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Old 17th Oct 2006, 7:25 pm   #1
boiss
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Default 'Deaf' Battery Valve portables

I've got a little battery valve portable set which uses the DF-DL etc series (4 valves ), but it appears to be a little deaf. There are no strong MW/LW stations here so it's difficult to judge the sensitivity. How much hiss or background noise should there be when it is not tuned to a station? At the moment there is virtually nothing from it when it is not tuned to a station. It has a 60V ht. Everything appears ok, some of the resistors have a slightly higher value than than the markings but not more than about 20% higher so they are virtually within tollerance. Voltages around the circuit seem reasonably correct.
Regards,
Mike.
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Old 17th Oct 2006, 7:40 pm   #2
paulsherwin
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Default Re: Battery Valve portable

Typically these sets are not particularly sensitive. Some manufacturers added an extra valve to try to improve things. The 60V HT used in your set won't help.

It's possible the DK9x or DF9x is weak - these battery valves don't last as well as indirectly heated valves, I guess because compromises were made to reduce filament current and improve battery life.

Best regards, Paul
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Old 17th Oct 2006, 7:44 pm   #3
'LIVEWIRE?'
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Default Re: Battery Valve portable

Hi from one Mike to another! Do you have either a signal generator or signal tracer? With the former you can check each stage of the set, working backward from the volume control 'hot' side (An Audio S/G is needed here) through the I.F. stages to the aerial, whilst with the latter you trace the progress of the signal, difficult if there are no strong MW stations in your part of Italy. I assume you've checked or substituted the valves already?
(See Paul's note re; Battery Vaves)
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Old 17th Oct 2006, 8:01 pm   #4
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Default Re: Battery Valve portable

Hello Mike,
Your little battery set should be quite lively and give enough sound.
You may find that you have some leaky wax caps, usually around four in that set up. The slightest leak even a couple of meg ohms will bias off these very sensive but totally amazing valves. I suggest you replace any you find usually .1uf and maybe .01uf. Even the non wax type are suspect.
As Paul says the H.T. is a little low at 60 volts but it should still give a good account of itself. The low H.T. will effect power [?] output more than station getting ability. Background noise is very low and at first it seems that the set is not going to work but tuning in should result in a good performance. Another thing to check is the aerial leads that connect to the frame aerial usually in the 'lid'. You may have a ferrite rod in yours and this is much less likely to suffer the connecting wires problem. Hope you liven it up a bit! Regards John.
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Old 17th Oct 2006, 8:46 pm   #5
batterymaker1
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Default Re: Battery Valve portable

One way to check to see if the audio section is functioning is to flick your finger against the output tube. You should hear a sort of "pwong" noise emit from the speaker.

Wiggle the tubes in and out of their sockets. Sometimes the pins get oxidized, and the wiggling scrapes off the oxidation.

I'll add one more thing--replace the electrolytics in these little sets. If they go out, usually the radio goes silent. I had a small Zenith that had its lytic go gradually out, and the sound dribbled into nothing. Replacement restored the signals.
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Old 17th Oct 2006, 10:21 pm   #6
Phil G4SPZ
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Lightbulb Re: Battery Valve portable

I would also add to check the coupling capacitor feeding the control grid of the audio output valve. Any leakage in this component will drive the valve to draw excess anode current, which could certainly affect the output volume but will definitely shorten the battery life, lower the HT and in bad cases eventually burn out the output transformer primary winding This is quite a common fault with these sets.

Good luck!

Phil
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Old 17th Oct 2006, 10:48 pm   #7
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Default Re: Battery Valve portable

Thanks everyone, there's a good bunch of things to try out here.
Cheers,
Mike.
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