|
Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
|
Thread Tools |
23rd May 2019, 12:44 am | #1 |
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 361
|
Using a GDO
I have a Qmax gdo which i use every now and again in the usual way to check resonant frequency of a LC circuit,recently i have been winding some coils for a 625 line tv if strip and wanted to check them.In this IF strip as i understand it there are no parallel caps to tune the coils,this depends on the stray capacity of the valves.I get that but wanted to ask is it still possible to use a gdo to check the coils.The circuit is from the Mullard design for a 625 line experimental tv which was published in about 1960 using ef80s.I have built this before using the coil details from the book with good results,this time i am using smaller diameter coil formers hence the above query. Regards Graham.
|
23rd May 2019, 3:09 pm | #2 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,924
|
Re: Using a GDO
I cannot think of any reason why that method should not work. However, what might be a useful exercise would be to wind the coils, but before putting them in-circuit, stick one or two fixed capacitors across them (e.g. 5 or 10pF) and use the GDO to see where they resonate, and that will also tell you their inductance. Then when you put them in the circuit, you have some reference points. IIRC, the IF is about 35MHz?
B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
23rd May 2019, 8:18 pm | #3 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
|
Re: Using a GDO
Hi Graham, if you can see if you can find a Q meter; the Advance T2 is usually a good and reasonably priced buy. It goes up to 100MHz and will tell you all you need to know about your coils.
Ed |
25th May 2019, 12:18 am | #4 | |
Hexode
Join Date: Oct 2017
Location: Manchester, UK.
Posts: 361
|
Re: Using a GDO
Quote:
|
|
25th May 2019, 1:57 am | #5 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,924
|
Re: Using a GDO
Mmmm, I have never thought about how the capacitance in a valve RF circuit changes between being powered on or off, but I'm sure someone on here does!
B
__________________
Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch. |
25th May 2019, 10:10 am | #6 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
|
Re: Using a GDO
I've never heard of any specific requirement for the valve to be heated when doing GDO-measurements - not even in situations where in normal-use the grid will be driven hard so significant grid-current flows (class-C RF amps).
|