The Repair and restoration of another early Racal RA17
Mar. 26 2009: Well . . . Today I had a look at another RA17 for a friend (as suggested earlier), which turned out to be another MK1. I had been forewarned that a previous owner had attempted to ‘perk up’ the front end by fitting an ECC189 (as fitted in the RA17L) in place of the the usual E180F or CV3998. Since the ECC189 is a Double Triode and the E180F is a Pentode, the two are not interchangeable. I have been informed that this is a not infrequent error made by some people and the result is always the same . . . R28 and R31 burn out . . . See the photograph below.
Something else caught my eye. It wasn’t a fault, but a label, similar to one on the front of my RA17. At first glance, these might be mistaken for serial numbers but my theory is that they are inventory labels; and this is where it gets interesting; the serial number of this receiver is N659 (mine is N664) and the number on the front panel is SIN16377 (mine is SIN16379) I know that N659 came from a Civil Service department in Edinburgh, but as far as I am aware, N664 came with it’s previous owner from the South of England. What is evident here is that at least one of these RA17s is well travelled!
Having received the necessary permission to carry out a full restoration, the next module to get the ‘works’ was the 100KHz IF where, since the AGC was not working and the BFO tone was rough, I was fully expecting to find a whole host of faults. I was NOT disappointed.
These two resistors are effectively in series with the E180F Anode. Substituting an ECC189 applies the 250V HT to the grid of V3B . . . NOT a good idea! This mistake also over-stresses R35 in the HT/Heater filter circuit. R35 is subject to up-rating as per standard procedures and was due for replacement anyway. With all three resistors replaced, I reassembled the receiver and switched it on. To my relief, it actually worked . . . but only just. Just like my specimen, sensitivity was low, the resolved audio was distorted and the front panel meter was evidently unserviceable. I decided to carry out a survey using the 2nd VFO unit as a test. There is a safety modification required to these units, so since it was going to be dismantled, I decided to ‘re-cap’ and ‘re-resistor’ it. The results were quite revealing. Of the nine resistors replaced, no less than three were high by at least 33% whilst a further two simply crumbled on removal! This gave me the excuse to recommend a complete refurbishment. The owner agreed . . But only after I had convinced him that I was NOT going to use old resistors and capacitors stored in his attic for the job!
