KW 160 low output... help please! - UK Vintage Radio Repair and Restoration Discussion Forum

thevalveset · 19th Nov 2018, 11:09 pm

HI
My pal is restoring a KW 160 top-band transmitter which is suffering low output.
He tells me it is running about 11W DC input but only getting 3W output which seems a little inefficient. (According to Derby Radio club it should run 12W input for 8W out?)
He has asked me to scour the internet to find any service/alignment information to help with the repair but I have failed to find any.

Does anyone know if such information was ever published ie service sheet, alignment information or official handbook etc?
All information gratefully received.... thanks in anticipation.
Dave

JohnBG8JMB · 20th Nov 2018, 12:05 am

hopefully, 2 files attached that should help
See also kw yahoo group

73
John
G8JMB

G3VKM_Roger · 20th Nov 2018, 11:04 pm

Dave,

The KW-Radios group is here:-

https://groups.io/g/KW-Radios The Yahoo group John mentions has QSYed to groups.io

I have a KW-160 (and the ATU of the same name) if you need any measurements or info.

73

Roger/G3VKM

James Duncan · 22nd Nov 2018, 4:18 pm

Are you sure that the tube has not deteriorated, sounds like it could be
check that the correct HT is there to drive the tube.

Nuvistor · 22nd Nov 2018, 4:34 pm

What dummy load are you using, according to the files in post #2 the output is 75ohm and using a 50ohm will reduce the output, the doc suggests a work around.

HamishBoxer · 22nd Nov 2018, 5:26 pm

Check R30/R29/R17/R21 and also what the voltage is there.I notice a few caps I would check as well though guess they are not waxies?

G3VKM_Roger · 22nd Nov 2018, 5:34 pm

A query about the KW-160 that the OP and others may be able to help me with.

Recently, I had a couple of power problems with my transmitter which I took care of, but I then found that the PA meter reads a standing 20ma when key-up and on transmit. My 160 has the 21v PA heater line going to a single silicon diode and a 25uF cap to provide protective bias. I measure about -22V on the control grid of the PL81 PA, key-up. From comments made on the KW-Radios thread, I think others have seen this on their 160s, but I can't find any reference to a standing current in the info I have on the set. From the PL81 characteristics, it would seem that the standing current is normal for that bias voltage.

Does anyone else see this with their transmitter?

73

Roger/G3VKM

PS: I tried to post a better copy of the KW-160 cct but messed it up, so I deleted the post and will redo it.

G3VKM_Roger · 22nd Nov 2018, 5:39 pm

This is a better cct IMO, than the SWM version.

73

Roger/G3VKM

19th Nov 2018, 11:09 pm	#1
thevalveset Tetrode Join Date: Oct 2007 Location: Nottingham, Nottinghamshire, UK. Posts: 73	KW 160 low output... help please! HI My pal is restoring a KW 160 top-band transmitter which is suffering low output. He tells me it is running about 11W DC input but only getting 3W output which seems a little inefficient. (According to Derby Radio club it should run 12W input for 8W out?) He has asked me to scour the internet to find any service/alignment information to help with the repair but I have failed to find any. Does anyone know if such information was ever published ie service sheet, alignment information or official handbook etc? All information gratefully received.... thanks in anticipation. Dave

20th Nov 2018, 11:04 pm	#3
G3VKM_Roger Heptode Join Date: Jun 2012 Location: Southeast Norfolk, UK. Posts: 773	Re: KW 160 low output... help please! Dave, The KW-Radios group is here:- https://groups.io/g/KW-Radios The Yahoo group John mentions has QSYed to groups.io I have a KW-160 (and the ATU of the same name) if you need any measurements or info. 73 Roger/G3VKM

22nd Nov 2018, 4:18 pm	#4
James Duncan Pentode Join Date: May 2010 Location: Wick, Scotland, UK. Posts: 227	Re: KW 160 low output... help please! Are you sure that the tube has not deteriorated, sounds like it could be check that the correct HT is there to drive the tube.

22nd Nov 2018, 4:34 pm	#5
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: KW 160 low output... help please! What dummy load are you using, according to the files in post #2 the output is 75ohm and using a 50ohm will reduce the output, the doc suggests a work around. __________________ Frank

22nd Nov 2018, 5:26 pm	#6
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: KW 160 low output... help please! Check R30/R29/R17/R21 and also what the voltage is there.I notice a few caps I would check as well though guess they are not waxies? __________________ G8JET BVWS Archivist and Member V.M.A.R.S

22nd Nov 2018, 5:34 pm	#7
G3VKM_Roger Heptode Join Date: Jun 2012 Location: Southeast Norfolk, UK. Posts: 773	Re: KW 160 low output... help please! A query about the KW-160 that the OP and others may be able to help me with. Recently, I had a couple of power problems with my transmitter which I took care of, but I then found that the PA meter reads a standing 20ma when key-up and on transmit. My 160 has the 21v PA heater line going to a single silicon diode and a 25uF cap to provide protective bias. I measure about -22V on the control grid of the PL81 PA, key-up. From comments made on the KW-Radios thread, I think others have seen this on their 160s, but I can't find any reference to a standing current in the info I have on the set. From the PL81 characteristics, it would seem that the standing current is normal for that bias voltage. Does anyone else see this with their transmitter? 73 Roger/G3VKM PS: I tried to post a better copy of the KW-160 cct but messed it up, so I deleted the post and will redo it. Last edited by G3VKM_Roger; 22nd Nov 2018 at 5:40 pm. Reason: Attachment messed up.

22nd Nov 2018, 5:39 pm	#8
G3VKM_Roger Heptode Join Date: Jun 2012 Location: Southeast Norfolk, UK. Posts: 773	Re: KW 160 low output... help please! This is a better cct IMO, than the SWM version. 73 Roger/G3VKM Attached Thumbnails