Where to get valves tested in Essex, UK - Page 1
Forum section: electronics / beginners

author: Specmaster
author_rank: Super Contributor
timestamp: August 16, 2017, 11:58:29 pm
content: I wonder if the UK lads can tell me where in Essex I could take some valves to be tested? I have just got a Marconi TF995A/5 and I think some of the valves are dodgy as it misbehaves sometimes and RF out is way down, Thanks in advance.

author: CJay
author_rank: Super Contributor
timestamp: August 17, 2017, 01:22:23 pm
content: No idea about local services or people who would help but if you're stuck, there's a handy little valve tester project in the latest issue of GQRP SPRAT magazine.

author: bd139
author_rank: Super Contributor
timestamp: August 17, 2017, 01:54:03 pm
content: If you don't fancy building anything, then ask around on:http://vintage-radio.net/forum/Personally my limit is testing heaters and then flogging the wretched things quick so I can buy more transistors

author: woodchips
author_rank: Frequent Contributor
timestamp: August 17, 2017, 04:49:25 pm
content: You don't really need a valve tester.A HT supply for the anode. Bench PSU for the heater. Another bench PSU with a pot across its output for the grid.Heat it up, change the grid voltage by 1V and measure the anode current change, gm.Heat it up, apply a megger across the other electrodes to measure any leakage.Done, just about.The tricky one is the HT supply if you don't have a suitable transformer, but a couple of 60V bench PSUs in series will just about do, and useful for lots of other things.

author: MosherIV
author_rank: Super Contributor
timestamp: August 17, 2017, 05:06:49 pm
content: You could come along totmnoc.orgOn a Sat and ask one of the volunteers if they can get your valves tested.

author: bd139
author_rank: Super Contributor
timestamp: August 17, 2017, 05:35:35 pm
content: Just as a tip, you can get a good enough HT supply out of a couple of transformers running back to back, a diode and an electrolytic filter cap. If you get dual 115/230 volt taps and 12v primaries you can get quite a wide range of voltages out.

author: Specmaster
author_rank: Super Contributor
timestamp: August 17, 2017, 07:14:20 pm
content: Quote from: MosherIV on August 17, 2017, 05:06:49 pmThanks but the link seems to be dead, could you please check and repost it?

author: MosherIV
author_rank: Super Contributor
timestamp: August 18, 2017, 07:48:18 am
content: Sorryhttp://www.tnmoc.org/

author: Specmaster
author_rank: Super Contributor
timestamp: August 18, 2017, 05:44:47 pm
content: Thats an idea, do they do valve testing there then? Shame its so far away though, I doubt the other half would appreciate a 160 mile round trip to test some valves some how

author: MosherIV
author_rank: Super Contributor
timestamp: August 18, 2017, 07:19:39 pm
content: QuoteNot normally but since I am a volunteer there I can ask someone to help you out, we are like that.I think that TNMOC has a valve tester. TNMOC has an extensive collection of valves, the valve museum even came to us to photograph some rare valves!

author: Specmaster
author_rank: Super Contributor
timestamp: August 18, 2017, 08:52:58 pm
content: Quote from: MosherIV on August 18, 2017, 07:19:39 pmI think I really must pay a visit there sometime, been past it a few times but never visited it.

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2017, 09:07:10 pm
content: Isolating transformer + Variac + mains rated bridge rectifier + filter caps makes a decent HT supply. The isolating transformer is absolutely essential. The bridge rectifier and filter caps can be scavenged from a dead SMPSU. You'll also need a grid bias supply - three 9V PP3 batteries in series with a pot in the 10K to 20K range across them should do nicely, or if you've got two adjustable bench supplies use one for grid bias and the other for the filament.