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Old 15th Sep 2021, 6:40 pm   #1
bobhowe
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Default 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.
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Old 15th Sep 2021, 7:05 pm   #2
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Default 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.
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Old 15th Sep 2021, 7:20 pm   #3
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Default 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
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Old 15th Sep 2021, 7:23 pm   #4
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Default Re: Roberts P4D

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

Ed
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Old 15th Sep 2021, 7:53 pm   #5
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Default Re: Roberts P4D

Quote:
Originally Posted by Ed_Dinning View Post
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
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Old 16th Sep 2021, 10:00 am   #6
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Default 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.
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Old 16th Sep 2021, 2:35 pm   #7
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
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
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Old 16th Sep 2021, 2:47 pm   #8
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Default Re: Roberts P4D

It's not a very good shortwave circuit.

Lawrence.
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Old 16th Sep 2021, 7:25 pm   #9
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
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
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Old 16th Sep 2021, 7:43 pm   #10
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Default 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 8:02 pm.
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Old 17th Sep 2021, 6:48 pm   #11
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
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
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Old 17th Sep 2021, 7:40 pm   #12
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Default 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
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Old 17th Sep 2021, 8:41 pm   #13
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Default Re: Roberts P4D

The circuit diagram of the audio amplifier.

DFWB.
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Old 18th Sep 2021, 12:38 pm   #14
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
The circuit diagram of the audio amplifier.

DFWB.
Thanks David i will keep you posted kind regards Bob
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Old 18th Sep 2021, 1:16 pm   #15
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Default Re: Roberts P4D

Quote:
Originally Posted by Ed_Dinning View Post
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
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Old 18th Sep 2021, 7:54 pm   #16
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Default 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
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Old 18th Sep 2021, 8:08 pm   #17
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Default Re: Roberts P4D

Hi Ed you have a PM kind regards Bob
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Old 20th Sep 2021, 5:01 pm   #18
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
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
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Old 20th Sep 2021, 8:15 pm   #19
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Default 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.
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Old 20th Sep 2021, 8:34 pm   #20
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Default Re: Roberts P4D

Quote:
Originally Posted by FERNSEH View Post
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
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