HMV 1122 Capacitor Confusion

[ValvoStef]

Also, the voltage accross R3 (V1 screen) is 100V. The grid voltage on V1 triode section is -0.5V. The grid voltage on the grid of the pentode pin 4 is 0 v.

[ValvoStef]

Annoyingly, now I receive a French station on AM.

[ValvoStef]

OK, both anode tags on V1 base are broken. I have to put in a new B7 base before I can carry on. Riveted in, damn.

[ValvoStef]

Originally Posted by GeoffK

HT voltages seem too high, voltage on the RF side of R16 should be about 200 Volts.

With the repaired V1 base I measure 245V. The French station I received earlier on has disappeared. I now suspect a bad contact on the selector switch. This, however, should not explain the high voltages.

[ukcol]

Going back to the voltages you reported in post 15.

Originally Posted by ValvoStef

As suggested, I measured the voltages on valves V1 and V2. On the service sheet the anode voltage should be 168V, I measure 233V.

Originally Posted by ValvoStef

The voltage before the HT 2K smoothing resistor is 293V and after the resistor it is 259V.

As I said in post 17 this suggest a 26 volt drop across the primary of both IF transformers. So either >

1] You have made an error measuring the voltages.

2] I have made a misinterpretation of the readings you reported.

3] There really is a 26 volt drop across the primary of both IF transformers.

In the case of 3] above you have a fault in the IF transformers. The DC resistance of the IF transformers is very low the order of a few ohms; to get a 26 volt drop there needs to be a number of AMPS flowing, clearly impossible. The only possibility is that the primaries have a high resistance fault that you can check easily with an ohm-meter.

Your high HT could be caused by an incorrect mains tapping set-up but it will not cause the receiver section to be dead.

[Tim]

Are V1 and V2 fed from a common anode resistor? If so this might have gone high/open.(or de coupler short?) I wouldn't be surprised as those little tubular carbon ones used in that set are prone to this.
I'm not a fan of these particular sets, but given the large speaker I'm sure you're tempted!

[ukcol]

Originally Posted by Tim

Are V1 and V2 fed from a common anode resistor?

For those of you without access to the HMV 1122 circuit the snip below makes things clear.

[peter_sol]

Hi Stef.
Can you measure the resistance (ohms) across the IF transformer windings all 4 of them.
With the set switched off.
The manual suggests 5 ohms.

[ValvoStef]

Originally Posted by ukcol

For those of you without access to the HMV 1122 circuit the snip below makes things clear.

Ukcol,
My schematics have different voltages! May I ask where you got yours from?
The schematics I have I downloaded from this site, together with some service pages. The voltages listed there are different.

[ValvoStef]

Originally Posted by peter_sol

Can you measure the resistance (ohms) across the IF transformer windings all 4 of them.
With the set switched off.
The manual suggests 5 ohms.

I measured the coils, they are within the 5 ohm range. So it is not that either.
Very strange fault(s) on this set.

[ms660]

I would measure the voltages again to avoid any confusion, measure the voltage on the HT side of the IFT's primary windings and then on the anode side.

Lawrence.

[ukcol]

Originally Posted by ValvoStef

My schematics have different voltages!

Hi Stef.

The voltages on my circuit snip are not those given on the service sheet.

They are my understanding of those measured by you and reported in post 15 above.

If correct they clearly show there is a 26 volt drop across both IF transformer primaries and indicate a problem with the IF transformers.


EDIT: I have just noticed that (in post 30) you have already measured the resistance of the IF primaries and they are OK; it follows therefore that the voltages you reported in post 15 must be wrong. That is good news as it means you haven't got burnt out IF transformers.

Try the trick I mentioned with a transistor radio to see if you can find if the local oscillator is working or not.

[ValvoStef]

Hi ukcl,

Thanks for the tip with the transistor radio, I'll gve this a try ...

[ValvoStef]

I also dig out my old analog meter just to double check the voltages again. Something is not quite right there.

Regards,

Stef.