Ferguson 342BU

[Northyorks1]

Can anyone point me to a source for this type of resistor, or if someone has one for sale. It is rated at 3k and 2.25k 2%. The 3k is reading at well over 5k. Pics added.

Thanks Ian

[Ed_Dinning]

Hi Ian, it is a dropper resistor and may be for your specific set; looks like a wire wound type which normally do not go up in value, just go O/C.

It will be difficult to find the exact value, but if you can get some RS dropper sections it should be quite easy to replace.
Note asbestos washer underneath.

Ed

[Northyorks1]

Thanks for reply Ed and pointing out asbestos washer, I did have doubts about it. The high readings previously shown are what I am getting, also R22 rectifier current limiter gets very hot, but reads as ok is this normal to get so hot. I have never ran the radio for any length of time so decided to let it run it lasted about an hr then goes off, if you turn the volume fully on you hear a hum from around the power connection rectifier area. If you leave it for a while it then plays when restarted. Seems as though it is overheating.

Ian

[Diabolical Artificer]

Did you unsolder the wire before testing, there's a good chance a tfmr or other component/s is/are affecting your reading.

Andy.

[Ed_Dinning]

Hi Ian, surge limiter will get hot, asbestos washer can be coated with PVA and should be OK if not messed about with as it presently serves a useful insulating purpose.
Mail me if you have problems as I may have some suitable resistors

Ed

[Northyorks1]

No Andy did not unsolder wire, will check later. Thanks for offer Ed. My post seems to be creeping away from a wanted item to radio advice, is this ok Mods.

Ian

[David G4EBT]

Originally Posted by Northyorks1

Can anyone point me to a source for this type of resistor, or if someone has one for sale. It is rated at 3k and 2.25k 2%. The 3k is reading at well over 5k. Pics added.

Thanks Ian

That's very odd Ian. It's a wire-wound resistor and as has been said, they don't drift high in value - they either retain their value or go open circuit, so it seems very odd that the 3K section is more than 60% above its stated value. The total value end to end should be 5.25K - are you saying that it's more than 7.25k end to end?

[AC/HL]

Originally Posted by Northyorks1

My post seems to be creeping away from a wanted item to radio advice, is this ok Mods.

We don't have a vintage radio thread to answer, so needs must. The 3K resistor (R19 in the manufacturers data) is the heater dropper for mains operation. You should have 85v at one end and 6.7 at the other, on mains operation with the mains voltage selector on the right tapping. If so, the resistor is OK.

[Northyorks1]

Hello David, yes that is the reading I am getting. I will take Andys advice and unsolder the wire later to see if any changes. I have followed a lot of your posts David, and they have been very helpful and informative for a novice like myself you are a great asset to this forum.

Ian

[Northyorks1]

Getting readings of 83.7v and 6.65v in relation to AC/HL advice,thanks. Which I guess makes the resistor ok.

Ian

[AC/HL]

What symptoms do you have? I'll move the thread to vintage radio.

[Northyorks1]

Ran radio for couple of hrs tonight, problem now is sound drifting up and down. Going nearly silent back to normal very regularly.

Ian

[David G4EBT]

Originally Posted by Northyorks1

Getting readings of 83.7v and 6.65v in relation to AC/HL advice,thanks. Which I guess makes the resistor ok.

Ian

I'd be quite happy with those voltages.

The max HT for which the valves are rated is 90V, and the filaments, 1.4V, but they'll tolerate 1.5V from a fresh LT battery, and will be happy down to maybe 1.2V. Better to slightly underrun the valves than to stress them, and when used on batteries, the set would still run down to maybe 67V HT. The role of R19 is to act as a filament ballast to drop the voltage from the 90V HT line to feed the filaments when used on mains. The filaments are low consumption (25mA) so are delicate. They're wired in series, and there are other components which affect the voltage to the filaments. R5 is V1 filament ballast, R11 is V3 filament Ballast, and R16 & R17 are V4 filament Ballast.

R21 is a wirewound adjustable pot, which should be adjusted for the correct mains voltage on which the set is to operate.

As to the audio fading in and out, and given that the set is 65 years old, I wonder if the metal rectifier is on its way out or C26,27,28 have gone leaky (in the electrical sense)? One way of checking that if you could, would be to run the set off batteries - ten PP3s in series for HT, five C or D cells in series for the LT supply. When the set is on battery power, several components are switched out of circuit. Namely:

R19, R20, R21, R22.
C26, C27, C26
Rectifier 'W1'.

If on battery power, the set doesn't fade in and out, I'd suspect the rectifier/C6,27&28. If the rectifier is failing, it could be replaced with a 1N4007 silicon diode, but may also need a series resistor if the voltage is too high. If the fading audio still persists when running on battery power, clearly the fault(s) would lie elsewhere.

I don't know if you've downloaded the service data. There are three lots on offer: The makers, which is 8 pages, plus a two page Trader Sheet and 2 page Radio Servicing.

As to the original query re R19, I've attached part of the circuit, which I've shown with the set switched to mains, so you can see the role it performs in the filament circuit.

Hope these thoughts might help. It's just my take on things - others may have different ideas and advice.

Good luck in your endeavours. It looks a nice set and would have been quite expensive back in its day (1955).

[Cobaltblue]

Hi Ian

Running off a battery as David suggests is a great idea but if it's not practical:

Does the filament voltage change when the radio fades?

If it does then I would be look at the filament supply circuit.

Is the station fading? Those of us who used to listen to Radio Luxembourg know all about fade.

It's normal for some degree of fading on distant stations and that normally compensated for by the AVC circuit.

The AVC circuit is very high impedance on these little battery sets, so I would look carefully for High value resistors and leaking capacitors.

R18, C6 and C19 in particular. (manufacturers numbers)

Just more possibilities

Cheers

Mike T

[Northyorks1]

Thanks very much David and Mike for all of your advice lots to take in. I will be out most of the day so probably post back tonight.

Ian

[Northyorks1]

Sorry not got back sooner been a busy weekend. Problem solved changed R18 as advised by Mike and sound drift has stopped. R18 was listed in schematic as 6.8m it had a 7.9m fitted original resistor which was reading at 7.2m. I have not had chance to run the radio for very long but all seems ok. Previous to changing the resistor the sound was drifting up and down from start up. I had previously changed all wax capacitors and out of spec resistors apart from this one. There is still cosmetic work to do, and I have just purchased a complete radio off ebay for spares as need a knob for it and both 2 and 3 pin connectors for battery are damaged. I would just like to thank every one for all advice given, very much appreciated. From a very grateful novice.

A couple of pics added from when purchased has been cleaned up since. Before buying I asked about cracks or chips to bakelite told there was none, as you can see on pic 2 a broken piece on bottom which is now fixed in place as best I could.

Ian