[ARC5] BC-454-B Power

[Brian Clarke]

Hello Michael,

 

The cold resistance of the heater strings is not a good indicator of heater wiring. All 6 tubes were rated at 12.6 V @ 0.15 A. So, for 24 V wiring, the hot resistance would be 56 Ohm; the hot resistance of 6 tubes with all heaters in parallel would be 14 Ohm. Another possibility is that the heaters were wired in parallel, and 6.3 V heater tubes fitted; that would give hot resistance of 3.5 Ohm. 

 

I have just measured the cold resistance of several tubes used in the BC-454 – average of 12.5 Ohm. So, cold resistance for 24 V wiring should be 8.3 ohm; if wired for 12 V operation, 4.17 Ohm. Even cold, 2 Ohm says you need to look for a short somewhere. 

 

Before undoing the screws to remove the bottom plate, try pulling one tube at a time – one or more may have internal shorts. Check the tube nomenclature. If that is inconclusive, remove the bottom plate and inspect the wiring strings between pins 2 and 7 of all tubes.

 

In summary, I certainly would not apply heater power.

 

73 de Brian, VK2GCE

 

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of MICHAEL BITTNER
Sent: Monday, 19 July 2021 10:52 AM
To: ARC5 at mailman.qth.net
Subject: [ARC5] BC-454-B Power

 

I recently acquired a BC-454-B (without dynamotor) that I suspect may have been wired for 12 Volt power.  The DC resistance across the dynamotor power input to ground measures 2 Ohms.  Is this normal for this receiver?  Shouldn't it be more on the order of 8 Ohms?

Thanks for any clarification that anyone might have on this.  Mike W6MAB

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