Hi all,
Currently working on a Mullard (MAS1111), radio section works great, however the output transformer primary is open. What is a suitable substitute? I tried a 100v line transformer I had on hand, but was greeted with the most hideous high pitched squeal, so it either didn't like
the substitute or there is another fault in the audio section.

thanks
Darrin

was greeted with the most hideous high pitched squeal

Typically a symptom of negative feedback connection -- if present -- made on wrong end of output transformer winding, resulting in positive feedback which creates an unwanted oscillator.

Thank you GTC, reversing the connections resolved the issue.

cheers
Darrin.

Typical Philips, Mullard, You wire that feedback from the output transformer inverted and it will virtually come with a guarantee to Oscillate.

Of course, and so it should! Your negative feedback becomes positive feedback!

What else would you expect??

One expects this to be the revealing of a trap for young players.

Especially with Philips you need to understand negative feedback as that has been one of the things I get to sort out frequently. My 132L that was salvaged from a recycle depot; Was such a case some goose put a new speaker transformer in it and in the process, drilled the speaker cone, stuffing it.

The feed back wires were already disconnected, which rang alarm bells. I did conclude that is was disconnected because it oscillated.

Anyone who has replaced many output transformers has done this at least once.

As they say "you have a 50% chance of getting it right and 100% chance of getting it wrong"

Thanks everyone!