its been a while, but im nearly done replacing the caps and resistors in my philco 118. ive been saving this one section for last, because it wasnt making any sense to me, and also because it had obviously been fiddled with at some point in its life.
the caps we are looking at are the big electrolytic caps, #73 and 74 on the schematic....73 is the 8mfd and 74 is a 8 and 10 mfd multisection. in my actual chassis, it looks like something happened to the 8mfd section of #74, so they put in a 20mfd replacement cap.
the part thats got me confused right now is it looks to me like theyve got ground running to the positive pole of the 10mfd cap in #74. correct me if im wrong, but the case of the can caps are ground, right? because theres definitely a ground lead from a nearby bakelite block (#34 if i remember correctly) going to the center pole of the 10mfd section of the can cap, not to its case. so is the 10mfd in the circuit backward? that is to say, positive to ground, and negative goes out to the rest of everything?
this is probably basic stuff for you guys, but im still learning the basics, so please bear with me. ive seen this before, where your electrolytic goes in backward with respect to ground because youre dealing with negative voltages, but its not clear to me if that is the case here.
ive included a picture of the schematic in the area im talking about, as well as a photo of my actual chassis. in that photo i have already clipped out the big replacement 20mfd they had stuffed in there, but you can clearly see the ground lead from the bakelite block on the left running to the silver lead in the cap on the right, which is 74.
any help you guys can give would mean the world, i really appreciate everyones help as i fumble through the learning curve.
The explanation is this: the other end of the cap goes to the negative of the rectifier circuit and this IS THE MOST NEGATIVE point in the whole of the schematic; everything else IS POSITIVE relative to it, hence the polarity of the cap.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
i mean, not real well yet, but i definitely picked up a couple station in both the AM and shortwave bands, so id consider that a smashing success so far!
so, now an onslaught of newb questions:
antenna....is there a preferred length, gauge, or type of wire? (stranded vs solid)
also, i have no idea what aligning a radio means....dont worry, ill do some research into it, so you dont have to necessarily walk me through step by step, but im sure ill have questions when it comes to trying it. but if anyone had a preferred page that describes what i'd be doing and why, id love to check it out.
im not sure if its totally functional, but a few months back i picked up this thing called a radio analyst, made by BK precision....if i had to guess, i can use that thing to do all sorts of fancy stuff. still have to read the manual on that though, and like i said, i dont even know if its fully functional or not.
the last bits are mostly cosmetic....i would like to replace the grill cloth because its a little kicked in, and there a significant hole knocked into the speaker cone, although it actually sounded pretty good last night, all in all. so until i get the radio tuned in properly, i guess im not too worried about reconing it. do you think i could get away with just sort of gluing a piece of thick paperboard to the cone and repairing it that way? i cant imagine it affecting the sound all that much.
does anyone have good recommendations for where to get grill cloth? i recently acquired a 1938 united american bosch radio that will also need some grill cloth after i rebuild its chassis and get it working again, as well as an old gretsch "twin reverb" guitar amp that im soon to be working on. i figure i might as well get it all at the same time...
as usual, all your help is invaluable, and i cant thank you guys enough for walking me through my first radio repair!
i was looking at the radio analyst manual; this thing will put out a signal at 260 KC, which if i understand it correctly, i should put into the clip off the 6A7, tune the radio to 550 and adjust a few condensors until you get "maximum output" on an output meter.
so......stupid question...what exactly do they mean by output meter? can you just use the speaker and adjust for maximum volume?
next newb question: wave traps. i read on here someplace that theyre basically obsolete at this point, and you can just leave them alone. or is it worth my time to attempt to adjust them per the manual?
I must again apologize if I'm barely making any sense, i basically learned everything i know about a half an hour ago.
> radio analyst, made by BK precision
960 or 970??
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
i hooked it up to my oscilloscope and managed to see a nice fat wave, which as i turned up the audio knob would start to distort the wave.....i admit i know next to nothing, but that seems like a good thing. like the wave was at that point carrying a signal.
strangely, when i would fiddle with the different band knobs, the sine wave didnt change at all. i sort of expected a change in frequency or something, but it pretty much stayed the same until i got to some of the higher frequencies. im not sure if this is normal, or if its my nearly complete lack of understanding of the subject, or if the analysdt is not working properly.
1. The meter is an AC Voltmeter, in today's case a DMM set at V~, that you simply put across the primary of the output xfmr, or in some cases across the voice coil of the speaker (or the secondary of the output xfmr which is the same).
You peak your signals by looking at the Voltage reading.
And, yes, it is possible to tune by ear but it is that much less accurate.
2. Yes, wave traps are obsolete.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
