Hmv 1128 - UK Vintage Radio Repair and Restoration Discussion Forum

Dorian27 · 2nd Jul 2022, 10:03 am

Hi i have the above model. And the sound from the speaker was very distorted as if the speaker cone itself was faulty. I looked at the service sheet and the output amp valve was EL85 which i cheked and was on its way out so i replced it with a new tested one still the same sounds. So i replaced capacitor C47 with a new one still the same. So i put in an EL84 valve and run it and it eorks perfect. What dammage am i doing by using EL84 instead of EL85 i have ran the radio for a few hours and sound and radio seem to work exellent.

Herald1360 · 2nd Jul 2022, 11:46 am

Overloading the heater supply! EL84 0.76A, EL85 0.2A. Depending on the cathode resistor you may also be hammering the HT too.

Edit: C42 (that capacitor) might be a potentially useful candidate for replacement!

cathoderay57 · 2nd Jul 2022, 3:00 pm

The main worry is that on the EL84 pins 1 and 6 are ic (internal connection) whereas in the EL85 they are grid 1 and grid 3 respectively. Whether this might cause problems depends whether there is anything actually soldered to those pins in the radio itself. I think it would be best to refit the EL85 and compare the voltages on its pins with those quoted in the Radio & TV Servicing Sheet. These should be measured under no signal conditions i.e. tune away from any stations. Anode (Pin 7): 220v (AM) / 200v (FM); grid 2 (Pin 9): 200v (AM) / 215v (FM); cathode (Pin 3): 10v (AM) / 9v (FM). Grid 1 (Pin 1) should be at or close to zero volts. Jerry

Dorian27 · 2nd Jul 2022, 6:48 pm

C42. 22uf 350v what would be a sutable replacement for this please

Herald1360 · 2nd Jul 2022, 7:50 pm

C42 is 22nF not 22uF! Any 22nF polyester or polypropylene capacitor with 350V or higher rating will be fine.

Silicon · 2nd Jul 2022, 9:46 pm

The 360 Ohm cathode resistor on the schematic was selected to give the correct bias and cathode current for the EL85.

If the EL84 is biased with a 360 Ohm cathode resistor it will be running at a much lower cathode current than is normally used. This won't hurt the EL84.

If there is a faulty component in the circuit it could get worse and damage the output transformer.

You say that you have replaced C47, the cathode bypass capacitor.

Leakage in C42 or C45 could affect the bias and cause distortion.

I would replace C42, measure the resistance of R26, disconnect C45 and put a healthy EL85 back in the circuit.
I would then measure the voltage across R26 to find the cathode current.

Dorian27 · 3rd Jul 2022, 10:27 am

Am I correct C45 is the 220pf capacitor next to C42? If I replace C45 what voltage would be OK?

2nd Jul 2022, 10:03 am	#1
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 564	Hmv 1128 Hi i have the above model. And the sound from the speaker was very distorted as if the speaker cone itself was faulty. I looked at the service sheet and the output amp valve was EL85 which i cheked and was on its way out so i replced it with a new tested one still the same sounds. So i replaced capacitor C47 with a new one still the same. So i put in an EL84 valve and run it and it eorks perfect. What dammage am i doing by using EL84 instead of EL85 i have ran the radio for a few hours and sound and radio seem to work exellent.

2nd Jul 2022, 11:46 am	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Hmv 1128 Overloading the heater supply! EL84 0.76A, EL85 0.2A. Depending on the cathode resistor you may also be hammering the HT too. Edit: C42 (that capacitor) might be a potentially useful candidate for replacement! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

2nd Jul 2022, 3:00 pm	#3
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Hmv 1128 The main worry is that on the EL84 pins 1 and 6 are ic (internal connection) whereas in the EL85 they are grid 1 and grid 3 respectively. Whether this might cause problems depends whether there is anything actually soldered to those pins in the radio itself. I think it would be best to refit the EL85 and compare the voltages on its pins with those quoted in the Radio & TV Servicing Sheet. These should be measured under no signal conditions i.e. tune away from any stations. Anode (Pin 7): 220v (AM) / 200v (FM); grid 2 (Pin 9): 200v (AM) / 215v (FM); cathode (Pin 3): 10v (AM) / 9v (FM). Grid 1 (Pin 1) should be at or close to zero volts. Jerry

2nd Jul 2022, 6:48 pm	#4
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 564	Re: Hmv 1128 C42. 22uf 350v what would be a sutable replacement for this please

2nd Jul 2022, 7:50 pm	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Hmv 1128 C42 is 22nF not 22uF! Any 22nF polyester or polypropylene capacitor with 350V or higher rating will be fine. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

2nd Jul 2022, 9:46 pm	#6
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: Hmv 1128 The 360 Ohm cathode resistor on the schematic was selected to give the correct bias and cathode current for the EL85. If the EL84 is biased with a 360 Ohm cathode resistor it will be running at a much lower cathode current than is normally used. This won't hurt the EL84. If there is a faulty component in the circuit it could get worse and damage the output transformer. You say that you have replaced C47, the cathode bypass capacitor. Leakage in C42 or C45 could affect the bias and cause distortion. I would replace C42, measure the resistance of R26, disconnect C45 and put a healthy EL85 back in the circuit. I would then measure the voltage across R26 to find the cathode current.

3rd Jul 2022, 10:27 am	#7
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 564	Re: Hmv 1128 Am I correct C45 is the 220pf capacitor next to C42? If I replace C45 what voltage would be OK?