31-10-2012, 06:46 PM
As with the DAC90A, fortunately the full maker's service data is available for the DAC90, which will prove useful. As with the DAC90A, it has a 0.1uF RF 'bypass cap/firework' (C24 on the maker's data) across the mains (under the chassis on the DAC90 - above the chassis on the 90A). That needs to come out before switching on. They seem to make no perceptible difference, so the only reason to replace them IMHO is to be faithful to the original design. If it is replaced, it needs to be with a class X cap. Then of course, at least the audio coupling cap to the audio stage grid needs to be replaced ('that cap') - 0.01 C20 on the maker's sheet.
Joe tells me that it came with its mains lead, and was described as 'working' so that's promising.
As with the DAC90A, most caps and resistors are mounted on a tag strip beneath the chassis, though not on the chassis floor as is the 90A, but on the rear chassis apron. If Joe intend to keep it, he'll no doubt wish to change the other paper waxy caps. One good thing about the '90 is that the dial bulb is 6.2V 0.3A (6.3V is fine so long as its 0.3A), so not only will it illuminate the dial properly, the bulbs are commonplace, unlike 3.5V 0.15A in the '90A. However, as the bulb is directly in series with the heater chain, if it fails, the heater chain is broken. A nice little earner in days gone by when a 'dead radio' was taken to the local dealer for 'repair'!! (6d for a new bulb, a fiver for knowing it needed replacement to bring the set back to life!)
The octal valves will most likely have a longer life than the ghastly 'rimlock' B9A valves in the 90A, though in fairness it only tends to be the UL41 that tapers off in the '90A. I think most valves that fail on the 90A are due to people unwittingly breaking the pips on the valves by pulling the valves out of the sockets before taking the precaution of removing and throwing away the springs around the valveholder. The valve retention springs may have served a useful purpose in a military setting where vehicles were driven over rough terrain, risking valves being dislodged in mobile radio equipment, but in a domestic radio rimlock valveholders serve no useful purpose.
The CCH35 is all but identical to the ECH35 apart from the heater voltage (7V in the CCH35 rather than 6.3V), and both that and the EF39 are known for longevity. I don't know about the rest of the valves, but maybe Joe will be on the lookout at the Golborne Swapmeet if he needs spares!
The DAC90 consumes 60 Watts compared to the '90A's 35 Watts, yet the '90 audio output is 1.5Watts (plenty) as compared to the '90A at 2 Watts. The mains dropper (R19 on the maker's sheet) is 30 Watts!, and is enclosed in its asbestos lined little home, intended as a heat shield, but which deflects the heat onto the back panel with predictable results. With the DAC90, you get two appliances for the price of one - a radio, which doubles as an electric fire!
I'm convinced that Joe only buys DAC90s to wind me up, but its all good clean fun! At least his recent PCR2 'adventure' has weaned him off hankering after an R1155.
Joe tells me that it came with its mains lead, and was described as 'working' so that's promising.
As with the DAC90A, most caps and resistors are mounted on a tag strip beneath the chassis, though not on the chassis floor as is the 90A, but on the rear chassis apron. If Joe intend to keep it, he'll no doubt wish to change the other paper waxy caps. One good thing about the '90 is that the dial bulb is 6.2V 0.3A (6.3V is fine so long as its 0.3A), so not only will it illuminate the dial properly, the bulbs are commonplace, unlike 3.5V 0.15A in the '90A. However, as the bulb is directly in series with the heater chain, if it fails, the heater chain is broken. A nice little earner in days gone by when a 'dead radio' was taken to the local dealer for 'repair'!! (6d for a new bulb, a fiver for knowing it needed replacement to bring the set back to life!)
The octal valves will most likely have a longer life than the ghastly 'rimlock' B9A valves in the 90A, though in fairness it only tends to be the UL41 that tapers off in the '90A. I think most valves that fail on the 90A are due to people unwittingly breaking the pips on the valves by pulling the valves out of the sockets before taking the precaution of removing and throwing away the springs around the valveholder. The valve retention springs may have served a useful purpose in a military setting where vehicles were driven over rough terrain, risking valves being dislodged in mobile radio equipment, but in a domestic radio rimlock valveholders serve no useful purpose.
The CCH35 is all but identical to the ECH35 apart from the heater voltage (7V in the CCH35 rather than 6.3V), and both that and the EF39 are known for longevity. I don't know about the rest of the valves, but maybe Joe will be on the lookout at the Golborne Swapmeet if he needs spares!
The DAC90 consumes 60 Watts compared to the '90A's 35 Watts, yet the '90 audio output is 1.5Watts (plenty) as compared to the '90A at 2 Watts. The mains dropper (R19 on the maker's sheet) is 30 Watts!, and is enclosed in its asbestos lined little home, intended as a heat shield, but which deflects the heat onto the back panel with predictable results. With the DAC90, you get two appliances for the price of one - a radio, which doubles as an electric fire!
I'm convinced that Joe only buys DAC90s to wind me up, but its all good clean fun! At least his recent PCR2 'adventure' has weaned him off hankering after an R1155.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
