28th Feb 2010, 11:09 am | #201 |
Dekatron
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Re: The "Sussex" Homebrew Valve Tester.
Hi Gents, transformers still available, I'm winding some for the US at present.
Ed |
28th Feb 2010, 12:34 pm | #202 |
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Re: The "Sussex" Homebrew Valve Tester.
Mike,
Thanks. All, Please note updated BOM. http://spreadsheets.google.com/ccc?k...pfMlE&hl=en_GB If anyone spots a discrepancy please let me know. Andy |
1st Mar 2010, 12:40 pm | #203 |
Heptode
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Re: The "Sussex" Homebrew Valve Tester.
Hi Mike
Sorry if this has been asked before. I had a look through the post and didn't find this question. In the circuit diagram R3(1M) and R4(10K) are connected in series is this correct? Thanks in advance Frank |
1st Mar 2010, 1:33 pm | #204 |
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Re: The "Sussex" Homebrew Valve Tester.
Frank,
Yes this is corect, the 10k is mounted as close as possible to the gate, acting as a stopper. Possibly an overkill, sort of "belt and braces" Regards Mike |
1st Mar 2010, 1:54 pm | #205 |
Heptode
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Re: The "Sussex" Homebrew Valve Tester.
Hi Mike
Thanks for clarifying that I didn't understand what it was for. For the sake of a resistor it is better to be safe than sorry. Frank |
1st Mar 2010, 3:10 pm | #206 |
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Re: The "Sussex" Homebrew Valve Tester.
Andy,
Looking over the schematics and BOM, the qty of relays is 3 instead of the noted 2. Jan |
1st Mar 2010, 5:12 pm | #207 |
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Re: The "Sussex" Homebrew Valve Tester.
Mike
I have a 20 k ten turn, I don't see this as a problem, can you confirm ?, its still well within dissipation etc. Regards Andy |
1st Mar 2010, 5:38 pm | #208 |
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Re: The "Sussex" Homebrew Valve Tester.
Andy,
I used a 30k just because I had one, I normally say get a 50k, but yours should work OK, although I haven't tried it Mike |
2nd Mar 2010, 11:02 pm | #209 |
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Re: The "Sussex" Homebrew Valve Tester.
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6th Mar 2010, 1:08 am | #210 |
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Re: The "Sussex" Homebrew Valve Tester.
This has gone quiet.
Is everybody building........................? |
6th Mar 2010, 1:37 am | #211 |
Heptode
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Re: The "Sussex" Homebrew Valve Tester.
...yes, albeit very slowly!
Rob |
6th Mar 2010, 8:26 pm | #212 |
Nonode
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Re: The "Sussex" Homebrew Valve Tester.
I may have missed this point earlier, as the thread is quite a long one now. I am looking at my own transformer stock to see if I have something suitable.
What is the maximum anode current that can be accurately measured for a given transformer. By my calcs, if the transformer actually produces 250V RMS at 120mA load (as per Ed's version) you could potentially produce (after rectification) about 350V at about 85mA . Does this mean that some output valves like EL34 or KT88/6550 may be pretty near max capability given screen current as well. Given this should I be looking for a 250V 150-200mA winding to give some headroom? Any enlightenment welcome. Many thanks
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7th Mar 2010, 1:23 pm | #213 |
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Re: The "Sussex" Homebrew Valve Tester.
Jeremy,
I have used a prototype of Ed transformer with no problems, as I don't tend to leave valves on extended soak test. Possibly your approach may be better if extended soak testing is envisaged, perhaps Ed may like to comment, as transformer theory is not my forte. Mike |
7th Mar 2010, 9:09 pm | #214 |
Dekatron
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Re: The "Sussex" Homebrew Valve Tester.
Hi Mike, Jeremy, the transformer is rated at 100mA on the HT winding for continuous operation and is designed to give the correct output at this level of current, while not overheating.
Short sessions (10-15 secs) at currents up to 300mA , repeated at say 10 min intervals should not be a problem for the transformer. However, if this is done near max voltage from the regulator, the additional resistive losses in the transformer may cause the anode and screen voltages to reduce on load due to regulation within the transformer. Hope this helps, Ed |
7th Mar 2010, 11:19 pm | #215 |
Nonode
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Re: The "Sussex" Homebrew Valve Tester.
Thanks Ed, that clears things up. I am sure the spec is fine for all normal uses. As I suspected, there may be an impact on the highest HTs but not at lower HT settings.
All I was trying to get straight is the RMS vs rectified DC currents. If the winding gives 100mA at 250V RMS and it is rectified, the DC current limit from the smoothing cap is derated to about 70mA. But at all normal settings (eg 250V DC), there will be ample headroom in the regulator section if slight excess current is drawn for short periods. Thanks
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12th Mar 2010, 12:47 pm | #216 |
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Re: The "Sussex" Homebrew Valve Tester.
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12th Mar 2010, 6:07 pm | #217 |
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Re: The "Sussex" Homebrew Valve Tester.
I have just joined this forum and love the look of this project.
Could Martin and Ed please email me their details for purchase of PCB and Tx. Many Thanks Alan E-mail address removed. Please use Private Message system for communication. Last edited by Brian R Pateman; 12th Mar 2010 at 7:31 pm. Reason: E-mail address removed, previous post reference deleted. |
13th Mar 2010, 2:36 am | #218 |
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Re: The "Sussex" Homebrew Valve Tester.
Chaps,
I've made a couple of changes to the BOM. The connector for an external heater supply would have been grounded to the chassis and was only rated at 1A 24V. I couldn't find a decent alternative so I've substituted with a pair of 4mm sockets. If anyone has a better idea I would appreciate it. Andy |
13th Mar 2010, 11:50 am | #219 |
Heptode
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Re: The "Sussex" Homebrew Valve Tester.
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13th Mar 2010, 10:23 pm | #220 |
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Re: The "Sussex" Homebrew Valve Tester.
I have been designing my panels using Front Panel designer.
See attached Last edited by Brian R Pateman; 23rd Mar 2010 at 10:17 pm. Reason: Large embedded images thumbnailed. |