Weyrad Superhet Circuit

[Neil Purling]

Thirty secs with my soldering gun & I switched the connections on one winding.
The voltage was initially positive, but plunged to approx -12V.
My Gould 'scope & X10 probe shows oscillation & frequency change when the variable capacitor was rotated.Nothing audible through the speaker, but I hardly expected there to be anything if it is far from being the right pitch.

If Ron or anyone else wants to pitch in with the dunces guide to alignment with use of a 'scope.
Idiot I may seem, but I want to learn.
You might want to send me a Private Message.
I would like to get sound on something like Magic 1161Khz and then also get the high freq end of MW, where the BBC R. Humberside is on 1485Khz.
I am happy I have oscillation.

[G8HQP Dave]

If you are starting with a set that could be hopelessly out of alignment then you will need some source of signals at known frequencies. If you are really careful (and a bit lucky?) you might get away with using off-air signals but this is not recommended. To put it bluntly, the less knowledge you have the more you need the right test equipment - in this case an RF sig gen.

[ronbryan]

Alignment is a lot easier if you have or can borrow an RF signal generator. This is a brief overview of what is required to do to your Repanco designed set.

It may be necessary to trouble-shoot the set before alignment, in case there is an assembly error or faulty component. Some sort of signal tracer (which can be home constructed) may be of some use.

Alignment is done in several stages in a superhet.

IF alignment is done first. The IF transformers are peaked at the nominated IF frequency - often 470kHz. A test signal of 470kHz modulated by a 400Hz tone is fed into each IF stage grid, working back from the 6Q7 and the IF transformer cores peaked, ideally with the cores in the outermost position if more than one peak is encountered.

RF alignment is done when the IF has been aligned. Again, use the sig gen to generate the required frequencies and feed the signal in to the aerial socket.

Padder capacitors on the oscillator such as TC5 are used to set the MW low frequency band edges, often at 600kHz. The main tuning capacitor would be near maximum capcitance and the tuning dial pointer would be set to 600kHz.

Trimmer capacitors on the oscillator such as TC3 (possibly fitted on the main tuning capacitor) would be used to set the high frequency band edge, often 1500kHz. The main tuning capacitor would be near minimum capcitance and the tuning dial pointer would be set to 1500kHz.

These adjustments (to receive the tone at max volume at the chosen frequency) need to be repeated until the effect of interaction of one adjustment on the other is minimised.

You have only one MW aerial trimming adjustment, TC1. This would be set with the tuning capacitor set to 1500kHz with the modulated generator also set to 1500kHz. Alternatively a signal received with the aerial plugged in around 1500kHz could be peaked with TC1.

Rpn

[Neil Purling]

I have a RF signal generator, though the dial does not always accurately reflect the output frequency.
This is it: https://www.vintage-radio.net/forum/...7&d=1232053275

It appears under around six guises & NTI were apparently a re-seller.
It's origin doesn't matter: I suspect it is a rather basic instrument.
I expect a high-end device would have means of ensuring the output closely agreed with the reading of whatever the tuning dial said.

[Neil Purling]

Further progress!
I have been playing with the signal generator & I now have music & speech.
Not very loud though & the gang is further open than I would expect.
I have Magic 1161 & Talk Sport. I am not sure what frequency it uses in the NE of England 1089 or 1053Khz). I have not yet got the BBC Radio Humberside transmitter on 1485 Khz.
Audio o/p is pretty low & this with about 30ft of fire in the loft.
I have another example of a DIY radio in a wooden case that does very well thank you on 5ft of fire that runs along the top of my bedroom door.

[Neil Purling]

You can view the scene for anyone unwise enough to enter my lair.
You can also view the patient on the operating table.
It really makes me envy other Members with spare rooms/sheds/garages given over to their hobby.

I will have to try more adjustments:
Does it matter which order you do the low frequency end and high frequency?
You just see-saw from one to the other.

[julie_m]

I remember thinking the 6K8 was odd in having the aerial signal go in on G3, but it actually makes a perverse kind of sense due to the construction. GT / G1 wraps around the cathode, with AT on one side; and G3 (with G2/G4 wrapped around it) and AH on the other side.

[Neil Purling]

Is it normal to notice the oscillator producing a higher output at the lower frequency end of the band?
It seems about 2X that for 1500 Khz. The thing is, there's nothing at that end of the band. Not after RTE1 went.

[Herald1360]

Originally Posted by Neil Purling

Audio o/p is pretty low & this with about 30ft of fire in the loft.

I hope there's not too much crackling from that

Oscillator level will usually vary quite a bit across the range- coil Q, feedback coupling levels etc all vary with frequency. As long as there's enough of it, it doesn't matter too much.

If the gang seems to be too far open, you may have more stray capacity in the circuit than desirable. Are the gang trimmers near full capacity? Providing you can get the oscillator frequency high enough (about 2070 KHz) for the HF end of medium wave with the gang fully open, it doesn't matter about appearances, of course.

[Neil Purling]

With all the up in the loft, both mine & the household usual I reckon you would get more than 30ft of fire.
I meant 30ft of wire of course.
I solved the low-level issue. It was the Hytron VR53. It was great in a TRF at RF, but there was some reason why it didn't like working at IF frequency.
I put it in the bin along with a dodgy 6Q7. If I have time before the bin men come i'll root out my other Hytron VR53. I want to see if it is a defective valve or perhaps due to physical or electronic differences inside the valve.
The Hytron VR53 (EF39) made in Canada has metalisation bonded on better than the surface in a pan. They should have whispered the secret to Mullard.
Anyway the place is stiff with EF39/6K7 and the other valves.

[Neil Purling]

The 6Q7 was not intermittent. I soon realised it was the base, which did not respond to a liberal dosing of Deoxit. I changed it on a foul Sunday afternoon.
The next upheaval is going to be a Weyrad coil pack if I ever figure out the connections. Hopefully Weyrad used the same wire colours for the respective connections across their range of coil packs. I am keeping my fingers crossed just in case member Roy is still around.

[Roy]

Yes, I'm still around, just been a bit quiet lately. I will take a look at my coil pack and report the findings in your other thread.

Roy

[Neil Purling]

Thanks Roy. If you & Ed both report the same connection details independantly I will know the matter is sorted.

[Neil Purling]

Thus far I have listened to Radio Romania, Bucharest on SW.
LW & MW need adjustment to bring up the signal levels on those bands & to have the stations in the right places. Thankfully there isn't a dial to calibrate as well. I did catch The Archers signature tune Borwick Green from BBC Radio 4 on LW at 7pm

[Neil Purling]

The above achieved with 6ft of wire.
I have an old Denco Technical Bulletin DTB9 on their coil packs. It has the adjustment procedure.
I am hoping that the contributors to my other thread can show me the geography of that particular coil pack