Hi Fred I replaced the 6J8G with a new old stock 6J8GA .
The padder that was in there belonged to the replacement gang and measured 920 Pf. I will now fit a fixed 400pf cap in there for the time being. Actually I did try some substitutions in the past to no avail.. I think somewhere I have some copper wire I might wind a coil.
Not about to give up anytime soon. However I do feel a bit of a Twitt.
Regards Jim

Well some small progress. I replaced the padder cap with a new silver mica 490pf fixed capacitor now got 40V p-P on pin 5 osc grid.
Frequency varies between approx 800 k Hz. Gang meshed 1.5 kHz gang open. So hey! Oscillating finally. Unfortunatley still not working aerial coil now needs further investigation tomorrow! Wife keeps telling me I need to get my head out of there, if I have a problem I cannot just leave it. I never have been able to. I guess it is another version of obsessive compulsive. I have tried several valves including a new 6A8 . I am back to the original 6J8G with a nice 40VP-P on pin 5 osc grid.

Still confused . The osc grid looks great vey clean 40 V P-P however the osc plate is very distorted and only about 20 V P-P nothing on the grid of the IF amp detector valve EBF2-G .
Regards Jim

I can only guess the wiring albeit its fairly standard & I can send a copy of it from the Radiotron Handbook. There is normally a 0.0001μF or so cap feeding to the grid & as before 50K grid to the cathode Not ground and a similar one between Triode plate & resonant coil of the oscillator coil . Messups & wrong, or a dud cap can be an issue and if there is a spurious oscillation that can generate AGC that will shut down the heptode.

With no signal on the antenna and therefore signal grid, there will only be the oscillator frequency, as there is no other signal to heterodyne with. Therefore there will be no IF signal unless you externally provide it with one.

Your next issue is likely tracking. This goes back to my matched coils. However, make sure that the antenna coil steps up & is not wired wrongly. Again the size of the winding is a hint. In order to receive the oscillator is normally (not always) the IF frequency above the received station.

That means that if the oscillator is 1460 kHz a transistor should pick that up and if the IF is 460kHz, a modulated signal of 1000kHz into the antenna (5-12 uV) should get through.

Marc

Hi Marc.
I see your email address is open .
I will send you a copy of the circuit. Thanks for all your help.
Kind Regards Jim

I could probably see if one of the older sets here has a similar circuit, to get voltages and oscillographs? I think Breville 730 maybe?

Marc

Re post 108.

The tank circuit of the oscillator will be a sine wave.
Thats the one with the coil and gang.
The plate circuit will have a large harmonic content, thats normal.
Check back on my "little general" photos of osc waveshapes for typical.
Your oscillator is working.................................ka ching!!!!!

NOW.
Without any input signal from the tuning coil to the 6J8 control grid,(short out aerial) check the plate of the 6J8 and JUST oscillator frequency should be there. Swing the gang up and down to be sure.
THEN if you let tuning signal through the 6J8 grid a whole mess of HF waves will be on the plate.

AND if the osc frquency is set to a value of frequency (455kHz or whatever your coils are rated at) HIGHER than a signal that you could pipe in to the 6J8 grid from your signal generator (or the tuning coil IF it is working properly),

THEN you will get an IF signal (IF frequency) product at the 6J8 plate, resonate through the IF coils and appear at the detector.
IF you have the sig gen set to MODULATE, THEN the detector will rectify that and you will get a tone in the speaker!!!!!!

Then as Marc says if the tuning coil is working and SET to a range 455kHz (or your IF coils) lower then you will tune in stations.
Nearly there!!!!!!!!!!!!!!

YOU are in control now!!!!!!
(and tell missus to pull her head in)
(with the greatest respect of course)

Fred.

Well what can I say. Marc was correct about the hexode being wiped out with specreious oscillations . I Could not achieve a result grounding the Arial. Pressing on I did notice the presence of radio signals . Some of the stability problems seemed to be coming from the EBF2G it was a silly choice for me to make .I wanted to keep the original valve line up. I do not have a replacement . I am hoping HRSA may have one. Ok I wrapped the valve in alfoil then wrapped tinned copper wire around it and earthed it that has made a big difference however very unstable , just got to touch the Arial or move slightly off a station and it takes off. I have just noticed the Arial coil has no tunning slug in it. It should shouldn't it? I may have to find another coil.
Regards Jim

Aha.
O golly yes, if the IF valve is not an internally shielded type (and that pin is grounded) then without a shield, just like Marc says the whole set will go bannanas and wipe out convertor action. Ditto with the 6J8.

The EBF2G I think is a metal painted on shield connected to pin 1?
Ground pin 1!

Then like Marc says, its all up to the coils "tracking" each other.
That is the oscillator coil always about 455kHz (IF frequency) above the tuning coil frequency at ALL points of the gang sweep.
You normally pick the padder size, the trimmer sizes, to get a "matched" set of coils to track.

Thats when you set the gang at a point and nudge and jiggle each coils resonant frequency (by the padders, cores and trimmers) so they are "IF" frequency apart. If you get 3 points of the gang range to agree, gang closed, half open and full open then the other points between will be close enough. From scratch, with home wound or unmatched coils I have got down to 10 kHz or so matching and that is well within the bandpass of the IF coils to let through. As in my "little general" scratch builds.

you are almost there!

Fred.

Hi Fred. The EBF2G has its filament pins 1 and 8 . The valve is metal shielded . Pin 2 is supposed to be grounded which it is however I could not get a measurement between the metal coating and pin 2 that is why I did what I did.
Should the 6J 8 have a goat shieldsd can around it . There is no mention of this in the text. Should the Arial coil have a tuneable slug.
Regards Jim

Ok I have changed the Arial coil not sure if it was an Arial coil however the windings had a few more ohms than the osc coil, about 4 ohms and 6 ohms. It is now completely stable but output level is fairly low if I touch the hex grid top cap the audio level comes up not sure what this means at this stage I have not done an alignment as yet . Down the track I will have to put a padder cap back in on the osc coil where I put a fixed value 490 pf silver mica temporarily. So I guess some progress has been made but not there yet.
Regards Jim

I should have mentioned now if I short out the antenna I get the sine wave on pin 3 hex plate the amplitude varies greatly depending on the gang position . From memory level is highest with gang fully meshed . Could this indicate not enough turns on the Arial coil secondary sorry about the dumb questions.
Regards Jim

I have sent an email with some info.

One of the things that can go wrong with metallised Philips tubes, results from a loose envelope & being removed by the envelope. That will cause the wire between pin 2 and the body to be broken & then you have a repairable problem: Even the Metallisation can be replaced.

The behaviour of a pentagrid normally see's the greatest amplitude at low frequency & as it dies the high frequency and modulation fall away. That has nothing to do with the aerial coil. It merely brings in signal. But must "track" with the oscillator, or you get signal attenuation. That's why they are a matched pair and subbing can cause "tracking issues (not as simple as it looks).

If you touch the signal grid and get better reception then there is signal attenuation between the antenna & signal grid. That could be tracking or not set properly. The antenna trimmer is normally set on a weak station at around 1500kHz, 2AY Adjustable padder (first) 600kHz.

Marc

Hi, sorry I got the EBF2 pin wrong!

If you pop a goat shield on the valves make sure you use the chassis clip so the shield gets connected to chassis.

You are now going through the pains of a designer doing the final tweaking on the protoype to make it all work properly.

What Marc says.

Fred.

The shape of the EBF2G is not suited to a goat shield.
I think I have given it a good shield it could be very low in gain I am going to try and buy another
Thanks Fred and Marc for all your help it would not be working at all without your collective inputs.
Kind Regards Jim.