1936 Marconiphone 365 Radiogram

[Station X]

That seems low given that calculations in post #88 suggest that resistors R41 and R42 will draw 15 to 20mA.

I'm afraid I'm stuck.

Does the reading change when switching between radio and gram?

Does the reading change when you insert V1, V2, V3 and V4 leaving V5 unplugged?

[kinnego07]

No change in reading between radio and gram

With all valves in place except V5 I get a pretty steady reading of 14.6mA.

There is much more fluctuation up and down on the reading with V5 in place

[Station X]

With V5 in place does the HT measured at point 2 or 7 take a dive?

[PJL]

I am wondering if the set is OK but the lamp limiter is a bit too aggressive in limiting the mains voltage? Earlier I think the bulb was given as 60W but bulbs may not all be equal. At this point I would put the link and valves back in and clip the meter so as to monitor the HT (7 or 2 and chassis) and switch on. The HT should steadily rise to well above 280V within a couple of minutes then gradually fall back as V5 starts conducting. If the voltage stops rising and is still below 280V then switch off.

[kinnego07]

With V5 in place 2/7 unconnected the HT at 2 is Zero - 317V at 7 (lead from speaker)
317V is measured at 1 & 3 as well.

With V5 in place 2/7 connected HT at 2/7 is 81
At 1 it is 81V and 100V at 3. These readings again fluctuate up and down by about 10V but pretty well maintain a difference of around 18V between 3 and 1&2

I checked voltage again across R51 and I now read 0.82V. My old meter won't read this on the 2V scale

[Station X]

Originally Posted by kinnego07

The bulb in the lamp limiter is 60W

My own lamp limiter is fitted with a 100W lamp and I've never known it to stop a normal domestic set from working when switched in.

[kinnego07]

I briefly tried what PJL suggested - Switched to full power

HT rose to 350V (measured at 2/7) then dropped to 270V. My power meter at the limiter climbed from about 20W to 76W and remained there. Amps at this meter read 0.35A

The speaker came alive! Toggling the internal/external switch resulted in a constant humming/crackling in two of the three positions the third being completely dead. No stations could be tuned and the volume switch will need cleaned as it cuts in and out on turning the knob.

I'm anxious about leaving it on any longer

[Station X]

That's looking good. What are the voltages on V5 now, in particular across R51 the cathode resistor?

[kinnego07]

Cathode = 5.66V
Anode = 230V
Screen = 261V

I'm at a bbq for the next couple of hours and it's wet

[Station X]

Still looking good. You have a voltage across the cathode resistor R51 which proves V5 is conducting. As a final check on V5 make sure there's no positive voltage on the control grid.

If that's OK I suggest taking voltage readings on V4 with the set switched to gram.

Then if that's OK we can think about injecting an audio signal at the PU socket to show that the audio stages are working.

[Station X]

Thanks to PJL for pointing out the problem with the test lamp. I hadn't realised it was 60W and I was concerned by earlier reports of smoking components.

[kinnego07]

As usual the BBQ went on much longer than expected.

I ran the set on full power this morning for a few minutes before taking the readings suggested.

Before taking readings I did temperature checks on both the speaker coil and T2. Speaker coil was sitting at 54 C (hot to the touch) and T2 at 30 C so I switched off.

Would this be normal working temperature? The speaker seems too hot to me. As you can tell I am still a tad anxious (I think the previous smoke spooked me)

[Station X]

What were the voltage readings?

[kinnego07]

I didn't have time to take readings before switching off. So now that it has cooled down -

V4 reading pins clockwise from the filaments and in gram position

Cathode 1.96V

Anode 134.5v

7.5mV

1.96V

0.5mV

V5 reading pins clockwise from the filaments in gram position

Cathode 6.1V

Anode 245 V

Grid 112mV

Screen 290V

[Station X]

V4 anode voltage is high, but probably explained by the fact that a DMM won't pull so much current through R43 and R45 as an analogue meter. It doesn't take much current through high value resistors to reduce the measured voltage at the anode.

With set switched to GRAM and the volume turned up, do you get a click or buzz when you touch the pick up sockets with a screwdriver blade?

[kinnego07]

Yes, crackles

[Station X]

The audio stages are working then. With an aerial connected can you receive anything on the radio?

[kinnego07]

No, nothing from radio with aerial connected and external/internal switch to internal.

In external there is a steady hum but speaker is completely dead at internal

[Station X]

I assume you're referring to the INTERNAL/EXTERNAL speaker switch? You shouldn't hear anything from the speaker unless the switch is set to INTERNAL. This makes your answer a bit puzzling.

I suggest taking voltages on the other valves, in particular the screen grid voltages which are switched by the RADIO/GRAM control.

Have the wave change switch contacts been cleaned? Any clicks from the speaker when swiching wavebands?

[kinnego07]

I connected up a bluetooth device to the PU and we have Jazz music! Speaker sounds good.

When I switch to internal on the Int/Ext switch and radio on radio/gram switch I have nothing

There is hum when in external position

It's heartening though!

I will take reading on other valves