My amp began to smell of burning today, the 470 ohm resistor in the power line was obviously very hot and discoloured. There was also a distinct hum which I've never had problems with before.
Being new to Tube Amps could someone kindly point me in the right direction ?
(I have some electrical background).
Thanks in anticipation.
Being new to Tube Amps could someone kindly point me in the right direction ?
(I have some electrical background).
Thanks in anticipation.
Hi Stephen,
Without being there or seeing a schematic, I can only give you the basics of what to look for in general order of preference. And I assume you mean a 470 ohm resistor in the B+ supply line. Not the AC mains.
1) Bad tubes, especially the output tubes.
2) Leaky coupling capacitors at the grid of the output tubes causing lowered bias and excessive current through the tube. (assuming you have fixed bias) Look for signs of tube overheating like a plate turning dull red.
3) Failing negative bias supply causing the same condition.
4) Leaky/failing power supply filter capacitors draging down the voltage level.
Hope this helps.
Victor
Without being there or seeing a schematic, I can only give you the basics of what to look for in general order of preference. And I assume you mean a 470 ohm resistor in the B+ supply line. Not the AC mains.
1) Bad tubes, especially the output tubes.
2) Leaky coupling capacitors at the grid of the output tubes causing lowered bias and excessive current through the tube. (assuming you have fixed bias) Look for signs of tube overheating like a plate turning dull red.
3) Failing negative bias supply causing the same condition.
4) Leaky/failing power supply filter capacitors draging down the voltage level.
Hope this helps.
Victor
Plugged in Cadet III - it works!!! much to my suprise as it had been thrown into the bottom of a wire cage in the recycling centre ( I had toclimb in to retrieve it).
Anyway, a worthwhile find although it is noisy (Hiss & Hum). One ECL86 tube is hotter than the rest - will test all electrolytic caps & replace.
Too soon to decide if I prefer tube to solid state. I can hear some potential (warmth,clear top end,etc) in the sound but maybe it's just not as precise as SS?
Anyway, a worthwhile find although it is noisy (Hiss & Hum). One ECL86 tube is hotter than the rest - will test all electrolytic caps & replace.
Too soon to decide if I prefer tube to solid state. I can hear some potential (warmth,clear top end,etc) in the sound but maybe it's just not as precise as SS?
That's what I call recycling
Thanks EC8010 - I also recycled from the same cage (although not at the same time) - three Samson Servo 550 solid state power amplifiers (all working), Ecler Smacpro40 mixer preamp, a Rega planar II turntable. I have only visited this recycling centre about 6 times & I often wonder what I have missed. It seems a shame that such useful & interesting equipment is being destroyed (I don't know what they actually do with it but I doubt it is refurbished).
Anyway, I will change the electrolytics & implement some of the changes you suggested on another thread - change 24uF smoothing caps for 47uF, change 100uF PSU caps for modern low ESR high ripple caps. There was also a mention somewhere about changing the biasing res from one shared 130R & bypass cap to 270R & bypass cap to each tube's plate(? - I'm not a tube guy so forgive me if this is the screen)
Other discussions I read concern the PU adaptor - I plan to try to run the Rega planar II with high output moving coil cartridge into the Rogers Cadet III & using my Rogers LS3/5a speakers - might well be a nice system - it looks nice & retro anyway with all that wood on display.
Thanks EC8010 - I also recycled from the same cage (although not at the same time) - three Samson Servo 550 solid state power amplifiers (all working), Ecler Smacpro40 mixer preamp, a Rega planar II turntable. I have only visited this recycling centre about 6 times & I often wonder what I have missed. It seems a shame that such useful & interesting equipment is being destroyed (I don't know what they actually do with it but I doubt it is refurbished).
Anyway, I will change the electrolytics & implement some of the changes you suggested on another thread - change 24uF smoothing caps for 47uF, change 100uF PSU caps for modern low ESR high ripple caps. There was also a mention somewhere about changing the biasing res from one shared 130R & bypass cap to 270R & bypass cap to each tube's plate(? - I'm not a tube guy so forgive me if this is the screen)
Other discussions I read concern the PU adaptor - I plan to try to run the Rega planar II with high output moving coil cartridge into the Rogers Cadet III & using my Rogers LS3/5a speakers - might well be a nice system - it looks nice & retro anyway with all that wood on display.
jrevillug said:
You should have said 'I wasn't going to pay for it, I was just going to take it away !'
.........................
I used to live near Farnham in Surrey.
Farnham recycling centre is Surrey County Council and does not permit sale of items.
4 miles away is Aldershot tip, run by Hampshire Council. They have a large shed where reuseable items are put for sale at a nominal price. A very popular place !!!!
Andy
I don't ask, I just take - I'm always dropping off something for recycling myself so it's not as if I wander in to have a look.
I was prevented when I asked staff to plug in a scrapped Mac G4. They then said that nothing could be taken out of the recycling centre - I argued that I was truly recycling but to no avail. Since then I just remove what I want & don't bother with the staff.
I was prevented when I asked staff to plug in a scrapped Mac G4. They then said that nothing could be taken out of the recycling centre - I argued that I was truly recycling but to no avail. Since then I just remove what I want & don't bother with the staff.
Checked the electro caps, so far all seem to be well (using a multimeter with uF reading) - so hum & hiss is probably inherent to the design. Checked the wiring runs & signal wires seem to be well seperated from PS wires - so problem not here then.
I have two spare 220uF 400V caps & I figured to parallel the existing Cadet Sprague 47uF (this is what I measure on the multimeter) smoothing caps with these - these are a higher value to the Cadet III component values list (16uF 350V) or the schematic drawn by dld in 2004 (24uF 450V).
I presume any cap above 300V rating will be fine here as the voltage test points on the schematic show 265 & 260V.
Other suggested ways of reducing hum are to try star grounding instead of plane (chassis) ground which is in the Cadet. Looking at the Cadet wiring this is probably a lot of work but does anybody know if it would be worthwhile?
One more mod suggested
Other than these mods does anybody have a good schematic which uses the 3 ECC807 & 4 ECL86 tubes?
John
I have two spare 220uF 400V caps & I figured to parallel the existing Cadet Sprague 47uF (this is what I measure on the multimeter) smoothing caps with these - these are a higher value to the Cadet III component values list (16uF 350V) or the schematic drawn by dld in 2004 (24uF 450V).
I presume any cap above 300V rating will be fine here as the voltage test points on the schematic show 265 & 260V.
Other suggested ways of reducing hum are to try star grounding instead of plane (chassis) ground which is in the Cadet. Looking at the Cadet wiring this is probably a lot of work but does anybody know if it would be worthwhile?
One more mod suggested
Other than these mods does anybody have a good schematic which uses the 3 ECC807 & 4 ECL86 tubes?
John
Attachments
Ah good point re smoothing caps - I didn't consider the extra stress on the rectifiers, EC8010.
Do you consider it worthwhile to change from common cathode bias resistor (130R with paralled cap) to individual bias res 270R with biased cap?
Another area that occurs to me is the power supply - it seems fairly basic - any ideas for upgrading it?
I take it ultra linear operation requires an ultralinear output transformer?
Don't get me wrong, I don't think this is a bad amp (especially for free) I'm just keen to get the most out of it.
Thanks for all your help
John
Do you consider it worthwhile to change from common cathode bias resistor (130R with paralled cap) to individual bias res 270R with biased cap?
Another area that occurs to me is the power supply - it seems fairly basic - any ideas for upgrading it?
I take it ultra linear operation requires an ultralinear output transformer?
Don't get me wrong, I don't think this is a bad amp (especially for free) I'm just keen to get the most out of it.
Thanks for all your help
John
I don't think there's much to be gained from modifying a Cadet, although separate bias resistors might help. You should accept it for what it is, a nice sounding, but very cheap amplifier. The output transformers are far too small to be able to manage bass with low distortion. They make a nice treble amplifier in an active crossover system, though.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.