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Model 80 Chassis/Tuner Isolation - Printable Version

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Model 80 Chassis/Tuner Isolation - Lewiss - 09-25-2018

Hi All, 
On the model 80 Jr, is the tuner assy supposed to be isolated from the chassis?
I'm reading 0 ohms between the two.
Also should the volume pot be isolated from the chassis?

Thanks for your help.

Lewis

RE: Model 80 Chassis/Tuner Isolation - morzh - 09-26-2018

Well, one side of the tuning cap is grounded. Another (the first stage, the antenna part) goes to the secondary antenna transformer's coil measuring 65 ohm, so the resistance across the tuning cap 1st section should be 65 ohm, one side (forgot which) grounded.

RE: Model 80 Chassis/Tuner Isolation - Lewiss - 09-26-2018

Thank you Morzh,

The model 80 I am working on had been kinda sorta "restored" years ago by someone.
I had read somewhere that the tunner assy was mounted on rubber bushings, so that's why I am asking if it is supposed to be shorted to the chassis or isolated?


The volume control has been replaced, I see a cardboard sheet sandwiched between it and the chassis, the front side has a washer and nut securing the pot to the chassis.
I had read somewhere about a  "fiber" washer on the potentiometer, so I  was wondering if it too should be isolated from the chassis?

Thanks for your help.

After doing the alignment, and per John Riders instructions on aligning Philco radios, I am only receiving on station, with a fair bit of noise. 
So was wondering if these may be affecting reception. 

I live south of Reno near Carson City, there are 10 AM stations in the area, but I can only pull in the one in Carson City which is nearby.

Thanks for your help.
Lewis

RE: Model 80 Chassis/Tuner Isolation - morzh - 09-26-2018

80 is a regen-superhet, and as any regen, especially a cheap one, is finicky.
Once aligned, try to play with that trimmer that sets the feedback. Just shy of chirping.

RE: Model 80 Chassis/Tuner Isolation - Radioroslyn - 09-26-2018

Hi Lewis,
>The model 80 I am working on had been kinda sorta "restored" years ago by someone.
I had read somewhere that the tuner assy was mounted on rubber bushings, so that's why I am asking if it is supposed to be shorted to the chassis or isolated?

The tuning capacitor is bolted directly to the chassis best I remember on this set. As Mike said the tuning capacitor is connected directly to the chassis.

>The volume control has been replaced, I see a cardboard sheet sandwiched between it and the chassis, the front side has a washer and nut securing the pot to the chassis. I had read somewhere about a  "fiber" washer on the potentiometer, so I  was wondering if it too should be isolated from the chassis?

One end of the pot is connected to the chassis. That's how the volume (rf from the ant is regulated by it) works.

>After doing the alignment, and per John Riders instructions on aligning Philco radios, I am only receiving on station, with a fair bit of noise. 
So was wondering if these may be affecting reception.

Am I reading that your complaint is poor sensitivity?? If so  then a few test are in order. Unplug for the socket, turn volume full up and measure the resistance from the ANT post to the GND post. Should see a low resistance like <20 ohms. Next test is measure the resistance from pin 4  to the pin on the osc coil w/the cap and resistor connected to it. Again should show a low resistance.

GL

RE: Model 80 Chassis/Tuner Isolation - Lewiss - 10-06-2018

Antenna Coil looks good, I will start a new post on this with under a new subject line of something like what did I get myself into.

Thanks Terry !!

RE: Model 80 Chassis/Tuner Isolation - Radioroslyn - 10-06-2018

I would suspect that the oscillator isn't running. Easy way to confirm whether it is is to use another radio (sm transistor set is handy). Set the Philco dial @ 100 (1000kc) and set the transistor set @ 1460kc. Position it near the #36 tube nearest to the ant post. Turn both on and listen to the transistor set for a loud hiss while tuning it around a bit. In a perfect world the signal should be @ 1460kc but it may be off a bit. The osc  frequency = frequency of the dial + the IF frequency (1000kc+460kc= 1460kc)

If you adjust the sensitivity capacitor on the back of the chassis can you get it to squeal from the speaker?

RE: Model 80 Chassis/Tuner Isolation - klondike98 - 10-06-2018

(10-06-2018, 03:05 PM)Lewiss Wrote:  .... I will start a new post on this with under a new subject line of something like what did I get myself into.

No...keep all of your Model 80 electronics questions and progress in this one thread. You can modify the original title if you like ...

RE: Model 80, 1st restore in over 40 years - Lewiss - 10-06-2018

Hi Terry,

Thanks for your help.
I haven't played with tube audio since I was in my 20's grew up on Heathkits, ELCO, Dynakits etc.
Have worked for over 40 years in Electronics, I thought this would be a fun hobby Icon_smile

This radio was "restored" back in 1990, noticed one of the tubes was a 44, not a 36
Here are before and after photos. I opened up the Bakelite caps and replaced the old caps.
       

My test equipment I have consists of:
Fluke 82 RMS Mulitmeter
60Mhz Tek analog scope
B&K 2050 RF signal generator
Tek Frequency counter
Heathkit AV-3 Audio analog VTVM (not very accurate, but great for tuning)
Knight 600 tube tester

I have performed the tuning procedure about 10 times, swept the IF, it seems to like 450KC better than 460KC.

Hooked the RF generator to the grid on top of Det/ Osc tube, removed clip first. also attached a 560 ohm to gnd per John Rider for bias.

Tuned using John Riders paper on Aligning Philco Radios and Philco Service Bulletin 120E.
The radio seems to like 450KC vs 460KC.
The radio seems to match the latest schematic shown with the values.

I have turned the sensitivity control till it squeals and backed it off 1/4 turn. 

The radio seems to only pull in one station at 1300KC, and very weak station at 780KC
I have a little Grundig M400 AM/FM SW mini radio, it seems to pull in these stations ok.
The Philco is very noisy and a bit distorted/ garbled. I hear some of the same noise on the Gundig.

I live south of Reno, south of Carson City in Carson Valley.
Since the Gundig only seems to pull in 2 stations, perhaps this is the best I can hope for from the Philco since I live in a valley?
I have a 25 ft wire antenna running outside.
I do notice that the kitchen LED lights seem to cause a lot of noise in the Philco.

The radio is nice and quiet with the volume turned down, can't even tell it's on.

Thanks for your help
Lewis

RE: Model 80 Chassis/Tuner Isolation - Radioroslyn - 10-06-2018

> I thought this would be a fun hobby [Image: http://philcoradio.com/phorum/images/smilies/icon_smile.gif]
I thought the same abt 50yrs ago [Image: http://philcoradio.com/phorum/images/smilies/icon_evil.gif]  [Image: http://philcoradio.com/phorum/images/smilies/icon_lol.gif]

> one of the tubes was a 44, not a 36
Would replace the 39/44 w/ a 36. Both tubes do share the same base connection be the grid bias voltage is abt twice as much for the 39/44.

> it seems to like 450KC better than 460KC.
I see conflicting information on the IF frequency the US Philco seen to be 450kc and Canadian diagram states the IF as 460kc.

http://www.philcorepairbench.com/model-80-performance-modifications/

RE: Model 80 Chassis/Tuner Isolation - Radioroslyn - 10-07-2018

Something else comes to mine, check #25 for the proper connections of it caps. If wired backwards it will give you low and muffled audio.

RE: Model 80 Chassis/Tuner Isolation - Lewiss - 10-07-2018

Hi Terry,

There's plenty of volume !!
I have installed new caps in the Bakelite case, a .015uF for #25 & and a .001uF for cap # 21.
Seem's I have just very weak reception.
When I hook up the RF signal generator to the antenna, set to a low level signal I have no issue receiving the signal at various frequencies.
For example, set the generator to 1300KC, change the tuner to 1300KC, or set the generator to 600KC, change the tuner to 600KC, no problem hearing the 400Hz tone. Looking on the scope at the speaker, it's a nice sine wave. And it's loud.
I changed R15 from 4M to 2M, it didn't help to bring in any stations, but it did make the radio even louder!

When I first started working on the radio I found the 6.45 ohm coil that is in series with C5 & R8 that connects to the cathode of the Det/ Osc open. I had found the wire from that coil was broken, so I found where it was open where it exited the coil and soldered it to the lug on the coil where the wire to cathode connects.
I replaced the incorrect 44 tube that was in the radio when I got it with a 36.

The only station that comes in is a country station from Carson City, but it has a lot of noise and is kinda garbled.
I just bought the AM transmitter kit from tubesandmore, when it comes, it will be interesting to see how well the radio picks up the signal from it.

This new hobby is getting expensive.
Just spent $80.00 on lacquer toner, sanding sealer, and semigloss clear for this cabinet. And some how I have ended up with 7 radios that all need to be refurbished. Including a Philco 14L.

Thanks for your help
Lewis