Silvertone 1484 OT #4

[Mick Bailey]

I only mention the glazed ceramics because that's what I have in stock. They're smaller in size and weight compared to a regular cement resistor - important sometimes if space is tight or the speaker socket is mounted on a PCB. Otherwise no difference at all.

[Helmholtz]

..is there anything here that could conceivably cause the multiple blown OTs? Bad choke? As mentioned, the screens are sitting 100V or so below the plates, which looks to be the intention of the design

I don't see how a bad choke could harm the OT.

The main risk for an OT is the high induction voltage generated if either the primary or secondary current is suddenly interrupted.
So also check the power tube sockets and contacts.

Some excellent information here: https://dalmura.com.au/static/Output...protection.pdf

[mhuss]

I wire a protection resistor across the speaker output with some amps. Not low enough to significantly affect the impedance, but enough to prevent oscillation if the speaker is disconnected. Usually a 7W or 10W glazed 220R wirewound (the small-bodied green glazed ones). I think it was pdf64 that put me onto this quite a few years back. It's 'fixed' a few problem situations over the years where I was convinced the speaker was getting disconnected.

I've been doing for a long while - cheap insurance.

[LarBal]

I don't see how a bad choke could harm the OT.

The main risk for an OT is the high induction voltage generated if either the primary or secondary current is suddenly interrupted.
So also check the power tube sockets and contacts.

Some excellent information here: https://dalmura.com.au/static/Output...protection.pdf

That was a great read! Thanks. I took all the advice in this thread and safeguarded the amp, and got a HRDlx OT in there yesterday, amp sounds great, no issues so far. I'll rewire the original cab today and hopefully put this one to rest. Thanks for the help y'all.