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Old 31st Aug 2019, 12:14 am   #21
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Default Re: Marconi TF144H/4S

So I've been making some checks. I picked 5 out to test this evening.

R208 4.7k reads just over 4.9k
R203 470k reads 676k
R202 100R reads 103.8
R212 150k reads 156k
R209 47k reads 55.73k

So it's mainly the higher resistance ones which have gone quite high so I'll assume to replace them all in that circuit. It would certainly explain the EL81 being burnt out.

I wonder if I should need to look at the LT area or any other area for that matter at this point?
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Old 12th Sep 2019, 11:34 pm   #22
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Default Re: Marconi TF144H/4S

I've just made up an order, to order the resistors which I need. So far I can't fault anything other than the EL81 which melted and the resistors which went over value. I don't have enough on the order to place the order (minimum order value) so I'm trying to think what else I could order!
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Old 13th Sep 2019, 6:22 am   #23
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Default Re: Marconi TF144H/4S

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I don't have enough on the order to place the order (minimum order value) so I'm trying to think what else I could order!
Happens to me every time, however I have all those values if you want I'll bung em in the post, 1/2W do?

Andy.
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Old 17th Sep 2019, 6:22 pm   #24
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Default Re: Marconi TF144H/4S

Thanks for the offer. I might have enough to make an order soon. I think everyone here is looking forward to 30kg of Marconi to leave the kitchen table
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Old 18th Sep 2019, 6:38 am   #25
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Default Re: Marconi TF144H/4S

No worries, yes, they're beasties, mines in my bedroom on the rountuit pile.

Andy.
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Old 28th Sep 2019, 9:42 pm   #26
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Default Re: Marconi TF144H/4S

Right, I have my resistors.....but my mind is boggling tonight.

On the 6U8, V202, pin 8 has a resistor junction where there is a 2.2k and 470k resistor and via the terminal strip there is a connection to a 2.7k resistor, but I can't seem to find the 2.2k on the drawings, or I'm missing it. Can someone point check this out for me please? I just want to be certain it should be there. Thanks.
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Old 28th Sep 2019, 10:51 pm   #27
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Default Re: Marconi TF144H/4S

Edit: It's the 2.7k I can't find on the drawings.
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Old 28th Sep 2019, 11:23 pm   #28
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Default Re: Marconi TF144H/4S

Found it, it runs off the page to the modulation circuit. That 2.7k resistor had gone high at just over 3k.
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Old 29th Sep 2019, 8:56 pm   #29
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Default Re: Marconi TF144H/4S

My VT203 (OC71) is a bit gooey and waxy, is that normal in one of these? Some kind of coating they used in the military sets?
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Old 29th Sep 2019, 11:26 pm   #30
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Default Re: Marconi TF144H/4S

So good progress so far. I replaced all of the resistors in the HT regulator last night. The crystal calibrator gets some of the HT and there was one carbon resistor there which was also out of tolerance. Generally I'm looking to replace all of the carbon ones as they do tend to go high even if by a few percent over the specification.

Tonight the LT regulator saw all of the carbon resistors replaced. The only two which were ok are R214 and R215 which are metal oxide resistors.

I just need to make checks in other areas before the valves go back in and the power goes on. Any suggestions of what else I should test before hand?
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Old 30th Sep 2019, 7:15 pm   #31
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Default Re: Marconi TF144H/4S

BR201, Brimistor was very brittle and as I touched it with my pointed pliers, it broke!

Is there a modern equivalent I could use? It's a type CZ3.
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Old 11th Oct 2019, 12:03 am   #32
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Default Re: Marconi TF144H/4S

I thought I'd take a look elsewhere before powering up and I'm amazed that not only in the HT and LT side, so many resistors are wildy out of tolerance. Not only carbon ones it appears.
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Old 11th Oct 2019, 2:36 pm   #33
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Default Re: Marconi TF144H/4S

Sounds like you have your work cut out for you, 10/10 for persistence. Have you had the back off the tuning section? From memory there's a few resistors in there I found off spec and a burnt out one which meant not OP.

Andy.
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Old 11th Oct 2019, 6:00 pm   #34
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Default Re: Marconi TF144H/4S

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Originally Posted by Diabolical Artificer View Post
Sounds like you have your work cut out for you, 10/10 for persistence. Have you had the back off the tuning section? From memory there's a few resistors in there I found off spec and a burnt out one which meant not OP.

Andy.
Yes playing about with this is just keeping me occupied in the evenings. Due to the thermocouple worries, I thought I'd check out the other areas.

As my other Marconi signal generators are working, but don't have this thermocouple, I've never had any reason to approach with such caution, but I am interested in checking a few out once this is completed.

I have had the tuning box open to gain access to the thermocouple. That turret of coils is a work of art in itself!
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Old 12th Oct 2019, 10:10 am   #35
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Default Re: Marconi TF144H/4S

"That turret of coils is a work of art in itself! " Isn't it, it should be on the outside housed in perspex : ) I never got an answer myself as to how to go about testing with the thermocouple, only to be very careful. I would presume you make sure there's no DC present and any components downstream are ok.

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Old 13th Oct 2019, 4:26 pm   #36
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Default Re: Marconi TF144H/4S

I wonder if you could confirm something for me. Looking at the inside of the tuning section, I'm looking at a resistor connected to switch S100A and the rf filter B. From the drawing I make it out to be R187 - 4.7k. The colour code suggests 470 ohms, my meter is reading it as 7k ohm!

I'd just like to clarify before replacing it with a 4.7k, when you get a moment, thanks!
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Old 13th Oct 2019, 4:48 pm   #37
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Default Re: Marconi TF144H/4S

The schematic has 4.7k and the component listing has 'met film 4.7k Ohm 2% 1/4" watt'.
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Old 13th Oct 2019, 4:52 pm   #38
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Default Re: Marconi TF144H/4S

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The schematic has 4.7k and the component listing has 'met film 4.7k Ohm 2% 1/4" watt'.
Yes, that I'm aware of as I said in my post above, but I wondered if Andy, or anyone else would confirm by taking a look in theirs if they can.
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Old 13th Oct 2019, 6:33 pm   #39
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Default Re: Marconi TF144H/4S

I'll have a look tomorrow, have to fish it out and dismantle, be with you quick as I can.

Andy.
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Old 13th Oct 2019, 6:48 pm   #40
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Default Re: Marconi TF144H/4S

I took some photos when I was working on my TF144H/4.

I can confirm that the highlighted resistor in your photo, is 4.7k Ohms in mine.
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