The PHILCO Phorum

I have a Philco 16B 5 band code 121 which I have totally recapped including the mica caps.  I pulled out the bandswitch and cleaned it in my ultra sonic cleaner and it came out squeaky clean.  I reinstalled the bandswitch.  I have also pulled out both antenna coils and both oscillator coils and measured them to the best of my ability and they appear to not be open.

I am able to feed a 460 khz signal to the grid of the 1st detector and peak all 3 IF transformers.  The dial is tracking pretty well right now after adjusting the 2 padders on the bottom of the chassis.  I get some broadcast stations with the antenna on the antenna jack but they come in more clearly when I put my finger on the grid of the 1st detector.  The issue is the volume is very low.  I also am not able to receive any shortwave stations.   Any suggestions would really be appreciated as I have spent many hours on this radio and your help would greatly be appreciated.

-Carlos

Back to troubleshooting 101.
 
We need to figure out where the lost of gain is. Does the IF play good and loud when injecting a 460kc modulated @ the grid cap of the 77 mixer tube? With the generator output turned down very low?

What sort of reaction do you get from the shadow meter when a strong signal is applied to the ant. If the coil is open it's not a big deal to rewind.

Check plate, screen grid, and cathodes voltages for too low or high readings.

What did you do to the DO NOT ADJ trimmers on the tuning capacitor?

Not that it matters much is it a cathedral or tombstone?

The 460 khz signal goes through loud and clear. The shadow meter was open so I replaced it with a 1.2K resistor. As far as the DO NOT ADJUST trimmers. I counted how many turns until they were fully tight and after cleaning the whole tuner assembly I returned the trimmers to their original setting. This is a tombstone. One thing I have noticed is that when I remove the grid cap from the QAVC tube #78 nothing happens its like the tube is doing nothing at all. I will start measuring the plate, screen grid and cathode voltages. Appreciate your help !!

-Carlos

I was not able to measure all the voltages because it is very hard to get at the pins but below is the list I was able to get at. What I see is that the Cathode of of the 1st IF is very high at 37 Volts. I hope this helps.

2nd IF - #78
Plate 220 Volts
SG 110 Volts
K 3 Volts

1st IF - #78
Plate 218 Volts
SG 110 Volts
K 37 Volts

Osc - #76
Plate 71 Volts
K 2.6 Volts

1st Det - #77
Plate 217 Volts
SG 110 Volts
K 6 Volts

2nd AF Driver #42
Plate 207 Volts
SG 207 Volts
K 0 Volts

-Carlos

Update :-)

There was a wire missing between the Cathode and the flexible 300 ohm resistor of the 1st IF tube. The radio is blasting now. I am picking up the broadcast stations pretty well and I also got a couple shortwave stations between 5 Mhz and 8 Mhz to come in but I am sure I still need to align the radio. The flexible resistor measures 325 ohms and the schematic says it should be 300 ohms. Should I replace the flexible resistor? I really appreciate your help with this !!!

Keep it. Easily within 10% tolerance. As yet, I have not had one of those fail - not to say that it couldn't.

For a 300 ohm resistor, 325 ohms is within 10%. Most resistors in these radios, unless otherwise marked, and noted in the parts list are 20% tolerance. I wouldn't sweat it, especially if your radio is working OK now.

See that was easy!!! Just needs to be a 300 or so ohm resistor. Flexible or not.

Out of curiosity if the trimmers that are not supposed to be adjusted are not in the correct setting is there a way to adjust them properly? I still have to get the shortwave bands to work properly hopefully the alignment will help.

-Carlos

One the do not adjust trimmers are set up to set the ant sections for bands 1 and 2. The other one is for bands 3,4,and 5. Using one trimmer to set two bands 540kc to 4.0mc and the other to 3.5mc to 22mc is a little daunting.

As far as I know there isn't any alignment procedure for these. I do know that it's not a great idea to pick a frequency that you favor and peak it there. It screws up the image rejection some terrible.

I have thought about add 3 more trimmers to make each tuned circuit peak on each band. Now days trimmers are much smaller and would be easy to add.

If any of you have any insight into how adjust these two trimmers over such a broad range frequencies I would be interested to hear.

How long should the antenna be for best shortwave reception? Is there some type of special antenna or should it just be a long wire? Is Litz wire better to use?

-Carlos

It's somewhat frequency dependent. I like dipole antennas they are much quieter than single wire antennas. The lower the frequency the longer the ant. Think of it in wavelength. You don't have to have a full wavelength for it to work well a 1/2 wave works well too and is 1/2 as long. For instance the 41m band (abt 6.8mc) works out to abt 140' for a full wavelength but you can use two 35' lengths of wire. The insulators can be a few short pieces of small pvc pipe w/holes drilled near the ends. The wire in the center can be coax but that's not a real good impedance match for your old set. Most are around the several hundred ohms. Coax is 50 or 72 ohms generally.

The wire for the ant it self I like copper plated steel. It's strong and conducts like copper. Ant length becomes critical when you use it to transmit on. If the ant stretches then it's resonant frequency changes too (lowers). Transmitter doesn't like that much at all. So strong is good. Copper is soft. Litz wire is for winding high Q coils.

https://www.researchgate.net/figure/The-..._320751102

For these old sets, if you want a higher imprdence line from a dipole or J pole to your set, use 300 ohm twinlead. You can also use 450 ohm ladderline.

Don't know if you have space limitations but an inverted v ant is a compact ant. I used one for a transmitting and receiving ant and it worked well. Was abt 38' tall and 50' wide. It's pattern is like a vertical so it doesn't have the directivity of a dipole. Simple to construct with some wire and hand tools. I got up to 38' by using some light steel tv ant mast strapped to my chimney. 1/4 or 3/8'' rope was used to hold the apex up to the mast and to tie off the ends to steaks driven into the ground.

I'd show you some pic of it but a tree fell on it and it is no longer. Just the mast remains.

basic-inverted-v-antenna.jpg (940×637) (dxzone.com)

Today I am trying to get the shadow meter functioning. The shadow meter that came with the radio has an open coil so I tried hooking up a shadow meter from a Philco 17 and the shadow shown is always wide it never narrows as I tune through the stations. Does this mean I should add a shunt resistor across the coil or does it have something to do with the alignment. What value shunt resistor should I use if that is what you suggest I should do?

-Carlos