29-06-2017, 09:45 PM
Well, as I haven't sent an email, I assume you mean that the notification email from the forum software is what ended up in your spam folder. Certainly, everything I've said is contained here in this thread.
Thanks for finally confirming what the set actually is. That helps.
I've done a lot of RP18s, and based on my experience, I can't help thinking there is a fault. I'm not sure what though, as I've never had to do more than "zap" the AF11x transistors and replace electrolytics that aren't made by Philips. I've never encountered one that needed an IF alignment - but as I keep saying, the RF alignment is normally a bit off. Likewise for AM. I might try and tune the IF section up a bit if I know the customer lives in a difficult reception area but there's never any real point as the gains are marginal at best.
If you are absolutely sure that someone else has upset the FM IF alignment, then peak all the FM IFTs. Normally this is not recommended, but as it is already wrong (and will eventually be properly lined up), you've nothing to lose.
The final coil - the ratio discriminator - has most influence on the distortion. By ear, you should be able to get this reasonably OK*
If doing that doesn't help, then yes, you have a fault.
But because you might have a fault, I'd be inclined to leave the IFTs alone and investigate. Try looking at the diodes in the ratio detector. And check the bias adjustment - details are in the manual. An off-tune IF strip will give really, really weak reception rather than bad distortion - and the fact you haven't mentioned the former is what I keep coming back to...
The offer of help stands, but you'd have to bring it here in person (I appreciate that's easier said than done). If you post it, it'll sit in the queue for months and months. I'm always far too busy. But looking at it on a "while you wait" basis works well, providing things don't escalate out of control. It's also a good way to control costs.
Cheers,
Mark
* It is entirely possible to line up an FM IF section using an RF generator and an audio distortion meter. It's easier than the wobulator method, and just as effective - I don't know why no-one else does it (every time I mention it on a forum, no-one believes me - but then, I'm an audio person, and understand that the point of getting that nice straight line is to make the whole thing as linear as possible, therefore least harmonic distortion). Frankly, doing it just by ear gets things surprisingly good with practice.
Thanks for finally confirming what the set actually is. That helps.
I've done a lot of RP18s, and based on my experience, I can't help thinking there is a fault. I'm not sure what though, as I've never had to do more than "zap" the AF11x transistors and replace electrolytics that aren't made by Philips. I've never encountered one that needed an IF alignment - but as I keep saying, the RF alignment is normally a bit off. Likewise for AM. I might try and tune the IF section up a bit if I know the customer lives in a difficult reception area but there's never any real point as the gains are marginal at best.
If you are absolutely sure that someone else has upset the FM IF alignment, then peak all the FM IFTs. Normally this is not recommended, but as it is already wrong (and will eventually be properly lined up), you've nothing to lose.
The final coil - the ratio discriminator - has most influence on the distortion. By ear, you should be able to get this reasonably OK*
If doing that doesn't help, then yes, you have a fault.
But because you might have a fault, I'd be inclined to leave the IFTs alone and investigate. Try looking at the diodes in the ratio detector. And check the bias adjustment - details are in the manual. An off-tune IF strip will give really, really weak reception rather than bad distortion - and the fact you haven't mentioned the former is what I keep coming back to...
The offer of help stands, but you'd have to bring it here in person (I appreciate that's easier said than done). If you post it, it'll sit in the queue for months and months. I'm always far too busy. But looking at it on a "while you wait" basis works well, providing things don't escalate out of control. It's also a good way to control costs.
Cheers,
Mark
* It is entirely possible to line up an FM IF section using an RF generator and an audio distortion meter. It's easier than the wobulator method, and just as effective - I don't know why no-one else does it (every time I mention it on a forum, no-one believes me - but then, I'm an audio person, and understand that the point of getting that nice straight line is to make the whole thing as linear as possible, therefore least harmonic distortion). Frankly, doing it just by ear gets things surprisingly good with practice.
