Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

RCA-76 cap question
#16

You can go higher with the resistor. I would try a 10K first and if the hum is still excessive go to 22K.

Check the voltage on the cathode of the AVC tube and see if it varies as you turn the volume control. The volume control pot is fed bias voltage from the power supply through another similar choke L 17 with a resistance of 2300 ohms, so perhaps it is open too?
#17

L17 checks good at 2190 ohms I have an inductance meter but it only goes to 40H and just shows OL meter checks against a choke that I have at 11h so your right it must be pretty high.
Cathode to plate went to 1vdc and was blasting if I turn the power down to 60vac it plays and I show .3vdc could c20 2400 mmf be bad?
One of my previous voltage checks I had 4.5vdc at that point.
#18

Consider that there should never be any positive voltage to ground on the AVC tube plate. I doubt there is anything wrong with C20 as it is a mica with very little voltage across it

The AVC tube cathode is always negative with respect to ground and the plate will vary from zero to some negative voltage depending on the volume control setting. Measuring with respect to chassis ground, the cathode will always be more or less negative. Unfortunately the schematic does not tell what the negative voltage should be but I would take a guess it would be around - 30 or -40 V at the choke L17.
#19

I will check L17 to see what I get.
But also came across this Hammond choke coil #155c 60H 2700 ohms I think this might work for L14?
#20

Ok checked L17 and I get 0 volts from when I turn it on to when it starts blaring
#21

That Hammond choke sounds like it will work fine for L14.

Are you measuring the voltage at L17 to chassis ground? There should be some negative voltage from either of its terminals to the chassis ground. If you measure across the two terminals of L17 you will read near 0 volts.
#22

yes went from each side of the coil to ground and got 0vdc
also just want to verify c38 pos goes to ground and the neg goes to the center tap

I'm going to order that choke coil
#23

Yes, the positive of C38 should go to ground and the negative to one side of L17. The center tap of the power transformer should connect to the other side of L17 and the field coil of the speaker L18.

Note the speaker has TWO field coils, L18 and L19. L18 should develop a negative voltage across it. What resistance do you read from the center tap of the power transformer to ground? Should be the same as across field coil L18.
#24

I get 2.8k from the center tap to ground.
Some where I have a component that is breaking down or a bad solder connection?
Right now it is playing and the vol appears to be functioning I get neg 110-120vdc on L17 where before I had 0. Other times it goes dead sometimes lots of popping and static. Not sure where to go from here?




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Model 70 Cabinet Trim
Although I have not made any cabinets or cabinet parts for a couple of years, I still have some parts left over, includi...Steve Davis — 06:26 PM
philcorepairbench.com - shadow-meter
Thanks Ron.fenbach — 02:43 PM
Model 70 Cabinet Trim
Thank you, Gary. Before making my original post, I had clicked on "Steve Davis Cabinets" only to find that it...musar — 02:25 PM
philco predicta
Welcome to the Phorum, cgl18! I am not your resource for television repair, but lots of friendly help is available here...GarySP — 02:12 PM
Model 70 Cabinet Trim
Welcome to the Phorum, musar! You can send Steve Davis a private message (PM). The site is at the top of the Home page...GarySP — 02:09 PM
Model 70 Cabinet Trim
How do I contact him? The only contact information for him I could find when searching online was a telephone number th...musar — 10:38 AM
philco predicta
Hello, good afternoon, I would like to ask what the possible problem could be if I don't have an image on the screen. I ...cgl18 — 10:19 AM
Philco model 38 code 121 not receiving signal.
So one last question before I finish this radio. Regarding the speaker and output transformer. I salvaged the original o...Stormlord5500 — 09:31 AM
462ron
It’s on the bottom of the homepage of our Philcoradio.com homepage! Ron462ron — 07:20 AM
Model 70 Cabinet Trim
Steve might have some trim left. Not sure he is making anything.morzh — 06:12 AM

[-]
Who's Online
There are currently 590 online users. [Complete List]
» 2 Member(s) | 588 Guest(s)
AvatarAvatar

>