View Single Post
Old 8th Jun 2008, 3:46 pm   #4
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Arrow Re: Racal RA17L BFO behaviour

Hi Paolo & welcome to the Forum.

Yes, the BFO in the RA-17L is a Hartley.
The "badly distorted waveform" is not correct: hence the harmonics.

For the purposes of servicing it and fixing your problem, I suggest that you disconnect the three wires from their main chassis connections (making careful notes of where the wires go first, of course) and then withdraw the BFO assembly from the unit for a thorough overhaul.
Alternatively, you could make up simple extensions of these wires to test the BFO on the bench whilst it is operational.
The BFO as a unit is not a complicated affair. I suggest that you replace the two Rs at the anode of the valve (R132 1K; R133 4k7) and the two Rs in the grid feed (R126 100R; R125 47k). Similarly, the three HT decoupling Cs: C207 and C208 (0.05 uF each); C214 (0.1 uF) and C199 (220pF) in the grid cct.
[The O/P C (C215, 47pF) is unlikely to require changing - unless you want to increase the injection level - which can be worthwhile in giving improved resolution of ssb signals. I haven't tried this myself, but a change to something like 100 - 150 pF should help.]
If, having replaced those Rs and Cs, the problem remains - suspect the valve: CV138 = EF91.
By and large, this assembly is usually quite reliable - but considering the other defective Rs and Cs that you have found, a complete overhaul of the BFO assy. (as suggested above) would seem worthwhile.

If you have any more problems with your RA-17 - don't hesitate to come back. As G4SPZ has commented, there are several people here who have had considerable experience servicing these fine radios.

Good luck !

Al / Skywave.
Skywave is offline