UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 24th Jun 2017, 10:12 pm   #181
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

Not a lot wrong there assuming R17 (cathode resistor) is on value.

What are the readings on V3?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 24th Jun 2017, 10:38 pm   #182
Boater Sam
Banned
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
Default Re: Bush A.C.91

One end of C26, 0.01 uf is also connected to pin 6 on V4 I assume?
Boater Sam is offline  
Old 25th Jun 2017, 11:07 am   #183
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

R17 (150 Ω) is measuring 140.5 Ω (in circuit).

Pin 6 of V4 is indeed connected to one end of C26 (and we have continuity) which of course has been replaced - That Capacitor!

Now we move on to V3 (EBC33) - Double Diode Triode - which has a number of Anode connections marked on the Mullard Valve Sheet as a, ad' and ad''
__________________
BVWS Member
DonaldStott is offline  
Old 25th Jun 2017, 11:17 am   #184
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

V3 is a triode and two diodes in the same envelope, hence the three anodes.

At this stage you only need to check pins 3 (anode of the triode) and 8 (cathode).
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 25th Jun 2017, 11:50 am   #185
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

Results for V3:-

Pin 3 - Anode 0v (although scratching and hum from speaker)

Pin 8 - Cathode 0v

This is a replacement EBC33.
__________________
BVWS Member
DonaldStott is offline  
Old 25th Jun 2017, 11:53 am   #186
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

Check the value of R12 (anode resistor 68k) and measure the voltage wrt chassis on both sides of it.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 25th Jun 2017, 1:53 pm   #187
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

At last some progress - R12 had been replaced by myself as the original was way over tolerance - can't remember the exact value but I operate a 20 % figure.

Value of new resistor is measuring 67.8 kΩ in circuit.

Then measured the voltages wrt chassis on both sides as helpfully suggested by Station X and was puzzled by a reading of Ov on the resistor leads on both sides.

When I measured at the base of the connector on the chassis side I suddenly got a reading of 132.1v and a loud hum from the speaker. So I carefully wiggled the connections and got the voltage and hum to remain steady - so a dodgy solder connection! Measuring on the anode side of the resistor is now giving a reading of 61.5v.

Tonight I'll remove and resolder R12 and then check the Anode reading on Pin 3 of V3 and the Cathode on Pin 8.

Loud hum but still no radio stations on any wave band with aerial plugged in??
__________________
BVWS Member
DonaldStott is offline  
Old 25th Jun 2017, 2:00 pm   #188
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,348
Default Re: Bush A.C.91

Is that a loud hum without intervention or a loud hum when touching grids etc with your meter probe?

Lawrence.
ms660 is offline  
Old 25th Jun 2017, 7:45 pm   #189
tim.norris
Pentode
 
Join Date: Feb 2012
Location: Blackburn, Lancashire, UK.
Posts: 224
Default Re: Bush A.C.91

Alistair , if you've sorted the supply side and the radio still doesen`t work. Just a thought ,have you tried turning the radio upside down ? to see if one or more of the ift slugs have come detached from the adjusters. hold the chassis upside down and listen for the knock as the ferrite hits the brass spindle. a common problem on the octal valved bush series. regards, Tim
tim.norris is offline  
Old 25th Jun 2017, 8:12 pm   #190
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

Oh great, now I've got even more problems to resolve!

Turned it upside down and heard two distinctive knocks - presumably the two ift slugs?

Meanwhile R12 removed and then re-soldered but still 0v on the V3 Anode and Cathode...!
__________________
BVWS Member
DonaldStott is offline  
Old 25th Jun 2017, 8:24 pm   #191
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

Quote:
Originally Posted by DonaldStott View Post
Meanwhile R12 removed and then re-soldered but still 0v on the V3 Anode and Cathode...!
Back to post #186 then!

If there's no voltage on either side of R12 it's become disconnected from the HT supply.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 26th Jun 2017, 11:36 am   #192
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

Looking back at the measurements for V4 (CL33): -
  • Anode (Pin 3) 255V (and some scratchy noise from speaker)
  • G2 Screen Grid (Pin 4) 138V
  • G1 Control Grid (Pin 5) 0V (hum and scratchy noise from speaker)
  • Cathode/G3 (Pin 8) 4.8V
G2 seems slightly high (should be 110V) but if these are within tolerance as are R16, R17 and R18 then can I assume that C27 and C29 are behaving themselves??

I'm still not satisfied that I've got the HT supply side sorted?
__________________
BVWS Member
DonaldStott is offline  
Old 26th Jun 2017, 11:48 am   #193
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,348
Default Re: Bush A.C.91

The HT measures high compared to the manual but by not a lot, it's rarely exact, give or take 10 volts or so won't make much difference, the output stage (V4) appears to be basically up and running, need to sort V3's stage next.

If you look, there's voltage errors in the manual anyways, check those in the valve table to those written on the schematic page.

Lawrence.

Last edited by ms660; 26th Jun 2017 at 11:54 am.
ms660 is offline  
Old 26th Jun 2017, 11:51 am   #194
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

If there's no voltage on R12 that's a show stopper and needs to be fixed.

Where's it wired to?
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 26th Jun 2017, 12:02 pm   #195
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

Quote:
Originally Posted by Station X View Post
If there's no voltage on R12 that's a show stopper and needs to be fixed.

Where's it wired to?
I know that one end of R12 has a short length of cable wired to Pin 3 on V3 (Anode) and I will confirm I have continuity there.

But I need to trace where the other end goes to - from the Circuit Diagram it should be linked to C27 and R18 so should be easy to find?
__________________
BVWS Member
DonaldStott is offline  
Old 26th Jun 2017, 12:19 pm   #196
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

A circuit diagram does not show actual routings or commoning points. Think of it as being like a London Underground map rather than an OS map.

R18, C27, V4 SG, R12, R9, R7, L1 and R1 should all be connected together, but not necessarily in that order.

It might be easiest just to do a continuity test between all those points or, with the set turned on, check for HT on all those points.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 27th Jun 2017, 9:36 am   #197
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

With continuity and HT testing ongoing I'm hopeful that something will be uncovered in the near future - aargh!

Need to acquire and build a Velleman Signal Tracer/Injector Kit K7000 as David G4EBT has politely reminded me.

Meanwhile what about those broken IFT slugs that tim.norris brought to my attention? Moderators - don't know if I should start a new Thread or just Post in this one, but I've attached a picture of one of the IF cans uncovered - where do I even begin??

Click image for larger version

Name:	Bush IFT.jpg
Views:	96
Size:	60.7 KB
ID:	145196

If I do (ever) get the IFT slugs repaired will I need to have the set re-aligned?
__________________
BVWS Member
DonaldStott is offline  
Old 27th Jun 2017, 9:43 am   #198
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,348
Default Re: Bush A.C.91

Here's one person's fix for the broken slugs:

https://richardsears.wordpress.com/2...m-transmitter/

Yes, the IF transformers will need aligning after being repaired.

Lawrence.
ms660 is offline  
Old 27th Jun 2017, 9:54 am   #199
Station X
Moderator
 
Station X's Avatar
 
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 15,145
Default Re: Bush A.C.91

I've fixed broken slugs by gluing them back together with two part epoxy, namely "Araldite Precision".

Get V3 sorted first though. Making some progress wil give you confidence.
__________________
Graham. Forum Moderator

Keep the soldering iron hot.
Station X is online now  
Old 27th Jun 2017, 10:06 am   #200
DonaldStott
Heptode
 
DonaldStott's Avatar
 
Join Date: Aug 2015
Location: Glasgow, UK.
Posts: 664
Default Re: Bush A.C.91

Thanks Lawrence and Graham for your almost instantaneous replies!

I will of course persevere with V3 before moving on.

I have no idea how to disassemble the faulty IF cans to get at the screw-adjuster and slugs - reading some other Threads you will appreciate that I'm a bit cautious about doing this " ... because you run the risk of damaging a possibly irreplaceable IF transformer by attempting to remove a cracked ferrite core."

And for the sake of my ongoing education (!) are these Bush IFT slugs ferrite cores or iron dust cores - just interested.
__________________
BVWS Member

Last edited by DonaldStott; 27th Jun 2017 at 10:10 am. Reason: Typos
DonaldStott is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:26 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.