Odd sound when changing wavebands, and some good news

[Gabe001]

Hello,

I've joined the bvws today, so fellow members, mainly because I found this forum really helpful. Thanks for the contributions in this forum which I've learn a lot from.

I've also got a beautiful JD graves (essentially a Raymond f17/Derwent) yesterday. It's already been serviced, quite competently I think, but I have the impression that whoever did it used whatever they had to hand. My only contribution so far was replacing the 25v electrolytic caps.

Based upon the Raymond f17 service sheet, can I have some views on the work done by my predecessor?

1. 400v caps were used instead of 500v ones (green and yellow). Are these ok to keep?

2. The service sheet has an error with regards to value of c17 (see pic). I cannot remember the original actual value from when I did the f17. The person who serviced the radio replaced c17 with a 0.22uf 1kv. I think this is too high considering the values of c18 and c19 and my vague recollection. What's s sensible capacitance to use in that position?

3. The radio seems to work, and I haven't done full testing yet (except checked HT, which is fine) but there is a strange undulating sound that only occurs when changing waveband at full (or almost full) volume. See video, at https://youtu.be/vDKiXga2yMQ

You can hear it best at 4s when I change MW to LW. Is this something anyone has experienced before? Usually when I change waveband I expect a hiss not a 'yodel'

Thanks in advance
Gabriel

[ms660]

0.22uF for C17 is a woefully low value, it's 25uF according to the snippets you've posted, try 22uF at least 450VDC.

Lawrence.

[cathoderay57]

Odd position in the circuit for a 25uF. Also it's described as "tubular" as opposed to C16 which is same value and "electrolytic". I'm tending to agree with Gabriel that the capacitance value may be a misprint. The yodelling sounds as if the set is on the verge of oscillation especially when you changed the tuning. Look for flaking paint on the EF39 and see if the paint has separated from the earthing wire wrapped just around the glass envelope immediately above the base. Check the HT volts immediately at switch-on.If you have a U50 rectifier that is indirectly heated and so the HT will rise substantially high before the other valves have warmed up. If the highest HT reads in excess of 350v then it would be wise to replace the 400v caps (apart from any used as cathode decouplers) with at least 450v components. You might find it easier to buy 630v rated items. If C17 was indeed supposed to be say 0.25uF then a 1kv rated component is OK. Higher is fine, marginal/lower isn't. Cheers, Jerry

[Gabe001]

Originally Posted by ms660

0.22uF for C17 is a woefully low value, it's 25uF according to the snippets you've posted, try 22uF at least 450VDC.

Lawrence.

Lawrence it's a misprint. When I did the Raymond which had the originals in place its more like a 0.05 but I can't remember!

[ms660]

Yes, sorry, I see now in the parts list.

Lawrence.

[Gabe001]

Thanks Jerry, so that is what oscillation sounds like.

I think you may be onto something with the quality of the metallisation. I'll try the foil trick and make sure there is continuity with ground and report back.

Gabriel

[cathoderay57]

Oh dear, another brain f*rt in my Post #3: Quote "U50 rectifier that is indirectly heated" Unquote. I meant, of course, DIRECTLY heated. Cheers, Jerry

[Gabe001]

I know you meant directly heated Jerry.

You were spot on with the diagnosis. I used tin foil to earth the ring on the ef39 and no more odd sounds with much better radio performance. Obviously this is a temporary fix, I suppose it will need a new valve unless anyone knows a good permanent easy fix.

Overall sound is quite low (say about 60% of what I got from the Raymond electric) on all bands and also via pick-up. It sounds good, but I need to turn it up to almost maximum. I think the el33 may be performing poorly and I may need to replace this valve too.

In any case happy with the progress for 1 day. Radio works well, just not loud enough. I'll put this on the back burner for now and finish the ambassador first.

Thanks
Gabriel

[cathoderay57]

Red EF39s nearly all do that sir! Apart from wrapping in earthed Bacofoil, the other codge, that works providing the metallised coating is reasonably intact near the base, is to wrap several extra turns of thin wire on top of the existing single turn and, if necessary, solder the ends of the wrapped wire to the stub of the existing single turn. If not possible, then the new wire can be bent down, wrapped around and soldered to the top of the M pin (Pin 1, earth shield) underneath. Be careful if soldering wires close to the glass envelope, as the heat might crack the glass. If you can get a silver coated VR53 or CV1053 the metallising usually seems to survive much better and these are military direct equivalents to EF39. (VR stands for "valve receiving" and CV for "civilian valve" I believe).

[mark2collection]

That'll explain my very early/black DAC90.

Perfect sound/reception when you tune (and your hand is still on the tuning control) but take your hand away ... you should see our cats ears, all directions at the same time!!

A job for the winter months me thinks. As it stands I have to 'go past' the required station a smidge, put up with the odd howl/screech for a brief moment, and when the hand is removed, perfect.

I wondered the cause, but the set is little used and so, wasn't too troubled. No excuses now.

Many thanks all, glad Gabriel and his set are getting on

Mark

[Gabe001]

Thanks Mike. Got a week off work so I've got some time to get things done at the moment