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Old 23rd Sep 2023, 10:14 am   #61
Montythegreat10
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Default Re: Issues with Philips B2F70U.

These are the voltages we are currently getting (ignore the heater readings)
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Old 23rd Sep 2023, 10:22 am   #62
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Default Re: Issues with Philips B2F70U.

It would be interesting to know the AC voltages across the other heaters. Once you've checked your meter is accurate of course.
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Old 23rd Sep 2023, 6:04 pm   #63
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Default Re: Issues with Philips B2F70U.

The confusing thing to people is you keep mentioning EL84! It's a UL84!! Please check your meter first before doing anything!! You only need a couple of known AC voltages (the mains for instance) and some known DC voltages. I fear we are going round in circles with this and we still don't know if your meter is working properly.

5V on the grid of the UBC81 is madness unless the valve itself has an internal leak....we've already mentioned that but still you have 5V on the grid! You know that control grids should NEVER be positive with respect to cathode so that should immediately tell you that something is very wrong either with the circuit or your meter.....
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Old 23rd Sep 2023, 8:05 pm   #64
Montythegreat10
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Default Re: Issues with Philips B2F70U.

I will try another meter on this at some point to see if that is our issue, as the one I was using is very cheap and has a dying battery, so I could see how it could be a problem. As for the UBC81, the reason I haven't been talking about that so much is because I don't believe that the problems we are having with the UL84 are related (sorry for calling it an EL84 a few times, the image I posted up there was taken a few days back, as none of the voltages seem to have changed with anything I have done) Absolutely correct me if I am talking nonsense about this, but I just think that the two problems don't seem to be connected. I might try measuring the grid of the UBC81 and switching between radio and phono to see what that does, as on phono there will be no connections to the grid from anything but chassis ground. It is possible that it is leaking because the anode voltage is currently too high due to the problems with the UL84.
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Old 23rd Sep 2023, 8:16 pm   #65
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Default Re: Issues with Philips B2F70U.

Monty, can I suggest you get a new battery for your meter now.
Then check your meter on AC mains voltage and on a couple of DC voltages.
After that start taking voltage readings as has been suggested and we may be able to assist.
Note that the UBC81 feeds the UL84, so problems in one will affect the other

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Old 23rd Sep 2023, 8:41 pm   #66
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Default Re: Issues with Philips B2F70U.

Some meters will give very odd results if the battery is low. You have to rely on your test equipment, however modest it may be so you must change the battery when the meter indicates it's low (assuming is does). Mine shows a flashing battery symbol. My ESR meter lights an LED when the battery drops to about 7.0 volts. Even my old (30 year old) analogue meter has a 'battery test' button which, when pressed, will deflect the meter into green or red areas on the scale. You MUST ensure that the battery is good at all times. At the moment you are groping in the dark by not knowing if your meter is correct or not...
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Old 23rd Sep 2023, 8:50 pm   #67
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Default Re: Issues with Philips B2F70U.

Quote:
Originally Posted by Montythegreat10 View Post
because the anode voltage is currently too high due to the problems with the UL84.
it could also be because your meter isn't working and the voltages are OK and you have another problem.....!
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Old 23rd Sep 2023, 10:22 pm   #68
Montythegreat10
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Default Re: Issues with Philips B2F70U.

The high DC voltages showed on two different meters, so I know they are likely to be correct. I will measure the heater voltage again with my nicer meter, which has good batteries
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Old 24th Sep 2023, 9:39 am   #69
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Default Re: Issues with Philips B2F70U.

Regarding the voltage measured on the grid of the UBC81, don't forget that the anode and grid pins on the UBC81 are next to each other, a possible point of any leakage.

The value of the measured grid voltage reported would result in the anode voltage being very low due to the high resistance of the anode load, if it's +ve grid.

Normally the bias voltage for the triode is produced due to a small amount of grid current flowing between the cathode and grid, hence the high value chosen for the grid-cathode resistor (6.8 Meg) Any other problems aside I would always replace the grid-cathode resistor as they do have a habit of drifting way off spec. or going virtually open circuit at some point.

Lawrence.

Last edited by ms660; 24th Sep 2023 at 9:49 am. Reason: extra info
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Old 24th Sep 2023, 3:39 pm   #70
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Default Re: Issues with Philips B2F70U.

Why keep changing meters?
For consistent readings always use the same one and remove measurement errors

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Old 24th Sep 2023, 6:41 pm   #71
Montythegreat10
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Default Re: Issues with Philips B2F70U.

Thanks for the info. So are you suggesting that this resistor could be part of our problem?
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Old 24th Sep 2023, 6:51 pm   #72
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Default Re: Issues with Philips B2F70U.

Quote:
Originally Posted by Montythegreat10 View Post
Thanks for the info. So are you suggesting that this resistor could be part of our problem?
No, but once you've sorted out what's what I would replace it anyways (R7, 6.8 megohm in the schematic)

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Old 24th Sep 2023, 6:58 pm   #73
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Default Re: Issues with Philips B2F70U.

Good for you Monty for sticking with it! Hope you get it working again.

It's very unusual that you went from a working set to one with multiple faults. Regardless of the ubc81, the ul84 should still be drawing current.
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Old 24th Sep 2023, 7:08 pm   #74
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Default Re: Issues with Philips B2F70U.

Quote:
Originally Posted by Montythegreat10 View Post
...
I have already checked continuity straight from the chassis to the holder, and it reads 150 ohms, as it should.
...
When looking at pictures of the innards of the Philips B2F70U, it is not clear to me what you mean with "chassis" since this radio has a circuit board with most of its parts on that circuit board.

Along the lines already set out by Gabe001 in his post #49:

Does the point you called "chassis" in the quoted post connects to the negative sides of C1 and C2? If you measure the resistance between the point you called "chassis" and the negative sides of C1 and C2, do you measure 0 Ohm?

Attached is the schematic I based this post on.
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Old 24th Sep 2023, 8:17 pm   #75
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Default Re: Issues with Philips B2F70U.

The metal chassis soldered connections to PCB ground can be seen in the last photo:

https://www.radiomuseum.org/r/philip...ub_2_f_70.html

In that photo the 150 Ohm cathode bias resistor R10 is horizontal at bottom left.

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Old 24th Sep 2023, 8:34 pm   #76
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Default Re: Issues with Philips B2F70U.

Still, I think it is wise for Montythegreat10 to measure whether or not there is continuity between the point he called "chassis" and the negative sides of C1 and C2.
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Old 25th Sep 2023, 9:27 am   #77
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Default Re: Issues with Philips B2F70U.

Correction to Post#75:

On closer inspection the metal chassis to PCB ground connections look to be by screws not soldered joints.

Some photo's in the link below shows this more clearly for what is essentially the same PCB from a different model:

https://www.audiovintage.fr/leforum/...ic.php?t=14289

Lawrence.

Last edited by ms660; 25th Sep 2023 at 9:32 am. Reason: extra info
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Old 25th Sep 2023, 11:46 am   #78
Montythegreat10
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Default Re: Issues with Philips B2F70U.

I have measured the continuity between the capacitor negatives and the chassis (what I am calling the metal frame that surrounds the radio and connects to ground) and they are connected. I believe the schematic that Robert Gribnau found was for a slightly different radio, I have linked what I believe to be the correct one.

I will also say that I am going to university tomorrow, so sadly I will have to leave this project at home. Therefore, while further suggestions are very much appreciated, I cant act on anything until I get back home in December. I would like to say a massive thank you to everyone who has helped me sort this out, and especially to sideband, who very generously gave me a UL84 to aid in my troubleshooting. I hope to be back here when I get home, so we can resume this project!
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Old 30th Dec 2023, 5:38 pm   #79
Montythegreat10
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Default Re: Issues with Philips B2F70U.

Sorry for the long delay, but I am pleased to say that the radio is working! It turned out that I the diode I used for the rectifier had a maximum reverse voltage of only 100V, and therefore burned out, causing the quality of the DC to go down, and the radio to stop working. I replaced the diode, and it works fine now, just waiting on some more suitable filter capacitors. I would like to say another massive thank you to everyone who has helped me repair this radio, as it has given me a great insight into the workings of valve electronics.

One last thing I will say is that the filament voltage of the UL84 is 53V, while it is rated for 45V, will this burn it out, or is it within tolerances?
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Old 30th Dec 2023, 10:14 pm   #80
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Default Re: Issues with Philips B2F70U.

Almost +20% is certainly not within the tolerances ...
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