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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 10th Jun 2022, 10:34 am   #1
deliverance
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Default R1155 bias.

Hi all, I have a R1155 which has a 6V6 fitted in place of a DF valve a output transformer all is good there. I found a amp chassis with a mains transformer with secondary outputs of 300 0 300 5v and 6.3 at 5 amps . I am using a 5Y3GT rectifier with a choke and electrolytics . My question is how to achieve the bias required using the centre tap on the 300 0 300 output. I have seen diagrams for power supplies which include the 6V6 housed in the power supply but I don't need that as mine has that all ready in the 1155 . So I am a bit confused on the bias side . Any advice. On this would be appreciated cheers Chris.
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Old 10th Jun 2022, 12:07 pm   #2
ms660
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Default Re: R1155 bias.

Bias for what?

Lawrence.
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Old 10th Jun 2022, 12:20 pm   #3
deliverance
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Default Re: R1155 bias.

Thanks for that. Mods close this now thanks.
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Old 10th Jun 2022, 4:23 pm   #4
Hartley118
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Default Re: R1155 bias.

Powering the R1155 needs some care because of two things:

1. The HT voltage requirement (between HT- and HT+) is only 220V.

2. The HT- connection is separate from chassis 0V. The voltage drop across the internal bias resistors provides the bias voltage for gain control of the RF/IF stages. So you need a 'floating' HT supply of between, say 200V and 240V. Any higher is risky.

Your 300-0-300 transformer isn't I'm afraid a good starting point because you'll need either some big hot dropper resistors which will give a regulation problem or a further transformer of around 100 - 130V secondary to 'buck' the 300V in antiphase to achieve the required HT.

If you search for R1155 power supplies on this forum and elsewhere, you'll find lots of accounts of other peoples' experience. I confess that for my own set, I used a 75V transformer from the junk box along with a silicon diode voltage tripler. It's an unlikely creation, but it works just fine.

Martin
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Old 10th Jun 2022, 4:39 pm   #5
cathoderay57
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Default Re: R1155 bias.

Martin is spot on. For the one I built a few years ago, I used a 0-250v AC HT winding. I ditched the 6F6 that had been fitted as an audio output valve, and that reduced the HT current requirement to about 50mA. I used a semiconductor bridge of 4x 1N4007 and needed to insert a 2k 7W dropper resistor in the HT line. For audio I used a simple IC audio amplifier housed in the same box as the PSU which was probably a bad idea because I had no end of trouble getting the hum to an acceptable level. Without the 6V6 you will need at least 3A for the 6.3v heater supply. Jerry
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Old 12th Jun 2022, 3:50 pm   #6
deliverance
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Default Re: R1155 bias.

Thanks for the advice .
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Old 12th Jun 2022, 4:14 pm   #7
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Default Re: R1155 bias.

Closed as requested in post #3

Cheers

Mike T
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