Konnichiwa,
Multiple paralleled 6DJ8/6922 sections (exact number depends upon the type as the ART has been also build in premier guise), cathode bias via 2pcs silicon diodes in series (appx. 1.2V bias), all anodes bussed up and one common Anode load resistor. Nothing differential, all SE.
Sayonara
Stefano said:
Multiple paralleled 6DJ8/6922 sections (exact number depends upon the type as the ART has been also build in premier guise), cathode bias via 2pcs silicon diodes in series (appx. 1.2V bias), all anodes bussed up and one common Anode load resistor. Nothing differential, all SE.
Sayonara
If my guess is correct
I would bet dinner that the power supply is based on BJT emitter followers. I have owned three CJ products, and worked on several others. I have a Premier Four of a friend's that he has been waiting years for me to fix. With some Vishays and RelCap foil and Polystyrene caps it is very nice sounding. The CJ stuff is interesting since it is so diametrically opposed to the Audio Research designs. I forget if it was Mr.C or Mr. J, but I remember one of them describing the AR designs as byzantine*. Having fixed a few AR products and wondering how many of the dozens of parts in a circuit had failed (and it is never just one) I would have to agree. One of Jocko's friends tried to give me an AR amp. Feeling that was a bit too generous I paid $100 bucks, spent a coulple of months getting it to stay fixed and sold it to another guy who popped $500 in cash in my hand one day when I was not even attempting to sell it. I gave no warranty with it. My CJ MV-75 that the purchaser of the AR sold me earlier blew up so many times that I sold the transformers from it and pitched the rest. So ended my ownership of CJ or AR tubed amps. the Counterpoint stuff blew up more than either the CJ or AR stuff so I just fixed it and didn't even think about owning it. Anybody wonder why I went solid state?
*Definition: A term describing any system that has so many labyrinthine internal interconnections that it would be impossible to simplify by separation into loosely coupled or linked components.
Not nostagic for tubes,
Fred
I would bet dinner that the power supply is based on BJT emitter followers. I have owned three CJ products, and worked on several others. I have a Premier Four of a friend's that he has been waiting years for me to fix. With some Vishays and RelCap foil and Polystyrene caps it is very nice sounding. The CJ stuff is interesting since it is so diametrically opposed to the Audio Research designs. I forget if it was Mr.C or Mr. J, but I remember one of them describing the AR designs as byzantine*. Having fixed a few AR products and wondering how many of the dozens of parts in a circuit had failed (and it is never just one) I would have to agree. One of Jocko's friends tried to give me an AR amp. Feeling that was a bit too generous I paid $100 bucks, spent a coulple of months getting it to stay fixed and sold it to another guy who popped $500 in cash in my hand one day when I was not even attempting to sell it. I gave no warranty with it. My CJ MV-75 that the purchaser of the AR sold me earlier blew up so many times that I sold the transformers from it and pitched the rest. So ended my ownership of CJ or AR tubed amps. the Counterpoint stuff blew up more than either the CJ or AR stuff so I just fixed it and didn't even think about owning it. Anybody wonder why I went solid state?
*Definition: A term describing any system that has so many labyrinthine internal interconnections that it would be impossible to simplify by separation into loosely coupled or linked components.
Not nostagic for tubes,
Fred
Re: If my guess is correct
Konnichiwa,
Yup. Spot on. Not the worst possible choice either.
Hmmm. While I very appreciate the legendary unreliability of ARC, CJ and Jadis it would be good to mention for contrast a pair of Quad II I came across a few years back. These had been modified by the BBC with regards to connectros and had done 5 - 6 Years service at the BBC before being replaced with transistor Amp's and sold off, where they reached the gentleman who had them checked out by my through two further owners.
I could tell upon opening the Amp's up that I had been the first person to open them up since the original BBC tech who had fitted the different connectors. The Valves also appeared original. The Amp's still played fine and obviously survived many years gracefully. Sure - most carbon composite resistors had drifted and the 'lytic cap's where near "shot though", but all in all fine Amp's.
After replacing many resistors and all 'lytic cap's plus a new set of Valves they have been playing since with no hitch whatsoever.
That is the difference between a design that operates all parts conservatively (all below 50% rated dissipation and good voltage headroom for cap's) and uses high quality (and relaible Valves) compared to designs that try milking every watt possible from inferior quality Valves and underrated parts.
Don't blame the fact that ARC, CJ and co used Valves, blame imprudent (at best - at worst highly incompetent) design for the lack of reliability. As a rule, competently designed valve gear is AT least as reliable as competently designed transistor gear, however it generally glows longer and sounds better... ;-)
Sayonara
Konnichiwa,
Fred Dieckmann said:
Yup. Spot on. Not the worst possible choice either.
Fred Dieckmann said:
Hmmm. While I very appreciate the legendary unreliability of ARC, CJ and Jadis it would be good to mention for contrast a pair of Quad II I came across a few years back. These had been modified by the BBC with regards to connectros and had done 5 - 6 Years service at the BBC before being replaced with transistor Amp's and sold off, where they reached the gentleman who had them checked out by my through two further owners.
I could tell upon opening the Amp's up that I had been the first person to open them up since the original BBC tech who had fitted the different connectors. The Valves also appeared original. The Amp's still played fine and obviously survived many years gracefully. Sure - most carbon composite resistors had drifted and the 'lytic cap's where near "shot though", but all in all fine Amp's.
After replacing many resistors and all 'lytic cap's plus a new set of Valves they have been playing since with no hitch whatsoever.
That is the difference between a design that operates all parts conservatively (all below 50% rated dissipation and good voltage headroom for cap's) and uses high quality (and relaible Valves) compared to designs that try milking every watt possible from inferior quality Valves and underrated parts.
Don't blame the fact that ARC, CJ and co used Valves, blame imprudent (at best - at worst highly incompetent) design for the lack of reliability. As a rule, competently designed valve gear is AT least as reliable as competently designed transistor gear, however it generally glows longer and sounds better... ;-)
Sayonara
Don't blame you a bit, Fred. The only tube stuff I'll use is diy. Commercial tube power amps nearly always suffer from one or more of the following:
Poor thermal management (heat flow)
Running output tubes too close to the edge
Overly high value grid resistors
Caps that tend toward leakage at high temperatures
Unsatisfactory grounding and power distribution
Unsatisfactory protection of solid state devices
Non-bulletproof regulators
Unreliable tube sources
Poorly controlled startup and shutdown
You could probably tack a few more items onto this list.
Poor thermal management (heat flow)
Running output tubes too close to the edge
Overly high value grid resistors
Caps that tend toward leakage at high temperatures
Unsatisfactory grounding and power distribution
Unsatisfactory protection of solid state devices
Non-bulletproof regulators
Unreliable tube sources
Poorly controlled startup and shutdown
You could probably tack a few more items onto this list.
Ad nausium...
Component penny-pinching
Insulation creepage distance "blindness"
Chaffing of wiring
Component and wiring anchorage deficiencies long-term
Susceptibility to mains-born interference of one or both kinds
Other than that, they're fine
But when well built, the small signal valves should last as long as most people would keep a SS amp. The output valves need replacement more often though.
Component penny-pinching
Insulation creepage distance "blindness"
Chaffing of wiring
Component and wiring anchorage deficiencies long-term
Susceptibility to mains-born interference of one or both kinds
Other than that, they're fine
But when well built, the small signal valves should last as long as most people would keep a SS amp. The output valves need replacement more often though.
Ditto to the tenth power
We have never been in greater agreement on anything. It is also possible to design unreliable solid state circuits as well I just don't seem to have to fix even a small fraction as many. I have cranked down bias levels in an effort to extend tube life with little improvement in tube life. I don't want to pays for new specialty tubes that are degrading at about the running time that the solid state stuff is breaking in. Yes, they can sound wonderful and it is very recently that solid state is closing the gap, but do you really want deal with idiosyncrasies of a racing car every time you want to go a couple of blocks to the store?
SY said:
We have never been in greater agreement on anything. It is also possible to design unreliable solid state circuits as well I just don't seem to have to fix even a small fraction as many. I have cranked down bias levels in an effort to extend tube life with little improvement in tube life. I don't want to pays for new specialty tubes that are degrading at about the running time that the solid state stuff is breaking in. Yes, they can sound wonderful and it is very recently that solid state is closing the gap, but do you really want deal with idiosyncrasies of a racing car every time you want to go a couple of blocks to the store?
A lot of things are so cheap now, that they don't justify any labour.
Valve equipment is eminently fixable for the following reasons:
1. It's expensive
2. Some parts last less than the unit's expected life
3. Most are understandable without a schematic
_____________________________________
Yes, I remember. Have built 'em
Cheers,
Valve equipment is eminently fixable for the following reasons:
1. It's expensive
2. Some parts last less than the unit's expected life
3. Most are understandable without a schematic
_____________________________________
Yes, I remember. Have built 'em
Cheers,
I have modified 2 of those, after which they never failed again( that is 4 years since).
The EL34's cannot withstand the 500V on their G2's. ( some brands seem to be less sensitive).
Modify the bias circuit so you can bias 6550's.
Take out the feedback capacitor from the outputanode, and replace the feedback resistor to 11k ohm. This reduces feedback to 6dB. If you don't like the extra gain add a voltage divider at the input.
Replace the EL34 for 6550 and you are done.
Both owners are very satisfied with the results.
Dick.
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