Rega Cartridge Impedance Help - Page 5 - UK Vintage Radio Repair and Restoration Discussion Forum

ms660 · 9th May 2018, 2:43 pm

If it's significantly out of specification/open circuit it will need replacing, if inexperienced, when replacing components replace one then test the unit before replacing another etc etc.

Having said that, I would consider getting someone who's qualified to sort out the amp etc.

Lawrence.

Bufo Bill · 9th May 2018, 2:48 pm

Thank you Lawrence, you've been very helpful.

julie_m · 9th May 2018, 3:08 pm

Quote:

Originally Posted by Bufo Bill

I looked at some YouTube videos last night, and some seem to suggest that you need to unsolder one end of the resistor before testing. I would much like to hear from my friends here if this is the best way of testing?

As a general rule, in a valve circuit, you can usually get away with testing a resistor in-situ; but in a semiconductor circuit, it's always best to disconnect one end before testing.

This is because semiconductor junctions might be turned on by the test voltage; but a cold valve is never going to conduct.

That being said, if there is something in parallel with a resistor that you are trying to test, you could get a false reading. If in doubt, always check the wiring diagram.

Bufo Bill · 9th May 2018, 3:14 pm

Julie, that's a very useful piece of advice, it's probably nothing to you but a little light went on in my brain then! I see why no one mentioned it now! Many thanks.
Bill.

Radio Wrangler · 9th May 2018, 4:37 pm

Every time a little light goes on, something becomes clearer and you can do something more, and most importantly, you've prepared the ground for the next little light to go on.

Some things are seen by some people as being so basic that they never mention them, and this creates a big step confronting the beginner. It's not intentional or malicious, it's just that some things are so familiar they become invisible.

Progress!

David

Bufo Bill · 9th May 2018, 5:07 pm

I've decided to replace R16 myself. Cathoderay57 (Jerry) has offered to help if I'm stuck after that. Thanks for the encouragement guys.
Bill.

cathoderay57 · 9th May 2018, 8:52 pm

Bill, before you start checking all the resistors hold fire a minute. R16 on the circuit diagram (assuming we're using the same diagram with the same numbering system) is 2.2M (red-red-green) but wired across S5 so when S5 is closed it will read short circuit (or 0.something ohms as you found). If you push the buttons in and out one by one with power off you should read R16 as a couple of Megohms. R16 is nothing to do with the HT supply so it's a red herring. With power on, you need to measure again the voltage between the "top" of R32 (25kohms) and chassis. It should be 330v or so. If it is zero then you don't have any HT voltage coming from the power amplifier. Either the plug has come out of the power amplifier, or there is a broken wire inside the plug, or the HT supply in the power amplifier has failed. Hope that helps. Cheers, Jerry

Bufo Bill · 9th May 2018, 10:16 pm

Cheers Jerry, very thankful you noticed that. I'll have another go tomorrow, and I'll be sure to keep you all updated.
Thanks from Bill.

Synchrodyne · 10th May 2018, 6:26 am

Quote:

Originally Posted by Radio Wrangler

It will have the effect of making the cartridge slightly less compliant in the L-R difference direction, up/down. Lenz' law.

Given the winding impedances and the velocity to voltage coefficient of a typical cartridge, I think it's fairly slight.

Cartridge conversion efficiency, power out/power in, is around 0.01% (*). The electrical loading effect on cartridge compliance is thus likely to be on the negligible side of fairly slight – nwwa.

Cheers

(*) According to Burrows, Wireless World 1971 July p.322.

Radio Wrangler · 10th May 2018, 7:23 am

Yup, that's slight

Well, I nearly chose 'The Mad Metrologist' as a forum name.

I think Burrows was talking about piezo-electric cartridges as well.

The Bailey-Burrows (and later Quilter evolved it further) preamp was quite interesting and introduced the idea of running a ceramic cartridge into a low impedance load and a charge amplifier. An easier impedance to make with bipolar transistors, but at the expense of needing equalisation.

I tried it with both Deram and 9TAHC cartridges, and I liked the results.

David

Edward Huggins · 10th May 2018, 11:42 am

The OP has struggled long and hard with this. I commend him for his perseverance. It this does go back cross-country to Huntingdon, please do report back on that legendary Quad service.

julie_m · 10th May 2018, 12:39 pm

Another way to look at is is through the Principle of Equivalence.

If loading a ceramic cartridge like that didn't work, you would have found a way to distinguish between a position sensor, and a velocity sensor / integrator combination. Which would go against all the laws of mathematics and physics. So it has to work.

If you take the abovementioned velocity sensor feeding into an integrator and put too small a resistance across the output, it keeps the capacitor from charging and effectively ruins the integrating action; giving you a velocity sensor with a simple resistive potential divider on the output. And you must get exactly the same thing if you connected a small resistance across an actual position sensor, because you can't tell the two apart looking only at their interfaces with the outside world -- i.e., the electrical terminals and the movable part.

Bufo Bill · 10th May 2018, 1:29 pm

Hi all, the good news is I have 355V at R32. My mistakes previously were caused by plugging the QCII into the mains via the extra socket on the side of the pre amp. Either there was a problem with the socket or the extra cable I had lying around. Next I will get those anode, cathode, and screen measurements you asked for. I am reading that on ef86 anode is pin6, cathode is pin3, and is screen pin1?
Thanks for your help.

Bufo Bill · 10th May 2018, 1:43 pm

EF86 Anode (pin6) 92.9V, Cathode (pin3), screen grid (pin 1) 1.44V.
Cheers from Bill.

ms660 · 10th May 2018, 1:53 pm

If the screen grid does measure 1.44V disconnect one end of C16 and measure the screen grid voltage again, if the same or similar check the resistance of R22.

Lawrence.

Bufo Bill · 10th May 2018, 2:00 pm

Sorry, ballsed that up. Pin 6=92.9V, Cathode Pin3=1.44V, screen grid pin 1=69.4V.
I do apologise old chap.
Bill.

ms660 · 10th May 2018, 2:03 pm

The voltages seem reasonable for a working valve.

Lawrence.

PJL · 10th May 2018, 3:54 pm

Are we back to working but low volume?

If the EF86 were low gain then due to the RIAA feedback network I would expect the high frequencies to be OK but the bass to be lost.

What do you mean by low volume? Is it just a different level from other channels or are you unable to get adequate sound levels from it even at full volume?

I would also like you to try without the parallel connection on the cartridge. This is for 2 reasons: a) you might have wired them out of phase b) I am not convinced it will track correctly if wired this way.

Ted Kendall · 10th May 2018, 4:31 pm

Quote:

Originally Posted by PJL

I am not convinced it will track correctly if wired this way.

You could short out both coils without affecting the physical behaviour of the pickup - not that you'd hear anything, of course...

Bufo Bill · 10th May 2018, 5:43 pm

Guys I think I have found the problem. When I plugged back in after cleaning the switches the volume problem was gone, but there was the same old distorted signal. I thought maybe the problem was as Synchrodyne said, so I tried the R2 unit which has an impedance of 50KOhms. The problem was still there. I looked at the cartridge again. Something has gone horribly awry, the cantilever is misshapen and bent. I must have cocked it up weeks ago. A generous gift from someone dear, and I trashed it. Sorry for excercising all your brains in vain. Thank you all for your generous help and offers.
Bill.

9th May 2018, 2:43 pm	#81
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Rega Cartridge Impedance Help If it's significantly out of specification/open circuit it will need replacing, if inexperienced, when replacing components replace one then test the unit before replacing another etc etc. Having said that, I would consider getting someone who's qualified to sort out the amp etc. Lawrence.

9th May 2018, 2:48 pm	#82
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Thank you Lawrence, you've been very helpful.

9th May 2018, 3:14 pm	#84
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Julie, that's a very useful piece of advice, it's probably nothing to you but a little light went on in my brain then! I see why no one mentioned it now! Many thanks. Bill.

9th May 2018, 4:37 pm	#85
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Rega Cartridge Impedance Help Every time a little light goes on, something becomes clearer and you can do something more, and most importantly, you've prepared the ground for the next little light to go on. Some things are seen by some people as being so basic that they never mention them, and this creates a big step confronting the beginner. It's not intentional or malicious, it's just that some things are so familiar they become invisible. Progress! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

9th May 2018, 5:07 pm	#86
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help I've decided to replace R16 myself. Cathoderay57 (Jerry) has offered to help if I'm stuck after that. Thanks for the encouragement guys. Bill.

9th May 2018, 8:52 pm	#87
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Rega Cartridge Impedance Help Bill, before you start checking all the resistors hold fire a minute. R16 on the circuit diagram (assuming we're using the same diagram with the same numbering system) is 2.2M (red-red-green) but wired across S5 so when S5 is closed it will read short circuit (or 0.something ohms as you found). If you push the buttons in and out one by one with power off you should read R16 as a couple of Megohms. R16 is nothing to do with the HT supply so it's a red herring. With power on, you need to measure again the voltage between the "top" of R32 (25kohms) and chassis. It should be 330v or so. If it is zero then you don't have any HT voltage coming from the power amplifier. Either the plug has come out of the power amplifier, or there is a broken wire inside the plug, or the HT supply in the power amplifier has failed. Hope that helps. Cheers, Jerry

9th May 2018, 10:16 pm	#88
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Cheers Jerry, very thankful you noticed that. I'll have another go tomorrow, and I'll be sure to keep you all updated. Thanks from Bill.

10th May 2018, 7:23 am	#90
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Rega Cartridge Impedance Help Yup, that's slight Well, I nearly chose 'The Mad Metrologist' as a forum name. I think Burrows was talking about piezo-electric cartridges as well. The Bailey-Burrows (and later Quilter evolved it further) preamp was quite interesting and introduced the idea of running a ceramic cartridge into a low impedance load and a charge amplifier. An easier impedance to make with bipolar transistors, but at the expense of needing equalisation. I tried it with both Deram and 9TAHC cartridges, and I liked the results. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

10th May 2018, 11:42 am	#91
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Rega Cartridge Impedance Help The OP has struggled long and hard with this. I commend him for his perseverance. It this does go back cross-country to Huntingdon, please do report back on that legendary Quad service. __________________ Edward.

10th May 2018, 12:39 pm	#92
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Rega Cartridge Impedance Help Another way to look at is is through the Principle of Equivalence. If loading a ceramic cartridge like that didn't work, you would have found a way to distinguish between a position sensor, and a velocity sensor / integrator combination. Which would go against all the laws of mathematics and physics. So it has to work. If you take the abovementioned velocity sensor feeding into an integrator and put too small a resistance across the output, it keeps the capacitor from charging and effectively ruins the integrating action; giving you a velocity sensor with a simple resistive potential divider on the output. And you must get exactly the same thing if you connected a small resistance across an actual position sensor, because you can't tell the two apart looking only at their interfaces with the outside world -- i.e., the electrical terminals and the movable part. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

10th May 2018, 1:29 pm	#93
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Hi all, the good news is I have 355V at R32. My mistakes previously were caused by plugging the QCII into the mains via the extra socket on the side of the pre amp. Either there was a problem with the socket or the extra cable I had lying around. Next I will get those anode, cathode, and screen measurements you asked for. I am reading that on ef86 anode is pin6, cathode is pin3, and is screen pin1? Thanks for your help.

10th May 2018, 1:43 pm	#94
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help EF86 Anode (pin6) 92.9V, Cathode (pin3), screen grid (pin 1) 1.44V. Cheers from Bill.

10th May 2018, 1:53 pm	#95
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Rega Cartridge Impedance Help If the screen grid does measure 1.44V disconnect one end of C16 and measure the screen grid voltage again, if the same or similar check the resistance of R22. Lawrence.

10th May 2018, 2:00 pm	#96
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Sorry, ballsed that up. Pin 6=92.9V, Cathode Pin3=1.44V, screen grid pin 1=69.4V. I do apologise old chap. Bill.

10th May 2018, 2:03 pm	#97
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Rega Cartridge Impedance Help The voltages seem reasonable for a working valve. Lawrence.

10th May 2018, 3:54 pm	#98
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Rega Cartridge Impedance Help Are we back to working but low volume? If the EF86 were low gain then due to the RIAA feedback network I would expect the high frequencies to be OK but the bass to be lost. What do you mean by low volume? Is it just a different level from other channels or are you unable to get adequate sound levels from it even at full volume? I would also like you to try without the parallel connection on the cartridge. This is for 2 reasons: a) you might have wired them out of phase b) I am not convinced it will track correctly if wired this way. Last edited by PJL; 10th May 2018 at 4:00 pm.

10th May 2018, 5:43 pm	#100
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Rega Cartridge Impedance Help Guys I think I have found the problem. When I plugged back in after cleaning the switches the volume problem was gone, but there was the same old distorted signal. I thought maybe the problem was as Synchrodyne said, so I tried the R2 unit which has an impedance of 50KOhms. The problem was still there. I looked at the cartridge again. Something has gone horribly awry, the cantilever is misshapen and bent. I must have cocked it up weeks ago. A generous gift from someone dear, and I trashed it. Sorry for excercising all your brains in vain. Thank you all for your generous help and offers. Bill.