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Old 11th Dec 2018, 2:12 am   #41
radiograham
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Default Re: R1155 Power supply question

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Originally Posted by GW3OQK Andrew View Post
I think I showed competence when I modified my R1155 at the age of 15. I could afford no better receiver then, but the bandwidth was much too wide for CW on the amateur bands. DF valve positions became a q-multiplier to provide narrow band single-signal reception, and a 6V6 audio amplifier. To give full break-in working I modified the bias arrangements for muting by back-contact on key-up. A scrapped domestic wireless provided many parts. I passed the morse test, RAE, and had my licence at 17.

Now I'm 75 I don't worry what people might say about me.
73, Andrew
Well said Andrew.
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Old 11th Dec 2018, 2:23 am   #42
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Default Re: R1155 Power supply question

This is what i did about 1978,job done.
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Old 11th Dec 2018, 6:40 am   #43
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Default Re: R1155 Power supply question

Ed Dinning is the chap to speak to on here re the R1155 psu's he has made several for me over the years as well as T1154 psu's, a friend also made me a dummy load for the 55 psu's which i can send a picture off with details if you like??

Cheers Mike

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I did fit the DF meter and wiring myself but this is the last project done an R1155 psu with DF meter, variable HT and audio stage.
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Old 16th Dec 2018, 4:53 pm   #44
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Default Re: R1155 Power supply question

The radio is alive using the attached circuit modification
The radio powers up nicely and the output with the radio on is 205v
The audio is good
The Amplifier is very noisy though, even when nothing is connected to the radio
I thought it could be due to non shielded wires so i tested it without input wire and it is still doing some hiss
I have tried a 10uf electrolytic cap from. 1 to 8, also a 100uf electrolytic from 6 to ground. Nothing makes it completely disappear
I guess the lm386 is not as quiet...
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Old 19th Dec 2018, 8:50 am   #45
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Default Re: R1155 Power supply question

Another thing with the circuit above is that it neads audio line out attenuation. When driving the audio with the AVG setting on the radio, it delivers too much audio and there is a lot of distortion. In fact I have seen that the audio line coming from the radio actually drives a speaker on its own with no amplifier.

I used an "L" attenuation with 10k In series with the line out, and 1K to ground from the line out
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Old 20th Dec 2018, 8:40 am   #46
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Default Re: R1155 Power supply question

It is performing well I think. I have to fine tune the oscillation segment though

https://www.youtube.com/watch?v=_Iu0ZW4pEcI&t=5s

Thank you all for your kind help
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Old 20th Dec 2018, 1:47 pm   #47
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Default Re: R1155 Power supply question

Nice work Cesar.
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Old 20th Dec 2018, 3:26 pm   #48
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Default Re: R1155 Power supply question

Well done Cesar,


I've been following this thread with interest and am pleased that you got a good result. Sadly, you seem to have a very high local noise level - I wonder what you are using for an antenna?
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Old 20th Dec 2018, 3:42 pm   #49
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Default Re: R1155 Power supply question

Thank you Keith! Unfortunatelly I live in the heart of Barcelona City... It is a pain in the neck being a radioamateur here. I hooked a long wire antenna, about 16 feet long, the one I use for HF

regards!
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Old 31st Dec 2018, 3:58 pm   #50
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Default Re: R1155 Power supply question

Be careful with your power supply
the HT minus is NOT to chassis!!
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Old 31st Dec 2018, 4:01 pm   #51
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Default Re: R1155 Power supply question

The July 1946 modification of the r1155 was definitely the best way to go and you had a reply containing this in pdf format, stick with it, perfect, I used this several times on these sets with no problems, still have one.
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Old 31st Dec 2018, 4:03 pm   #52
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Default Re: R1155 Power supply question

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Be careful with your power supply
the HT minus is NOT to chassis!!
Hello! What do you mean? I did not connect the chassis to anything i guess. The only ground i see coonectes to the chassis of the psu is the speaker i guess, as it touches the case.
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Old 31st Dec 2018, 4:59 pm   #53
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Default Re: R1155 Power supply question

Where people typically get tripped up by this requirement to keep the HT negative separate from chassis is in the use of electrolytic smoothing capacitors in aluminium cans.

Most of these have the negative side of the capacitor connected to the aluminium case. So if you then mount that capacitor directly to the chassis of your power supply, the HT negative will automatically be connected to chassis too. Then you have a problem.

Of course its very easy to overcome. Just use electrolytic smoothing capacitors in insulated cases - as indeed most are these days. The problem usually arises when someone digs out one of the old style electrolytics from their junk box......


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Old 31st Dec 2018, 8:13 pm   #54
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Default Re: R1155 Power supply question

My R1155 came with a power supply and the remains of some wiring. Having sorted it out somewhat, I found a significant problem was that the audio ground is shared with the heater ground. The several amps of 6.3V AC heater current creates a noticeable voltage drop in even a fairly heavy-gauge wire, and thus appears in series with the audio output. This gives terrible hum on the audio. Running a separate audio ground to the receiver only helps if there's no mains earth anywhere else in the system - the heater return is also chassis and thus the safety earth on the R1155, so the conditions for an earth loop are perfect.

Has anyone else come across this problem and solved it? The best fix I could think of was to add an audio isolating transformer in the cable to the Jones plug which fits the receiver. I'm trying to leave the receiver unmodified. I suppose taking a pair of wires from the receiver's audio output and its chassis and then feeding that to a transformer or differential amplifier at the audio amplifier would also work.

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Old 1st Jan 2019, 12:29 pm   #55
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Default Re: R1155 Power supply question

Chris, it's ok if you have 6.3v DC on the heaters, as for the T1154, but unfortunately I did same as you for a latest psu. I did use a screened cable for the audio line although I know the screens get joined to the same place. There is a moderate hum, certainly not terrible. A transformer at the amp end would have been a good idea.

I included a switchable parallel LC circuit to peak audio at about 700 Hz for CW and that takes out all hum. I could experiment with a switchable 50Hz notch filter if I could find a suitable small size L.
73, HNY
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Old 8th Jan 2019, 5:06 pm   #56
James Duncan
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Default Re: R1155 Power supply question

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Originally Posted by CesarLG View Post
Hello!
I am building it up from a diagram I found on this forum published by Radio_Dave (thanks!).
I see pin 5 is sharing 2 wires... one is the audio wire. Is it fine?

thank you!
Just be aware the HT neg does NOT go to chassis.
your amp will not be as good as the standard 6V6, stick to the well proven mods on these sets.
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Old 8th Jan 2019, 5:12 pm   #57
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Default Re: R1155 Power supply question

Quote:
Originally Posted by CesarLG View Post
Quote:
Originally Posted by James Duncan View Post
Be careful with your power supply
the HT minus is NOT to chassis!!
Hello! What do you mean? I did not connect the chassis to anything i guess. The only ground i see coonectes to the chassis of the psu is the speaker i guess, as it touches the case.
Look at the R1155 circuit and you will se the HT neg floats above chassis, this is due to the bias arrangement
If you connect your power supply HT Neg to chassis and the pos to HT line you will not have bias
see attached circuit.

http://www.tuberadio.com/robinson/mu.../R1155bias.gif
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Old 8th Jan 2019, 7:46 pm   #58
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Arrow Re: R1155 Power supply question

Quote:
Originally Posted by cmjones01 View Post
My R1155 came with a power supply and the remains of some wiring. Having sorted it out somewhat, I found a significant problem was that the audio ground is shared with the heater ground. (And various problems thus arising).
► Text in blue added by me: keeps the quote short, but relevant.

Although it was many decades ago when I owned an R1155 and made various modifications to it, I very vaguely recall that I rewired the heaters so that they were above ground. Why did I do that? Too long ago: can't remember!

Al.
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