Service sheet error, HMV 2011 - UK Vintage Radio Repair and Restoration Discussion Forum

Boater Sam · 7th Jul 2018, 5:55 pm

Have a record player to renovate, HMV 2011, the one with a radio included.
Replaced all the Hunts Horrors, all leaking madly or with no capacitance.

Its been got at before. One end of the MW aerial coil on the ferrite disconnected.

Works well now but checking the valve voltages threw up a mistake in the circuit diagram according to Radio Servicing page 150 off the CD.

This shows the pin 1 of the UCH81 and pin 1 of the UBF89 connected together onto a common 33k resistor.
But pin 1 on the UCH81 show it should have around 51 volts on it, however pin 1 of the UBF89 shows 128 volts!
So is it a length of resistance wire between the two ? No, its an error but which is correct?

Sam.

ukcol · 7th Jul 2018, 11:28 pm

Hi Sam,

Trying to find you an answer I discovered that quite a few models marketed on different brand names from the Thorn group have the same error repeated in their R&TVS pages. I even found an ERT sheet with the same error which suggests that the mistake was on a common document used by R&TVS and ERT.

Taking the typical operating screen currents for both valves from the valve data sheets and using ohms law to calculate the volts drop in the 33k resistor suggested a figure greater than the HT supply voltage

so that was a dead end.

Looking at circuits for other manufacturers I couldn't find a circuit where the UCH81 & UBF89 shared a 33k screen resistor but, with one exception all the voltages given were much nearer to 51 volts than 128 volts.

As regards the circuit error, I wonder if the mixer voltage was measured under no signal conditions and the IF stage voltage with signal. Such an elementary mistake could have lead to those figures.

Boater Sam · 8th Jul 2018, 9:30 am

I checked and the screens are running at 49 volts, seems to be correct so leave as is.
I considered signal conditions and also gram position but it makes very little difference to the voltage.
Pobodies nurfect.

ms660 · 8th Jul 2018, 10:19 am

Quote:

Originally Posted by ukcol

As regards the circuit error, I wonder if the mixer voltage was measured under no signal conditions and the IF stage voltage with signal. Such an elementary mistake could have lead to those figures.

That's what I was thinking as well, no signal/strong signal, vari mu and sliding screen.

Lawrence.

7th Jul 2018, 5:55 pm	#1
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Service sheet error, HMV 2011 Have a record player to renovate, HMV 2011, the one with a radio included. Replaced all the Hunts Horrors, all leaking madly or with no capacitance. Its been got at before. One end of the MW aerial coil on the ferrite disconnected. Works well now but checking the valve voltages threw up a mistake in the circuit diagram according to Radio Servicing page 150 off the CD. This shows the pin 1 of the UCH81 and pin 1 of the UBF89 connected together onto a common 33k resistor. But pin 1 on the UCH81 show it should have around 51 volts on it, however pin 1 of the UBF89 shows 128 volts! So is it a length of resistance wire between the two ? No, its an error but which is correct? Sam.

7th Jul 2018, 11:28 pm	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Service sheet error, HMV 2011 Hi Sam, Trying to find you an answer I discovered that quite a few models marketed on different brand names from the Thorn group have the same error repeated in their R&TVS pages. I even found an ERT sheet with the same error which suggests that the mistake was on a common document used by R&TVS and ERT. Taking the typical operating screen currents for both valves from the valve data sheets and using ohms law to calculate the volts drop in the 33k resistor suggested a figure greater than the HT supply voltage so that was a dead end. Looking at circuits for other manufacturers I couldn't find a circuit where the UCH81 & UBF89 shared a 33k screen resistor but, with one exception all the voltages given were much nearer to 51 volts than 128 volts. As regards the circuit error, I wonder if the mixer voltage was measured under no signal conditions and the IF stage voltage with signal. Such an elementary mistake could have lead to those figures.

8th Jul 2018, 9:30 am	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Service sheet error, HMV 2011 I checked and the screens are running at 49 volts, seems to be correct so leave as is. I considered signal conditions and also gram position but it makes very little difference to the voltage. Pobodies nurfect.