R1155 HT supply - UK Vintage Radio Repair and Restoration Discussion Forum

newlite4 · 28th Jan 2011, 10:32 am

Just making up heater and HT supplies for this set. I have a 6.3V 4A heater transformer ready to go in so thats sorted. I have assembled a DC supply (transformer, bridge rectifier and 50uF/350V cap) that provides 240V at 80mA, this sits at about 340V on no load. On test with an external PSU the set is up and running very quickly, however I was concerned about wether having this amount of HT at start up was a good thing. Should I have a series load resistor or something? The set is only ever going to drive headphones so there is little extra load on the system.
Neil

XTC · 28th Jan 2011, 12:05 pm

You can use the PSU design software from the Duncan's Amps site to predict the effects of adding loading without guesswork or experimenting.

http://www.duncanamps.com/psud2/index.html

If this is a simple 50µF filter it may not give that much smoothing and you might look at something else such as a two caps and a resistor, or adding a choke if you have a suitable one to hand. You can investigate with that software.

Another possibility is to use an NTC thermistor to give a gentle start.

When I had this problem I modified his solid state HV regulator to provide the HT.

http://www.duncanamps.com/technical/mosfet.html

Of course, if you've replaced the paper caps, having 340V across the HT+ and HT- may do no harm, but it would make me feel a bit uneasy - asking for trouble.

Pete.

newlite4 · 28th Jan 2011, 12:36 pm

Thanks for that Pete, I have downloaded the software. I may go for the two caps and choke approach, this would give the HT a bit of a soft-start characteristic or I could easily reduce the HT since the transformer is multi-tapped.
Neil

Sean Williams · 28th Jan 2011, 5:38 pm

Please remember that the chassis of the 1155 is at bias potential - connecting HT- to the case will result in a seriously deaf RX!

newlite4 · 28th Jan 2011, 5:48 pm

Yes, a good reminder from Sean there just in case one was tempted to mount electrolytic cans straight to chassis. I have selected axial leaded electros which can be mounted such that -HT is kept clear of the chassis.
Neil

28th Jan 2011, 10:32 am	#1
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	R1155 HT supply Just making up heater and HT supplies for this set. I have a 6.3V 4A heater transformer ready to go in so thats sorted. I have assembled a DC supply (transformer, bridge rectifier and 50uF/350V cap) that provides 240V at 80mA, this sits at about 340V on no load. On test with an external PSU the set is up and running very quickly, however I was concerned about wether having this amount of HT at start up was a good thing. Should I have a series load resistor or something? The set is only ever going to drive headphones so there is little extra load on the system. Neil __________________ preserving the recent past, for the distant future.

28th Jan 2011, 12:05 pm	#2
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: R1155 HT supply You can use the PSU design software from the Duncan's Amps site to predict the effects of adding loading without guesswork or experimenting. http://www.duncanamps.com/psud2/index.html If this is a simple 50µF filter it may not give that much smoothing and you might look at something else such as a two caps and a resistor, or adding a choke if you have a suitable one to hand. You can investigate with that software. Another possibility is to use an NTC thermistor to give a gentle start. When I had this problem I modified his solid state HV regulator to provide the HT. http://www.duncanamps.com/technical/mosfet.html Of course, if you've replaced the paper caps, having 340V across the HT+ and HT- may do no harm, but it would make me feel a bit uneasy - asking for trouble. Pete.

28th Jan 2011, 12:36 pm	#3
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: R1155 HT supply Thanks for that Pete, I have downloaded the software. I may go for the two caps and choke approach, this would give the HT a bit of a soft-start characteristic or I could easily reduce the HT since the transformer is multi-tapped. Neil __________________ preserving the recent past, for the distant future.

28th Jan 2011, 5:38 pm	#4
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: R1155 HT supply Please remember that the chassis of the 1155 is at bias potential - connecting HT- to the case will result in a seriously deaf RX! __________________ Engineers make things work and have spare bits when finished

28th Jan 2011, 5:48 pm	#5
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: R1155 HT supply Yes, a good reminder from Sean there just in case one was tempted to mount electrolytic cans straight to chassis. I have selected axial leaded electros which can be mounted such that -HT is kept clear of the chassis. Neil __________________ preserving the recent past, for the distant future.