|
Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
|
Thread Tools |
19th Jan 2022, 12:44 pm | #1 |
Heptode
Join Date: Feb 2006
Location: Marlborough, Wiltshire, UK.
Posts: 915
|
Switching off EM34
Trying to preserve the EM34 in my Philips 170A. Is there any problem simply switching off the heater supply to the EM34 only, for most of the running time of the set ? Thinking of fitting a hidden switch.
Tks Ken |
19th Jan 2022, 1:23 pm | #2 |
Pentode
Join Date: Sep 2021
Location: Aabenraa, South Jutland, Denmark.
Posts: 219
|
Re: Switching off EM34
Hi Ken,
There is no problem in that at all. It only serves as an indicator, and can be switched off or removed without altering anything in the set. Regards, Jan |
19th Jan 2022, 2:48 pm | #3 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: Switching off EM34
If you have a switch, I'd make it a double-pole switch and cut the HT also.
|
19th Jan 2022, 3:57 pm | #4 | |
Guest
Posts: n/a
|
Re: Switching off EM34
Quote:
|
|
19th Jan 2022, 6:39 pm | #5 |
Heptode
Join Date: Feb 2006
Location: Marlborough, Wiltshire, UK.
Posts: 915
|
Re: Switching off EM34
Thanks for the replies. I was concerned that maybe having ht etc present but no heater would cause some deterioration
Ken |
19th Jan 2022, 7:32 pm | #6 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
|
Re: Switching off EM34
Could there be a problem just after the heater is disconnected?
The HT will be present but the cathode will be cooling down. |
19th Jan 2022, 8:17 pm | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
|
Re: Switching off EM34
I've got a "VI103" [essentially the RAF version of the 6U5G] magic-eye in my PCR communications-receiver, and to prolong its glowy life I fitted a 3-position switch in the HT circuit. It's a centre-off switch with one position spring-biased back to the centre, the other a normal position.
Up [against the spring bias] - Eye comes on so long as you keep the switch toggle lifted. Centre - off Down - Eye stays on.
__________________
I'm the Operator of my Pocket Calculator. -Kraftwerk. |
19th Jan 2022, 8:57 pm | #8 | |
Guest
Posts: n/a
|
Re: Switching off EM34
Quote:
|
|
20th Jan 2022, 6:28 am | #9 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,676
|
Re: Switching off EM34
I always thought it was the opposite scenario that should be avoided, ie heater on, but no HT, because of the possibility of so-called cathode poisoning.
__________________
-- Graham. G3ZVT |
20th Jan 2022, 8:11 am | #10 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: Switching off EM34
I have a tape recorder which uses an EM34 as record level indicator. It has HT switched on only on record. It has the original EM34 which is good and bright, no indication of cathode poisoning at all.
Certainly, many hours of heater with no HT has not caused a problem here. The other way round - I was just thinking of the visual effect of switching off heaters and leaving HT on, the display would fade out... Personally, I'd rather see an abrupt switch-off, hence the suggestion! |
20th Jan 2022, 10:33 am | #11 |
Heptode
Join Date: Feb 2006
Location: Marlborough, Wiltshire, UK.
Posts: 915
|
Re: Switching off EM34
I was aware of cathode poisoning being mentioned in connection to switched ht in vhf front ends, hence my switched heater suggestion. It’s also easier to do so I will go that route.
I am making an led “substitute” but modern bar graph drivers ( not NS/TI) don’t seem to meet the data sheet specs ! |
22nd Jan 2022, 6:22 pm | #12 |
Pentode
Join Date: Apr 2013
Location: Manchester, UK.
Posts: 177
|
Re: Switching off EM34
I have a Graetz Melodia. It also uses an EM34. It has a switch on the front that allows me to switch it off as and when.
Not sure if it cuts the 6.3 or the HT, or both, but it's definitely a good idea. If you want a cheaper alternative, you can use a Russian 6E5C, but you'll need to re wire the valve socket. If you want to know how let me know. At a quarter of the cost it is well worth it Michael |
22nd Jan 2022, 8:12 pm | #13 |
Heptode
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 637
|
Re: Switching off EM34
I don't know much about valves, but I have a radio with a button to enable the magic eye when needed.
It looks like the circuit does not cut the heater, but does something with the cathode. I'll let the valves experts explain, then I'll learn something as well !. Cheers, Buzby |