Nein! .Typo 6J6 is a double triode like 6A6 with a common cathode. Pentagrids like volts, so make sure they're right.

The most common killer of oscillators in situations like yours is to wire the tickler coil backwards. An Oscilloscope or transistor radio should pick up on a dead oscillator and some modern DVMs have counters. The 455kHz on the IF would be missing if the meter could read that far?

The catch 22 with the transistor is predicting where it will fall on a non calibrated radio. Its IF heterodyne would be 910 on BC band & the oscillator itself 455 above the frequency tuned to. for a 455kHz IF.

A tube swap with a 6A8 is ok if there is a perceived issue with the 6J8 and no spare.

Where there is AGC a weak signal from a strong station can get through to the 2nd detector & give the illusion that the oscillator is working. The IF will calibrate (weak signal if there is AGC), even if the oscillator is dead and not the tube. That proves the RF & audio is working

Marc

Hi Marc.
I am fairly sure the 6J8 is good . It tested good in the Hickok valve tester, I would have another but I had not considered it to be faulty.
Which winding of the oscillator coil would require reversing.I hate hacking things apart after I have just built it .
Regards Jim

On BC the resonant coil will have the greatest resistance and the tuning gang on it, the tickler will be the smaller coil with lower resistance & most likely on a 6J8 go to ground and have a pF cap in series going to the triode grid. Grid resistor is normally 50K connected to the cathode, not ground. Plate Triode is 20K for a 250V rail. G2 100V

https://frank.pocnet.net/sheets/127/6/6J8G.pdf

Often the resonant coil has a padder of around 400pF in series with it If this is a coil foreign to this radio, it may be pertinent to refer back to what it came out of, as coils & tuning gang are a matched set.

Marc

Hi Marc.
I am not sure what it came out of it was an incomplete chassis I was given.
Should I try to reverse the small winding? It makes sense what you are saying about it being a matched set.
Kind Regards Jim.

Jimb, when you build a superhet from scratch it is a 50-50 chance that the osc will work or not from coil phase..
Just swap the ends of either winding, the easiest one is what I do.
Fred.

This can also happen if the tickler is open and one winds a new one over the top of the old.

Marc

Thanks Fred and Marc.
I will do phase swap. The coil was not in great shape the connection tags were loose so after I soldered on new leads I araldited them but that is ok I can snip them off a little away from the coil. I appreciate your help as I have said before it is a new learning curve building from scratch instead of repairing a commercial set.
Regards Jim

Well,I tried reversing one of the osc windings still no good. I then replaced the osc coil no result, tried reversing one winding still no result.
I am pretty well at point zero with this. I have taken some bias measurements from the cathode of the 6J8 to top cap hex Grid one. -2.7
Volts . Osc. grid one, minus 112 mv . Are these measurements meaningful ?
I injected the signal generator between 700k and 1000kHz into g1 top cap hexode and moved the tunning Gang through its range no result . I thought if the aerial coil was faulty this would test it out. I am overlooking something but I do not know what.
Regards Jim

Jimb, typically the triode section of a 6J8 has a whopping sine wave on both grid and plate at the osc frequency and the grid is driven negative to the tune of 20-30 volt negative.
You will measure the minus 20-30 volts on pin 5 and a 100 volt plus or so on the plate pin, (which I have forgotton the number!)

If the minus volts are not on the grid the osc is not running.
You will have exactely the situation you have now as no 455kHz is being generated at the main plate of the 6J8.
At this point I patch in another osc coil on leads and make it work.

Obviously the thing to do is clip the CRO on the 6J8 pins and see what the heck is going on.
Any CRO will do this job but I dont think you have one?
Even a 10MHz minidigital "Veller" type will be good for 1MHz frequencies.

Your DMM may respond real well to IF 455kHz AC frequency.
If you had access to another superhet with a running oscillator you may be able to measure typical DC and RF/Osc AC voltages.
Then compare to yours .
Use meters and imagination!

Keep at it mate.

Hi Fred. I did patch in another osc coil to no avail.
I do have a Cro not in the best condition. I will have to drag it out, it is large and heavy so Imtend to use it as a last resort. I have now reached that stage. I may get some time tomorrow.
Regards Jim

Changing significant parts when there is a fault is not a good idea as you risk adding another one. It would be interesting to see the actual circuit you are working to. One should not take as gospel that a tested valve is a worker. There are two ways to get an idea if its working other than testing: you sub it, or shove it in another radio that was working before you touched it.

A shorted gang plate can kill the oscillator, so it is important to check for that as well as the voltages.

An oscilloscope & signal generator are formidable latch up for finding a broken signal path. Be careful as to where you put the oscilloscope probe and watch out for the input voltage it can handle. Wrong placement of the probe can in itself kill the oscillator.

Marc

Hello Marc.
Before reading your post I have discovered some problems you are suggesting namely the tunning capacitor I had previously checked it and itt appeared ok however on rechecking it last night it has multiple shorted positions in parts the osc sec shorted further around the aerial gang shorted , usually it is only a slightly bent plate not the case with this. The front bearing has sevearal ball brearings missing tried realigning it to no avail . I am scrounging around for another and yes I will replace the 6J8 I don't know if it would have suffered damage having its grids shorted. And yes again my next visit will be with the Cro. I have a signal generator which I have been using.
Initially it was looking fairly neat it resembles a dog's breakfast at the moment . The limited space I am working in affects what I try not to use because of the space it takes like my 1960's Japanese Cro which in itself now needs work. It would be nice to have one of those little solid state CRO'S . One of my DVM's has a frequency counter but it is useless because it requires a large amount of signal to drive it. Having made that remark . When the oscillator is oscillating I may well have the signal I need to drive it.
By the time I have got this working I will have gained a lot more knowledge. Thanks for your help.
Kind Regards Jim

That gang sounds like the Government here. Very unusual to see bearing loss in a gang, unless someone interfered with an adjustable nut on the shaft and it lost its balls: Not squeaky is it?. Those are a similar size as the ones used in the older bicycles: They can be bought, loose the ones I have & the ones to replace ones that have vanished from wafer switches are engineering supply.

Beware with Oriental CRO this may have "Oil filled caps". My experience with them, has them in the same basket as, "Micamold" just about everything, and Waxed Paper caps: Waste basket. It is fascinating to watch the old 2.5MHz Heathkit CRO with a signal past that; Probably as it has 6BL8's, just keeps going in just loosing resolution. The Transistor one, once its past its spec. dies.

If you need to replace the gang. Rat it from a set that still has its coils. Band-spread might be an issue, but at least they will track one another.

Its always the set that fails to play ball that is educational. You actually have to learn how it works, to understand why it wont.

Marc

Hi Marc.
Rather a frustrating day but I have no intention of tossing in the towel.
I replaced the Gang what a drama! Height 13 mm lower ok I made up some spacers . This is a good gang checked it with a capacitance meter no shorts 420pf down to about 20pf I think ,can't remember. Did a trial fit into the case and it hit on the top. No problem took a bit out of the top support timber. Now fits however did not think about the the horizontal alignment it is about 20 mm of centre to the right . No worries I can deal with that later, I have some ideas. Osc. Still dead swapped winding still dead. The hexode plate 238V screen Grid 114 volts . Osc plate pin 6. 96V. Osc Grid to Gnd.. + 1.8 V . Osc grid to cathode minus 0.8 volts. .
Not sure what value the the padder cap should be originally used the one that was with the gang about 900pf changed to a trimmer about 6pf. . I will have to again try another osc coil.
Regards Jim

Hi Jimb, padders are usually in the 100's pf like 420pf typical.
ANY coil, even a aerial coil should fire up and oscillate at some frequency if the circuit is right.
All a coil has to have is a primary and a tickler coil I have wound them and used all sorts of coils to oscillate.
Typically I would have 200 turns on the main and 30 turns on a tickler.
I have seen oscillator coils with heaps of turns on both windings as well.

Your 6J8 is not oscillating.
The grid voltage tells me that let alone anything else.
There has to be a reason why so just keep going on.
Not too sure you have been able to try a known good 6J8?
Even a 6K8 or 6A8 should work for a try.

I have even breadboarded circuits outside the chassis, as you would be aware in some of my projects.
That was either to prove a concept, or the parts. Get them to work daisy chained on the bench and then transfer the lot into the chassis.

Once you have an oscillator working you will have products coming out of the convertor and the set will come alive!

Fred.