3 Tube Ocean Hopper (battery type)

[Spencervs]

Hi all,

I am in he process of making this little battery set and I was wondering if someone could assist me with some minor questions:

1. There seems to be three batteries, a 67v HT, a 1.5v LT and another 4.5v battery which is supplying negative negative volts to the screen of a DL91 but the positive volts to ground? can positive even go to ground? and how critical is this battery?

2. I have noticed again regarding batteries, the option for 45v goes to the pot/switch and joins what would have been the 67v line via 'Y' connection but this doesn't seem to be the case the other way around. As I am choosing to use 67v as I don't own a choke, would this mean the HT battery isn't switched? I can see how the LT is switched in this circuit but not HT.

3. Would it be appropriate to solder a ground connection to chassis? I want to avoid ground loops, so was thinking to use a standard co-axial connector and solder the outer bit to the chassis and connect the relevant bits direct to chassis. does that work?

4. This radio interestingly has a variable capacitor (C3) which is unlabeled or mentioned in the article it is in. The image of the radio as built only shows a tuning capacitor, volume pot and a jack for headphones. So what does it do? I have made a hole in the box and mounted both C1 and C3 next to each other so they are on display and adjustable as I feel they should be?

5. This radio has no operating instructions and has the bandset capacitors as trimmers inside the coils themselves. How do I know if I have set the band correctly?

I'm sorry for all the questions and I am sure that this radio may not be the most efficient but I have a lot of the parts and I am intrigued by it. Any answers to these questions would be amazing.

Thanks,

Spencer

[snowman_al]

I see it like this, I've often been wrong though.

1, Yes positive to ground for the 4.5 volt battery. It is the grid bias for the output valve and connects to grid 1 not the screen. You do need it to make the grid 1 negative with respect to the ground line.

2, no need to actually switch the HT+, once the filaments are off as long as the caps across the HT are good, there is no current flow.

3, Too many choices...

4, C3 is coupling the RF amp 1T4 1 to the tuning/detector stage 1T4 2. It will alter the signal strength to a degree. (The first stage is wide open and has no way to turn its gain down.)

5, Put the band spread cap in its central position, tune the band set cap to the centre of the band you want to tune.

[frsimen]

Broadly I agree with snowman_al's comments, but there are a few quirks in the circuit that need to be addressed.

With the filament supply switched off AND the switch connected to the 50k potentiometer open, there will be no current drawn on the HT rail, so it can be fed all the time. It might be wise to add a switch to avoid the risk of a nasty surprise one day!

It does appear that the 67.5V supply is only used for the detector, the circuit is looking for 45V for the other valves. If you don't have the 45V supply, you will need to drop the voltage to 45V for the rest of the set.

On the grounding question, keeping ground connections short is probably the best way. One approach is to make all the ground connections for a valve to one point.

As stated above, C3 is used to adjust the coupling between the RF amplifier (V1) and the detector stage. I would expect that it is a trimmer capacitor rather than a panel control. Keep it well away from C1 otherwise the RF amplifier could oscillate. C3 should be adjusted so that the detector stage can be made to oscillate by the reaction control (R2) over the whole of the tuning range. If it can't, you need to reduce the capacitance of C3.

An alternative to the method for setting the band set capacitor is this:

Adjust the band spread capacitor to maximum capacitance, then adjust the band set capacitor so that you are tuned to the lowest frequency of the band that you wish to receive. Once set, you do all the tuning on the band spread capacitor.

[snowman_al]

Ooops,
I did say up front!
Good spot, yes you do need to switch the HT exactly as frsiman explains...

[Spencervs]

Thanks a lot for the clarification. Makes sense! Regarding the switching though, do you mean to say that I should add a HT switch just to ensure it's safe?

I'm thinking with the ground connections, I should get away with making short connections to chassis, maybe some put together so its not all over the place.

Seems a silly question, but lets say I use method 2 when setting the bandset cap, how do I know that I have managed to get to the lowest frequency? is it when I first hit a squeal/noise?

Oddly with this set R2 is listed as a volume pot so I assume it is also the regeneration?

Sorry for all the questions!

[frsimen]

At the very least you need a switch to disconnect R2, otherwise that will still be drawing current when the filament supply is removed. Switching off the HT supply will reduce the risk of you getting a shock because you forgot that HT is still applied, even though the radio appears to be off.

You could connect all the earths for V1 to one point, those for V2 to another, so long as you keep the connections short.

To set the lowest frequency you will need to have some way to identify that you are tuned to the right frequency. Methods that you may be able to use are:

1) Use a signal generator, set to produce a signal at the lowest frequency that you wish to listen to. Adjust the band set capacitor to tune in the signal from the signal generator, with the band spread control at maximum capacitance.

or

2) If you have another radio that covers the frequency that you wish to set, tune that radio to your chosen frequency. It the radio has a BFO, switch it on. Adjust the reaction control (R2) so that the detector is oscillating. Adjust the band set capacitor until you hear you hear the oscillator of your battery set on the other radio. If the BFO is switched on, you will hear a whistle when the frequency is close to correct. Adjust the band set capacitor for the lowest pitch whistle. IF there is no BFO, you will hear a hissing as you tune to the right frequency, adjust for the least noisy his. It's hard to describe but you will understand when you try it.

or

3) Try to measure the frequency of the oscillation using a frequency counter with a pick up loop positioned near the tuned circuit.

Yes, R2 controls the amount of regeneration and that will alter the volume The sensitivity and selectivity are at their best when just below the point of oscillation, for AM reception. Go beyond that point a little and you will be able to detect CW and SSB signals.

[Spencervs]

Thank you so much for the info! I have been working some bits together and the switch confuses me a little due to the way it is drawn on the diagram with a cross in the middle... Is anyone able to kindly draw an alternative? I tried wiring it up and the filament supply doesn't disconnect. Luckily my pot seems to be a dpdt, so I plan with the other side to use it to disconnect the HT supply. Would that be ok?

[snowman_al]

Does the enclosed help?

If you have a double pole switch you can use one pole for HT and the other for LT. Just be sure to get the connections correct!

If you follow the example, you put the HT switch just after the battery / power supply. Then the earphone socket is 'dead' when power is off. Then the switch shown on the original circuit (the cross) is not needed you wire the bottom connection of the pot to the 0v / earth line.

[Spencervs]

That's amazing! Just what I thought I should do logically. I'm going to assume one side of the pot still goes to ground? Also I must ask about the positive rail. Do I connect the 67v (I actually have to use 72v) to the pot too? Or do I use a 45v battery here? I'm assuming it needs some positive voltage

[snowman_al]

Yes one side of the pot to the ground line and the other side to the 45 volt line.

And yes you need a 45 volt supply for the connection marked 45 volts. It is the HT+ supply to the first 1T4 (RF) and the 1S4 (audio amp), it will not work without it...
You can do as frsimen says in post #3 and use a resistor to drop the 72 volts to 45 volts. Or follow the diagram and use just a 45 volt supply in which case join the 45 v and 67 v lines together using the 'Y' connector.

[Spencervs]

Thank you, that makes a lot of sense. I'm learning so much with this project. I hope it works!

Also another question, when I adjust C3 to gain oscillation, I'm assuming I will do this first when operating the set and hear a specific noise like white noise or something. I'm so sorry for all the questions!

[snowman_al]

C3 is the coupling between the 1st and second 1T4s.
The reaction control is the pot R2. You should start to hear a 'wooshing' followed by an increasing 'howl' as you advance the control. The correct position for AM reception is just before the wooshing starts. You will notice the sensitivity increases as it advances too.
This is a simple set and the reaction will need to be adjusted as you change frequency. Also anything that changes the damping of the C to D coil will alter the exact point.

All things are a compromise for this set.
If you want broadcast stations on a single band there may be a setting of C3 and R2 that gives you reasonable performance.
If you want the maximum performance then be prepared to twiddle C3 (for a sort of gain control) and R2 to just before oscillation (the wooshing) as you tune into various frequencies.

And if you want to listen to amateur bands SSB and CW you need to advance the reaction control just into oscillation to resolve them.

You will find out once it is working, they are much more fun to get the best out of than superhets and more sophisticated radios...

[G6Tanuki]

Originally Posted by snowman_al

And if you want to listen to amateur bands SSB and CW you need to advance the reaction control just into oscillation to resolve them.

You will find out once it is working, they are much more fun to get the best out of than superhets and more sophisticated radios...

Indeed: I cut my ham-radio-receiving teeth on juat such a battery-valve regenerative receiver, learning how to drive it for maximum efficiency, the effects of different antenna/earth arrangements - and the dreaded hand capacitance effects - best summed up as "You've got it tuned just right; now don't move - don't even breathe!".

There's also a bit of a thrill to be gained from hearing American and Russian ham operators on a radio you built yourself.

[Spencervs]

Hi all,

This thread has been so helpful! I've hit another snag and I'm hoping someone can help. One of my chokes started to smoke when I applied battery power and I was wondering if someone can help me identify the problem? Below are some pics and of course I uploaded the diagram earlier. The choke is attached to C3 and the third pin of V1.

Also I am aware that it is very messy. This is my first homebrew project so please do let me know if you have tips on how to tidy it up. I made the red wires the lines that take positive power from the batteries and the negative is direct to chassis.

[Cobaltblue]

Are you sure that C3 isn't shorting to ground?

You often have to mount these on an insulated board which in turn creates all sorts of hand effects when adjusting.

Cheers

Mike T

[snowman_al]

^^^ This.
C1 and C3 both have to be isolated from the chassis / ground lines.

Also what value is the choke? It is supposed to be 2.5mH (milli Henrys). The one that is cooked is rather small for that, is it 2.5uH perhaps?

[Spencervs]

What material would you recommend for insulating c1 and 3? Also yes I just checked them with a metre and they read at 2mh, though sold and labelled at 2.2mh

[Cobaltblue]

Paxolin, Perspex, even plywood will do.

Virtually any insulator that is stiff enough will suffice.

Cheers

Mike T

[Spencervs]

Thanks, as luck will have it, I had one layer of plywood about 2 or 3 mm thick which is now insulating the caps. I was thinking about the chokes, they are very small and when I got them, I worried they were incorrect. Though they do measure at 2-2.2mH and were advertised as radio chokes ... I assume it's ok?

Also front panel, what is the recommended? Aluminium, steel or some kind of plastic?

[snowman_al]

Aluminium. Easy to work and will help with the hand capacitance effect...

If that is what they measure the they should be fine. (Easy to mistake MilliHernry mH and microHenry uH.)