Ekco A274 hum from loudspeakers but nowt else - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

mole42uk · 2nd Feb 2024, 6:24 pm

Yes, the A274 packs quite a punch from it's EL84.

It might be worth checking the resistor R14 (470k?) which might be high and give a dim tuning indicator. Mine is the original EM80 and very bright.

Martin G7MRV · 2nd Feb 2024, 6:55 pm

Ah yes thats mounted on the socket of the EM80 and is above the tube, so likely to get rather warm - its totally blackened on mine!

Martin G7MRV · 4th Feb 2024, 6:53 pm

Quote:

Originally Posted by mole42uk

Yes, the A274 packs quite a punch from it's EL84.

It might be worth checking the resistor R14 (470k?) which might be high and give a dim tuning indicator. Mine is the original EM80 and very bright.

As well as being rather dim, I note on this set that the response of the tube seems poor - the lines dont move as far over as I would have expected. However, I have very little knowledge or experience of magic eye tubes and so not sure.

I note though that it is fed from the EABC80 via 2M2 R11. Would I be correct in deducing that R11 going high will result in reduced response?

mole42uk · 4th Feb 2024, 7:23 pm

My tuning indicator has a very good response to the signal strength. I was looking at the circuit yesterday and thought that the 2M2 going high might be a culprit - I'd check that it is still about the correct value. I don't know too much about those valves either but my set has been in fairly constant use for nearly 70 years, I do know that carbon composition resistors are rather less reliable and being a tight Yorkshireman I'd replace something cheap before I replace something expensive.......

paulsherwin · 4th Feb 2024, 7:49 pm

As I think I said upthread, the EM80 is just a voltage indicator showing the level of the signal hitting the discriminator. If you don't have a strong signal from a good aerial, it won't move very much.

The internal VHF aerials in 50s valve sets are really just a token effort. These sets were intended for use with horizontal dipoles on the chimney, like TV sets. Modern mixed polarisation transmitters allow them to be less fussy, but any indoor aerial is still a big ask unless the local signal is very strong.

2nd Feb 2024, 6:24 pm	#21
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,618	Re: Ekco A274 hum from loudspeakers but nowt else Yes, the A274 packs quite a punch from it's EL84. It might be worth checking the resistor R14 (470k?) which might be high and give a dim tuning indicator. Mine is the original EM80 and very bright. __________________ Richard Index: recursive loop: see recursive loop

2nd Feb 2024, 6:55 pm	#22
Martin G7MRV Heptode Join Date: May 2008 Location: Selby, North Yorkshire, UK. Posts: 955	Re: Ekco A274 hum from loudspeakers but nowt else Ah yes thats mounted on the socket of the EM80 and is above the tube, so likely to get rather warm - its totally blackened on mine! __________________ I got food in ma belly and a license for ma telly My Blog - http://g7mrv.blogspot.com

4th Feb 2024, 7:23 pm	#24
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,618	Re: Ekco A274 hum from loudspeakers but nowt else My tuning indicator has a very good response to the signal strength. I was looking at the circuit yesterday and thought that the 2M2 going high might be a culprit - I'd check that it is still about the correct value. I don't know too much about those valves either but my set has been in fairly constant use for nearly 70 years, I do know that carbon composition resistors are rather less reliable and being a tight Yorkshireman I'd replace something cheap before I replace something expensive....... __________________ Richard Index: recursive loop: see recursive loop

4th Feb 2024, 7:49 pm	#25
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 28,012	Re: Ekco A274 hum from loudspeakers but nowt else As I think I said upthread, the EM80 is just a voltage indicator showing the level of the signal hitting the discriminator. If you don't have a strong signal from a good aerial, it won't move very much. The internal VHF aerials in 50s valve sets are really just a token effort. These sets were intended for use with horizontal dipoles on the chimney, like TV sets. Modern mixed polarisation transmitters allow them to be less fussy, but any indoor aerial is still a big ask unless the local signal is very strong.