I have replaced all caps and out tolerance resistors. I checked all coils and the field coil and output transformer. All checked good. At power up I get a 60 hz hum and no audio. I checked B+ and the output of the 5y4 is only 270v. I checked the plate of the det/ocs and it is also low (180v vs 240v) and the plate of the 2nd det is 0v vice 40v. I started looking at the dc power. I checked the 5y4 in my eico 666 and it is marginal. I don't have a replacement so I made and socket adapter to use a good 5y3. Results only slightly improved. I did some resistance checking and I am confused by the resistance measurement from + of the 8 mfd electrolytic to the - of the same cap. I get ~16K ohms. I have been trying to find the parallel path that would give this result. I removed the tubes during this measurement and that has no effect. I replaced the already replaced 8mfd lytic with no effect. I thought it was the 16k resistor (12), and If I lift one side the resistance goes up to 240k but why? I need a circuit lesson on this. I just don't see how I am getting such a low resistance. I am going to study the schematic some more, but please set me straight.
Andy
Schematic here
Ok just fer grins let's start from the 6F6 and work towards the mixer. What voltage do you have @ pin 3 to ground and pin 4 to ground? Do you have some negative voltage on pin 5 ? If you remove the 6F6 does the plate voltage go up to a more normal level? Check #20 for a short to the chassis. That could explain the 240K read @ the 16K resistor.
The hum is normal and isn't from the power supply. It's from the regenerative detector.
Hats off to you if you can read that na mess, this is much better:
https://philcoradio.com/library/download...l.%202.pdf
Thanks Terry. Next time I'll make it difficult! I checked the voltages. pin3 -185v, pin 4 -2v, pin5 - 0V. removal of the 6f6 caused the plate voltage to go to 350v. All that being said there was a short to ground at the #20. I have worked on a couple other philcos with bakelite blocks and drillled out the center of the tabs and soldered replacements on the outside until I got the radio running. After that I removed the blocks and restuffed. This worked great on the others. I had previously drilled out the ground tab on this block but the short remained and after I discovered the short tonight, I could not drill it (or the #20 tab) out enough to get rid of the short. I removed it restuffed it and short is gone and plate voltage is now 235V. The hum is mostly gone and I put a 1000khz modulated signal on the antenna and it could be heard out the speaker. Its very low but did respond to the volume pot. Thanks for the schematic link. That is sooooo much better.
Andy
It's important to do a good job on the IF alignment, being sure that it's at 470kc. It can make a big difference in the overall sensitivity. Good set of hot tubes doesn't hurt either. I've been listening to a 2nd gen 84 over the last few weeks and considering it's a pretty impressive. It's fairly sensitive but the selectivity is not so great.
Glad to help out.
Obtw I'll mention in passing it's very easy to wire #20 backwards so the that the .015 is connected to the plate of the detector and ground, and the .001 ends up being the couple cap. What this amounts to is that the audio sounds weak and muffled. Have done it before...
I was going to check over my documents here cause I thought I saw both 460 and 470 for the IF. OK Ill check the caps tomorrow. Thanks for the help.
Andy
84 code 121 460kc 37-84 code 122 470kc
I accidentally got the #20 caps wired correctly. I'll get harder next time.
I started the alignment and the IF alignment was going well (although I used a dmm connected to the voice coil vice a VTVM across the plate and cathode of the 6f6. I did have a vtvm connected to the plate/cathode but its was 240v vice less than 30v as the instructions indicated. The DMM level varied with the adjustments to IF PRi/SEC 11 and 15. The VTVM never changed. I followed the instructions for the IF alignment and the adjustments went well until the last adjustment which was to turn the sensitivity cap until a hiss is heard. I don't get the hiss. The instructions are clear and easy to follow but I get no hiss.
I decided to move to the RF section and the instructions are confusing me. I tried and failed to translate the instructions to actions that resulted in the expected results.I watched a video of a 84 alignment and it follows different instructions, I think. I need to rewatch it.
Andy
Andy,
Judging from what is expected, 30 volts, I think the voltage readings should be in AC volts at the 6F6. Yes, there are usually quite a few methods of aligning the IF.