[ARC5] BC-453 B dynamotor hum

Kenneth G. Gordon kgordon2006 at frontier.com
Sun Nov 1 11:30:24 EST 2015


On 1 Nov 2015 at 15:24, J Mcvey via ARC5 wrote:

> The problem only occurs when the radio gets warmed up.
> Uh-oh could this be a bad output transformer arcing internally? There isn't much
> else to the 12a6 circuit! HELP!!!

Hmmm....I too have yet to find a "bad" 12A6. 

But audio transformers are one of the particularly unreliable elements in the 
ARC-5 receivers, so that is a possibility. In fact, in my hacked-up pile of 
rejects, bad, or completely missing, audio transformers show up regularly. I 
would guess that at least 1/3 of the receivers I have here have bad audio 
transformers.

However, one of the easiest and quickest checks you can perform is to 
simply try a new 12A6. Doing so would eliminate that from concern.

Do you have any extra 12A6s? If not, I can send you one. I have a box of 
NIB tubes for the receivers which I received in that estate that was given to 
me many years ago. The only tubes in that pile which are "rare" are the 
12SF7s....of course... :-(

Ken W7EKB


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