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Old 8th Feb 2019, 5:08 pm   #21
David G4EBT
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Default Re: Capacitors for Trio 9R 59D

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Originally Posted by Humptydumpty View Post
David Will they have negative marked on them or is it the length of the lead i can see that one wire one side is shorter than the other .
The long lead is positive, and there will be a minus sign repeated several times down the case showing that the shorter lead is negative. If you look at the caps in the first pic in post 15 above, you'll see the minus sign, which is fairly standard on any radial electrolytic caps.
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Old 8th Feb 2019, 8:49 pm   #22
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Default Re: Capacitors for Trio 9R 59D

David , I do remember thank you for puting me right on that one .The earth minus sign on the 3 capacitors that i fitted in to Trio no1 the first receiver .. But i could still hear the hum so i removed them .And wired it back to how it was to start with .Then after i had removed them i fitted them right in to Trio no2 . A lot better on set 2 . I think i should have another go at set no 1 again now .This is what they are for ,set number 1. The C40-41 -42 looked ok from under the chassis .On no 1 but real bad bleed out on set 2 .
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Old 9th Feb 2019, 12:10 am   #23
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Default Re: Capacitors for Trio 9R 59D

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The C40-41 -42 looked ok from under the chassis on no 1 but real bad bleed out on set 2 .
Yes, it was evident from the picture of the cap on your second set had leaked and was clearly in need of replacement. However, when you say the cap on your first set 'looked OK', you can't assume that just because it looks fine cosmetically, that it's fine electrically. You can only ascertain that by testing it to see if it's leaky (in the electrical sense) and thus passing excess current, and by checking the capacitance.

Often, on sets that are decades old it may indeed be the reservoir/smoothing capacitor causing excessive hum, but not always. For example, hum in Bush DAC90As is more likely to be caused by the output valve. The twin can capacitor in the '90A is very reliable - I won't be the only one to have needlessly changing one only to discover that the culprit was the output valve.

'Excessive' hum is a subjective term, but as you have two sets, you can at least compare them.
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Old 9th Feb 2019, 3:24 am   #24
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Default Re: Capacitors for Trio 9R 59D

C40, C41 & C42 were only originally rated at 250V. This is reasonable commercial practice in a price-sensitive design.
Since electrolytic capacitors are much cheaper in real terms than 50 years ago, we can allow much more generous margins:
The transformer's output is 160V. Multiplying by SQRT2, adding 10% for mains being 10% over 230V, and another 10% for surges due to regulation of the transformer during valve warmup and good luck gives around 294V, so 300-V or 350-V electrolytic capacitors are more than adequate.

Another thing, looking at the circuit, the AF Gain is directly coupled to V7b's grid.
This makes it prone to being "scratchy."
When changing the pot., I'd suggest adding a capacitor (say, 10nF, only needs to be rated at a few volts) in series with the wiper and a resistor of 2M2 -4M7, from the capacitor's junction with the wire to V7b's grid, to the low end of the track(screens).
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Old 9th Feb 2019, 10:34 am   #25
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Default Re: Capacitors for Trio 9R 59D

Martin i dont understand the bottom of your post . The wiper being the centre of the pot ,i have that bit Fix a capacitor to wiper, then from the other end of the capacitor to a resistor of 2m2 or 4m7 . Have i got this part right ?
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Old 9th Feb 2019, 11:36 am   #26
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Default Re: Capacitors for Trio 9R 59D

David .I fitted the three caps in to the set 1. Only to find at that time it made no change to the hum , so i removed them , and i then replaced all three wires back on to C40 cap again.I am interested in Martins plan in post 24.
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Old 9th Feb 2019, 8:28 pm   #27
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Default Re: Capacitors for Trio 9R 59D

Martin i could do with a dummys diagram .
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Old 10th Feb 2019, 3:34 am   #28
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Default Re: Capacitors for Trio 9R 59D

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Martin i dont understand the bottom of your post . The wiper being the centre of the pot ,i have that bit Fix a capacitor to wiper, then from the other end of the capacitor to a resistor of 2m2 or 4m7 . Have i got this part right ?
Sorry, no picture to paint 1000 words and I'm a bit terse at best!

Yes, with the junction of the resistor and capacitor going to the wire that used to go to the wiper and dangling free.
And the other end of the resistor going to the end of the pot. that the screens go to (the anti-clockwise/ minimum end)

This is adding under 10-p worth of components. to a set that that was originally over 39 (1969) despite penny-pinching new, equating to over 600 now!

And a reversible modification, if I'm talking rubbish. (Not unknown...)

Last edited by G8UWM-MildMartin; 10th Feb 2019 at 3:43 am.
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Old 10th Feb 2019, 11:38 am   #29
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Default Re: Capacitors for Trio 9R 59D

i am lost sorry .Think i will just put up with the hum for now its not that bad . I will see what its like after i fit the three new smoothing caps next week. You know i sketched your plan this out half a dozne times, and i still dont know how it goes .
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Old 10th Feb 2019, 12:08 pm   #30
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Default Re: Capacitors for Trio 9R 59D

Trevor,

That modification #24 is unnecessary and would not further reduce the hum.

John

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Old 10th Feb 2019, 3:37 pm   #31
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Default Re: Capacitors for Trio 9R 59D

Keeping grid current away from a pot will lengthen pot life, although it will not reduce hum.
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Old 10th Feb 2019, 3:42 pm   #32
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Default Re: Capacitors for Trio 9R 59D

Right so its a good thing i did not know how to do it.
The first Trio has more hum than the last one .
The last Trio looks as if its had a hard life .Even so the knobs are hard to turn The cabinet cover needs repainting . Also small paint chips on the dial apertures .The cabinet is going to the sand blasters ,and then powder coating storm grey.The first set looks the part with no marks or damage . But it gives out a little more hum .But both work extremely well .
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Old 10th Feb 2019, 4:43 pm   #33
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Default Re: Capacitors for Trio 9R 59D

Opinions differ.

In my experience, it is a very poor engineering to connect a valve grid only to the slider of a pot for its DC connection. Pot sliders do not always make good contact, and with the tiniest amount of leakage or grid current, you get scratchy noises as you turn the pot. as it gets worse, scratches turn into crackles. In the worst case, pot sliders eventually go open circuit, leaving the valve with a floating grid, which is definitely a bad thing.

It is penny-pinching and unprofessional, though it usually seems alright for a time.

David
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Old 11th Feb 2019, 8:37 pm   #34
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Default Re: Capacitors for Trio 9R 59D

David i notice a noise now on the pot , and it is a new pot that i fitted .
Today i went through the eexact same job that i did a few weeks ago .You remember David i fitted the three large axial caps to set 1 This made no change in reducing the hum.The C40 was rewired back to how it was with new wires .So i went through it again today with set no1 , again with three new caps that we chose last week . And i thought at the time that it would make no difference .And it did not, then i reversed the whole procedure and change it back [ again ] to how it was . With 3 new red wires again . I am stuck with this hum more from set 1 than set 2... Set one this looks mint .But is not as good as the second set i purchased for spares. So before i strip out set 1 for the face plate, reason is ,, its in good condition fit it to set 1 and build one good receiver. I have read some place about a valve that could cause this type of hum .Any ideas what valve it could be ?.
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Old 11th Feb 2019, 9:38 pm   #35
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Default Re: Capacitors for Trio 9R 59D

Above post was ment for David G4EBT . If you picked this up RadioWrangler i am sorry my friend .
But i think that this idea is worth a try . I will for now, put up with the humif its unstopable .Its easy to replace the pot if it goes bad. I looked at the under part of chassis at the pcb . To the place the wire goes to on the v7. This is the grey shielded wire i fitted in there when i replaced the pot with a new one I do need to know if the Trio 9r59d receiver has in the valve layout a phase inverter valve . Reading that if there is, then i need to get a balanced valve for the receiver.There is a good chance that a balanced valve will stop the hum. Only what i have read .
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Old 11th Feb 2019, 10:59 pm   #36
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Default Re: Capacitors for Trio 9R 59D

I worked it out

Sets like the 9R 59 were not designed with much care over low hum. It was assumed that it wouldn't degrade the readability of the limited bandwidth signals it was aimed at. You should expext some, but not so much as to be distracting. There are causes such as a limited amount of HT filtering, unbalanced heaters and also chassis currents from the mounting of the transformer core screws. There are several areas where you could make a series of small improvements.

David (GM4ZNX)
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Old 12th Feb 2019, 10:38 am   #37
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Default Re: Capacitors for Trio 9R 59D

Radio Dave . I think the reason for the hum is the mains 240v transformer .With the set on and speaker removed , i can hear a noise from the main transformer . I am sure its the problem .I said before that i would remove it and take a good look inside ,i did not . .And i dont know if i could de solder all the conections on the base of the transformer to remove it.And re fit it again after . So i am looking at removing the transformer if i can. I have made the laminations and built the ransformers and assembled them in past employment at the BSR .The problem is the laminations go loose inside .And its only varnish on the steel coils we used to pressed the laminations out of . David thumbs up for that,, i will do what you said and isolate the transformer . .Good idea .Watch this space .

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Old 12th Feb 2019, 10:43 am   #38
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Default Re: Capacitors for Trio 9R 59D

Also, designers of low cost transformers tend to run the core flux levels rather high to save on both iron and copper.... oh and it's smaller and it saves a bit on shipping costs half way round the world.

THe downside is that the resulting transformer is prone to clatter, even with no loose lams.

David
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Old 12th Feb 2019, 5:03 pm   #39
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Default Re: Capacitors for Trio 9R 59D

I am going to see if i can isolate the transformer right now .
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Old 12th Feb 2019, 5:38 pm   #40
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Default Re: Capacitors for Trio 9R 59D

Soon back . No way am i going to move the transformer pins and nuts without desoldering half the bottom end of the set .Lots of wires are in the way . Three nuts are clear ,but one is obstructed by the loom .But with a push i think its just possible .
But i did rumage around in there and i found an item that was very hot .To hot to touch truth be told. Its about 2" long by a 1/4" and close to the C40 .Post a picture in my next post . Need to know what it is to replace it .
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