Repairing a HK1400 Amplifier

[Alistair D]

I totally agree that limiting the current available on the LT side of the mans transformer is the way to do it.

A mains lamp limiter was mentioned in post #5 so it was worth mentioning a potential pitfall of using it.

Al

[Murphyv310]

Remember the Sony 27PS1?
The PSU on these were prone to blowing up and Sony supplied a kit. The instructions clearly stated "Under no circumstances use a variac" If you did the PSU blew up again.
As Inspector Clouseau said to Kato.............. beware of the humph.

[Mark Hennessy]

A mains lamp limiter was mentioned in post #5 so it was worth mentioning a potential pitfall of using it.

Yes, but when you read the whole post, it's clear that I'm suggesting that as a last resort. "Just do something - anything!"

The case you linked to earlier was an interesting read - I didn't follow that one at the time. I haven't read the whole thread - it runs to 101 posts - so I didn't get to the point you were making. The page numbers you suggested don't help, as I've changed the settings to give me 50 posts per page, and can't remember what the default is - but give me some post numbers and I'll take a look.

Either way, it's relatively unusual for a mains lamp limiter to cause problems with the basic power amplifier circuit IME. And whatever happened, it's surely preferable to toasting the replacement output devices?

Chaps, can we leave the infamous Sony sets out of this as they are completely OT - start a new thread if you wish to remember the "joys" of them. Thanks.

Mark

[ppppenguin]

In general a mains lamp limiter is, at worst, harmless. In many cases it can save a lot of anguish and magic smoke. But there are exceptions as Trevor has noted.

More generally there are some switchmode PSUs that work OK around 110V and 220V but change their operating mode at some voltage in between. Never use a variac on one of these. Not sure what a lamp limiter would do.

If you have the misfortune to be working on some blown up kit which has one of these PSUs then you really want to use a bench PSU to power it for test purposes.

For us vintage enthusiasts we're almost always dealing with pure linear PSUs

[Alistair D]

The case you linked to earlier was an interesting read - I didn't follow that one at the time. I haven't read the whole thread - it runs to 101 posts - so I didn't get to the point you were making. The page numbers you suggested don't help, as I've changed the settings to give me 50 posts per page, and can't remember what the default is - but give me some post numbers and I'll take a look.

Posts 78 to 88 cover the fact that even after the amp was fixed it would not start on the limiter even with 2 bulbs adding up to 160W.

Al

[Mark Hennessy]

Thanks. I read all of page 1 (the first 50 posts), but not page 2.

Looking at the schematic, this amp is largely very conventional, but the biasing arrangements are a bit unusual. From a Google Image search, I see "Non Switching Amp" emblazoned across the front panel, and I guess that explains the complexity. Presumably it ensures that neither power transistor can turn off completely while the other one is supplying current to the load, but it's too late in the day for me to think too much more

But, it's perhaps not surprising it has some issues at power-up. There's always an exception to the rule!