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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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23rd Aug 2007, 12:55 pm | #1 |
Nonode
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RAP 846 drawing too much current.
After checking and changing all the usual caps, etc I tried this radio for the first time today.
My series light limiter was useless (too bright) so I used a variac set to 200V and discovered the radio is drawing, nearly, 450mA and not sounding too good. I've got no idea where I should start looking for the problem, but I must mention that the mains transformer has been replaced at some point... please don't say it's the transfomer! David |
23rd Aug 2007, 1:06 pm | #2 |
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Re: RAP 846 drawing too much current
Hi Dave,
How about disconnecting everything from the secondaries of the transformer, then seeing what happens? I presume this set uses a mains isolating transformer, and not some odd autotransformer design. Did you ever manage to get hold of a circuit diagram? Nick. |
23rd Aug 2007, 1:14 pm | #3 |
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Re: RAP 846 drawing too much current
Take the valves out - making sure you know where they go! - and see if the current drops. If it does not, then you're looking at the Transformer.
If it does, re-cap it and try it one valve at a time. There could be a duff valve or two. Cheers, Steve P
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23rd Aug 2007, 1:25 pm | #4 |
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Re: RAP 846 drawing too much current
With all the valves and dial lamps out the current drops to 63mA
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23rd Aug 2007, 1:33 pm | #5 |
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Re: RAP 846 drawing too much current
The current must be going somewhere. I'd bet on leaky smoothing capacitors, but you've checked them. Try checking for voltage across all resistors. There should be none unless the set uses a potential divider to derive the screen voltages.
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23rd Aug 2007, 2:07 pm | #6 |
Nonode
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Re: RAP 846 drawing too much current
Unfortunately, with all the valves removed the transformers secondaries aren't connected to anything Is the transformer dead?
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23rd Aug 2007, 2:10 pm | #7 | |
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Re: RAP 846 drawing too much current
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It does sound like a transformer fault or wiring short circuit. Paul |
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23rd Aug 2007, 2:33 pm | #8 |
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Re: RAP 846 drawing too much current
Yes, I know what you mean. But not necessarily so. The primary will be across AC Mains, so it will form a circuit, so some current will flow. The issue is how much. Check for Hum Caps, etc though.
Put the valves in one at a time, and measure the current every time. If it's had a transformer change in the past, is the new transformer right. I think the problem is the transformer too, but check everything else first! Then find a transformer that will take the load (or an origional transformer) or get yours rewound. Cheers, Steve P
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23rd Aug 2007, 2:39 pm | #9 |
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Re: RAP 846 drawing too much current
Where are you measuring the current? Is it AC Mains Current or DC HT current you're measuring?
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23rd Aug 2007, 2:50 pm | #10 |
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Re: RAP 846 drawing too much current
63mA = 15W sounds like it might still be OK - I would not have expected it to have reduced from 450mA so much with shorted turns.
Faulty rectifier or electrolytics or maybe even a wiring error if the transformer has been replaced. Have you reformed the electrolytics and checked they are not leaking at the expected volts? Worth checking the wiring around the rectifier to make sure it makes sense - then power up using the variac without the output valve in place (assuming this is 6.3V heater set!) whilst monitoring the HT volts. |
23rd Aug 2007, 2:57 pm | #11 |
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Re: RAP 846 drawing too much current
I'm measuring AC current from the variac.
I've disconnected all the secondaries and chassis connections but it's still drawing around 60mA. I've checked for resistance between all the windings, but can't find anything I'm, now, clinging to the slim hope that my AVO is broken. Would 60mA light up the 100W bulb in my series lamp limiter, because it doesn't David |
23rd Aug 2007, 3:03 pm | #12 | |
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Re: RAP 846 drawing too much current
Quote:
Paul |
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23rd Aug 2007, 3:09 pm | #13 |
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Re: RAP 846 drawing too much current
There's still 390mA to be accounted for. What are the specified. heater consumptions of the valves
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23rd Aug 2007, 3:20 pm | #14 |
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Re: RAP 846 drawing too much current
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23rd Aug 2007, 3:29 pm | #15 |
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Re: RAP 846 drawing too much current
450mA AC doesn't sound too unreasonable for a big set like that. A 100W light bulb will indeed drop too much voltage and glow brightly with that type of set, they're really only suitable for standard domestic superhets.
Are there any signs of distress when you bring it up (burning smells, smoke etc)? Paul |
23rd Aug 2007, 3:36 pm | #16 |
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Re: RAP 846 drawing too much current
6K7, 300mA
6K8, 300mA 6K7, 300mA 6Q7, 300mA 6J5, 300mA 6V6, 450mA 6V6, 450mA 5Z4, 2A Excluding the rectifier that's 2.4 amps at 6.3V which would mean about 10mA being taken from the 240V Mains. The rectifier would draw about 8mA from the mains. So if my sums are right that's about 18mA. A long way short of 450-63=387mA
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23rd Aug 2007, 3:38 pm | #17 |
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Re: RAP 846 drawing too much current
Well Paul, you've saved me looking up all the valves! As well as Paul's question, what exactly do you mean by 'Sounds Bad'.
Are those 6V6's Output Valves, and if so are they in Push-Pull ? Cheers, Steve P
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23rd Aug 2007, 3:50 pm | #18 |
Nonode
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Re: RAP 846 drawing too much current
There's no burning smells or smoke. Yes the 6V6 are push pull .
I suspect the radio sounds bad because I'm only running it on 200V, via a variac. The reason for not applying more voltage (and this thread) was because of the 450mA current drawn Regards David |
23rd Aug 2007, 3:50 pm | #19 |
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Re: RAP 846 drawing too much current
Hi David, Since my RAP 646 was accessible , I measured the AC input current, With the set working normally at 240V I get 260mA, minus the rectifier, 120mA, minus all valves but with the 3 dial lamps, 90 mA. As the 846 has a push-pull output with extra valves and presumably a bigger mains transformer, your figures don't seem too unreasonable .
Reards, Mick. . |
23rd Aug 2007, 3:50 pm | #20 |
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Re: RAP 846 drawing too much current
450mA at 200V equates to 90W, so presumably at full mains voltage, power consumption would be somewhat over 100W. Sounds fair enough to me, especially if the transformer runs fairly cool
Is there a ratings plate stating power consumption anywhere? Nick. |