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Homebrew valve tester

 
Posts: 706
Joined: Sat Jan 07, 2012 10:21 am
Location: Sleaford lincs

Homebrew valve tester

Post by Dr Wobble » Tue Apr 07, 2015 9:58 am

Someone kindly gave me a heavy metal box some time last year and have finally got round to building a simple valve tester. It has two HT PSU's using a IRF740 mosfet 0 - 300v, a heater supply switched between 5,6.3,12.6 and adjustable @ 2.5A at a push using a LM317AVH. I've used whatever bits I had apart from the two big pots I got from Birkitts to adjust the HT, at £2.50 each I'm well happy. Sere pic.

For testing rectifiers I'll put the VT on my isolated variable supply for the ac and I've wound a few turns round an existing transformer to give me 5v @ 3A ac.

As you see I've used a jumper panel to switch anode, cathode etc between pins. The amp meter can read either up to 20mA or 100mA, I prefer digital meters but as I had the old panel meters, I used them. I have another HT PSU to make amd some wiring up of the front panel but that's about it. If I get time I will wind a proper transformer, but it will do the job for now.

Andy.
Attachments
VT 2 .1.jpg
Big 10k 70mA pots from Birkitts.
VT 2 001.jpg
HT and Heater PSU
VT 2 002.jpg
Front panel minus screen meter and heater meter-in post.

 
Posts: 209
Joined: Mon Jun 04, 2012 11:40 am
Location: Newcastle on Tyne

Re: Homebrew valve tester

Post by Ed Dinning » Tue Apr 07, 2015 9:10 pm

Hi Andy, looking at you layout, you may need to beware of the rather long leads to the regulators, as this may cause oscillation and instability.

Ed

 
Posts: 706
Joined: Sat Jan 07, 2012 10:21 am
Location: Sleaford lincs

Re: Homebrew valve tester

Post by Dr Wobble » Wed Apr 08, 2015 8:51 am

Do you mean the two TO220's? They are TIP3055's there to boost the current.; it's not the best layout for sure, but havn't had a problem with similar in the past. I know a few people had problems with oscillation on the Sussex and had to put ferrite beads on the leads.

The heater board got filled with caps as I had to use 4 1000u 50v leaving no room for the power transistors, as I had no big 63v caps. The sec winding off the tfmr is 58v.

Andy.


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