Racal RA17L Strong Heterodyne - UK Vintage Radio Repair and Restoration Discussion Forum

brunocorte · 17th Jul 2014, 2:14 pm

Hello everyone, I just joined the forum and I liked the posts I've read, then here I am with the hope of being able to solve my problem.

I possess a beautiful RA17L that works pretty well, but kilocycli 0 at the beginning of each band and the origin 1000 kcs a loud whistle.
I checked voltages and components, it seems all right. I must say that the whistle and very strong and just beginning to 1000 kcs kcs always 0 for each band.

some good man can help me? infinite thanks.

Skywave · 20th Jul 2014, 11:56 am

This is not uncommon. The Racal manual mentions it: "I Mc/s Harmonic Break-through". Here's the extract . . .

There are two conditions under which that break-through can occur:
1. If the response is dependent on the setting of the 1 Mc/s dial setting, the 1 Mc/s spectrum is probably breaking through to the first mixer stage.
2. If the response is independent on the setting of the 1 Mc/s dial setting, it is due either to break-through of the second and / or third harmonic to the second or third mixer stage. Remove the second mixer valve to eliminate this stage and so determine in which stage the break-through occurs.

End of extract.

In a radio like the RA-17, with its multiple frequency conversion processes, it is difficult (if not impossible) to eliminate all spurious responses: Racal admit that. Racal's aim was to reduce all spurious responses to below the inherent noise level of the set. It is essential that all internal screens are fitted and that where those screens make a metal-to-metal contact, the mating surfaces are clean and a tight fit is obtained. Make sure that all screen securing screws are fitted. The extent of the decoupling in the RA-17 is extensive and comprehensive, for obvious reasons. As the years have passed, many of those networks will have resistors and capacitors that have changed values - especially capacitors that have become 'leaky' and resistors that have gone 'high'. Therefore all such resistors and capacitors should be checked and replaced where necessary.
To do any serious work on a RA-17 an oscilloscope is essential. Check the waveform and operating conditions of the 1 Mc/s crystal oscillator: you may find excessive harmonic content in its waveform.

Skywave. / July 20, '14

brunocorte · 21st Jul 2014, 12:48 pm

Hi, many thanks for your reply. As soon as I have time to play with the radio I will investigate nad when I have found in the the cause will let you know.

Thank you and good day.

Skywave · 22nd Jul 2014, 12:19 am

Just to add one small thing. If you are going to do anything serious to a RA-17, make sure you have a copy of the manual and read it through thoroughly before you start. The RA-17 is a complicated animal and unless you are quite familiar with the way it works, it is easy to really mess things up.

Good luck with it.

Al.

brunocorte · 24th Jul 2014, 9:36 am

hello, I am pleased to let you know that I placed the receiver ra17L and rich with your suggestions now everything is working.
the loud whistle that was at the beginning and end of every frequency is now down almost imperceptible without an antenna, with the antenna no longer feel and listening on the frequency limits now you can.

the receiver has been visited with a spectrum analyzer and a few small capacitor of 33 pF were replaced in filter 37.5. all tubes have been removed and its accommodation has been thoroughly cleaned so also all the screens of the various sectors. other skills have been replaced in the cathodes of the mixer 2 and 3. were broken.

when the receiver is on and receiving station for hours with sample freq filter 100c / s added.

on the high freq is to help an antenna-preamplifier.
my antenna is not generous.

I found it very useful forum where I searched and found a lot of information and other web sources. in particular, this where I could
finally see the freq response and the relative shape of the filter 40.
is located here: http://www.recelectronics.co.uk/ct501.htm

is very, very useful.

again many thanks to you soon.

73 and GL de i5cty

17th Jul 2014, 2:14 pm	#1
brunocorte Retired Dormant Member Join Date: Jul 2014 Location: Arezzo, Italy Posts: 4	Racal RA17L Strong Heterodyne Hello everyone, I just joined the forum and I liked the posts I've read, then here I am with the hope of being able to solve my problem. I possess a beautiful RA17L that works pretty well, but kilocycli 0 at the beginning of each band and the origin 1000 kcs a loud whistle. I checked voltages and components, it seems all right. I must say that the whistle and very strong and just beginning to 1000 kcs kcs always 0 for each band. some good man can help me? infinite thanks.

20th Jul 2014, 11:56 am	#2
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Racal RA17L Strong Heterodyne This is not uncommon. The Racal manual mentions it: "I Mc/s Harmonic Break-through". Here's the extract . . . There are two conditions under which that break-through can occur: 1. If the response is dependent on the setting of the 1 Mc/s dial setting, the 1 Mc/s spectrum is probably breaking through to the first mixer stage. 2. If the response is independent on the setting of the 1 Mc/s dial setting, it is due either to break-through of the second and / or third harmonic to the second or third mixer stage. Remove the second mixer valve to eliminate this stage and so determine in which stage the break-through occurs. End of extract. In a radio like the RA-17, with its multiple frequency conversion processes, it is difficult (if not impossible) to eliminate all spurious responses: Racal admit that. Racal's aim was to reduce all spurious responses to below the inherent noise level of the set. It is essential that all internal screens are fitted and that where those screens make a metal-to-metal contact, the mating surfaces are clean and a tight fit is obtained. Make sure that all screen securing screws are fitted. The extent of the decoupling in the RA-17 is extensive and comprehensive, for obvious reasons. As the years have passed, many of those networks will have resistors and capacitors that have changed values - especially capacitors that have become 'leaky' and resistors that have gone 'high'. Therefore all such resistors and capacitors should be checked and replaced where necessary. To do any serious work on a RA-17 an oscilloscope is essential. Check the waveform and operating conditions of the 1 Mc/s crystal oscillator: you may find excessive harmonic content in its waveform. Skywave. / July 20, '14

21st Jul 2014, 12:48 pm	#3
brunocorte Retired Dormant Member Join Date: Jul 2014 Location: Arezzo, Italy Posts: 4	Re: Racal RA17L Strong Heterodyne Hi, many thanks for your reply. As soon as I have time to play with the radio I will investigate nad when I have found in the the cause will let you know. Thank you and good day.

22nd Jul 2014, 12:19 am	#4
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Racal RA17L Strong Heterodyne Just to add one small thing. If you are going to do anything serious to a RA-17, make sure you have a copy of the manual and read it through thoroughly before you start. The RA-17 is a complicated animal and unless you are quite familiar with the way it works, it is easy to really mess things up. Good luck with it. Al.

24th Jul 2014, 9:36 am	#5
brunocorte Retired Dormant Member Join Date: Jul 2014 Location: Arezzo, Italy Posts: 4	Re: Racal RA17L Strong Heterodyne hello, I am pleased to let you know that I placed the receiver ra17L and rich with your suggestions now everything is working. the loud whistle that was at the beginning and end of every frequency is now down almost imperceptible without an antenna, with the antenna no longer feel and listening on the frequency limits now you can. the receiver has been visited with a spectrum analyzer and a few small capacitor of 33 pF were replaced in filter 37.5. all tubes have been removed and its accommodation has been thoroughly cleaned so also all the screens of the various sectors. other skills have been replaced in the cathodes of the mixer 2 and 3. were broken. when the receiver is on and receiving station for hours with sample freq filter 100c / s added. on the high freq is to help an antenna-preamplifier. my antenna is not generous. I found it very useful forum where I searched and found a lot of information and other web sources. in particular, this where I could finally see the freq response and the relative shape of the filter 40. is located here: http://www.recelectronics.co.uk/ct501.htm is very, very useful. again many thanks to you soon. 73 and GL de i5cty