Craftsmen 500
- Thread starter perchdog
- Start date
perchdog
AudioDouchebag
It seems I have 2 different configurations of this amp yet all 3 are 500's.
The 1st one I found has the rounded corner opt with 7 leads. The 2nd one has a square cornered opt with 6 leads. The one I bought today has the square cornered opt with 7 leads and appears to be wired exactely like the 1st...
Its all so sorted but there is also another avenue I have been working. There is another amp floating around and I sure you are familer with it, I have to follow up on that as well. The chassis on the newest has some scratches but is pretty presentable.
So yes I guess I am on my way. At least they seem simple enough for me to play with, learn on..
The 1st one I found has the rounded corner opt with 7 leads. The 2nd one has a square cornered opt with 6 leads. The one I bought today has the square cornered opt with 7 leads and appears to be wired exactely like the 1st...
Its all so sorted but there is also another avenue I have been working. There is another amp floating around and I sure you are familer with it, I have to follow up on that as well. The chassis on the newest has some scratches but is pretty presentable.
So yes I guess I am on my way. At least they seem simple enough for me to play with, learn on..
perchdog
AudioDouchebag
Well there is another piece of the overall pic thats missing, this is bad ass
mc'killers, we will see :yes:
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perchdog
AudioDouchebag
This is what I have so far, I wish I had a cleaner copy
mpholland
R.I.P. Michael Sheppard
I am thinking the square OPT are the 500A, which run ultralinear at about 15 watts vs the 500's 10 watts. The sound of a 500 is hard to beat (even with a MAC), but you may like having the power (extra headroom) of the MACs. I notice you have two of the square ones and one of the rounded ones. If you ever decide to let the round one go would you please let me know? I have two of them, but they have small differences and would like to have an identical pair.
Marc
Marc
Actually, the C500A is a later and slightly modified version of the 500 and still runs the finals strapped as triodes for 12-15W depending on how you choose to measure power. The 550 made the switch to UL for say 25W.
perchdog
AudioDouchebag
I believe all (3) in my posession are 500's...
Per the article linked the 500A has a larger choke which appears to have forced the can cap to be mounted on the underside of the chassis. If you look at the pics early on in the thread and my dialog you will note the 1st amp (smooth corner opt) has 7 leads comimg from opt. The 2nd amp (sharp corner opt) that came into my posession has 6 leads coming from opt and a slightly different circuit. The most recent amp has 7 leads coming form opt (sharp corner) and appears to be same circuit as the 1st (smooth corner opt).
MPHolland, wondering if you could post pics of the underside of both the ones you have ? Especially the area around the opt leads..
http://www.vintage-hifi.2itb.com/photo2_3.html
PS, I have been informed the 7th lead is there because the opt is strapped or something like that. I can read a schematic but my understanding of what is actually going on is weak, as is my understanding of the terminology. Please bear with me guys if I make dumb sounding statements but I am hear to learn about these fascinating creations..
PPS, 500A schematic attached for sake of arguement
Per the article linked the 500A has a larger choke which appears to have forced the can cap to be mounted on the underside of the chassis. If you look at the pics early on in the thread and my dialog you will note the 1st amp (smooth corner opt) has 7 leads comimg from opt. The 2nd amp (sharp corner opt) that came into my posession has 6 leads coming from opt and a slightly different circuit. The most recent amp has 7 leads coming form opt (sharp corner) and appears to be same circuit as the 1st (smooth corner opt).
MPHolland, wondering if you could post pics of the underside of both the ones you have ? Especially the area around the opt leads..
http://www.vintage-hifi.2itb.com/photo2_3.html
PS, I have been informed the 7th lead is there because the opt is strapped or something like that. I can read a schematic but my understanding of what is actually going on is weak, as is my understanding of the terminology. Please bear with me guys if I make dumb sounding statements but I am hear to learn about these fascinating creations..
PPS, 500A schematic attached for sake of arguement
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mpholland
R.I.P. Michael Sheppard
Here are pics of the underside of mine. I left them fairly large so you can see them close.
The first which at one time blew a power tranny...hence the discoloration of chassis and choke.
The second, which was modified by previous owner and will be resored back to stock.
The first which at one time blew a power tranny...hence the discoloration of chassis and choke.
The second, which was modified by previous owner and will be resored back to stock.
Compared to a Turret board 550, That's positively NAKED inside there, Dave! Wish the Hell I hadn't sold my 550.
Oh well, When the Eagle ****'s this year, I'm gonna check the Flea market shop and see if it's still there. If so I'm gonna make an offer on it and the Model 10 Tuner.
Larry
Oh well, When the Eagle ****'s this year, I'm gonna check the Flea market shop and see if it's still there. If so I'm gonna make an offer on it and the Model 10 Tuner.
Larry
perchdog
AudioDouchebag
OK,
A little foward progress on power supply today, never fast enough but usually foward momentive.
Wondering... I am trying to connect added caps under chassis with the one new can (40, 40, 20 and 20uf). Am I setting myself up for hum problems by bunching wires together between caps ? Please note the 4.7uf can cap does not have neg hooked up, it should be acting as just a connection point as pictured, it has been replaced by the white CD poly. The black Mundorf is added capicitance per advice given and pos wire not yet hooked up but will run along the same path as the rest of the red and orange wires
A little foward progress on power supply today, never fast enough but usually foward momentive.
Wondering... I am trying to connect added caps under chassis with the one new can (40, 40, 20 and 20uf). Am I setting myself up for hum problems by bunching wires together between caps ? Please note the 4.7uf can cap does not have neg hooked up, it should be acting as just a connection point as pictured, it has been replaced by the white CD poly. The black Mundorf is added capicitance per advice given and pos wire not yet hooked up but will run along the same path as the rest of the red and orange wires
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Perch -- Steve O has it right. All the triode connected versions are pure class A output stages, as the original Williamson design was. They all produced between 10 to 15 watts RMS power output. The difference in power output between any of the triode connected models is simply due to the amount of B+ present, as it changed somewhat over the years.
In one of your original posts, you questioned the white wire present in one version, while missing in the other. The white wire is the wire providing NFB from the output back to the input stage. If it is missing, the NFB circuit cannot operate, meaning that the overall gain, distortion characteristics, and electrical damping produced between this particular unit, and that of another stock unit will be radically different. To preserve the original (superb) performance these units produced, I would make certain that this portion of the circuit is carefully reinstalled to insure matched performance with your other units.
The extra seventh wire on some versions could possibly be a 4 ohm tap that was simply dead ended underneath the chassis, since the unit only specified 8 and 16 ohm output connections. The other possibility, is that some of the OPTs may have been wound with a split primary winding, necessitating two B+ leads to power both output tubes. If that is the case, there will be two leads coming from the OPT which will be connected together, and then connect to the appropriate B+ supply point in the power supply.
These were likely the very best commercial versions produced of the original Williamson design. The components used and build were superb, with all the well documented stability weaknesses of Williamson's original offering properly dealt with. I have no doubt they will sound excellent when you are finished. Good luck with your amps!
Dave
Edit -- Looking back at the pics of mpholland's unit, the seventh wire is indeed a second B+ lead for the output transformer. That means that the transformers having the "extra" wire were in fact wound with a split primary winding.
In one of your original posts, you questioned the white wire present in one version, while missing in the other. The white wire is the wire providing NFB from the output back to the input stage. If it is missing, the NFB circuit cannot operate, meaning that the overall gain, distortion characteristics, and electrical damping produced between this particular unit, and that of another stock unit will be radically different. To preserve the original (superb) performance these units produced, I would make certain that this portion of the circuit is carefully reinstalled to insure matched performance with your other units.
The extra seventh wire on some versions could possibly be a 4 ohm tap that was simply dead ended underneath the chassis, since the unit only specified 8 and 16 ohm output connections. The other possibility, is that some of the OPTs may have been wound with a split primary winding, necessitating two B+ leads to power both output tubes. If that is the case, there will be two leads coming from the OPT which will be connected together, and then connect to the appropriate B+ supply point in the power supply.
These were likely the very best commercial versions produced of the original Williamson design. The components used and build were superb, with all the well documented stability weaknesses of Williamson's original offering properly dealt with. I have no doubt they will sound excellent when you are finished. Good luck with your amps!
Dave
Edit -- Looking back at the pics of mpholland's unit, the seventh wire is indeed a second B+ lead for the output transformer. That means that the transformers having the "extra" wire were in fact wound with a split primary winding.
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perchdog
AudioDouchebag
Thanks for the responce Dave.
The two amps that I am restoring both have the split primary's and yes the extra wire was hooked up to the B+ so all should be good in that regard.
It was suggested the feedback circuit may not be needed and installing a switch to turn on and off would be an option. I have not installed the circuit yet but will towards end of project. I am currently working around amps trying to leave anything I may want to fuss with as open and easy to work with as possible including the FB circuit. I also am debating in my mind weather or not to retain the domino caps or replace with the nice micas I purchased fo this project. I will sort it out soon, I am not in a real hurry because I cannot afford a set of tubes for a few weeks. I do have enough to get one amp up and running but not for the 2nd, I just had the time and parts and decided it was a good time to get these going.
