Class A or AB

[nzst205]

Thanks Ian, I guess the DCA is good for determining that they do at least work at low voltages. Thanks for your detailed explanation.

 

[restorer-john]

As Ian points out, the only real way to determine and match parameters is a curve tracer. I was fortunate to pick up a classic Leader LTC-905 for peanuts that has helped me immensely over the years, particularly with high voltage breakdowns on transistors which cannot be determined with a DCA or DMM or cheap eBay do-it-all unit.

It's a pain to set up, interpret and use, but, seriously, I wouldn't part with it. When you find RETs that breakdown at 100v but are fine below or bodgy FETs that throw curves all over the place. The A-B matching switch is awesome for matching.

It was a relatively inexpensive attachment to a CRO.

 

[nzst205]

Tks John, I've seen a Leader LTC-905 on eBay for $NZ150 but freight at $NZ 190. What would one expect to pay for one of these do you think ?

 

[restorer-john]

Mate, I've seen them at all sorts of prices, from $50 to many hundreds in online sales. I paid $15, complete with the hard to find in circuit probe (it's a triple sharp tipped spring loaded pen like attachment) and a set of normal leads. That was years ago at a flea market and I haven't seen another in the flesh since. Old test gear has disappeared from boot sales and flea markets as the old techs retired/died off I reckon 🙂

It's a relatively simple piece of gear, but hard to DIY due to the multi-tapped transformer used for the sweep voltages. I can send you the schematic if you'd like to look at a DIY option maybe?

John

 

[nzst205]

John, Would appreciate that, I've had some luck getting really good multistep transformers out of Poland, so might give it a go.