G & E Bradley CT-471 - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

M3VUV51 · 17th Oct 2018, 9:10 pm

i just tried 2n3096 pnp silicon transistors in my amp board,in place of the oc170 trannys ,still got the oscilations but not so bad on the ohms scale but at least it goes to the right when i short the leads now,cant set the zero tho on ohms.

im going to birketts in the morning,may get another meter and see what germainium pnps he has

Sinewave · 17th Oct 2018, 11:33 pm

Have you gone through any other fault finding?

I was hopeful that the famous tin whisker was the problem, but there appears to be other issues, I'm going to take a good look through the circuits and make some measurments and see if the voltages on the schematics are correct or not when I measure them to see if I can pin point some issues.

It might help me understand the theory behind this meter to establish what should be happening.

M3VUV51 · 18th Oct 2018, 1:37 am

to be honest im finding reading the schematic a nightmare,so many wafer switches!,just slowly working on checking components voltage rails etc,ive so far changed nearly every electrolytic,may start checking for of spec resistors,i find lack of test points an issue,from a repair point of view the manual is crap i find!,regards Paul.

Sinewave · 18th Oct 2018, 11:14 pm

So if my transistors are marked as VT, I take it I'll be using the incorrect drawings if any are market TR on the drawings?

M3VUV51 · 19th Oct 2018, 1:20 am

Don't fret, the transistors are all marked "VT" same as all the diodes are marked "MR", any joy with it yet? I'm still doing battle, I've got 6.3 volts on the 20 volt rail, just trying to see what's dragging it low!

Regards, M3VUV.

Sinewave · 19th Oct 2018, 2:08 am

I went through the amplifier board tonight, checking the reactance of the caps with my scope, most seemed pretty good. C111 was open, so replaced that with a poly film cap for now.

The meter appears to respond on DC current, though only on the lower ranges and it the readings don't appear to correlate with what I'm feeding it, but it's a responce I've not seen before.

Also, noticed a high pitched whine, typical of RF type equipment, not noticed that before.

I can't really see much else going on with the amplifier board, but there's more to do.

I should also do some of the DC rail checks like you're doing.

M3VUV51 · 19th Oct 2018, 5:13 am

Well I don't know if it's progress but I changed all the OC170 transistors for 2N3906 silicon ones just to see what happened. I notice if I lift the gate of the FET, if I touch it with my finger it pegs the meter hard, that's on the check zero position and the + position. If I put it in the negative position, it slams the meter hard to the left, well it looks like at least the amp's working. Still won't measure anything with the gate of the FET back in the board though and with the FET gate connected the needle oscillates. I'm starting to think it's pointing towards the chopper circuit. Also while messing about one of the legs on VT21 was broken where it exits the case of the transistor, looked like corrosion ,looked fine at a glance though!

It's 5.00AM now so gonna hit the sheets!

M3VUV.

Sinewave · 19th Oct 2018, 8:38 am

There doesn't appear to be a FET in mine and according to information, that is the case for the earlier 471C as my serial number also confirms that.

FETs fitted after serials BGB 2329.

Something along those lines, so there are some differences to ours. My serial is BGB1973XF.

russell_w_b · 19th Oct 2018, 2:55 pm

Check your battery negative (earth return) supply is contiguous around all the boards and the board frame. Of the two CT471s I've fixed, the first one had a coruscating flicker on one of the ranges.

A broken earth return is all the problem was; I was lucky!

M3VUV51 · 19th Oct 2018, 7:33 pm

Worth a look.

russell_w_b · 19th Oct 2018, 9:00 pm

I would also go bit mad with digital photos prior to diving in there, as it's jolly easy to inadvertently dislodge wires from that nightmare of a board arrangement!

Sinewave · 19th Oct 2018, 9:24 pm

It's something I should look at. I did have the flicking on the scale until I replaced the tin whisker affected transistors. I did notice on another thread that someone had a -ve issue which was the only fault.

I've been spending a lot of time this evening with the schematics, seperating the different functions of the circuits.

I'm somewhat happy with the amplifier board, so next it's the chopper and the power supply board, as well as checking all of the groundings.

M3VUV51 · 20th Oct 2018, 12:42 pm

well i popped into birketts yesterday,i picked up a bag of ac128 transistors 50 for a quid!,ive checked them and all good,there nos,the only differences i can see is the gain is 40 min as opposed to 150 and transition frequency is 1mhz as opposed to 150,otherwise they seem to better the oc170 on specs,i may try those in it and suck it and see!.m3vuv.

Sinewave · 20th Oct 2018, 11:39 pm

I've made some tests to the amplifier board, checked the 20v rail, getting 19.3v so that's pretty good. 2.4v on the 2.5v rail, so that's pretty good. So, amplifier board should be ok then, unless there's something else on there which I've missed.

Onto the next boards......

Sinewave · 21st Oct 2018, 12:03 am

Quote:

Originally Posted by m3vuv51

well i poped into birketts yesterday,i picked up a bag of ac128 transistors 50 for a quid!,ive checked them and all good,there nos,the only differences i can see is the gain is 40 min as opposed to 150 and transition frequency is 1mhz as opposed to 150,otherwise they seem to better the oc170 on specs,i may try those in it and suck it and see!.m3vuv.

Have you replaced any mustard caps?

M3VUV51 · 21st Oct 2018, 1:22 am

no mine seemed ok.

M3VUV51 · 21st Oct 2018, 2:27 am

just wondering about the high pitched whine you hear,i would think thats from the chopper transformer,it should oscillate at 550hz is it that you can hear?

Sinewave · 21st Oct 2018, 9:00 am

It could be.

Some of the caps which were ok for ESR are a bit leaky, but I don't have replacements for them all.

I think some of my capacitors in stock which are new are leaky. Perhaps they've been sat on the shelf for too long. I've only in stock what was the remaining amount of a minimum purchase. So I might have to get buying again.

Sinewave · 28th Oct 2018, 11:28 am

Power supply seems ok. 12v cal check is working.

Sinewave · 28th Oct 2018, 5:38 pm

So, what's happening now and I don't know why, as I have no idea how these things work is....

on DC current, on the 0.4 range I get meter movement, but the reading doesn't correleate at all with what I'm sending it.

The same on DC volts, on the 0.4 and 1.2 range.

So I need to work out why that is and why still nothing on any other range.

Though if I go to AC, the needle moves around to the centre and floats about a little.

17th Oct 2018, 9:10 pm	#41
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 i just tried 2n3096 pnp silicon transistors in my amp board,in place of the oc170 trannys ,still got the oscilations but not so bad on the ohms scale but at least it goes to the right when i short the leads now,cant set the zero tho on ohms. im going to birketts in the morning,may get another meter and see what germainium pnps he has

17th Oct 2018, 11:33 pm	#42
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 Have you gone through any other fault finding? I was hopeful that the famous tin whisker was the problem, but there appears to be other issues, I'm going to take a good look through the circuits and make some measurments and see if the voltages on the schematics are correct or not when I measure them to see if I can pin point some issues. It might help me understand the theory behind this meter to establish what should be happening. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

18th Oct 2018, 1:37 am	#43
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 to be honest im finding reading the schematic a nightmare,so many wafer switches!,just slowly working on checking components voltage rails etc,ive so far changed nearly every electrolytic,may start checking for of spec resistors,i find lack of test points an issue,from a repair point of view the manual is crap i find!,regards Paul.

18th Oct 2018, 11:14 pm	#44
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 So if my transistors are marked as VT, I take it I'll be using the incorrect drawings if any are market TR on the drawings? __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

19th Oct 2018, 1:20 am	#45
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 Don't fret, the transistors are all marked "VT" same as all the diodes are marked "MR", any joy with it yet? I'm still doing battle, I've got 6.3 volts on the 20 volt rail, just trying to see what's dragging it low! Regards, M3VUV.

19th Oct 2018, 2:08 am	#46
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 I went through the amplifier board tonight, checking the reactance of the caps with my scope, most seemed pretty good. C111 was open, so replaced that with a poly film cap for now. The meter appears to respond on DC current, though only on the lower ranges and it the readings don't appear to correlate with what I'm feeding it, but it's a responce I've not seen before. Also, noticed a high pitched whine, typical of RF type equipment, not noticed that before. I can't really see much else going on with the amplifier board, but there's more to do. I should also do some of the DC rail checks like you're doing. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

19th Oct 2018, 5:13 am	#47
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 Well I don't know if it's progress but I changed all the OC170 transistors for 2N3906 silicon ones just to see what happened. I notice if I lift the gate of the FET, if I touch it with my finger it pegs the meter hard, that's on the check zero position and the + position. If I put it in the negative position, it slams the meter hard to the left, well it looks like at least the amp's working. Still won't measure anything with the gate of the FET back in the board though and with the FET gate connected the needle oscillates. I'm starting to think it's pointing towards the chopper circuit. Also while messing about one of the legs on VT21 was broken where it exits the case of the transistor, looked like corrosion ,looked fine at a glance though! It's 5.00AM now so gonna hit the sheets! M3VUV.

19th Oct 2018, 8:38 am	#48
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 There doesn't appear to be a FET in mine and according to information, that is the case for the earlier 471C as my serial number also confirms that. FETs fitted after serials BGB 2329. Something along those lines, so there are some differences to ours. My serial is BGB1973XF. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

19th Oct 2018, 2:55 pm	#49
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: G & E Bradley CT-471 Check your battery negative (earth return) supply is contiguous around all the boards and the board frame. Of the two CT471s I've fixed, the first one had a coruscating flicker on one of the ranges. A broken earth return is all the problem was; I was lucky! __________________ Regds, Russell W. B. G4YLI.

19th Oct 2018, 7:33 pm	#50
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 Worth a look.

19th Oct 2018, 9:00 pm	#51
russell_w_b Dekatron Join Date: Jul 2007 Location: Penrith, Cumbria, UK. Posts: 3,687	Re: G & E Bradley CT-471 I would also go bit mad with digital photos prior to diving in there, as it's jolly easy to inadvertently dislodge wires from that nightmare of a board arrangement! __________________ Regds, Russell W. B. G4YLI.

19th Oct 2018, 9:24 pm	#52
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 It's something I should look at. I did have the flicking on the scale until I replaced the tin whisker affected transistors. I did notice on another thread that someone had a -ve issue which was the only fault. I've been spending a lot of time this evening with the schematics, seperating the different functions of the circuits. I'm somewhat happy with the amplifier board, so next it's the chopper and the power supply board, as well as checking all of the groundings. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

20th Oct 2018, 12:42 pm	#53
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 well i popped into birketts yesterday,i picked up a bag of ac128 transistors 50 for a quid!,ive checked them and all good,there nos,the only differences i can see is the gain is 40 min as opposed to 150 and transition frequency is 1mhz as opposed to 150,otherwise they seem to better the oc170 on specs,i may try those in it and suck it and see!.m3vuv.

20th Oct 2018, 11:39 pm	#54
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 I've made some tests to the amplifier board, checked the 20v rail, getting 19.3v so that's pretty good. 2.4v on the 2.5v rail, so that's pretty good. So, amplifier board should be ok then, unless there's something else on there which I've missed. Onto the next boards...... __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

21st Oct 2018, 1:22 am	#56
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 no mine seemed ok.

21st Oct 2018, 2:27 am	#57
M3VUV51 Banned Join Date: Feb 2018 Location: Horncastle, Lincolnshire, UK. Posts: 203	Re: G & E Bradley CT-471 just wondering about the high pitched whine you hear,i would think thats from the chopper transformer,it should oscillate at 550hz is it that you can hear?

21st Oct 2018, 9:00 am	#58
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 It could be. Some of the caps which were ok for ESR are a bit leaky, but I don't have replacements for them all. I think some of my capacitors in stock which are new are leaky. Perhaps they've been sat on the shelf for too long. I've only in stock what was the remaining amount of a minimum purchase. So I might have to get buying again. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

28th Oct 2018, 11:28 am	#59
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 Power supply seems ok. 12v cal check is working. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

28th Oct 2018, 5:38 pm	#60
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: G & E Bradley CT-471 So, what's happening now and I don't know why, as I have no idea how these things work is.... on DC current, on the 0.4 range I get meter movement, but the reading doesn't correleate at all with what I'm sending it. The same on DC volts, on the 0.4 and 1.2 range. So I need to work out why that is and why still nothing on any other range. Though if I go to AC, the needle moves around to the centre and floats about a little. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.