Roberts P4D - UK Vintage Radio Repair and Restoration Discussion Forum

bobhowe · 15th Sep 2021, 7:40 pm

Hi. I purchased this on the 14th of July at the same time as my Philips V5A discussed in another thread. As i was going to visit David Boynes' shop today to give him some DAC90 parts I asked if he could test my Roberts P4D on his 90V/1.4V power supply to see it there was any issues with this set as it has not been used for a long time before I make a power supply and if the valve heaters are open circuit the set would be not economical as the valves are not cheap and I am pleased to say that when powered up for its first Squeak we got quiet distorted sound

Next step is to replace the grid coupling capacitor. David has kindly lent me his power supply so I can get the set working and build a power supply here si a picture of the set and power supply the power supply looks like it was made for this set.

Kind regards, Bob.

Sideband · 15th Sep 2021, 8:05 pm

These are good sets. Mine has a mock battery fitted that looks original but has 10 PP3's for HT and 2 D cells for the LT. They last ages. MW and LW performance is good but it's a bit deaf on SW even with a very long aerial.

Valves are only about £5 each if you do need any replacements.

bobhowe · 15th Sep 2021, 8:20 pm

Hi Sideband thanks for reply this one even so if needs replacement capacitors it is going to perform well when its done thanks about valves they look like they are ok posted on the wanted section for parts needed kind regards Bob

Ed_Dinning · 15th Sep 2021, 8:23 pm

Hi Bob, my version has the similar PSU fitted, I think it was an OEM unit

Ed

bobhowe · 15th Sep 2021, 8:53 pm

Quote:

Originally Posted by Ed_Dinning

Hi Bob, my version has the similar PSU fitted, I think it was an OEM unit

Ed

Hi Ed this power supply was hand made by David the same as your circuit using a VCR transformer works very well . This set i bought for Sheila kind regards Bob

FERNSEH · 16th Sep 2021, 11:00 am

The power supply unit was made for the Ever-Ready Sky "Monarch" AM radio.
The battery connector plug in the Roberts radio is the same type, a four pin B4.
Initial tests indicated the the receiver was drawing excess HT current, >20mA.
It's certain the coupling capacitor between the DAC32 and DL35 output valve is leaky. Only the strongest local station could be received but with terrible distortion.

DFWB.

bobhowe · 16th Sep 2021, 3:35 pm

Quote:

Originally Posted by FERNSEH

The power supply unit was made for the Ever-Ready Sky "Monarch" AM radio.
The battery connector plug in the Roberts radio is the same type, a four pin B4.
Initial tests indicated the the receiver was drawing excess HT current, >20mA.
It's certain the coupling capacitor between the DAC32 and DL35 output valve is leaky. Only the strongest local station could be received but with terrible distortion.

DFWB.

This Power Supply is well made by David and does the job vary well you would think it was made for The Roberts Radio is it fits perfectly were the battery used to be kind regards Bob

ms660 · 16th Sep 2021, 3:47 pm

It's not a very good shortwave circuit.

Lawrence.

bobhowe · 16th Sep 2021, 8:25 pm

Quote:

Originally Posted by FERNSEH

The power supply unit was made for the Ever-Ready Sky "Monarch" AM radio.
The battery connector plug in the Roberts radio is the same type, a four pin B4.
Initial tests indicated the the receiver was drawing excess HT current, >20mA.
It's certain the coupling capacitor between the DAC32 and DL35 output valve is leaky. Only the strongest local station could be received but with terrible distortion.

DFWB.

Update using trader sheet 828 i changed the grid coupling capacitor ( c12 ) a lot louder but still got distortion wired a remote known good speaker still the same . a few checks later & found ( C14 ) Electrolytic 50UF 12VDC is OC . David did say to me that there might be an Electrolytic capacitor that might be OC . The volume pot has a dead spot on it just above half volume ( That would have been the must used volume setting ) i will replace the Capacitor and volume pot and see what happens kind regards Bob

FERNSEH · 16th Sep 2021, 8:43 pm

Hi Bob,
worthwhile checking the components associated with the DAC32 detector and audio amplifier. The anode load resistor might possibly gone high value and as the triode amplifier will be biased by grid current, the coupling capacitor will be most likely be leaky.

DFWB.

bobhowe · 17th Sep 2021, 7:48 pm

Quote:

Originally Posted by FERNSEH

Hi Bob,
worthwhile checking the components associated with the DAC32 detector and audio amplifier. The anode load resistor might possibly gone high value and as the triode amplifier will be biased by grid current, the coupling capacitor will be most likely be leaky.

DFWB.

Hi David better progress today cleaned the volume pot snipped out ( c13 tone corrector capacitor ) and changed ( C14 ) on the 828 trader sheet 50UF 12VDC that was OC for a 47UF 100VDC that improved the performance as well but still not right will check the anode load resistor and change ( C11 AF coupling for DAC32 ) next as you suggested kind regards Bob

bobhowe · 17th Sep 2021, 8:40 pm

Hi without starting other threads on this radio and getting shot down the Roberts P4D is a lot easier to service than the Bush DAC90 /DAC90A and it shares the same components as the Bush sets as well same makel capacitors DAC90A & speaker DAC90 kind regards Bob

FERNSEH · 17th Sep 2021, 9:41 pm

The circuit diagram of the audio amplifier.

DFWB.

bobhowe · 18th Sep 2021, 1:38 pm

Quote:

Originally Posted by FERNSEH

The circuit diagram of the audio amplifier.

DFWB.

Thanks David i will keep you posted kind regards Bob

bobhowe · 18th Sep 2021, 2:16 pm

Quote:

Originally Posted by Ed_Dinning

Hi Bob, my version has the similar PSU fitted, I think it was an OEM unit

Ed

Hi Ed your version might have been the Roberts RMB did it have a Ferrite Aerial ? & did it have B7G valves ? as my P4D has a an internal loop ( frame Aerials ) & octal base valves & without going OT and getting shot down the Roberts RMB was released in September 1952 for £26.00 & the Roberts P4D was released in 1946 for £18.00 my P4D is dated 1949 > 1950 as the 50UF TCC capacitor has AUG 49 on it kind regards Bob

Ed_Dinning · 18th Sep 2021, 8:54 pm

Hi Bob, not sure of the model at present and its well buried in the TUIT pile.
The eliminator looks as if it was designed to fit into the battery space

Ed

bobhowe · 18th Sep 2021, 9:08 pm

Hi Ed you have a PM kind regards Bob

bobhowe · 20th Sep 2021, 6:01 pm

Quote:

Originally Posted by FERNSEH

The circuit diagram of the audio amplifier.

DFWB.

Hi working of Davids circuit diagram to check the values as David suggested grid resistor on the DL35 is 2MEG the actual reading in picture 1 . The anode load resistor on the DAC32 is 1MEG the actual reading in picture 2 . The anode is 78V the actual reading in picture 3 . Next step is to change C19 & C20 as David says there will leaky more to follow kind regards Bob

FERNSEH · 20th Sep 2021, 9:15 pm

Hi Bob,
At 78V the anode voltage of the DAC32 is too high. A figure near 30 volts should be expected. Unless there is a negative voltage on the grid and the valve is cut-off it would be safe to say the triode has gone low emission.

DFWB.

bobhowe · 20th Sep 2021, 9:34 pm

Quote:

Originally Posted by FERNSEH

Hi Bob,
At 78V the anode voltage of the DAC32 is too high. A figure near 30 volts should be expected. Unless there is a negative voltage on the grid and the valve is cut-off it would be safe to say the triode has gone low emission.

DFWB.

Hi David my fault the anode voltage was measured from the DL35 not the DAC32 kind regards Bob

15th Sep 2021, 7:40 pm	#1
bobhowe Heptode Join Date: Jun 2005 Location: Sunderland, Tyne and Wear, UK. Posts: 661	Roberts P4D Hi. I purchased this on the 14th of July at the same time as my Philips V5A discussed in another thread. As i was going to visit David Boynes' shop today to give him some DAC90 parts I asked if he could test my Roberts P4D on his 90V/1.4V power supply to see it there was any issues with this set as it has not been used for a long time before I make a power supply and if the valve heaters are open circuit the set would be not economical as the valves are not cheap and I am pleased to say that when powered up for its first Squeak we got quiet distorted sound Next step is to replace the grid coupling capacitor. David has kindly lent me his power supply so I can get the set working and build a power supply here si a picture of the set and power supply the power supply looks like it was made for this set. Kind regards, Bob. Attached Thumbnails

15th Sep 2021, 8:05 pm	#2
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,566	Re: Roberts P4D These are good sets. Mine has a mock battery fitted that looks original but has 10 PP3's for HT and 2 D cells for the LT. They last ages. MW and LW performance is good but it's a bit deaf on SW even with a very long aerial. Valves are only about £5 each if you do need any replacements. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

15th Sep 2021, 8:20 pm	#3
bobhowe Heptode Join Date: Jun 2005 Location: Sunderland, Tyne and Wear, UK. Posts: 661	Re: Roberts P4D Hi Sideband thanks for reply this one even so if needs replacement capacitors it is going to perform well when its done thanks about valves they look like they are ok posted on the wanted section for parts needed kind regards Bob

15th Sep 2021, 8:23 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Roberts P4D Hi Bob, my version has the similar PSU fitted, I think it was an OEM unit Ed

16th Sep 2021, 11:00 am	#6
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Roberts P4D The power supply unit was made for the Ever-Ready Sky "Monarch" AM radio. The battery connector plug in the Roberts radio is the same type, a four pin B4. Initial tests indicated the the receiver was drawing excess HT current, >20mA. It's certain the coupling capacitor between the DAC32 and DL35 output valve is leaky. Only the strongest local station could be received but with terrible distortion. DFWB. Attached Thumbnails

16th Sep 2021, 3:47 pm	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Roberts P4D It's not a very good shortwave circuit. Lawrence.

16th Sep 2021, 8:43 pm	#10
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Roberts P4D Hi Bob, worthwhile checking the components associated with the DAC32 detector and audio amplifier. The anode load resistor might possibly gone high value and as the triode amplifier will be biased by grid current, the coupling capacitor will be most likely be leaky. DFWB. Last edited by FERNSEH; 16th Sep 2021 at 9:02 pm.

17th Sep 2021, 8:40 pm	#12
bobhowe Heptode Join Date: Jun 2005 Location: Sunderland, Tyne and Wear, UK. Posts: 661	Re: Roberts P4D Hi without starting other threads on this radio and getting shot down the Roberts P4D is a lot easier to service than the Bush DAC90 /DAC90A and it shares the same components as the Bush sets as well same makel capacitors DAC90A & speaker DAC90 kind regards Bob

17th Sep 2021, 9:41 pm	#13
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Roberts P4D The circuit diagram of the audio amplifier. DFWB. Attached Thumbnails

18th Sep 2021, 8:54 pm	#16
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Roberts P4D Hi Bob, not sure of the model at present and its well buried in the TUIT pile. The eliminator looks as if it was designed to fit into the battery space Ed

18th Sep 2021, 9:08 pm	#17
bobhowe Heptode Join Date: Jun 2005 Location: Sunderland, Tyne and Wear, UK. Posts: 661	Re: Roberts P4D Hi Ed you have a PM kind regards Bob __________________ Kind regards, Bob.

20th Sep 2021, 9:15 pm	#19
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Roberts P4D Hi Bob, At 78V the anode voltage of the DAC32 is too high. A figure near 30 volts should be expected. Unless there is a negative voltage on the grid and the valve is cut-off it would be safe to say the triode has gone low emission. DFWB.