Lafayette HE-40

[Station X]

Reading previous posts suggests that a mains transformer has been fitted? If so the wiring to this should be one of the first things to check. You should not assume that the set worked in previous ownership.

[ms660]

That BFO circuit was also used in the Hallicrafters S120, similar looking receivers in many respects.

Lawrence.

[Herald1360]

There's been a lot of posts crossing with my edits to 11:09 (post #17) one! Hope not too much confusion as a result!

[ORAWA01]

Originally Posted by Herald1360

Edit: Just seen crossed post...

The set sounds lethal from your description of connecting an earth! The only isolation between mains and the earth connection is C5 in parallel with R16(?). I would replace C5 with a suitable Y-class safety rated capacitor and make doubly sure that mains neutral not live ends up connected to the HT- line.

To be honest, what you can get away with on a non isolated set on 120V mains can be rather too risky on 240V. I would seriously recommend running this one from an isolating transformer or at the very least via its own dedicated RCD.

C5, would it be 100PF one?
Numbers are very difficult to read in the schematic.

The set was plugged into the Lamp Current Limiter, and it looked OK when powered on - nothing super bright, just medium brightness.

When I replaced the burnt electrolytic caps. it was receiving very well. I liked the tone and, it was fairly sensitive.
Then the BFO stopped working, and I opened it up again to see why the BFO is not working.

I probed here and there with my DMM to check continuity and ohms, and the resistor on the BFO was starting to burn with live flames like BBQ. I couldn't believe what was happening in front of me.

[Herald1360]

Aargh! Should have said C12 not C5! It's the furthest left capacitor on the circuit diagram and is 0.05uF. A 47nF safety suppression type capacitor would be the suggested replacement.

[ORAWA01]

Yup, I noticed that cap, it was piggybacking a resistor and sitting on a valve pins.
Could it be replaced with a poly capacitor of 630V 47nF?

[Station X]

C21? across the mains supply needs to be a Class X component. It can be snipped out for the present. That's assuming it wasn't removed when the mains transformer was fitted.

[ms660]

Originally Posted by ORAWA01

Then the BFO stopped working, and I opened it up again to see why the BFO is not working.

I probed here and there with my DMM to check continuity and ohms, and the resistor on the BFO was starting to burn with live flames like BBQ. I couldn't believe what was happening in front of me.

Checking Ohms with a meter on a live circuit is a no no.

So far as I can make out the resistor that burnt up that you've described is R5 on the schematic, it's value being given as 5k.

Lawrence.

[Dave757]

Hi,

I seem to remember that UK HE40s had a 240 - 120v transformer
installed but not sure if it was an auto transformer. I had one once
but I can't be sure my mind isn't playing tricks on me!

Kind regards
Dave

[ORAWA01]

Originally Posted by ms660

Checking Ohms with a meter on a live circuit is a no no.

So far as I can make out the resistor that burnt up that you've described is R5 on the schematic, it's value being given as 5k.

Lawrence.

Can ACV be checked on the valve pins safely?

Would it be not the R7 300R?
R5 at 5K - is it the one?

[ms660]

Originally Posted by ORAWA01

Can ACV be checked on the valve pins safely?

Would it be not the R7 300R?
R5 at 5K - is it the one?

Not sure what you mean by ACV....Do you mean AC Voltage? If so then no problem so long as you're careful.

Yes, R5 (5k) so far as I can make out.....as per these photos:

Lafayette HE 40:

https://civil.trcvr.ru/wp-content/up...te-HE-40-3.jpg

Hallicrafters S120:

https://antiqueradios.com/forums/vie...p?f=5&t=197286

Note: The Hallicrafters S120 uses a 470 ohm resistor for the resistor that's designated as R5 (5k) in the Lafayette HE 40.

Lawrence.

[Herald1360]

Originally Posted by Station X

C21? across the mains supply needs to be a Class X component. It can be snipped out for the present. That's assuming it wasn't removed when the mains transformer was fitted.

Give or take all the confusion I may recently have created....


C12 0.05uF is connected between HT- (ideally mains neutral, but could be mains live) and the receiver chassis. The chassis is used for the front end RF ground and also connects to the antenna ground external connector. It should be a Y-class part. Unfortunately it's got a functional (RF ground) role as well as being connected between mains (potentially mains live) and user accessible metalwork so it can't just be snipped out.



C21 0.02uF is connected across the mains supply after the single pole switch and should be an X-class part. It may be snipped out without affecting function though this might degrade the set's resistance to mains borne interference.



Functionally either could be replaced by a 1000V dc or higher polypropylene film type but these types, whilst arguably better than the original parts, will not meet present safety standards required for mains connected capacitors.

[ORAWA01]

Thanks for your confirmation. R5, 5K resistor for the burnt resistor on the BFO pot. I am not sure if there is one of the value in my parts drawers. Will search for it.

With the 12AV6 valve unplugged, the set will not come on. When it is plugged in, the set will come on, but the 12AV6 is not lighting up, and there is no signals heard. There is some hum and tiny little signals of MW stations on all band selections. Even when the main tuning dial turned, it doesn't change anything.

When the set is powered off, the 12AV6 is warm all around the glass.
I am a bit scared of probing anything on this set with DMM, because it might set on fire on something.

There is continuity between the heater pins 3 and 4.
The pin 2 (cathode) has no continuity with any pins.

There is a mains transformer on the chassis, and it looks like single coiled one. - no primary and secondary type. Just one chunk of coil in the core looking like audio transformer.

[Station X]

See post #11.

[ORAWA01]

Originally Posted by Station X

See post #11.

No AC volts on the pin 3 and 4.
So the 12AV6 is gone bad?

[ORAWA01]

Originally Posted by ms660

Yes, R5 (5k) so far as I can make out.....as per these photos:

Lafayette HE 40:

https://civil.trcvr.ru/wp-content/up...te-HE-40-3.jpg

Hallicrafters S120:

https://antiqueradios.com/forums/vie...p?f=5&t=197286

Note: The Hallicrafters S120 uses a 470 ohm resistor for the resistor that's designated as R5 (5k) in the Lafayette HE 40.

Lawrence.

Found a 4.7K ohms resistor. That is the nearest value to 5K I have.

[Station X]

Originally Posted by ORAWA01

No AC volts on the pin 3 and 4.
So the 12AV6 is gone bad?

Yes. It would appear that the heater is short-circuit. Not something I've come across before, but that's what the test result says.

As an additional check you could measure the volts across the other heaters and lamps.

[ORAWA01]

Originally Posted by Station X

Yes. It would appear that the heater is short-circuit. Not something I've come across before, but that's what the test result says.

As an additional check you could measure the volts across the other heaters and lamps.

Yes, that is very strange. It was working before the R5 burnt out.
After that, it was not lighting up.

The only pin has voltage out is the pin 5, about 4V AC.

Do you mean to check the other valves heaters and the tuning dial lamps voltages?

[Herald1360]

Originally Posted by ORAWA01

Found a 4.7K ohms resistor. That is the nearest value to 5K I have.

Should be fine.


If you're worried, just use a couple of 10K in parallel or a 270R or 330R in series with the 4k7.

[ORAWA01]

Thanks.

What are the substitute valves for 12AV6?
I think the tube is defective, which makes the set not receiving any signals.

It has noise and weak MW signals, but not tuning for the right signals on the bands.

I have a few old valve sets, and trying to find the tube equivalent to 12AV6.

Some valves I see in the other sets are,

6AU6