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Radio Craftsmen mono amps

Maybe the licensing reference is a generic statement placed on all RC product to cover radio and TV products and anything that could possibly have leaked in to an amp product - and people have just assumed a direct association with the 500/550 product, or just copied comment from others.

If there was a transformer related patent then I doubt it was related to the Williamson audio aspect.

The engineering effort on the amp, given that it used the same circuit and valves, would have been mainly related to construction and confirming reliable operation with locally sourced parts - eg. transformers, layout and feedback.
 
Hello,
i owned (and own) and restored several RC 500 and 500a over the last 20 years. Soundwise the early 500 (without a) is the clear winner.

WE was the manufacturer of the RC500 output transformers.
You couldnt -according to the original RC service manual- get a new one without swapping your defect transformer.

gourmet
 
Well, I suppose I could add to an old thread. I finally got started on my round cornered 500's. Just ordered a replacement choke this morning in fact. As to licensing from Western Electric, it seems back in the 20's, WE and AT&T (Ma Bell) owned pretty much all the patents involving audio frequency amplification. Any company that wanted to build an amplifier pretty much had to use at least a portion of a Western Electric circuit, and therefore had to obtain licensing from WE. Radio Craftsmen was just one of many. The last of the patents lapsed in 1954, and most of the vintage amps people are familiar with weren't around yet. I believe the McIntosh 50W-1 and some other manufacturers were able to get past licensing as their amps were introducing new patents such as unity coupling, but not absolutely positive of that.
 
I have a single Craftsmen 500, C-400 and three RC-2 Craftmen amplifiers. The 500 is clearly the winner. The RC-2 amplifiers are much earlier and have an additional gain stage making them unusually sensitive. I found that bypassing that first stage lowered the gain and significantly reduced the hum and noise. With that simple modification, the RC-2 sounded very good, depending on the speakers used. I used them with a pair of QUAD ('57) electrostatic loudspeakers and that combination was synergistic. :music:

Craftsmen 500
 
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tcdriver said:
I have a single RC-500, RC-400 and three RC-2 Craftmen amplifiers. The RC-500 is clearly the winner. The RC-2 amplifiers are much earlier and have an additional gain stage making them unusually sensitive. I found that bypassing that first stage lowered the gain and significantly reduced the hum and noise. With that simple modification, the RC-2 sounded very good, depending on the speakers used. I used them with a pair of QUAD ('57) electrostatic loudspeakers and that combination was synergistic. :music:

RC-500
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Sweet! I've always had a liking for the RC amplifiers, they always looked well done. Sadly, never had the opportunity to come across one for sale back when, and now prices have been high. Still, a stunning amp.:drool::drool:
 
gourmet said:
Hello,
i owned (and own) and restored several RC 500 and 500a over the last 20 years. Soundwise the early 500 (without a) is the clear winner.

WE was the manufacturer of the RC500 output transformers.
You couldnt -according to the original RC service manual- get a new one without swapping your defect transformer.

gourmet
Click to expand...

round corner ? square corner ??

I would love to see the supporting documentation in regards to WE winding those transformers. My guess if they were those amps would go for a lot coin than they do.

I have two round corner and one square opt, can anyone come up with a WE part number, they surely are not marked WE.
 
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http://vintagehifiexperience.blogspot.com/2006_06_01_archive.html

The first two generations of C500 was mostly worked by Sid Smith and licensed by Western Electric. The first generation C500 was introduced in 1951, it comes with a smooth corner Stancor output transformer. In 1952, smooth corner version replaced by the sharp corner version output. Radio Craftsman C500 is based on Williamson design which operated with 2 x KT66 output tube in triode but pure class A operation with 10 watt output. It has very natural sweet, clear and transparent tone. However, it has very clear, natural, realistic and transparent tone than many vintage and modern hi-fi amp.

The Radio Craftsman C500 was replaced by C500A in 1953 and the same years Sid Smith left Radio Craftsman. I believe the Radio C500A is the final work of Sid Smith. The different between Radio Craftsman C500A is it has much higher plate voltage in triode class AB and the output increase to 15 watts per channel. It also has much large size choke than C500, it also licensed by Western Electric as well. The rectifier tube also changed to 5U4G instead of 5V4G.

The final version is Radio Craftsman C550 and it replaced Radio Craftsman C500A in 1954. Honestly, the sound of Radio Craftsman C550 sounds slightly different than C500 and C550A, it has better body but not as transparent sweet and natural than C500 and C500A. The reason is simple, the C550 is operated in Ultra-linear instead of triode operation, the output also increase to 30 watt instead of 15 watts. The amplifier also used a B+ delayed turn-on via a slow warm-up, it required 60 seconds to preserve the cathodes on the KT-66s. FYI, Radio Craftsman C550 was not designed by Sid Smith, but actually designed by Bob Grodinski, this guy took over Sid smith work as Smith already left the company and joined Marantz in summer of 1954...!
Click to expand...
 
It took me (years ago) more than a dozen Craftsmen to match a very early (both under #1000) pair of RC 500 in this original condition.

Still my holy tube grail!

gourmet
 
gourmet said:
Hello,
i owned (and own) and restored several RC 500 and 500a over the last 20 years. Soundwise the early 500 (without a) is the clear winner.

WE was the manufacturer of the RC500 output transformers.
You couldnt -according to the original RC service manual- get a new one without swapping your defect transformer.

gourmet
Click to expand...

Just curious why you like the 500 over the 500c?
 
kbuzz said:
Just curious why you like the 500 over the 500c?
Click to expand...

I'd be curious to known as well. I have a pair of 500As. Haven't had a chance to hear the others.

According to SAMs there's some differences in the output transformer resistances.

550 OPT - 6.1kohm
500A OPT - 8.6kohm
500 OPT - 5kohm
 
Not sure what SAMS folder you were looking at, but the original 164-8 for my 500's clearly states 8KΩ primary/340Ω DC resistance.
 
Call it ironic, but I found my first shiny chrome 500 with two good GEC KT66 in a wheelbarrow under a window screen in the backyard of a local estate sale. I put it in a yellow wooden Nehi soda box that was a few feet away. I then proceeded to fill the box with a few old Western Electric mikes and various other odds and ends that were just laying on a tarp in the back yard and purchased it all for 20 bucks. Turns out the guy used to work for KGW radio in Portland years before.
 
This thread is getting old, but I'm listening to my pair now (choke input PS, square corners), which I meticulously restored almost 10 years ago - I can't believe how clean, focused, and neutral they sound when running properly. With my best and freshest complement of tubes (new Gold Lion KT66s, carefully selected and matched Raytheon 6SN7GTs, and <100 hour RCA 5U4Gs), they are still my favorite amps.

They do a few things that my Citation II couldn't dream of (dead silence into any speaker and zero listening fatigue), despite being rather short on power. I use them mostly with modern speakers, GR Research Diluceos, but they sound incredibly transparent on vintage Bozaks, too.

Although this is surely posted elsewhere, my pair's plate resistors are all vintage Allen Bradley carbon comps that were baked and then matched to better than 1% from amp-to-amp. Jensen copper PIOs and K40Y9s, Solen film power supply decoupling caps, and LCR 50/50 main filter caps.

The only reason I don't use them as primary amps anymore is that I can't afford to be cooking through sets of tubes this expensive (When I did, I ran through two quads of KT66s per year). Of course, switching back to the Citation isn't too bad, since I can rock out again.
 
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kbuzz said:
Anyone have any updates or comments on this old thread....
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Sent you an email!

And... Regarding past discussions here, I'm also not sure about the appeal of the 500 over the 500a. I would pick the later one for the choke input power supply. But, then again, I've only owned the later one.
 
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jon_s said:
And... Regarding past discussions here, I'm also not sure about the appeal of the 500 over the 500a. I would pick the later one for the choke input power supply. But, then again, I've only owned the later one.
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Pure speculation, but the lower plate voltage class A of the C500 seems to be preferred by many over the higher plate voltage class AB of the latter version. The same reason why no one would even bother with the ultralinear version...:smoke: less stress on the output tubes and less demand on the power supply...
 
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jazbo8 said:
Pure speculation, but the lower plate voltage class A of the C500 seems to be preferred by many over the higher plate voltage class AB of the latter version. The same reason why no one would even bother with the ultralinear version...:smoke: less stress on the output tubes and less demand on the power supply...
Click to expand...

The lower plate voltage probably does make it a lot easier on tubes! That alone probably makes a difference, especially with modern KT66s (mine always glow).

The 500a still runs (for any reasonable purposes) as a class A amplifier, though, and overloading either into AB will result in excessive distortion due to the cathode bias configuration. Any usable power advantage of the 500a is probably just by a slight extension of the class A region by the obnoxious plate supply - if it was advertised as AB it was due to a tiny bit of headroom before distortion became excessive.
 
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