Output transformer HT connection. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

GrimJosef · 27th Nov 2022, 2:41 pm

A sort-of hybrid solution if you want to stick to a smaller valve rectifier is to generate the output valves' anode HT using solid-state rectification but everything else, including their screen grid HT, using a valve rectifier. The slow warm-up of the valve rectifier can protect the output valves' cathodes from a high electric field at switch-on via the screening action of the screen grids. The valves do need to be able to survive a large anode to screen voltage briefly though. And you do need two HT filters, of course.

Cheers,

GJ

Diabolical Artificer · 27th Nov 2022, 3:59 pm

Thanks again all. I'll do some experiments at some point but the consensus seems to be connect the OPT CT after the choke.

Andy.

joebog1 · 27th Nov 2022, 10:08 pm

Using valve rectifiers today is a bit of a problem unless you already have decent ones available.
Modern rectifiers are not as reliable as the genuine article. I used buy up every valve rect that I could find providing it was NIB. VERY hard to find these days and for those that are out there, some are as expensive as a very good quality 50 watt output transformer.
So, me, the audiophool purist has changed over to sand rectifiers. Fast recovery in large currents are cheap and plentiful. I still use capacitors across them though just to make sure.
If you have "delicate " output valves a soft start and HT delay are very easy and cheap to organise.

Just my two bobs worth.

Joe

27th Nov 2022, 2:41 pm	#21
GrimJosef Dekatron Join Date: Sep 2007 Location: Oxfordshire, UK. Posts: 4,311	Re: Output transformer HT connection. A sort-of hybrid solution if you want to stick to a smaller valve rectifier is to generate the output valves' anode HT using solid-state rectification but everything else, including their screen grid HT, using a valve rectifier. The slow warm-up of the valve rectifier can protect the output valves' cathodes from a high electric field at switch-on via the screening action of the screen grids. The valves do need to be able to survive a large anode to screen voltage briefly though. And you do need two HT filters, of course. Cheers, GJ __________________ http://www.ampregen.com

27th Nov 2022, 3:59 pm	#22
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,657	Re: Output transformer HT connection. Thanks again all. I'll do some experiments at some point but the consensus seems to be connect the OPT CT after the choke. Andy. __________________ Curiosity hasn't killed this cat...so far.

27th Nov 2022, 10:08 pm	#23
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: Output transformer HT connection. Using valve rectifiers today is a bit of a problem unless you already have decent ones available. Modern rectifiers are not as reliable as the genuine article. I used buy up every valve rect that I could find providing it was NIB. VERY hard to find these days and for those that are out there, some are as expensive as a very good quality 50 watt output transformer. So, me, the audiophool purist has changed over to sand rectifiers. Fast recovery in large currents are cheap and plentiful. I still use capacitors across them though just to make sure. If you have "delicate " output valves a soft start and HT delay are very easy and cheap to organise. Just my two bobs worth. Joe