Bush AC41 - UK Vintage Radio Repair and Restoration Discussion Forum

Sinewave · 14th Sep 2020, 4:24 pm

A little while ago I picked up an AC41. Rather than just switch it on, I made a few checks inside, then brought it up slowly on the variac. Being aware of the live chassis possibility, I did some searching and from what I've found, I believe that this isn't a live chassis set? However, I didn't reach full voltage when bringing the set up on the variac as I stopped when I were measuring 50v on the chassis.

There were some glowing valves, so some signs of life!

Freya · 14th Sep 2020, 4:29 pm

Where did you have your probes ?

It's not live chassis as it has a mains transformer

HamishBoxer · 14th Sep 2020, 4:32 pm

Not a live chassis.

Sinewave · 14th Sep 2020, 4:35 pm

I went from the chassis to the earthed casing of my variac, then that's when I realised something may not be quite as it should, so it's on the bench in Sinewave Laboratories...

If fact the drawing extract you've posted looks a little different to the one I have here.

Freya · 14th Sep 2020, 4:41 pm

The dotted line on the schematic showing the transformer core to Chassis may have something to do with it, if a winding is breaking down to the laminations.

music-centre · 14th Sep 2020, 4:43 pm

Definitely not a Dac41 with an Ac41 back transferred to it? over the years like they do!
Steve.

Sinewave · 14th Sep 2020, 4:45 pm

Quote:

Originally Posted by Freya

The dotted line on the schematic showing the transformer core to Chassis may have something to do with it, if a winding is breaking down to the laminations.

Will test the winding to chassis in a moment.

Sinewave · 14th Sep 2020, 5:04 pm

Quote:

Originally Posted by music-centre

Definitely not a Dac41 with an Ac41 back transferred to it? over the years like they do!
Steve.

Here's the front

music-centre · 14th Sep 2020, 5:12 pm

It would look the same from the front but in the case of this model if you have a mains transformer it would be an AC41 as the DAC 41 uses a dropper type strip.
Steve.

John10b · 14th Sep 2020, 7:43 pm

What valves are fitted?
John

Herald1360 · 14th Sep 2020, 8:10 pm

If the AC 41 chassis isn't earthed, a DVM or other high resistance meter could show a significant reading simply from the stray capacitance in the transformer between its mains winding and core/screen.

Sinewave · 14th Sep 2020, 8:13 pm

All Mullards

ECH42
EBF80
EL41
EZ40

Sinewave · 14th Sep 2020, 8:33 pm

Ok, tested the mains TX, the windings are fine, nothing down to chassis.

Sideband · 14th Sep 2020, 8:41 pm

Quote:

Originally Posted by Herald1360

If the AC 41 chassis isn't earthed, a DVM or other high resistance meter could show a significant reading simply from the stray capacitance in the transformer between its mains winding and core/screen.

Yes indeed. A DVM can measure sometimes over 100V but this is a capacitive coupling as noted above. It isn't actually 'live'.

Sinewave · 14th Sep 2020, 8:53 pm

Quote:

Originally Posted by Herald1360

If the AC 41 chassis isn't earthed, a DVM or other high resistance meter could show a significant reading simply from the stray capacitance in the transformer between its mains winding and core/screen.

I did wonder if it was induced voltage with not enough current behind it.

I'll touch it and see how many buzzes I get

I've got some three core cable I can replace the twin with.

Herald1360 · 15th Sep 2020, 2:15 am

Quote:

Originally Posted by Freya

The dotted line on the schematic showing the transformer core to Chassis may have something to do with it, if a winding is breaking down to the laminations.

That dotted line is actually the usual symbol for an electrostatic screen and as such definitely has something to do with it breakdown or not!

John10b · 15th Sep 2020, 9:47 am

This is part of the AC41 circuit I’ve got, slightly different to the other one shown.
John

HamishBoxer · 15th Sep 2020, 10:36 am

Bit of capacity coupling?

Herald1360 · 15th Sep 2020, 11:35 am

Quote:

Originally Posted by John10b

This is part of the AC41 circuit I’ve got, slightly different to the other one shown.
John

Looks like exactly the same circuit just drawn differently with a chassis symbol on the 0V end of the HT secondary.

AC/HL · 15th Sep 2020, 12:21 pm

Post 2 is the Trader iteration, post 17 the Bush original. Same set, although the Trader drawing style looks much older.

14th Sep 2020, 4:24 pm	#1
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Bush AC41 A little while ago I picked up an AC41. Rather than just switch it on, I made a few checks inside, then brought it up slowly on the variac. Being aware of the live chassis possibility, I did some searching and from what I've found, I believe that this isn't a live chassis set? However, I didn't reach full voltage when bringing the set up on the variac as I stopped when I were measuring 50v on the chassis. There were some glowing valves, so some signs of life! __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

14th Sep 2020, 4:29 pm	#2
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Bush AC41 Where did you have your probes ? It's not live chassis as it has a mains transformer Attached Thumbnails __________________ Stephen _________"It`s only an old telly" ___ Last edited by Freya; 14th Sep 2020 at 4:34 pm. Reason: added part circuit

14th Sep 2020, 4:32 pm	#3
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Bush AC41 Not a live chassis. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

14th Sep 2020, 4:35 pm	#4
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: Bush AC41 I went from the chassis to the earthed casing of my variac, then that's when I realised something may not be quite as it should, so it's on the bench in Sinewave Laboratories... If fact the drawing extract you've posted looks a little different to the one I have here. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

14th Sep 2020, 4:41 pm	#5
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Bush AC41 The dotted line on the schematic showing the transformer core to Chassis may have something to do with it, if a winding is breaking down to the laminations. __________________ Stephen _________"It`s only an old telly" ___

14th Sep 2020, 4:43 pm	#6
music-centre Heptode Join Date: Sep 2007 Location: Brentwood, Essex, UK. Posts: 687	Re: Bush AC41 Definitely not a Dac41 with an Ac41 back transferred to it? over the years like they do! Steve.

14th Sep 2020, 5:12 pm	#9
music-centre Heptode Join Date: Sep 2007 Location: Brentwood, Essex, UK. Posts: 687	Re: Bush AC41 It would look the same from the front but in the case of this model if you have a mains transformer it would be an AC41 as the DAC 41 uses a dropper type strip. Steve. Last edited by music-centre; 14th Sep 2020 at 5:32 pm.

14th Sep 2020, 7:43 pm	#10
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush AC41 What valves are fitted? John

14th Sep 2020, 8:10 pm	#11
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Bush AC41 If the AC 41 chassis isn't earthed, a DVM or other high resistance meter could show a significant reading simply from the stray capacitance in the transformer between its mains winding and core/screen. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

14th Sep 2020, 8:13 pm	#12
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: Bush AC41 All Mullards ECH42 EBF80 EL41 EZ40 __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

14th Sep 2020, 8:33 pm	#13
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: Bush AC41 Ok, tested the mains TX, the windings are fine, nothing down to chassis. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

15th Sep 2020, 9:47 am	#17
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush AC41 This is part of the AC41 circuit I’ve got, slightly different to the other one shown. John Attached Thumbnails

15th Sep 2020, 10:36 am	#18
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Bush AC41 Bit of capacity coupling? __________________ G8JET BVWS Archivist and Member V.M.A.R.S

15th Sep 2020, 12:21 pm	#20
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Bush AC41 Post 2 is the Trader iteration, post 17 the Bush original. Same set, although the Trader drawing style looks much older.