Dansette Bermuda MK II ?? - Page 6 - UK Vintage Radio Repair and Restoration Discussion Forum

martinpinner · 27th Feb 2018, 10:19 am

The voltage readings are as follows:

100R resistor 230 and 243

Can terminals 245, 235 and 103

Welwyn measures correctly.

Martin

Station X · 27th Feb 2018, 10:23 am

Nothing wrong there then.

What's the DC voltage across the cathode resistors? The cathodes are pins 2 and 8 of the UCL82.

martinpinner · 27th Feb 2018, 10:57 am

Thanks. Should I bridge C8 at both end of the cap to the circuit below or is it not necessary?
Martin

Station X · 27th Feb 2018, 11:22 am

I'm not sure that I understand what you mean by bridging a capacitor.

The track, which one end of the capacitor C8 is connected to, should be bridged to the adjacent track as described in post #86.

martinpinner · 27th Feb 2018, 11:46 am

In post 93 I ask the question and try explaining what I mean.
C8 is connected to different tracks and I believe that when I removed the old capacitor it could have been also connected (bridged) to the track below.
Martin

martinpinner · 27th Feb 2018, 5:20 pm

Voltage across pins 2 and 8 of UCL82 is 18 volts.
Whilst taking the reading if the probes are on the pins too long you get aloud crackly sound.
Martin

Station X · 27th Feb 2018, 5:30 pm

You need to measure pin 2 to chassis and pin 8 to chassis. That gives the voltage at each of the two cathodes.

A voltage here indicates that there is a volt drop across the cathode resistor from which it can be deduced that the valve is passing anode and/or screen current. A practical application of Ohms law.

martinpinner · 27th Feb 2018, 5:53 pm

Pin 2 is 19.70 volts
Pin 8 is 1.20 volts

Station X · 27th Feb 2018, 8:56 pm

Those readings are good.

Please check that you have around 230 VDC on pin 6, the anode of the pentode section of the UCL82. Measure this w.r.t chassis. A good reading here will indicate that the output transformer primary is OK.

If the voltage is as suggested, there isn't much wrong with the amplifier.

Next step is to check that you get a loud hum or buzz when you touch the centre tag of the volume control with a screwdriver blade.

ms660 · 27th Feb 2018, 9:09 pm

Quote:

Originally Posted by martinpinner

Pin 2 is 19.70 volts
Pin 8 is 1.20 volts

Lawrence.

Station X · 27th Feb 2018, 9:18 pm

Valve Museum suggests -22.5 volts max on g1 of the pentode section. I'd expect the cathode to be at a similar voltage, but positive?

Station X · 27th Feb 2018, 9:46 pm

I see what you mean. I'd forgotten to take into account the value of the cathode resistor.

ms660 · 27th Feb 2018, 10:00 pm

Quote:

Originally Posted by Station X

Valve Museum suggests -22.5 volts max on g1 of the pentode section. I'd expect the cathode to be at a similar voltage, but positive?

That's the Valve Museums headline figure, those headlines figures are wrong in many instances, I've had it show the wrong heater current amongst others for some valves, I suspect the -ve 22 volts quoted is for grid cut off, the UCL82 data sheet reveals all:

http://www.r-type.org/pdfs/ucl82.pdf

The highest quoted is -ve 16 volts @ Va & Vg2 = 200 volts, that gives a cathode current of 42mA which implies a cathode resistor of approx. 380 ohms. Max. Ik is quoted as 50mA. In the Dansette 19.7 volts means approx. 90mA if the cathode to chassis resistance is 220 ohms as suggested in the schematic, either that or possibly the cathode to chassis resistance has gone high.

EDIT: Post crossed.

Lawrence.

Station X · 27th Feb 2018, 10:10 pm

The Bush RP60 service sheet suggests cathode voltages of 0.75V for the triode section and 8.8V for the pentode section. That's with a 180R cathode resistor.

I think it would be best if the OP checked the value of the cathode resistor (as indicated by the colour code and as measured) and gave us voltage readings for all the UCL82 valve pins except pins 4 and 5 which are the heaters.

EDIT. Cathode resistor seems to be colour coded red, red, brown (220R) assuming pic is of the actual amp.

martinpinner · 28th Feb 2018, 1:08 pm

Thanks for your posts here are some reading as suggested.
Pin 1 1.40 control grid of triode
Pin 2 19.80 cathode of pentode
Pin 3 19.30 control grid of pentode
Pin 6 219.00 anode of pentode
Pin 7 99.80 screen grid of pentode
Pin 8 1.20 cathode of triode
Pin 9 3.52 anode of triode

No loud hum or buzz when putting screw driver blade on the centre tag of volume control.Does the volume control have to be high?

Cathode resistor reads 230R.

The Welwyn resistor gets extremely hot - is that ok?

Martin

ms660 · 28th Feb 2018, 1:17 pm

Looks like lots of g1 volts at the expense of triode anode volts, I would check the grid coupling capacitors and the circuit around there, remember there are in effect two g1 coupling capacitors in this amplifier.

The cathode resistor reads ok.

The large Welwyn resistor will get very hot because it will be dissipating approx. 15-16 watts or so.

Lawrence.

Station X · 28th Feb 2018, 1:35 pm

What sticks out there is that pin 3 (the control grid of the pentode) is at 19.3V, it should be at zero volts. Check the wiring, there may be some kind of connection between pins 2 and 3. Check the resistance between these two pins. It's made up of three resistors in series, but their values are unclear from the diagram apart from the 220R.

The anode voltage of the triode (pin 9) is extremely low too. Check the value of the anode resistor (100k?) and the voltage on either side of it.

EDIT. Crossed with Lawrence.

martinpinner · 28th Feb 2018, 1:40 pm

Thanks - I cannot check the capacitors on my DMM. I replaced 3 of the sufflex capacitors as recommended by you and there are only 2 remaining. Should I replace them?
Unfortunately I am not familiar with g1 volts / triode anode volts.
Martin

Station X · 28th Feb 2018, 1:42 pm

OK.

As a first step, check the resistance between pins 2 and 3 of the valve with the power off.

EDIT. Expect a reading of around 713k.

martinpinner · 28th Feb 2018, 4:47 pm

No resistance between pins 2 and 3 of the valve.

The 100K resistor is connected to pins 7 and 9 by the PCB board but has a reading of 140K. The volt measurements at both ends are 100 and 3.6.
The 1.5K resistor is connected on the top track of the PCB board to Pin 7 via the PCB board.It reads 1.45K. The volt measurements 1.2 and 0.

27th Feb 2018, 10:19 am	#101
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? The voltage readings are as follows: 100R resistor 230 and 243 Can terminals 245, 235 and 103 Welwyn measures correctly. Martin

27th Feb 2018, 10:23 am	#102
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? Nothing wrong there then. What's the DC voltage across the cathode resistors? The cathodes are pins 2 and 8 of the UCL82. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 10:57 am	#103
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? Thanks. Should I bridge C8 at both end of the cap to the circuit below or is it not necessary? Martin

27th Feb 2018, 11:22 am	#104
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? I'm not sure that I understand what you mean by bridging a capacitor. The track, which one end of the capacitor C8 is connected to, should be bridged to the adjacent track as described in post #86. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 11:46 am	#105
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? In post 93 I ask the question and try explaining what I mean. C8 is connected to different tracks and I believe that when I removed the old capacitor it could have been also connected (bridged) to the track below. Martin

27th Feb 2018, 5:20 pm	#106
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? Voltage across pins 2 and 8 of UCL82 is 18 volts. Whilst taking the reading if the probes are on the pins too long you get aloud crackly sound. Martin

27th Feb 2018, 5:30 pm	#107
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? You need to measure pin 2 to chassis and pin 8 to chassis. That gives the voltage at each of the two cathodes. A voltage here indicates that there is a volt drop across the cathode resistor from which it can be deduced that the valve is passing anode and/or screen current. A practical application of Ohms law. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 5:53 pm	#108
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? Pin 2 is 19.70 volts Pin 8 is 1.20 volts

27th Feb 2018, 8:56 pm	#109
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? Those readings are good. Please check that you have around 230 VDC on pin 6, the anode of the pentode section of the UCL82. Measure this w.r.t chassis. A good reading here will indicate that the output transformer primary is OK. If the voltage is as suggested, there isn't much wrong with the amplifier. Next step is to check that you get a loud hum or buzz when you touch the centre tag of the volume control with a screwdriver blade. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 9:18 pm	#111
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? Valve Museum suggests -22.5 volts max on g1 of the pentode section. I'd expect the cathode to be at a similar voltage, but positive? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 9:46 pm	#112
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? I see what you mean. I'd forgotten to take into account the value of the cathode resistor. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Feb 2018, 10:10 pm	#114
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? The Bush RP60 service sheet suggests cathode voltages of 0.75V for the triode section and 8.8V for the pentode section. That's with a 180R cathode resistor. I think it would be best if the OP checked the value of the cathode resistor (as indicated by the colour code and as measured) and gave us voltage readings for all the UCL82 valve pins except pins 4 and 5 which are the heaters. EDIT. Cathode resistor seems to be colour coded red, red, brown (220R) assuming pic is of the actual amp. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Feb 2018, 1:08 pm	#115
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? Thanks for your posts here are some reading as suggested. Pin 1 1.40 control grid of triode Pin 2 19.80 cathode of pentode Pin 3 19.30 control grid of pentode Pin 6 219.00 anode of pentode Pin 7 99.80 screen grid of pentode Pin 8 1.20 cathode of triode Pin 9 3.52 anode of triode No loud hum or buzz when putting screw driver blade on the centre tag of volume control.Does the volume control have to be high? Cathode resistor reads 230R. The Welwyn resistor gets extremely hot - is that ok? Martin Last edited by Station X; 28th Feb 2018 at 1:23 pm. Reason: Electrode designations added.

28th Feb 2018, 1:17 pm	#116
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Dansette Bermuda MK II ?? Looks like lots of g1 volts at the expense of triode anode volts, I would check the grid coupling capacitors and the circuit around there, remember there are in effect two g1 coupling capacitors in this amplifier. The cathode resistor reads ok. The large Welwyn resistor will get very hot because it will be dissipating approx. 15-16 watts or so. Lawrence. Last edited by ms660; 28th Feb 2018 at 1:26 pm.

28th Feb 2018, 1:35 pm	#117
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? What sticks out there is that pin 3 (the control grid of the pentode) is at 19.3V, it should be at zero volts. Check the wiring, there may be some kind of connection between pins 2 and 3. Check the resistance between these two pins. It's made up of three resistors in series, but their values are unclear from the diagram apart from the 220R. The anode voltage of the triode (pin 9) is extremely low too. Check the value of the anode resistor (100k?) and the voltage on either side of it. EDIT. Crossed with Lawrence. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Feb 2018, 1:40 pm	#118
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? Thanks - I cannot check the capacitors on my DMM. I replaced 3 of the sufflex capacitors as recommended by you and there are only 2 remaining. Should I replace them? Unfortunately I am not familiar with g1 volts / triode anode volts. Martin

28th Feb 2018, 1:42 pm	#119
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Dansette Bermuda MK II ?? OK. As a first step, check the resistance between pins 2 and 3 of the valve with the power off. EDIT. Expect a reading of around 713k. Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Feb 2018, 4:47 pm	#120
martinpinner Hexode Join Date: Oct 2015 Location: Sheffield, South Yorkshire, UK. Posts: 252	Re: Dansette Bermuda MK II ?? No resistance between pins 2 and 3 of the valve. The 100K resistor is connected to pins 7 and 9 by the PCB board but has a reading of 140K. The volt measurements at both ends are 100 and 3.6. The 1.5K resistor is connected on the top track of the PCB board to Pin 7 via the PCB board.It reads 1.45K. The volt measurements 1.2 and 0.