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Radio Craftsmen mono amps

N

Normo

Well-Known Member
I have been trying to figure out the relative desirability of the various models. Does anyone have any expertise where they can talk about the pluses and minuses of the rc 2, vs the rc-400, vs the rc 500 or rc-550? From what I have been able to glean from the web, is that radio craftsmen made some fine equipment back in the 50s. I think I would like to pick up a matched pair of amps and have seen many offered on the bay, but I just don't really know enough about the different models to pull the trigger. Thanks Norm
 
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The RC500 and 500a were a Western Electric licensed design that Sid Smith then further massaged, before he went over to Marantz as their lead designer.

The others are above average in design and performance, but Radio Craftsmen hit their peak with the 500s.
 
Rc-2, c400

Both the RC-2 and C400 are 6V6 PP amps. I rebuilt four and was not very impressed with the output transformers at high frequencies - very restricted power bandwidth. As mentioned above the 500/550 series aimed higher with PP KT66 outputs. The 500's run in triode mode producing about 15 W and the 550 in ultralinear mode producing about 30W. All are cathode biased. Unfortunately, I've never had a chance to work on or hear the 500s, but they have many fans and high prices.
 
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I'm not sure where Western Electric comes into this, but I do know that the C500 was a near exact copy of the original British Williamson amplifier, including some of the enhancements that Dr Williamson ultimately recommended to enhance HF stability -- something the original Williamson amplifiers were loudly condemned for, and rightfully so. Sid improved on those stability measures even further, making the C500 of superb amplifier.

The C-550 is simply the UL version of the 500, and employes the usual upgrades that had found they way into all such "converted" Williamson amplifiers of the day. Because it is still primarily the Williamson design, it is known as a UL Williamson amplifier. The C550 was also a superb instrument, capable of about twice the power of the C500.

Dave
 
I have been reading more and found a reference on vintagehifi. That lucky gentleman had heard the 500 and the 550 and either he felt the 500 sounded "better" or a reference he cited, stated that the 500 was "sweeter". His point was that Sid Smith did work on the design of the 500 but left radiocraftsmen and some one else did the "work' on the 550. I don't understand this, but he referenced the "ultralinear" operating mode of the 550 and this, in his opinion, changed the character of the sound from the C500. I think he preferred the C500 over the 550. Has anyone had a chance to compared both of these models? To be honest I don't really understand the sonic characateristics that stem from the design changes. Norm
 
Thanks for the kind offer, but I live in Mass. and don't travel that much. What are you using as the pre amp and speakers if I may ask? Norm
 
Preamps include the Brook 7, HH Scott 121C, Heathkit SPA2, or McIntosh C104 to choose from. I go between an Electrovoice Georgian, Aristrocat, University Dean, Heathkit AS21, or JBL C40 Harkness for speakers.
 
That's some really nice equipment. Is there any particular synergy between any of those pre's, the C500 and a particular speaker? Norm
 
Norm, the synergy exists among most everything, except the McIntosh preamp. It needs a rebuild, but doing such will kill the "original" value for the Mc collectors. The Brook and Fairchild excel at being quiet, the Scott has a tremendous phono section.

The speakers all are around 100 dB sensitivity, so there is no chance of overworking the RC. Most people would be stunned at what a 1952 system can do.
 
I have / had a pair of the C500's gone through that I was fortunate enough to A-B against a pair of MC30's which I also gone through. Both pairs of amps were done up with much the same scheme (components), premium resisters, orange drops, Russian pio's and the like, CDE caps and Mills resistors in power section. They were both somewhat budget builds, no silver foil, teflon caps or the like. Both pairs played through Fisher 400C also refurbed in same manner and Fisher 400CX2 in stock form. The speakers are GPA 416 bass drivers in JBL scoop cabs, EV Sentry 3 horns, tweets and x-overs.

The Craftsmen's edged the Macs on sweetness of sound, unfortunately weighing in at 10-12 watts they could not push the speaks as hard as the Macs, the Craftsmen's lacked head room, I could not push early as hard as with the Macs, but they sounded great never the less. I have recently lost a power tx in one of the Craftsmen's, well known problem. I have replacement picked out from triode, both will done at same time. I have other projects in the way, probably do them back up in the sub-freezing months

http://www.audiokarma.org/forums/showthread.php?t=303689

http://www.audiokarma.org/forums/showthread.php?t=355076
 
I own a pair of 500s, but they have been out for "repair" for a long time so i cant recall/comment on the sound since its been so long.

I should also ad that last months absolute sound had a review by dick olsher which commented that his reference amps were a pair of "modified c500s". I would love to know what mods/changes were done to his pair. And for general suggestions re modding them.

I tried emailing Olsher at his black Delilah website but got no response.
 
I have a pair of 500s, but they're on the "to do" list.
These are quite old and have some of the normal bugaboos of '50s gear. That is, they need a full overhaul.
Chromeo . . .wherefore art thou Chromeo . . . 'tis it better to replate in Nickel? Or to send it to a bike shoppe for a full rechromeo?
Then there's tube sockets and it just goes on from there.
 
Dave, the output transformers for quite a while were purchased from Western Electric, and RC paid them a licensing fee for all amps built, as noted on the nameplate.

 
sheltie dave said:
Dave, the output transformers for quite a while were purchased from Western Electric, and RC paid them a licensing fee for all amps built, as noted on the nameplate.
Click to expand...

Granted circuit was licensed by Western. All I have read shows Stancor supplying transformers. Where did you pick up on WE iron ?
 
Sheltie -- Thanks so much for supplying that information! No doubt they would have paid a licensing fee to use WE's branded transformers for sure, and that certainly explains where WE became involved with the RC product.

Perch -- No doubt RC used multiple transformer venders, as so many of the manufacturers did back in the day.

On the other hand, I can't believe they were paying (or even should have been paying) a thin dime for the circuit, as it is (for all intents a purposes) a direct knock off of the original Williamson design as published in 1947, and revisited by the good doctor in 1949. Does anyone know otherwise?

Dave
 
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