R.L. Drake

Drake Mods - R4B and R4C

Authored by VE3EFJ

3.6 R4B AND R4C

    You could liken the Drake twins operationally to the Heath SB301 and SB401 from the fact that they would transceive. Stand alone SSB transmitters are all pretty much the same. The T4C is a bit like an SB401 functionally. In regards to the SB301, the Drake 4 line receiver, especially the R4C, is in a completely different league.

    All Drake receivers in this series are sensitive and selective. On either series, a healthy receiver should exhibit noise peaking on all bands as the preselector is adjusted with no antenna connected. It will not be an extreme increase in noise level, but it should definitely be there on all bands.

    Drake enthusiasts generally prefer the B series receiver. The B series has built in a number of items that were options on the R4C. There are few mods for the R4B. When you buy an R4B, there is not much else to get EVERYTHING is there that you need - noise blanker, calibrator and 4 selectivity settings. The B series was dual conversion, the last IF at 50 kHz determined the selectivity and provided notch filtering. The B receiver is noted for its clean recovered audio, good signal handling and solid engineering. Because the selectivity is determined by LC filters, the skirt selectivity is not on par with crystal filter radios. Since the B receiver was dual conversion and the C receiver is triple, it is generally assumed that the B receiver is 'quieter'. This will appear from time to time throughout this treatise and I'm skeptical whether this is in fact true or yet another example of theory not born out in practice.

    The noise blanker in the B receiver works quite well, but not as good as the R4C or TR4 blanker. The B blanker is more sensitive to noise 'quality' - duration, period and rise time. Some noise will be nearly eliminated and yet other noise which sounds the same won't be touched. The R4C and TR4 blankers are more effective across broader noise characteristics. The R4B blanker is a 'Lamb IF Noise Silencer'. Detail on its workings can be found in most Handbooks dated around 1972. Intermod characteristics are not degraded in either receiver with the noise blanker turned on.

    The R4C is in fairly high demand. It is a triple conversion receiver and completely different from an R4B. While the R4B does contain some semi conductors, the R4C is more of a hybrid design. There were at least 3 different types of R4C receivers. Generally an early R4C has a 4 position crystal filter switch and a later model has a 5 position switch. In the later model, the AM filter location was moved inside the chassis and mounted on an extra bracket.

    There is no discernible performance difference amongst ANY of the Drake R4C series receivers. Collectors want the later model; practical owners shouldn't care.

    The R4C - in all models - came with an 'OK' sideband filter. You will need to upgrade the filters and add some filters if you want to get this receiver to perform. There is only one source of filters for the R4C - International Radio in Florida (***). These filters are expensive (about $110 ea. US) and excellent. The most important filter is the 8 kHz first IF filter known as a GUF-1. Replacing the stock Drake filter with the GUF-1 transforms the receiver. If you have the 6 kHz GUF-1 installed, noise blanker performance is compromised. The GUF series filter is difficult to obtain and they are not drop in replacements. You will be required to drill holes in the chassis or build an adaptor board from double sided G10 and mount the assembly underneath using some stand offs. The results are worth it, however. (ref Letters)

    A stock R4C is a bit of a waste. Under those covers is goodness just dying to get out. When the R4C came out, there were some compromises that had to be made to keep the price point. The trade offs were mostly in the area of filters and no noise blanker. The first IF amp crystal filter is a pretty sad excuse and unfortunately sets the character of the receiver. What you have to do to make it what it could of been is to make some investments that Drake could not afford to do. With decent filtering and maybe some mods, the receiver is as good as and maybe better than just about anything available to date. Some aspects of the R4C design cause one to question the engineers at Drake. The audio amp in the R4C is frankly terrible. The 12 volt regulated power supply is an incredibly BAD design. Drake had this 'thing' about running transistors from the plate B+ supply using huge dropping resistors and zener diodes. The above causes an inordinate amount of heat to be generated. Regarding the R4C audio amp, it is reminiscent of a 60's car radio what with its class A output stage. Except for some cost savings it was an unnecessary design and using the SPR-4 as an example, Drake knew better.

    Given all these things to be said about an R4C, why would anyone want one? It depends if the C in question is loaded or not. The stock audio and power supply is offensive from a design aspect, but it does work. The transformation of the receiver with decent filtering is phenomenal. What really happened to the C is that Drake held costs and left the underlying receiver alone. That receiver base is extremely strong but the strengths are buried by the cost cutting.

    In all fairness, the C must have been very expensive to produce. Crystal filter technology was no where near what it is today. In the glory days of the R4C, band conditions were nothing like they are today, so in the area R4C filters, we'll call it 'adequate for the time period." But not today. A GUF-1 or similar filter from Sherwood Engineering as a substitute for the first crystal filter in the R4C is a tremendous improvement.

    Aside from nostalgia what makes this equipment attractive is that it works, works well, is reliable and of high quality. The AGC on most of the receivers is superior to most foreign equipment. Considerable thought went into its design. It is overbuilt - you cannot break this equipment through age or use. While it may not have been built with the intent for it to still be working 20 years later, most of the Drakes I've seen have had a minimum of repair. All 'old' equipment suffers some abuse as it trades from hand to hand. Surprisingly, the Drake equipment seems to survive at the same level as Collins. Rarely is it butchered and then usually this happens from an inexperienced person attempting repair.

    Amongst Drake receivers a stock B is vastly superior to a stock C. Compared side by side in stock form, The B sounds MUCH better and has all the goodies right there. Your priorities and opinions may differ. Some folks insist on having a late model C - "high serial number" without perhaps knowing what they're asking for and willing to pay a premium for. Fine, if you're a collector. They don't even care what options its got, yet if you were to filter up a C and find a noise blanker, it will cost more than the radio. The strange thing is all that stock C's have is not much more than 'potential'. All work pretty well the same. The B requires no work at all and can be had for a song, but don't expect to wade through a pile up on 20 SSB with a B - it can't do it, at least not very well. The B represents balance. It comes from a period where commercially available, cost effective crystal filters where yet to be widely available. If you're inclined to have a B after reading this, I'm flattered - its an excellent receiver, but it is not Excalibur. The C receiver is an incredibly good receiver, but ONLY if it is loaded up with filters and some cost cutting problems are attended to. The International filters are better than the filters that Drake supplied. The recovered audio on a stock R4C receiver is quite bad without some change. Just changing the value of 1 capacitor makes a considerable improvement. Once loaded up, the R4C becomes a real DX receiver and can 'slice and dice' with the best. The only way to overload a properly set up R4C is to connect the antenna terminal directly to the transmitter, its that good. In stock form, you'd have no idea what is there.

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