Ekco A274.

[robreddog]

hi,
can anyone help with info about the cap in the picture (tone control)c23 220pf,it appears to be labelled as 1.75 kv pk and the only one i can find at cricklewoods is rated 630v.
i powered the ac cct only with a lamp limiter ok, and after a good clean and inspection powered up dc for some quick checks, but clearly need to change a few caps at the amp end.I have seen there are some very useful post's regarding this radio.
hope someone can help.

[paulsherwin]

It needs to be high voltage because you get high AC voltages on the output valve anode.

[Nuvistor]

220pfd 2kv working ceramic capacitors are available from RS and eBay.

[Station X]

C23 Manufacturer's Sheet.
C33 Trader Sheet.

https://www.cricklewoodelectronics.c...iABEgIG3_D_BwE

[robreddog]

HI ALL THANKS , so i can use a ceramic,but the origional one is not a ceramic is it.
i'm new to old valve design but do know my gas turbine control sytems and equipment up to 11kv.

[paulsherwin]

You can normally use any modern types to replace old waxies if the ratings are OK - ceramic, plastic film etc.

[robreddog]

Hi, a problem has cropped up that I hope I can find some help to sort out, been running the radio for the last 5 weeks chassis on bench while I attend to the cabinet.
I noticed in the last week that the stations were starting to move downscale as it were, so that today radio 2 is not tuneable, now this is new territory for me, so I swapped valves except I don't have ef89, with no change, is there are part of the cct that I should look to,I only have 2 multimeters
Rob

[cathoderay57]

Bit tricky unless you have a signal generator, sounds like you don't. Referring to Trader Sheet #1269, the frequency drift could either be in V1b mixer/oscillator circuit (second half of ECC85) or in the IF amplifiers V2 and V3 circuits. If you have tried a different ECC85 and the problem remains, it is probably unlikely that any of the capacitors in the ECC85 tuned circuit are causing the issue since they are small value jobbies (C5 - C9). Worth checking C10 and C13 if you haven't replaced them - bad decoupling of the HT line could be upsetting things. Also check the valve anode and screen voltages of the ECC85 and the IF valves compared to the Trader Sheet. Cheers, Jerry

[Nuvistor]

Have look at this sticky, it may help.
https://www.vintage-radio.net/forum/...ad.php?t=16470

Has stated check the voltages, no point chasing LO faults if it’s a simple voltage problem.

[robreddog]

hi, thanks for the replies, so i went to the cct around ecc85 poked around connections,(loose connections were always the first check fault finding)and found that when i pushed the terminal indicated in the pic, back came radio 2 on 88.3 and other stations more or less where they should be,am now looking where this is on the scheme,its not easy to check around the base of the valve,should i resolder or leave well alone now and/or change those capacitors in second pic
Rob.

[Sideband]

NO!! Don't change any of the ceramics (unless they are non-critical decouplers) or you will open a whole can of worms. It's unusual for ceramic capacitors to fail unless they have been physically damaged. Try a spot, just a spot of switch cleaner on the valve pins first. Don't be tempted to spray the valveholder. If this doesn't cure the problem then it might be a resistor changing value as the valve warms up. Check that the HT voltage on the smoothing caps doesn't change as the radio drifts. If it does it's likely to be something like a low emission rectifier or something pulling the HT down. Try the switch cleaner on the valve pins first then come back if there is no change.

[robreddog]

yes of course,i have read before changing those ceramics would likely mess up the alingment,the valve pins are clean, it was just prodding that little connection on the end of the copper winding that brought radio 2 back into position.
Rob.

[Simon Gittins]

If you used the screwdriver to prod the connection, that could be misleading. If Radio 2 comes back into position when it's prodded with something plastic however, it may be worth re-soldering the connection.

[cathoderay57]

At risk of repeating myself, it's really important to check first of all that the dc conditions on the valve electrodes are within at least 20% of those stated in the Trader Sheet, and that dc decoupling capacitors are all good. If there is a dc problem then it will likely get worse not better and so any adjustments to tuning circuits that you make at this stage will either have to be repeated or undone. Cheers, Jerry

[robreddog]

I probably didn't explain very well, the radio worked fine after I prodded the connection, I resoldered the joint and all has been OK since the voltages on the around ecc85 were all in spec.