The chassis was covered with some tar like substance and a bit of rust to the point that I broke the 6A8 prying it off. Well I recapped it and checked the tubes all were good and I had a 6A8 to replace the broken tube also the Rectifier tube was supposed to be a 5W4 but had a 5Y3 there but my chart says this is a good sub. It had some brittle wiring and I replaced it as I went along and the Candohm Resistor had a lower value resistor spliced in R4. So I took it out and put in 5w ceramic resistors for R1-R5. Checked the resistors and replaced a few that were over 20%.
Problem is it only partially powers up. I stop bringing up the voltage I when I reach .7a and have about 80vac I don't want to hurt the transformer. C1 I get 120vdc and C2 is dead. I have powered it up with all the tubes out and the Transformer is fine as I get 350vdc to chassis off the 5W4. Now on Friday twice it actually powered up properly and I was able to put 115vac and drew about .55a. Now here is the kicker thought I had it but it won't power up! Back to square one!
Here is what I have done
1 recapped
2 replaced candohm resistor
3 replaced other resistors as needed
4 exchanged all tubes with other tubes I had.
5 Checked all the coils in the IF cans 1,2,3 (all seem to run about 6 ohms)
6 because I have a wiring diagram I have traced all the wiring for the candohm strip and the 5W4 ckt.
On page 7-15 Fig 3 C-1 & C3 shows -16v on a strap? but neither of the ecaps were insulated from the chassis so I put the neg of the new caps to chassis. Could this be where the problem is?
Looks like the c-1 c-2 should not be connected to the chassis. The schematic shows the neg. going to point E.
The -16 volts shown is the difference between the center tap and the chassis. Center tap is 16volts more neg. than chassis. If I'm wrong someone will correct but I believe this is the case.
Hi Eric,
Is Cumming cover in snow???
Yes Mike is correct the - side of both filters are connect to the center tap of the HV winding of the power transformer(not the chassis). By connecting them to the chassis you have shorted across R-1 this eliminates the negative bias voltage on the control grid ( grid closest the the cathode) of the 6F6. It need to have about -16 to -25v depending on the plate voltage (sez RCA)
If there is no voltage on C-2 Check the resistance between the two + end of the filter. You may have an open FC or an open R-1.
If you change this wiring error and it doesn't change the AC amps much, pull the rectifier tube and see if the current is much lower.
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!
Terry
(This post was last modified: 01-08-2017, 03:44 PM by Radioroslyn.)
Looks like I had the neg on the filter caps wrong as you guy's indicated. It now powers up and at 110 vac it pulls .55a. now for my other issue the only band that gets anything is "D" or (sw) I do pull in stations, don't expect anything on "C" (police) on "B" I do not get any stations but if I wave my soldering iron near the chassis it will pick that up. I do get constant static which is louder at the lower end as opposed to the the 1600 end.
Terry
We got a light layer of ice and about 1" of the white stuff, It got down to 11 last night but there saying 65-70 by thursday
>We got a light layer of ice and about 1" of the white stuff, It got down to 11 last night but there saying 65-70 by thursday
Just wanted to make sure you got your fair share! We got abt 3" here but pretty cold too.
You know the drill, Make sure the bandswitch is clean and make good connection at the contacts.
Have a look at pin 6 of the 6K8, should have HV (180v) on it on all bands. As you change bands the HV is routed though the band switch to that pin.
Check R-6,7,and 8 for drift 20% is ok.
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!
Did some Voltage checks and have two that are not right all the rest look pretty good.
1 6K7 2nd If pin 3 plate should have 245v I get 125v
2 6A8 pin 6 G2 should have 180v I get 2.5 except when I turn the selector to SW (which works) I get the 180v
Resistors 6, 7 & 8 are good <20%
(This post was last modified: 01-08-2017, 06:13 PM by Eric.)
Ok So check R-17 (supplies the plate voltage for the 2nd IF amp)
Check L-10 and L-15 for open winding and the associated switch contacts.
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!
The coils are good measuring 6.7 and 5.6 ohms here is what I've found on the two resistors that are in the can.
R-16 calls for 68k measures 75.5k so that's about 10%
R-17 is the problem the print calls for 2200 ohms what was in there is a green, black, orange (50k) measures 59K but the resistor looks original(?) in the parts list I cannot find R17 listed to verify the schematic. Any harm in putting the 2.2k in and checking it?
Ok seems to me that the source of the 180vdc is R4. On the schematic that goes to 'B' goes up to L10 then to L15 then to L12 then to the switch. Have I got that straight?
Yes, that is correct. The B+ 180V from R4 is fed to the three coils L10, L15, and L12. You should have 180 V on both ends of each coil.
The selector switch connects one end of each coil to pin 6 of the 6A8. Since the short wave band works you know that the 180V is getting to the coils from R4. The problem must be the switch or some of the coils are open and not passing the 180V to the 6A8 pin 6.
on L12 there are 3 connections I only get the 180 on the top connection as I rotate the switch if I attach to any of the others I get nothing. Also connecting to the top and the left or right I get 15kohms now the trick will be to get it out.
L12 is the short wave coil which works, so the problem is not there. You need to check L10, which is the coil for the broadcast band. See the coil drawing on the wiring diagram.
[attachment=12148][attachment=12148]Took me a while to get the coil out as I had to make a diagram and get it out, I figured out which coil and was lucky it was on the top as I was probing there was a piece of insulation at each end ,so I figured I had nothing to lose so I pried it up gently and sure enough there was a green dot (Corrosion) as I brushed the dust up popped the broken end. So I cleaned the end and spliced a new piece and reinstalled and checked it and got 2 ohms. reinstalled it and it plays great.
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