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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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2nd May 2022, 2:32 pm | #121 |
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Re: 1936 Marconiphone 365 Radiogram
Very good!
I suspect the knob on the INTERNAL/EXTERNAL switch is fitted the wrong way round or something like that. It's unclear from the circuit whether it has two or three positions.
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2nd May 2022, 3:01 pm | #122 |
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Re: 1936 Marconiphone 365 Radiogram
With switches in Internal and radio positions and reading clockwise from filaments
V1 pin 1 1.68V pin 2 75V pin 3 1.5mV pin4 350mV pin 5 1.68V V2 pin 1 0.0V pin 2 262V pin 3 352V pin 4 4.5mV pin 5 74.6V V3 pin 1 1.38V pin 2 74.1 pin 3 1.39V pin 4 0.5V pin 5 1.4V There are three positions on the switch Position 1 is internal and 2&3 I can put bluetooth through. All wiring looks original and untouched at the switch as with the rest of the radio |
2nd May 2022, 3:16 pm | #123 |
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Re: 1936 Marconiphone 365 Radiogram
What about the voltage on the top caps?
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2nd May 2022, 3:46 pm | #124 |
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Re: 1936 Marconiphone 365 Radiogram
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2nd May 2022, 4:14 pm | #125 |
Tetrode
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Re: 1936 Marconiphone 365 Radiogram
Thanks ms660 for the pin numbers.
V1 269V V2 0.98V V3 270V V4 5mV I got carried away with the jazz music and forgot about top caps |
2nd May 2022, 8:29 pm | #126 |
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Re: 1936 Marconiphone 365 Radiogram
There seems to be a distinct lack of screen grid voltage on V1 and V3. This derived from the potential divider R41/R42 which we visited earlier.
V3 should have a permanent screen grid supply. The screen grid supply to V1 and V2 is only present in RADIO mode and is fed from S16 contacts 5 and 6. The screen grids of all three valves should be at the same voltage.
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2nd May 2022, 8:54 pm | #127 |
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Re: 1936 Marconiphone 365 Radiogram
Graham, I think the pin numbering is wrong, there is 75V on V1 pin 2, V2 pin 5 and V3 pin 2. The pin numbers should read 7, 3, 7.
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3rd May 2022, 10:10 am | #128 |
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Re: 1936 Marconiphone 365 Radiogram
Best to use the correct valve pin numbers.
V3's screen grid supply is switched along with that of V1 and V2 in the schematics I have. Lawrence. |
3rd May 2022, 10:22 am | #129 |
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Re: 1936 Marconiphone 365 Radiogram
Agreed. I got confused following parallel lines.
I'll analyse the voltage readings later once I've reconciled the pin numbering.
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3rd May 2022, 11:34 am | #130 |
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Re: 1936 Marconiphone 365 Radiogram
Apologies for causing confusion with pin numbering. I was unaware of the proper pin numbering until ms660 post.
As my late father said "ups and downs we've had a few but here we go again" |
3rd May 2022, 1:45 pm | #131 | |
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Re: 1936 Marconiphone 365 Radiogram
Quote:
V1 VMP4G Pin 1 Metallisation 1.5mV Pin 2 g1 350mV Pin 3 g3 1.68V Pin 4 Heater Pin 5 Heater Pin 6 Cathode 1.68V Pin 7 g2 75V TC anode 269V. V2 X41 Pin 1 a(t) 352V Pin 2 g1(t)g3 4.5mV Pin 3 g2, g4 74.6V Pin 4 Heater Pin 5 Heater Pin 6 m, Cathode 0V Pin 7 Anode 262V TC g1 0.98V V3 VMP4G Pin 1 Metallisation 1.39mV Pin 2 g1 0.5V Pin 3 g3 1.4V Pin 4 Heater Pin 5 Heater Pin 6 Cathode 1.38V Pin 7 g2 74.1V TC anode 270V. Anyone disagree?
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3rd May 2022, 2:08 pm | #132 |
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Re: 1936 Marconiphone 365 Radiogram
I would have expected to see a voltage on V2 pin 6 cathode, ie across R9 150R. Is a voltage present here on any of the five wavebands?
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3rd May 2022, 2:44 pm | #133 |
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Re: 1936 Marconiphone 365 Radiogram
There is no voltage at pin V2 pin 6 (Cathode) in any ot the four wavelengths.
Resistance across R9 is 226 ohms Your valve pin listings are correct apart from V3 pin 1 should be 1.39mV Switching to Gram cuts grid supply to all three valves. You are correct - the Int/Ext Knob is on the wrong way around |
3rd May 2022, 3:17 pm | #134 |
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Re: 1936 Marconiphone 365 Radiogram
Error corrected.
Have you cleaned the contacts of the wave change switches with contact cleaner such as Servisol 10? I would suggest replacing R9 which has drifted high. Also check R8 and replace if necessary. Replace C18 0.1uF if you haven't already done so.
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3rd May 2022, 3:31 pm | #135 |
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Re: 1936 Marconiphone 365 Radiogram
No, I shall order some today. Is there any other readily available product I could use as a substitute?
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3rd May 2022, 3:33 pm | #136 |
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Re: 1936 Marconiphone 365 Radiogram
Anything branded as "Contact Cleaner" will do, but don't use ordinary WD40.
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3rd May 2022, 4:35 pm | #137 |
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Re: 1936 Marconiphone 365 Radiogram
Those V2 voltages suggest that V2's heaters aren't working, or if they are there's no emission.
Lawrence. |
3rd May 2022, 5:23 pm | #138 |
Tetrode
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Re: 1936 Marconiphone 365 Radiogram
So I have cleaned all the switches with contact cleaner but no change.
V2 pin 6 has no voltage. There is hum from the speaker which increases and fizzes when I touch V2 metallic coating |
3rd May 2022, 5:25 pm | #139 |
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Re: 1936 Marconiphone 365 Radiogram
Is V2 lit up?
Check for an AC voltage across pins 4 and 5. Clean the valve's pins. Gently nip up the valve holder sockets if they're a loose fit.
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3rd May 2022, 6:26 pm | #140 |
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Re: 1936 Marconiphone 365 Radiogram
4V AC present at pins 4&5 of all valves
I cleaned the valve pins and holders I can not see any glow from the valve but it is metalized and in an awkward place to see. It feels warm to the touch but this could be radiated heat from the neighbouring valves. I have to say that the quality of sound from the speaker is fabulous. |