middle of the useful range put the IF at about 250 khz. The RF and LO could be adjusted 455 khz apart but it was all the adjustments could do. Assuming the IF of 250 khz I went ahead and alligned the radio and it works fine, quite well actually. The bottom half of the band is pretty quiet. Our most powerful stations are in the top half so I am not sure this is a problem. I am thinking the next step is to use the signal generator and check the sensitivity across the band. One possibility is that the RF and LO are diverging toward the bottom of the band. I'll do some checking.

The big question is the accuracy of the published IF frequency. Has anyone alligned one of these to 455 khz IF or seen a published IF in the 250 khz range? Any enlightenment would be appreciated.

keithw

RE: Model 80 Compact alignment - Radioroslyn - 06-25-2013

Bet your feedback winding on the osc coil is bad. Rewind and call me later.
Terry

RE: Model 80 Compact alignment - keithw - 06-25-2013

Hello Terry,

While waiting I checked the sensitivity with my signal generator. It is consistant across the entire dial. I think the answer is antenna and low power stations low on the band. I think that I will try my tuned loop antenna this evening. It really sucks in the stations.

The antenna and ground wires come out of the chassis and just end. I was thinking about a couple of fanestock clips. Any thoughts?

keithw

RE: Model 80 Compact alignment - Radioroslyn - 06-25-2013

Measure resistance from ant the chassis with volume all the way up . Should read a few ohms if not ant coil pri is open.
Terry

RE: Model 80 Compact alignment - keithw - 06-25-2013

Helly Terry,

The resistance measurement came up good. I hooked my 4' tuned loop antenna to it and received stations all over the dial. This just isn't a very sensitive receiver and needs a good antenna.

I tried to do the allignment by the book with the signal generator set at 460 khz for the IF. It acted like it wanted to work but just didn't behave properly. Set the signal generator at 230 khz (half of 460) and it tuned right up and works nicely. I can see why these have a reputation for being hard to allign if the IF spec is double what it is supposed to be. Being double what the tank is tuned for it will try to work but just not very well.

keithw

RE: Model 80 Compact alignment - BrendaAnnD - 06-26-2013

Make sure that you have the regeneration control properly set. These sets can be quite sensitive if properly set up.

RE: Model 80 Compact alignment - keithw - 06-26-2013

Yep, the regen is the last step of the alignment. A little too much and it sounds like mush and then starts oscillating. I set it as high as I could without it getting ugly. We did find a performance increase mod that we will try once we are sure we have it sorted out in stock form. With a decent antenna I am pretty happy with it. It has plenty of volume but just doesn't want to pull signals out of the grass. The tubes all tested good but one may be a bit weak. If we ever come across another one of these the first place I am looking is the IF. That 460 vs 230 thing is just bugging me.

keithw

RE: Model 80 Compact alignment - BrendaAnnD - 06-26-2013

It's bugging me too. I've got two of these sets, and both lined up well at 460 KHz. You're right, they aren't stellar performers, meant to be a basic urban radio. But mine both do very well with "local" stations up to 50 miles or so with a 30' antenna. Not a lot of "grass" there to deal with, when compared to an AA5. Still not bad sets, really.

You may want to check the integrity of that IF trimmer. It should definately tune 460 KHz. Odd, though that you receive stations across the board with it tuned to 230.. perhaps some doubling going on there, and your IF is being badly overloaded when you put in a signal at 460?

RE: Model 80 Compact alignment - Arran - 06-26-2013

Actually I think that someone may have refinished that cabinet, as far as I know Philco didn't produce any cabinets with a blond finish prior to the war. Even though the cabinet was made out of maple they very likely finished it with a medium walnut laquer. There is an example of one in the gallery but it looks like the front panel may be walnut instead of maple, though a tinted lacquer can fool the eyes, oddly enough it seems to have the same grille cloth as yours so that part may be original:

http://www.philcoradio.com/gallery/1932c.htm#j

I don't know how well these sets were supposed to work, the story I heard is that Philco may have marketed these, the 81, and the model 84 as somewhat of a loss leader. They were cheap sets to start with so I don't think you can expect too much from them, kind of like an early 30s version of a tin box Arvin.
Regards
Arran

RE: Model 80 Compact alignment - keithw - 06-26-2013

Hello BrendaAnnD,

The first step of the allignment is to pull the grid cap lead off one of the tubes and inject the IF frequency from the test generator into the top of the tube. Then the IF cap is adjusted for peak. Would you be interested in trying one of yours at 460 KHZ then again at 230KHZ and see what you get? I did get a peak at 460 but is was very weak compared to what I got at 230. What let to this entire quandry is that I swept the tank circuits before I powered it up. I injected a signal across the LC tank through a 10k resistor. The freq counter was on the signal generator side of the resistor and the o-scope was on the tank side. This is the classic way to measure resonance of a tank circuit. As I swept through resonance the amplitude of the signal on the o-scope would peak. With the 10k resistor the peak is unmistakable. With the trimmer cap all the way open (minimum value/maximum frequency) the resonant frequenct was only about 300 khz. About the mid range of the cap adjustment is 230khz. The cap appears to be fine and failing in a way that increases capacity puzzles me.

So, the components I tested seem fine, the dial is spot on, it works great, and the IF is tuned to 230 KHZ when the documentation says 460 khz. An IF frequency of 230 khz is not out of line for the period. It is possible to allign the radio with the signal generator set at 460 as the tank has a weak peak at the second harmonic. While I am fairly confident in my technical ability and testing methods, I am not past missing the obvious.

keithw

RE: Model 80 Compact alignment - Ron Ramirez - 06-26-2013

Is it possible that someone swapped in a 260 kc IF coil, modifying it as needed (i.e. tickler winding) for use in the 80?

RE: Model 80 Compact alignment - keithw - 06-26-2013

Hello Ron,

Possible of course but the repairs done to this before I got it were fairly ham fisted. (not saying mine are a lot better) The coil looks unmolested. Having a sample size of one makes this a bit more difficult. That is why I was hoping someone with experience on these could shed some light on things. I don't have a lot of experience with these old radios so I am doing a lot of poking and prodding trying to understand what is going on with them. Things are pretty straight forward for the most part but this is puzzling. I have been involved with some reverse engineering of stuff where documentation simply was not available. Approached from that angle I would report the IF on this individual radio as 230 khz. Once again, having only one is a problem. I do aplogize for being so wordy. Sometime I feel like I am writing a bunch but not saying much useful.

keithw

RE: Model 80 Compact alignment - Ron Ramirez - 06-26-2013

I seem to recall that RCA also made a "gutless wonder" 4-toober with a regenerative IF stage? If my memory is correct...does anyone know what the IF frequency was of that model, and could someone have placed such an IF transformer into this Philco?

Since you say "ham fisted" repairs were done to it, everything becomes suspect underneath the chassis. As designed and shipped from the factory, the Model 80 had either a 450 or 460 kc IF (depending on which documentation you are reading).

Oh, I meant to mention earlier...I saw your thread on this radio over at the other forum where people were urging you not to refinish that "nice original finish." If that finish is original, then my 2007 Mustang was made by Chevrolet. Philco never built an 80C Jr. with a blonde finish, as Arran correctly pointed out.

Edit: Could you try using an IF from another 80, or from an 84? There are plenty of those sets around, many in poor to awful condition...excellent for parts. Again, just a thought.

RE: Model 80 Compact alignment - keithw - 06-26-2013

By ham fisted I was more meaning that what they touched was obvious rather than incorrect. There is a big difference between the original soldered connections and later repairs. The connections on the transformers look original. I found a lot of out of spec resistors and caps but no miswires. It apparently can be aligned using a 460 khz signal generator so that is correct in that the procedures work. The problem is my annoying habit of digging a little deeper.

The case was quite likely refinished at some time. However, it doesn't look bad and I don't think we will refinish it at this point. If it had been sprayed pink or had that fake wood grain brush on stuff we obviously would redo it.

keithw