Hacker RP 25 -Motorboating now now AM and high quiescent current

[Bonky]

Hi. 1kHz and 470kHz. 5V. Sine wave

Thanks,

Richard.

[Murphyv310]

Hi
Richard you obviously don't insert 1Khz into IF stages as this is an audio frequency. You are inserting 470Khz into the IF stages T2, T3 & T4 which is correct but your generator needs to have an AM modulated 470Khz. I take it that it has this facility, if not does it have an external AF (Audio) input that you could feed audio in to modulate the 470Khz carrier.

[Bonky]

Hi, I don't believe my sig gen is capable of this.

I have one of these:

Mohoo FY2202S 2MHz Dual Channel DDS Function Signal Generator Sine Square Wave Sweep Counter

Manual:

 FY2200S User's Manual_V2.0.pdf

I also have a Vellemann K700 sig tracer.

Thanks again,

Richard

[pwdrive]

Richard, just to confirm, if you want to check the RF/IF stages with a signal generator then a modulated signal is best as any sound can be instantly heard if the detector and AF stages are working ok, you can check without modulation but it would mean monitoring the output of the detector with a DC meter or a 'scope set to DC and you would also need to be able to "interpret" the result(s)

For sure the best type of generator for injecting RF/IF is one that has built in modulation facilities, that is, one that contains it's own internal AF oscillator (usually oscillating at a fixed frequency such as 400Hz or 1kHz or there about) that can be switched in to modulate the RF/IF carrier that's generated within, you'll struggle without one if you want get into all this radio stuff, they can be broadly cast as two types, AM signal generator and FM signal generator, an AM signal generator is the most useful for most needs.

This post might cross.

Lawrence.

[Mark Hennessy]

Yes, this is the problem. As your FY2200S generator doesn't do AM, we can't test as nicely as we'd like. It's possible that we'd hear an audible "click" as you connect and disconnect the generator, or that you'd see a DC voltage at the detector diode, but a nice AM source is what we really need because it means you can use your ears. Sorry I can't give specific recommendations - there's lots to choose from. Perhaps have a look on eBay and start a new thread asking for our opinions?

Interesting that you mention an AF114. These sets were originally built with AF117s, so that transistor is a replacement. Have you looked to see if it has tin whiskers? When not in the circuit, just check with your meter for resistance between the wires and the can. Ignoring the screen lead - for obvious reasons - the resistance between the can and the other leads should be infinite according to your DMM. If not the case, you'll need to "zap" them. Forgive me if I've already posted this link, but here's what I do: http://www.markhennessy.co.uk/articles/v...with_af11x

As I explained earlier, the diode is inside the IFT. Unless you remove the IFT and take it apart, you can't get to both ends of the diode.

To give you a better idea of what I'm trying to convey, take a look at the attachments. These show a different unit (from the FM IF PCB), but you should get the idea. There are more components in here, but there's more space as the coil is only a single one (IFTs have 2, and are surrounded by a ferrite outer which occupies most of the space). This particular one is related to the ISM feature on AM, and this one did have a faulty diode, but as far as I (or my photo collection) can recall, this is the only diode I've changed in a Hacker IFT.

[Murphyv310]

Hi.
All the advice is exactly the way I'd be doing things.
If you were not a beginner I'd also say you can check this with an un-modulated signal generator and DVM. The detector diode does a dual purpose, it demodulates the IF signal and you get two resultant end products. Audio and a DC component. If you have no modulated carrier from the signal generator you still will have the DC component so connecting your DVM to the detector diode and common or chassis when you apply the signal generator to sat T4 base there should be a small voltage on the diodes cathode. If you work back to T3 base the voltage should be higher due to having the amplification added to T4 from T3, the same goes for T2 if you apply the signal to its base.
If you want to try this there is a resistor (R14) 2.2k ohms, connect your positive lead from your DVM to its connection nearest the IF transformer, connect the negative lead of your DVM to the positive side of C21 350Uf electrolytic cap.
Like I say you should see an increasing positive voltage the further you go back, don't expect more than a few millivolts on the base of T4 though, more when on T3 and some more on T2.

The best option though is a signal generator with a modulated tone to make it easier.
Do you have a scope?

[Bonky]

Thanks again Mark.

The AF114 which I used as a replacement for T3 I tested with a multimeter (with specific PNP and NPN holes -if you know what I mean), and as it had a high hFE value (around 500) I assumed that the whisker problem didn't exist.

Am I correct?

Thanks for the pics - especially as it shows that if I did need to dismantle it there only seems to be 2 lugs to unsolder. I had assumed there were more.

I'll look around for a better sig gen.

Thanks again,

BW

Richard.

[Bonky]

Hi.
All the advice is exactly the way I'd be doing things.  
If you were not a beginner I'd also say you can check this with an un-modulated signal generator and DVM. The detector diode does a dual purpose, it demodulates the IF signal and you get two resultant end products. Audio and a DC component. If you have no modulated carrier from the signal generator you still will have the DC component so connecting your DVM to the detector diode and common or chassis when you apply the signal generator to sat T4 base there should be a small voltage on the diodes cathode. If you work back to T3 base the voltage should be higher due to having the amplification added to T4 from T3, the same goes for T2 if you apply the signal to its base.
If you want to try this there is a resistor (R14) 2.2k ohms, connect your positive lead from your DVM to its connection nearest the IF transformer, connect the negative lead of your DVM to the positive side of C21 350Uf electrolytic cap.
Like I say you should see an increasing positive voltage the further you go back, don't expect more than a few millivolts on the base of T4 though, more when on T3 and some more on T2.

The best option though is a signal generator with a modulated tone to make it easier.
Do you have a scope?

Thanks again for all the detail. I'll experiment in the morning and report back.

Sorry, no 'scope. Do I need one????

Thanks,

Richard.

[Bonky]

Richard, just to confirm, if you want to check the RF/IF stages with a signal generator then a modulated signal is best as any sound can be instantly heard if the detector and AF stages are working ok, you can check without modulation but it would mean monitoring the output of the detector with a DC meter or a 'scope set to DC and you would also need to be able to "interpret" the result(s)

For sure the best type of generator for injecting RF/IF is one that has built in modulation facilities, that is, one that contains it's own internal AF oscillator (usually oscillating at a fixed frequency such as 400Hz or 1kHz or there about) that can be switched in to modulate the RF/IF carrier that's generated within, you'll struggle without one if you want get into all this radio stuff, they can be broadly cast as two types, AM signal generator and FM signal generator, an AM signal generator is the most useful for most needs.

This post might cross.

Lawrence.

Thanks Lawrence,

I'll start looking for a suitable model.

David Taylor recommends using the Vellemann K7000 sig tracer (which I have) and a suitable probe (I have just got the parts to make it).
See: http://www.vintage-radio.net/forum/showt...p?t=138951

Scan down for the probe.

Thanks

BW

Richard

[Murphyv310]

Hi.
If you are going to do this as a hobby and gradually learn what to do and have more sets then i'd say yes.
If this is a one off then no.
Your set could be multi faulted as from the readings you've posted up i'd say T1 the mixer/oscillator isn't running, a scope would confirm this in a matter of seconds. Again it depends how far you want to go and of course your budget or what the other half allows you to spend.