[bm071]

Hi,

I've been working on this Model 8A..was dead, now playing, however I have too much voltage on both sides of the circuit for example...checking plate voltage on the 6k7's, 6l7, 5y3, 6c5, spec is 240v. I'll have 245v for about 5min then it jumps to 345v. In turn the voltage at pin4 of the 6k7's and 6l7 should be 105v and I have 155v(exactly 1/2 of the excess plate voltage. Bias voltage reacts the same 50v more.  All resistors & tubes check good but I'm replacing all resistors anyways. Have about 8 to go...The only oddity is no signal thru the antenna wire(if it's correct..wire goes to thru band selector switch to ground) and volume seems low until 50% after 70% it's a little distorted....If I hook an antenna lead up to the cap of the 6l7 or plate wire of the 6k7 reception is outstanding. Is there something obvious I am missing? Transformer is super cool, even after an hour. The only thing I have not checked is field coil resistance. Will do that tonight. All three bands are sensitive..can pick up more stations then my 38-116 hi fidelity.
 
Thanks in advance for any suggestions  

Bob  

[bm071]

Thanks to all who read my first post. I can guess that all of you figured out I was confused..and I was so here is the latest and acccuarte account of the problem I am searching for.

I finished replacing all resistors, caps, and filters. I also put in new tubes just to be sure.  My problem is lower than average volume with a little distortion above 65%(almost like not enough wattage?).....I did a voltage check of the tubes and here is what I now have,

5y3...300v at pins 2&8...-54v at pins 4&6..spec is 245v and -95...high B+ and low bias..correct?
6l7....3oov at pin 3....150v at pin 4 spec is 240 and 105.

Similar pattern throughout th rest of the tubes.  B+ voltage at the filter is 300v bias -54.

The field coil resistance is 795ohms cold, 839 after 2 minutes...spec is 1000 ohms hot.  I did not want to play for too long with the high B+ v.

I do not have any specs on the transformer, only the schematic from Nostalgia Air.

Could I have a transformer issue or is there something I am missing to cause the low bias?  

There is supposed to be an antenna lead and a ground wire, only one is left and I'm thinking since it goes to the a band selector 
lug that in turn goes to ground...means itis the ground and not the antenna lead right?  If so where would be a good place to attach a lead for antenna? 

   Bob

[Ron Ramirez]

(update: I restored your deleted thread and answered before I discovered your other thread. I have merged both into this reopened thread.)

Answering your first post first...

It sounds like you have an issue with your intermediate (RF) coil(s).

Let's look at the schematic.
http://www.nostalgiaair.org/pagesbymodel...005757.pdf

Do you have any plate voltage at the 6K7G RF tube (far left on the schermatic)? Your symptoms indicate there is no plate voltage here, which could be causing the plate voltage to rise on your other tubes since it isn't drawing any plate current.

The set of coils connected to band switch section 5C are suspect. Check that voltage and get back with us.

Normally, if you're connecting an antenna lead to the plate of the 6K7G, you're applying high voltage B+ to that antenna lead...don't ever do that...shock hazard! But if the B+ isn't getting to the 6K7G, then the problem must be in those coils connected to band switch section 5C, as stated earlier.

Now, let's examine the issue of the antenna and ground leads. The antenna lead should connect to band switch section 5B as shown on the schematic (see link above). If this set had a ground lead, it would be connected to the chassis at any convenient point.

[bm071]

Thanks for responding Ron.... I have 300v at the plate of the 6k7 located by the 5y3 and 6v6 tube.  The 6k7 on the other side of the chassis has 300v at the plate when the band selector switch is moved to either of the short wave
bands.  I have voltage going to the rf coil, the antenna coil only seems to have heater voltage going to it or I should say the broadcast band of the selector only has heater voltage for the dial lamps. (I don't mind telling you I'm still not the greatest reading schematics so some things slip by me)  Pin 4 of the 6k7's in turn
have 150v instead of 105v.  I did a simple continuity check on the rf coil and every lug had a partner. Ran out of time and did not do the antenna coil. Is that the only test I can do? I did not see where the antenna coil would have any other voltage going to it unless I'm missing something in the selector switch itself. (Both trimmer coils (screws #1,2,3,4,) are good cleaned and working) 

Thanks for the advice on the antenna lug.....I had it where the schematic showed and picked up nothing. I removed it from that 6k7 plate terminal on the band selector and have it on the middle rod going from the selector center gang to the center band switch for now (must be 1st shortwave?) Guess that could be 1st indication of an antenna coil issue?
    
Bob

      

[bm071]

I should say that I have voltage to the rf coil only on the shortwave bands when the 6k7 has the voltage also. Even then plate  voltage is 300v and pin 4 is 150. On Broadcast band that particular 6k7 (rf?) only has heater voltage 6.3 ac  the other 6k7 (if)has voltage all the time 300v plate 150 at pin 4..Sorry if did not make that clear.  

With the radio on shortwave and all tubes showing plate voltage....voltage is still 300v plate 6k7's and at the 5y3, bias is -55v at the filter, -60v at the 5y3. 

Thanks,
Bob

[bm071]

Please dis-regard my last post....I double checked voltage going to the rf coil and the osc. coil. I do have voltage going to the rf coil at all times. 300v. Checked continuity on all terminals of both the rf coil and the osc. coils appears fine. The osc coil has
 -54v.   
 From what I can tell by looking at the band switch, the 6k7(left side of schematic by the coils) only gets plate voltage on the two short wave bands. Pin 4 always has voltage(my mistake dirty terminals first check) 125v with no plate voltage, 154v with plate voltage. Looking at the chassis the only two things I visually see connecting the antenna coil to the rest of the circut is ground and the 47000 ohm resistor.(#16 on schematic if I'm reading it correctly...no voltage detected.)

   

I checked continuity on both of the if coils(ones with trimmers) and they check good. Have voltage on red and blue wires, none on the blacks.  

The other 6k7(if tube?) has voltage all the time plate and pin 4(300 & 154v)..

bm


. 

[bm071]

I've been going thru the schematic and if I'm reading it properly I've found 4 resistors and three capacitors have been removed at some point.  History of the radio is unknown. I purchased it over ten years ago and had a supposedly radio tech try to get it operational. He replaced the caps and a few resistors then gave up. Since then I 've been dabbling in radio repair and trying to learn as you all know from my horrible posts in the past.(38-116 fix, Philco 70,71) 

I counted all the resistors in the chassis then compared to the schematic and come up 4 short...so far I cannot find 3of the 4.... #59 the 2.2.meg, #22 - 1000ohm and #23 - 15,000ohm.   I cannot see where they may have once been in the circuit is the other problem. The caps are #8,9,38 (I think). 

If those resistors were back in the circuit would that fix my problem or does their placement not affect the low bias, high b+?

Bob 

[Ron Ramirez]

Mike...Terry...can you help, please?

[Eliot Ness]

......I counted all the resistors in the chassis then compared to the schematic and come up 4 short...so far I cannot find 3of the 4.... #59 the 2.2.meg, #22 - 1000ohm and #23 - 15,000ohm.   I cannot see where they may have once been in the circuit is the other problem. The caps are #8,9,38 (I think). 

If those resistors were back in the circuit would that fix my problem or does their placement not affect the low bias, high b+?.......

It depends on exactly which caps and resistors are missing if they might be causing your problem.

I once had a Zenith chassis that had been hacked on and I had to retrace everything to make sure parts were where they should be.  I made a copy of the schematic and used colored pencils to slowly trace things out, correcting problems as I went.  It can be slow and tedious, but you need to find what is missing and try to correct it before doing much more troubleshooting.

[bm071]

......I counted all the resistors in the chassis then compared to the schematic and come up 4 short...so far I cannot find 3of the 4.... #59 the 2.2.meg, #22 - 1000ohm and #23 - 15,000ohm.   I cannot see where they may have once been in the circuit is the other problem. The caps are #8,9,38 (I think). 

If those resistors were back in the circuit would that fix my problem or does their placement not affect the low bias, high b+?.......

It depends on exactly which caps and resistors are missing if they might be causing your problem.

I once had a Zenith chassis that had been hacked on and I had to retrace everything to make sure parts were where they should be.  I made a copy of the schematic and used colored pencils to slowly trace things out, correcting problems as I went.  It can be slow and tedious, but you need to find what is missing and try to correct it before doing much more troubleshooting.

[bm071]

10-4..I  downloaded the parts description page from radio museum web site today and was planning to match actual numbers and parts together on the schematic.. I had been working only with the schematic from Nostalgia Air...no parts description to associate with.

Bob
 

[bm071]

I followed the schematic line by line and replaced the missing resistors and caps.  Fixed a majority of the issues. Volume is great and the garble is gone.  B+ is down to 270v and the bias is at -75v.  The antenna lead now works very well on the shortwave bands but not broadcast. 

Would someone be kind enough to look at  the scematic and help be figure out how to read the band switch. Resistor#22 is missing along with the connection to band swich (reference 5f).  I'm not sure which lug on the band switch that connection goes to. .
Thanks,
Bob