Another Mk I TR82C.

[Joe]

Should have said: red lead to chassis, black one on the transistor legs.

- Je

[pwdrive]

Ignore my last post. If the emitter was the collector the voltages would make more sense?

Lawrence.

[Joe]

That's what I was thinking. According to the sheet though they should be: Emitter 6.4V, Base 1.0V Collector 6.4V. The limited experience I've had with transistors has been with silicon NPNs so things apparently been bottom first is making my brain hurt, not that that takes much.

- Joe

[pwdrive]

That's what I was thinking. According to the sheet though they should be: Emitter 6.4V, Base 1.0V Collector 6.4V. The limited experience I've had with transistors has been with silicon NPNs so things apparently been bottom first is making my brain hurt, not that that takes much.

- Joe

If that's what your sheet says I would suggest the sheet is wrong, the emitter voltage is always lower than the base voltage.

Lawrence.

[Robert Darwent]

Do the three voltages on the diagram for TR1 roughly agree with readings taken in your set Joe? (B=1.0V, C=6.4V, E=1.1V)

If that's what your sheet says I would suggest the sheet is wrong, the emitter voltage is always lower than the base voltage.

Lawrence is correct Joe. I copied the readings the Bush service sheet gives back in post #20 and quoted again above.

Regards

[Joe]

Mea culpa. I said I was getting it 'round my neck.

- Joe

[Robert Darwent]

About a third of the LW band is receiving Absolute Radio weakly. This too is a strong signal as it shares the Radio Sheffield transmitter.

That sounds like RF break-through into the IF stages due to the close proximity of the transmitter site at Tapton Hill to your location.

I get the same thing from the Magic AM transmitter at Skew Hill, Grenoside with being in N.E. Sheffield. I believe you're South of me Joe nearer the town centre.

Regards

[Joe]

I'm in Millhouses and the Absolute/Radio Sheffield transmitter is on Broadfield Road. They are the only stations I can get on cyrstal sets and I've even know them come unbidden through amplifiers, though Radio Moscow used to be the worst offender for that. Magic AM is very weak here, in fact I use it to test just how well radios are performing as if I can get that there's not much wrong.

Any road, the figures I previously gave are correct but mis-identified, ie the Collector and Emitter are inverted.

I've just double checked that the transistor is correctly fitted, ie the leg next to the red dot goes to pin 6 of the L6/7/8 can, the middle one goes to the junction of a 100kΩ and a 22kΩ resistor and the other to pin 1 of L6/7/8.#

I have also warned this radio that if it doesn't behave it's going on e-Bay at the w/end - in bits.

- Joe

[pwdrive]

Joe, according to your recent posts it would seem that MW has packed up since delving into the osc coil can.
That might be coincidence or it might be that the transistor has given up the ghost altogether in oscillator terms.
For what it's worth I would check the continuity of all three osc coil windings, if they are ok then check the two bias resistors (100k & 22k) if they are ok then change the transistor.
It's not uncommon for a transistors gain to fall over time, that transistor needs all the gain it can get due to the oscillator design, the oscillator tank on LW has a low LC ratio due to it using a tank coil common to both wavebands.

Lawrence. [EDIT: High LC ratio should have read low LC ratio.....now corrected....]

[Robert Darwent]

I'm in Millhouses and the Absolute/Radio Sheffield transmitter is on Broadfield Road.

I wasn't aware of the transmitter on Broadfield Road, only knew of Tapton Hill. Anyway, same difference - you're virtually on top of it signal wise as I am with Skew Hill.

I've just double checked that the transistor is correctly fitted, ie the leg next to the red dot goes to pin 6 of the L6/7/8 can, the middle one goes to the junction of a 100kΩ and a 22kΩ resistor and the other to pin 1 of L6/7/8.

TR1 is correctly fitted if the leads are; Blue (Collector), Green (Base), Yellow (Emitter) - from left to right looking at the chassis as its normally fitted into the set. All the other transistors follow the same colour code on their leads but are fitted the opposite way around, ie: Yellow, Green, Blue.

The readings you've took are within the range expected, but I still suspect TR1 is low gain and the source of the problem. Might be worth checking by substitution if you have a spare OC44, failing that even transposing TR1 and TR2 temporarily and see what happens.

Regards