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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 26th Jun 2022, 2:49 pm   #21
Spencervs
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Default Re: 3 Tube Ocean Hopper (battery type)

So I used some plywood to insulate the caps and a new choke but when I attached the 45v battery, the same issue happened a sudden hiss and a plume of smoke. Perhaps the wood is damp and needs a few days? Or do we think it's more sinister? If someone would be kind enough to check my wiring, I would be most grateful!
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Old 26th Jun 2022, 3:27 pm   #22
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Default Re: 3 Tube Ocean Hopper (battery type)

Spencer,
Remove the coil.
Use your meter on resistance, ohms, and check C3 is not shorted - fixed vanes to moving vanes. Should be open circuit.
If that is good now check both sides of the capacitor C3 to the chassis / GND.
The choke side should read 50K (the resistance of the pot) with the choke in circuit and the 'coil' side should be open circuit (O.L)

The pictures are very difficult to make out.

Question, why did you choose this design and are there any constructional notes that go with it? Or a site we can see the whole thing. It has a number of 'gotchas' for the novice unfortunately.
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Old 26th Jun 2022, 10:04 pm   #23
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Default Re: 3 Tube Ocean Hopper (battery type)

Ah your help pays off again, the vanes are indeed shorting on both caps. I'm unsure if there is a way to clean them perhaps? No idea why they are shorting, but I suspect that this must be the issue.

I don't particularly know why I chose.it, I seemed to have a lot of the little components and it seemed not overly hard to make but a challenge for a novice like me where I could learn a lot. In hindsight, I should have picked a two tuber. The book I have which features it is linked below (page 9):


PDF for How to Build Radio Receivers

It is also featured on pages 11 and 29 in this magazine too 10 years.earlier in 1940:

PDF Radio and Television Magazine

Last edited by Spencervs; 26th Jun 2022 at 10:11 pm.
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Old 27th Jun 2022, 7:38 am   #24
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Default Re: 3 Tube Ocean Hopper (battery type)

There is sometimes a screw at the opposite end od the cap to the shaft, this will centralise the vanes. Outer vans sometimes get bent.
A close inspection should help solve the problem

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Old 27th Jun 2022, 10:07 am   #25
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Default Re: 3 Tube Ocean Hopper (battery type)

Can you take a picture of the caps? Better out of the set if possible.

It might be time to look at alternative circuits too. Practical Wireless and Radio Constructor did lots of 1, 2 and 3 battery valve TRF circuits (often using the 1T4 / DF91.) They at least gave a layout and more detailed explanation of what where why etc.. Much easier to follow than invent! And the variable caps use the chassis as a connection!
This is just an example http://vintageradio.me.uk/radconnav/2_valve.htm

PW and RC are archived on the Worldradiohistory.com site.
PW here https://worldradiohistory.com/Practi...s_Magazine.htm
RC here https://worldradiohistory.com/Radio_...r_Magazine.htm
Worth a trawl through.

It is a pity that Denco Green coils are so expensive or there are standard TRF circuits that are listed...
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Old 27th Jun 2022, 1:20 pm   #26
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Default Re: 3 Tube Ocean Hopper (battery type)

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Originally Posted by Spencervs View Post
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?

Thanks,

Spencer
That's one 100pF trimmer for each coil then.

I assume that the intention was to use that bandset trimmer when initially setting up each coil, to adjust its capacitance with the bandspread capacitor at the centre of the dial so that you can then tune the desired range either side of that central pre-set frequency. Having set the trimmer, it would then be left alone. (Rather like aligning a superhet front end).

If all six coils were wound, that would need six 100pF trimmers, one for each coil. On the circuit diagram, they used the legend for a variable capacitor which is a bit misleading, when in the UK, that would generally be depicted as a pre-set trimmer.

I'm a bit puzzled as to the vanes of the capacitors shorting out.

Apart from the 100pf trimmer, there are three variable capacitors in the circuit, each 35pF, (which, apart from the aerial trimmer seem unusually low values). Ordinarily, for such a low capacitance, I'd expect to only see a few vanes - maybe five fixed and four moving - with a reasonable air gap between the vanes, hence, with little risk of shorting.

As to the 2.5 mH RF choke, originally they would no doubt have used a 'pi wound' choke, typically with four piles such as the ones depicted below. They appear from time to time on eBay, but not at sensible prices.

I wonder if any forum members might have any in their spares boxes? (None in mine).

This video on RFCs is instructive:

https://www.youtube.com/watch?v=6LlcRENlnrY

Good luck with the project Spencer.
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Old 5th Jul 2022, 10:14 am   #27
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Default Re: 3 Tube Ocean Hopper (battery type)

Excellent, thanks all. So I have had a look and managed to insulate everything much better. I don't get shorts now and the valves have been replaced. I am not getting any life though and I have an interesting observation that 40v seems to be going direct to my headphones which doesn't seem healthy. Perhaps I have wired this incorrectly? The 40v goes to the tip of the phones. Perhaps I need specific headphones? Or maybe an incorrect piece of wiring.
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Old 5th Jul 2022, 12:46 pm   #28
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Default Re: 3 Tube Ocean Hopper (battery type)

You are correct there has to be 40+ volts on one side of the phones, it is connected to the battery. The phones are the anode load of the 1S4, remember they have to be high impedance types 2000 to 4000 ohms. Or you need to pop an output transformer in their place and use low impedance phone off the secondary... Anther gotcha with these circuits.
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Old 5th Jul 2022, 2:05 pm   #29
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Default Re: 3 Tube Ocean Hopper (battery type)

Of course, both sides of the phone socket Have to be isolated from the chassis / ground, or you short the battery down through the phones...
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Old 5th Jul 2022, 11:39 pm   #30
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Default Re: 3 Tube Ocean Hopper (battery type)

Hi alan, does it really need crystal headsets? The circuit diagram suggests that magnetic phones are called for. But there is a special set up for crystal sets.
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Old 6th Jul 2022, 7:23 am   #31
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Default Re: 3 Tube Ocean Hopper (battery type)

Ahh hang on, just looked into things a little and older magnetic phones were of higher impedance to our modern equivalents. So this must be why? That would make sense. Now I'm wondering where to find some suitable headphones!
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Old 6th Jul 2022, 8:05 am   #32
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Default Re: 3 Tube Ocean Hopper (battery type)

If you have a Single ended transformer tucked away for say a ECL86 or similar, use that, put the primary where the High impedance headphones would go and listen across the secondary/normal speaker output.
It's what I did when I built a 1920/1930 style radio, as I did not want HT by my ears.

An old output transformer from a valve picnic radio, or even a small mains to 6 or 9 Volt transformer around 100mA may be worth trying.

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Old 6th Jul 2022, 9:50 am   #33
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Default Re: 3 Tube Ocean Hopper (battery type)

Quote:
Originally Posted by Spencervs View Post
Ahh hang on, just looked into things a little and older magnetic phones were of higher impedance to our modern equivalents. So this must be why? That would make sense. Now I'm wondering where to find some suitable headphones!
They are magnetic and were typically 2,000 Ohms impedance.

(Not to be confused with 'crystal earpieces').

Sometimes they're 1,000 Ohm wire in series, sometimes both are 2000 Ohms wired in parallel.

They crop up from time to time often not tested and found to be in need of rewinding doe to 'green spot' corrosion

There are two coils on a 'pole-piece' in each earphone. Sometimes just one of the four will be defective.
They can be rewound by hand, but it's a bit tedious and that takes you down another 'rabbit hole' away from your 'Ocean Hopper' project.

Best to buy a tested pair, but they're not especially cheap. There's a pair for sale here:

https://www.amateurradiosales.co.uk/...hones-2000-ohm

Two pairs untested here 'Buy it Now/Make an Offer':

https://www.ebay.co.uk/itm/363894979...IAAOSwcXxh~69l

Maybe a forum member has some they'd be willing to part with?
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Old 6th Jul 2022, 4:17 pm   #34
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Default Re: 3 Tube Ocean Hopper (battery type)

As the currents are fairly low here, one of the LT700 type output transformers will give reasonable results here too. Some of the newer high impedance headphones are actually low impedance ones with a built in matching transformer, so the LT700 approach will give much the same performance.

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Old 13th Jul 2022, 3:39 pm   #35
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Default Re: 3 Tube Ocean Hopper (battery type)

So a little update! I have got a set of high impedance headphones and not only do they work, but I am getting something from the set!

When I turn the regeneration control, I do get the hiss but no squeel. In fact, when I go to high, the hiss increases then goes away. Also, adjusting C3 doesn't do anything it seems and I have a microphonic valve. Presumably my dl91?

Perhaps I need to set my handset condenser first?

Any extra tips would be fantastic!
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