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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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22nd Aug 2017, 12:18 pm | #1 |
Hexode
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 440
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R1155 psu
Hi,
In the R1155 psu circuit here: http://www.vintageradio.me.uk/milita...2/R1155psu.gif What is the function of the 5K 25W variable resistor? Is it really necessary? Don m5aky |
22nd Aug 2017, 12:25 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: R1155 psu
The 1155 circuit needs a negative bias voltage for certain valves - this is developed by way of a resistor in series between the -ve output of the PSU and the radio's earth (the WWII-vintage AR88 receiver does the same thing).
In some 1155s this resistor is fitted internally, in some it's in the power-supply. The value of it (irrespective of where actually fitted) can need changing if, for example, your 1155 has had something like a 6V6 audio-power stage fitted in place of one of the DF valves (a very common, and worthwhile 'mod' that was popular in the 1950s/1960s). |
22nd Aug 2017, 12:52 pm | #3 |
Hexode
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 440
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Re: R1155 psu
Hi,
Thanks for the reply. I think in my case the bias resistor is in the receiver as the existing, rather large, psu which I am replacing does not have a resistor. The DF valves are still in the 1155 and I will be using the 6V6 amplifier as shown. 5K 25 Watt pots are not that common these days. Don m5aky |
22nd Aug 2017, 4:01 pm | #4 |
Hexode
Join Date: Oct 2007
Location: Bristol, UK.
Posts: 440
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Re: R1155 psu
Just found a previous thread of a few years ago that I'd completely forgotten about.
Looks like in this case it's not essential. Don Last edited by vosperd; 22nd Aug 2017 at 4:20 pm. |
22nd Aug 2017, 4:41 pm | #5 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,510
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Re: R1155 psu
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22nd Aug 2017, 4:54 pm | #6 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: R1155 psu
One of the Naval versions I recall seeing inside while at a joint Army/Navy summer-camp near Folkestone in the mid-70s had the bias resistor in the power-supply rather than in the receiver itself. It also used circular metal-shell plugs/sockets for the interconnecting cables - like the ones used on the TCS-series of naval radios - rather than the traditional Jones plugs.
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22nd Aug 2017, 6:22 pm | #7 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,510
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Re: R1155 psu
Very odd! Presumably 'locally modified' for some reason, so arguably not really an R1155 at all any more!
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