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Lineair

Good evening everyone,

I try to fix this 483x Phillips tube radio from audio stage until this converter stage, and get stuck a couple of months because of this converter stage. No reception at all from this radio.

Here are the details that i collected :
1. Using volt meter there is -8v at grid triode converter, and this oscillator signal appeared on oscilloscope.
2. If i chose band selector at bc band, frequency counter display at 900KHz - 2 MHz about.
3. If i inject 452KHz using Eico generator at top cap or grid input heptode, i could hear a loud tone from my speaker.
4. There is 150v at anode ech4 tube, and 50 volt at g2 heptode ech4 tube.
5. If i try replace the tuned coil (coil between rf and converter stage) with resistor 220k,and put the antenna at this point still no noise sound. No reception.
6. Replace the existing ech4 tube with a good one still no reception

Kindly need your help.

Beste,

Winstony

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Are you sure about the mixer type number?
Equivalent chassis for the Dutch market used ECH3's.
An ECH4 needs an outside connection ,3rd mixergrid -osc.grid (5 and 6),
and different triode and kathode connections .

--
het experiment heeft altijd gelijk

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Hi Sieme Nierk,

Thank you for your fast response.

The 483x has mixer stage with ech4 tube,please see https://marnette.home.xs4all.nl/radio/indischeradio/483X.htm.

Yes, pin 5 and 6 i've already connected it.

Regards,

Winstony

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Found indeed a schematic Philips 478ML that has ECH4.

Rare tube to be used in Philips receivers.

Ok, problem,

So
oscillator is working
Demodelation is working
Amp is working

Than look at the antenne circuit.
Antenne coil OK?
Antenne tuning Varicap OK? ,Not a shortage in plates or contacts?

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Goede morgen Maurice,

Thank you for your fast response.

Yes, ech4 tube is a rare tube but it can be easily find in auction site.

I've already bypass the rf stage, ussually using a long wire antenna at the grid input or top cap on ech4 tube, but still no reception or noise at all.

For your information, i've already fixed the 3 gang of the variable capacitor.

Warm regards,

Winstony

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Hi all,

Is there any way to test the ech4 tube in another real circuit only, i just want to check if the ech4 tube and tube socket works well ?
The oscillator of this converter tube is working good. There is rf signal 452 KHz on pin 8 (anode of heptode) of ech4 tube, but no modulated rf signal just flat rf 452 KHz. No reception or noise at all, but when i injected modulated rf 452 KHz using Eico generator, i could hear loud tone on speaker.

Thank you, your respond is highly appreciate it.

Warm Regards,

Winstony

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What is the (negative) voltage (AGC) on pin 9 (topcap)?
Is the hephode in cut-off mode, or very low gain ?

[image]

--
Cees PA1DBA

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Hi Goldline,

Thank you for your fast respond.

There is 0 volt at the top cap of ech4 tube since the grid is connected to rf tuned coil. Please see Philips 900x schematic.

Heptode is in cut-off mode or low gain ? For this question, i've already replace the existing tube with a good one, there is 150 volts at pin 8, 50 volts at pin 7, and 1 volt at pin 1.
There if a flat 452 Kc rf signal (no modulated rf signal) at pin 8 by using oscilloscope. I guest this heptode works well.

Warm Regards,

Winstony

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With correct osc-signal and a loud and clear if out,
Looks like the hf stage is oscillating, should indeed cause neg grid 1 voltage.
I expect troubles in the agc-line.

--
het experiment heeft altijd gelijk

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The HF stage is oscillating on 452 (IF freq). That is my guess. This explains the flat 452 signal and the RF signal block. There is a shortage or feedback in the Heptode anode circuit to the control grid. The 452 output filter sets the frequency.
Also a cap may fail that shorts the 452 signal.

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4th grid cap or kathode cap ?
try to bridge these with a other cap. observing the anode with the oscilloscoop.

please disconnect top grid and ground it ,to see of the oscilation at 452 stops.
i suppose that you already have removed the 1th stage tube (rf amplifier)?
so this one will not disturb everything.

--
Cees PA1DBA

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It is not likely that the front stage tube will oscillate at just 452 kHz, since there is no such filter nearby.

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Goede morgen,

Thank you for Goldline, Ruudtx, Sieme for your fast response.

I did observation to the oscillator and pin 8 or anode heptode. It has same frequency output between oscillator and anode heptode which was arround 1.25 MHz. So, it was not 452 KHz at pin 8 anode heptode.

I tried to grounded the top cap of ech4 tube, the oscillator signal still appear at pin 8 anode heptode.

Warm Regards,

Winstony

[image]

Below picture is oscillator signal
[image]

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This 1.25 signal is generated by the triode (ECH4)?
If so, try to disable the oscillator by disconnecting anode triode from supply.

There is alo a possibility that the front stage is oscillating at the tuned frequency, this will also result in a blank 452 signal. So try to disable this as well by removing tube. Is there still a 452 signal?

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Goede morgen,

Hi Ruudtx, thank you for your kind respond.

I did do grounded the connection between c21 and switch (after grid triode), there was no 1.25 signal after grounded this connection.
I think, if i pull the ech4 tube there will no 1.25 signal again since it was from oscillator signal.

Regards,

Winstony

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It is normal to have the oscillator signal (from triode) on the anode of the heptode.
There should be 3 signals - the rf signal when receiving a station, the osc signal and the difference signal, this is the IF signal 452 kHz. (Also the added signal rf + osc signal is somewhere theoratically, but is highly suppressed.)

As I understand the problem is that an unmodulated IF signal appears at the anode of the heptode. So the question is, where does this come from.

1) The heptode is occillating at 452
20 The front stage, the rf amp, is oscillating at tuned frequency. This can easy be eliminated by removing the tube.

So is there still a silent 452 kHz signal without the 1st rf amp?
If so, the heptode circuit is faulty, if not, it is the first stage causing the problem.

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Hi Ruudtx,

Thank you for your fast response.

I've asked the seller whom had sold this used ech4 tube. He said to me that he had tested this tube using funke tube tester as "good" only.
I will test this tube and send the result on this forum.

Regards,

Winstony

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Dear all,

Thank you for your kind response regarding troubleshooting of Philips 483x tube radio.
I had bought nos ech3 tube as ech4 tube replacement. Then i rewired the tube connection, now the radio has reception (although broadcast band only). The used ech4 tube has weak on heptode section.
Well, it is no warranty if used ech4 tube will work properly eventhough the tube seller had said tested on funke tube tester.

Again, thank you very much.

Best Regards,

Winstony

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