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Old 17th Oct 2018, 9:49 pm   #61
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Quote:
Originally Posted by Skywave View Post
So this receiver is a Chinese product and the original title (in Chinese) has, presumably, been translated into English. However, one must be cautious of such translations: the Chinese have a tendency to use certain adjectives to make their products sound exciting, typically by inserting the word 'super' (or the Chinese near-equivalent for that word) in their product description.
As in Super duper regenerative receiver for example.

Regards,
Symon

Last edited by Philips210; 17th Oct 2018 at 9:54 pm.
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Old 17th Nov 2018, 5:23 pm   #62
regenfreak
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

I bought one a while back. I am sure I put everything and the coils correctly. It was a dead circuit. I made many valve AM regen receivers before, every one of them worked. Maybe the chinese kit is junk
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Old 23rd Dec 2018, 11:59 pm   #63
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

I have finally got around to having a look at the 1A2 kit and must say that I'm confused about the orientation of coils U2 and U3. Initial checks on the tuning capacitor suggest it is somewhat higher in value to the specified 2-10pF.

I've been having a search around on the internet this evening and found a reference to the kit here https://www.youtube.com/watch?v=GwYuaTp7F4o (read the replies) and in that link the chap refers to this link https://www.youtube.com/watch?v=Z5GKsWtMT7w and amazingly, he actually gets this little kit working by making a change to one of the inductors.
Also, looking at his revised circuit diagram in the video, he has made a number of circuit changes.

I note the positioning of the aerial coupling coil and tuning coil. This has given me more confidence to proceed further with the kit over the Christmas break.

Regards
Symon.

Last edited by Philips210; 24th Dec 2018 at 12:10 am.
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Old 24th Dec 2018, 12:23 am   #64
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

Further to my previous post, reference is made in the video concerning the 33uH RF chokes. He does away with the supplied chokes and winds his own on a plastic former. I checked my 33uH chokes and they appear to be low in value, approximately 20uH. Other circuit changes include replacing the 100pF capacitor (the one in parallel with the 5.1M Ohm resistor) with a 1nF type. The 20k pot appears to be replaced by a 2k resistor. The aerial coupling coil is replaced by a twisted wire capacitor, coupling the signal direct to the lower end of L2.

There is some confusion with the coil reference numbers. In some kits the aerial coupling coil is L1 and in others is U2.
Also, the tuning coil is referred to as L2 in some kits but U3 in others.

Regards
Symon
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Old 24th Dec 2018, 7:39 am   #65
Neil Purling
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

So... They do work. Just not with the parts they supply.
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Old 24th Dec 2018, 1:12 pm   #66
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

Yes, I was quite surprised to see the kit working albeit slightly modified. So rather surprisingly, the 1A2 should be OK for Band 2 frequencies.

The interesting thing about the kit is its outstanding quality through-plated hole PCB and it begs the question why make such a decent PCB if the circuit as it stands is not viable? I still think it may be possible therefore to get the original circuit working. I think part of the problem may be out of spec coils and the tuning capacitor. My 1A2 valve has considerable green corrosion on the pins but hopefully will clean off. The supplied valve holder is a decent ceramic type, nothing but the best, for low losses etc.

I've downloaded the Youtube video and I'm going to follow it carefully.

Regards
Symon.
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Old 24th Dec 2018, 10:33 pm   #67
Neil Purling
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

There is some hope for the kit, which is good. But it ought to have an advisory that it is only for someone with experience of working with fabricating tuned circuits at Band 2 frequencies.
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Old 26th Dec 2018, 11:16 pm   #68
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

I've been assembling the 1A2 radio kit and something that I noticed is there's an error in the PCB copper foil pattern. This concerns the tuning capacitor. The required capacitance swing is 10 to 20pF but with the supplied PCB, and the tuning cap as connected, gives 20 to 40pF, so would tune below normal Band 2 frequencies. A cut is made to the copper foil on the central connections and a link is applied on the other end of the tuning cap (see attached pics). So in summary, the required connections to the tuning cap are to the end connections only, the central connections being isolated.

I decided to mount the aerial coupling and tuning coils on the solder side of the board as there's lack of space on the component side unless they're mounted higher off the board. As this is a VHF circuit, short lengths of any connections are preferable so a good reason to mount the coils close to the board. As a consequence of mounting the coils on the solder side, the tuning cap is also mounted on the solder side otherwise the tuning cap knob will foul the coils.

I used a few 0.1" 2-way connectors for the LT and HT battery supplies and the aerial connection. I hope to try out the circuit in the coming days.

Regards
Symon.
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Old 27th Dec 2018, 12:23 am   #69
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi

Please disregard the info I gave in the previous post regarding the tuning capacitor, I've confused myself over the required value which should be 2 to 10pF according to the circuit diagram. I am not sure how this can be achieved with the supplied cap, not to mention stray capacitance as well. I may use an air-spaced Jackson type for initial tests.

Regards
Symon

EDIT: Maybe the trimmer caps on the tuning cap may be the answer. I'll have a look tomorrow. S

Last edited by Philips210; 27th Dec 2018 at 12:32 am. Reason: Additional info
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Old 27th Dec 2018, 10:14 pm   #70
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

Sure enough, by carefully adjusting the two trimmers on the tuning cap to near minimum, the tuning cap swing is approximately 2 to 12pF which I'll settle for. The tuning coil will be 'adjustable' by compressing or expanding it slightly to attain the correct frequency coverage. I suppose I could try using the GDO to assess the coverage.

I'll report back when further progress is being made.

Regards
Symon.
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Old 30th Dec 2018, 5:05 pm   #71
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

I have made some progress with this kit and can report actually getting it to work after a fashion.
First off, the tuning cap as supplied needed its trimmers set to near minimum. As previously mentioned, there is an error on the PCB regarding connections to the tuning cap. The rest of the circuit was built as per the circuit diagram. The two 33uH RF chokes were replaced with some better ones that I had to hand.
The 100pF capacitor was changed for a silver mica type that I had available and fits the board without reshaping the leads.

On testing, all that I could get was a faint whistle and little else.
I changed the 1A2 valve for a new Pinnacle DK91 and it started to work. The setting of the 20k pot is critical as it starts to oscillate if advanced too far and could cause a nuisance to other radio users as the super regen circuit behaves like a transmitter. The tuning cap adjustment is also quite critical and hand capacitance effects are a problem. The audio is somewhat distorted but at least the circuit can work so I'm pleased that I have got this far.

Regards
Symon.
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Old 30th Dec 2018, 5:39 pm   #72
VT FUSE
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Well done on a tough project.

As an early doubter that the (1939 origin 1R5) clone, 1A2 freq changer may function at fm broadcast freq's,it may be timely for me to head off and stew a hat to eat at my leisure!
I guess, but cannot remember, that the 1A2 must be pentode strapped here?

With the dogged perseverance displayed it can only be a short time until at least one of the four 25kW fm transmissions from Redruth's Four Lanes transmitter is monitored clearly,in fact the whole board is probably overloaded due to high field strengths and possibly moving a little further distant when testing may prove this?

Doubtful if the weak re-radiated oscillation would trouble anybody in such a strong signal field.

Mike
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Old 30th Dec 2018, 6:27 pm   #73
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi Mike.

I'm not really sure about the configuration of the 1A2 pentagrid valve but it seems a miracle it is able to work at broadcast VHF frequencies. So far though, I haven't been able to get to work above 102MHz and it was really struggling at that frequency. My experiments with the aerial found that about 48" was OK for the lower end of the band and about 18" for the upper end.

For the HT supply, I used my excellent 90V battery valve PSU https://www.vintage-radio.com/projec...y-set-psu.html

One thing that does need looking at is the operation of the 20k pot. There needs to be finer control over a more limited range. Also, the tuning capacitor would benefit from being an air-spaced type and a parallel low value variable cap for bandspreading and hence fine control. These would need to be fitted with longish spindles to mitigate hand capacitance effects.


One thing is for sure, there's no way the circuit will work as the supplied PCB has an error on the foil layout and the setting of the trimmer caps on the tuning cap need to be set up. I'm sure many people have been disappointed with this kit but it can work with a little bit of attention to the points mentioned. It's a pity there aren't any proper instructions with the kit. Also, I think the 1A2 valve as supplied is duff. It had corroded pins so wasn't a good sign. The heater is OK, maybe it has an impaired vacuum. I'll have to dust off my AVO VCM Mk3 and see what it says.

It's been an interesting little project and when time permits, I'm going to see if further improvements can be made.

Regards
Symon.
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Old 30th Dec 2018, 7:20 pm   #74
VT FUSE
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi Symon

My trusty Type G RAF cloth flying helmet has been selected for the slow cooker.

Wiki states: Redruth Four Lanes Transmitter site has the following high power senders (Arqiva) R2 89.7 mHz , R3 91.9mHz , R4 94.1mHz & R1 99.3mHz.
These are quoted as 25kW but goodness knows what the EIRP from these would be in reality? the field strengths from all of these freq's falling within a 10mHz width would challenge a Superregen Rx configuration,not known for any resemblance of selectivity but high in sensitivity.

Without back reading the posts,I am sure the 1A2 was pentode wired.

A write up would be of interest once you have endowed it with a life as we know it-relative to radio listening.

A quantitative AVO test of the 1A2 Vs DK91 would be interesting.

ps. Just read back to post no.33 and it seems that I (luckily) did not suggest that my hat would be eaten if/when proven wrong!

Regards

Mike

Last edited by VT FUSE; 30th Dec 2018 at 7:37 pm. Reason: addition-ps.
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Old 30th Dec 2018, 10:05 pm   #75
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Quote:
Originally Posted by VT FUSE View Post
My trusty Type G RAF cloth flying helmet has been selected for the slow cooker.
Ha Ha.

Mike, I have had another look at the 1A2 and found that I hadn't sufficiently cleaned off the green corrosion. After a thorough clean, I tried this valve and lo and behold it is serviceable after all. I will try to get my Avo VCM out tomorrow and compare with the DK91. One thing that is evident with the 1A2 is that it seems more microphonic compared to the DK91.
For better stability, I think the circuit would benefit from being mounted in a screened box.

Regards
Symon.
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Old 30th Dec 2018, 10:38 pm   #76
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

One other small point I noticed, there's a difference in the heater current between the two valves:

1A2 31.5mA

DK91 50mA

This should not be the case as the 1A2 heater is meant to draw 50mA. I wonder why it's on the low side.

Regards
Symon
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Old 30th Dec 2018, 10:46 pm   #77
VT FUSE
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Yep- the 1A2 is the" low consumption" fil equiv of the DK91,rather like DK91 Vs DK96, 0.025A versus 0.05A,there seems to have been a little East/West variation on nomenclature and also fil technologies,Philips in Holland worked very hard back in 1953 to increase the work efficiency of the oxide draw coated fils in order to halve LT consumption.The other eastern b7g RF valves were in truth around 0.031-0.033mA rather than our 0.025mA series.

This green corrosion product results from long years stood on pins in damp cardboard multi compartment boxes usually in damp storage.

Thanks for info on radio.

Cheers

Mike

Last edited by VT FUSE; 30th Dec 2018 at 10:54 pm.
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Old 31st Dec 2018, 12:24 am   #78
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Thanks Mike for confirming the heater current of the 1A2.

Regards
Symon
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Old 31st Dec 2018, 12:32 am   #79
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Hi.

OT I know but there's an interesting 2-valve VHF super regen project in January 2019 PW magazine. It uses a ECC81 and EF91. Looks a good project to build.

Regards
Symon.
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Old 15th Apr 2019, 3:28 pm   #80
Philips210
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Default Re: Chinese 1A2 Super Regenerative FM radio kit

Quote:
Originally Posted by VT FUSE View Post

This green corrosion product results from long years stood on pins in damp cardboard multi compartment boxes usually in damp storage.


Mike
Hi.

Yes, that's understandable. I've also seen severe corrosion on valve pins in Mullard boxes that use the plastic "Kradlepack" packaging.

I tried an experiment to see how well valve pins corrode if the valve was left outdoors. Back in 2010 I put an old B9A type valve (possibly a 6F22 from a GEC TV) out in my garden. I retrieved it a few months ago and was amazed to see virtually no corrosion on the pins.

Regards
Symon
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