Can a valve be "boosted"? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Lucien Nunes · 15th Apr 2010, 10:00 am

I've just tried the 3-step process on a 57 (signal pentode) and it seems to have made a useful improvement. The valve was initially very low, barely 800uA on test instead of 2mA. I gave it:
Vh=5V for 1 minute (normally 2.5V) everything else disconnected
Vh=4V for 1 hour with Vg1 adjusted to keep Ia=3mA
Vh=2.5V for 8 hours with Ia approx. 2mA
On test Ia has now stabilised at 1.8mA, within spec and over twice its previous value. The gm has changed little, previously 1.1 now possibly 1.15 but the precision of readings on the AVO down in that range is a bit marginal. Either way it's perfectly good enough. I cannot measure any gas current but now need to test it in circuit (prewar Hammond organ) once I have done the equally bad 56 that works with it.

Will keep an eye on performance drift and report back...

Lucien

Tractorfan · 18th Apr 2010, 7:48 pm

Hi and thanks for all your replies. However, I've just made a complete and utter prat of myself because the FM front end isn't an ECC85 at all

. It is in fact an ECC81, silly b

r . I wondered why an '85 wouldn't light up (different heater connections). The cause of no FM is therefore deeper within the set. I'll wait for a rainy day then whip the chassis out

.
Sorry for the wild goose chase, chaps.
Cheers de Pete

15th Apr 2010, 10:00 am	#21
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Can a valve be "boosted"? I've just tried the 3-step process on a 57 (signal pentode) and it seems to have made a useful improvement. The valve was initially very low, barely 800uA on test instead of 2mA. I gave it: Vh=5V for 1 minute (normally 2.5V) everything else disconnected Vh=4V for 1 hour with Vg1 adjusted to keep Ia=3mA Vh=2.5V for 8 hours with Ia approx. 2mA On test Ia has now stabilised at 1.8mA, within spec and over twice its previous value. The gm has changed little, previously 1.1 now possibly 1.15 but the precision of readings on the AVO down in that range is a bit marginal. Either way it's perfectly good enough. I cannot measure any gas current but now need to test it in circuit (prewar Hammond organ) once I have done the equally bad 56 that works with it. Will keep an eye on performance drift and report back... Lucien

18th Apr 2010, 7:48 pm	#22
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,180	Re: Can a valve be "boosted"? Hi and thanks for all your replies. However, I've just made a complete and utter prat of myself because the FM front end isn't an ECC85 at all . It is in fact an ECC81, silly br . I wondered why an '85 wouldn't light up (different heater connections). The cause of no FM is therefore deeper within the set. I'll wait for a rainy day then whip the chassis out . Sorry for the wild goose chase, chaps. Cheers de Pete __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."