I think I am going to the route that nightanole suggested and use one 10 pounder to construct a 50 watt amplifier initially. My ideas on using Edcor OPTs:
1.) 50W 3.4K Ohms with with an 8 Ohm tap and leave this as a permanent setup.
2.) 100W 3.3K Ohms with 4, 8 and 16 Ohm taps and maybe use the second 10 pounder to reconfigure as a 125 Watt amp. Edcor doesn't have a 125 Watt OPT so would the lower ratting kill it?
3.) 100W 6.6K Ohms with 4, 8 and 16 Ohm taps and using the 16 Ohm tap for my 8 Ohm speakers as George did. My thoughts on this were that I could use the OPTs in other projects at a later date if 6.6K Ohm designs are more common.
Do any of these ideas make sense?
1.) 50W 3.4K Ohms with with an 8 Ohm tap and leave this as a permanent setup.
2.) 100W 3.3K Ohms with 4, 8 and 16 Ohm taps and maybe use the second 10 pounder to reconfigure as a 125 Watt amp. Edcor doesn't have a 125 Watt OPT so would the lower ratting kill it?
3.) 100W 6.6K Ohms with 4, 8 and 16 Ohm taps and using the 16 Ohm tap for my 8 Ohm speakers as George did. My thoughts on this were that I could use the OPTs in other projects at a later date if 6.6K Ohm designs are more common.
Do any of these ideas make sense?
Just to clarify. I am going to build as the 50 watt version. #2 and #3 are assuming I want to change the setup at a later date. The speakers that I have now would not be able to handle 125 watts anyway. I built an audio rack out of 80/20 square tubing and 1 1/2 inch thick laminated oak for shelves so it will be able to handle the size and weight of the 125 watt version.
update
Regarding a stock P-P design I can confirm the following facts:
1. In regards to overall gain I can confirm it is a problem of source voltage. I tried several sources and by far a preamplified source (specifically a cd player) yields the best results compared to ipods, mp3 players and cell phones.
2. The IXYS part can BE EFFECTIVELY REPLACED with the supertex DN part as long as the resistor for current setting is (in this design) 56 ohms. The part is plug and play, fits perfectly in the board and no other modification is needed.
Questions
1. I have noticed the edcor power transformer gets fairly hot. I have collected over 48hours of long operating sessions and even though there have been no problems the transformer does get hot....sometimes just beyond what I can stand with my bare hand.
Musical output is nowhere near theoretical maximum. The amp does not clip. The transformer is wired for 240v use.
2. I can hear a very low and faint hum from the transformer. Has anyone else heard this?
Thanks!
Regarding a stock P-P design I can confirm the following facts:
1. In regards to overall gain I can confirm it is a problem of source voltage. I tried several sources and by far a preamplified source (specifically a cd player) yields the best results compared to ipods, mp3 players and cell phones.
2. The IXYS part can BE EFFECTIVELY REPLACED with the supertex DN part as long as the resistor for current setting is (in this design) 56 ohms. The part is plug and play, fits perfectly in the board and no other modification is needed.
Questions
1. I have noticed the edcor power transformer gets fairly hot. I have collected over 48hours of long operating sessions and even though there have been no problems the transformer does get hot....sometimes just beyond what I can stand with my bare hand.
Musical output is nowhere near theoretical maximum. The amp does not clip. The transformer is wired for 240v use.
2. I can hear a very low and faint hum from the transformer. Has anyone else heard this?
Thanks!
These are very common problems of cheap EI M6 core transformers. I suggest you to find and order custom low-flux toroidal power transformer from your domestic manufacturer with M4 or better. It should cost you around 120 Euro. Properly made toroid is absolutely silent and its temperature raise is only 7 - 10C.
Alexontherocks:
I'm running mine stock with the Edcor power transformer (XPWR139-120/240) wired for 120VAC and the transformer barely gets warm. Transformer is silent. Plenty of volume too driving it with a CD player.
Maybe the hot transformer is another symptom related to the low gain you are experiencing. Have you checked the B+, grid and bias voltages on the board? If not, do so while observing safety practices for measuring high voltages and report back on the measurements.
Other thoughts: Is the transformer wired correctly for 240V operation (Black connected to Line, Green/White connected to common, Black/White and Green connected together)? Short circuit somewhere? Bad MOSFET? Bad output tube pulling excessive current? Bad power transformer? I believe someone has reported a failure with an Edcor in another thread. The poster contacted Edcor and they sent a replacement.
I'm running mine stock with the Edcor power transformer (XPWR139-120/240) wired for 120VAC and the transformer barely gets warm. Transformer is silent. Plenty of volume too driving it with a CD player.
Maybe the hot transformer is another symptom related to the low gain you are experiencing. Have you checked the B+, grid and bias voltages on the board? If not, do so while observing safety practices for measuring high voltages and report back on the measurements.
Other thoughts: Is the transformer wired correctly for 240V operation (Black connected to Line, Green/White connected to common, Black/White and Green connected together)? Short circuit somewhere? Bad MOSFET? Bad output tube pulling excessive current? Bad power transformer? I believe someone has reported a failure with an Edcor in another thread. The poster contacted Edcor and they sent a replacement.
Last edited:
@all
The sound is really great so I am unsure where to look for problems...
The voltages are fine.
Bias balance ecc have been set properly.
The current across the resistor for the supertex part is 33mA
I will replace the tubes shortly so I might want to wait untill then however is there a cheap replacement transformer somwehere on ebay/web?
The sound is really great so I am unsure where to look for problems...
The voltages are fine.
Bias balance ecc have been set properly.
The current across the resistor for the supertex part is 33mA
I will replace the tubes shortly so I might want to wait untill then however is there a cheap replacement transformer somwehere on ebay/web?
I could have some conductivity due to some flux on the board.... I usually use acetone to clean it up but with the red board I am afraid I might melt the coating. Suggestions?
In any case music quality is excellent...I might just let it be, keep an eye on it, replace the tubes with different types and couple the amp qith a preamp. I should be fine...
In any case music quality is excellent...I might just let it be, keep an eye on it, replace the tubes with different types and couple the amp qith a preamp. I should be fine...
I can't advise on the use of acetone. I cleaned my board thoroughly before use by scrubbing it with an old tooth brush using naptha as a solvent. Drying with a paper towel between applications. It took several applications and scrubbings. I used cotton swabs to clean under the tube sockets. I followed with a denatured alcohol rinse. Maybe others can provide better methods.
If you have enough conductivity to heat up a power transformer you would know it. The flux residue would be smoking.
The two posters who ststed that their Edcors were only warm were from 60 Hz countries. It is normal for a transformer to run hotter on 50 Hz. I would try disconnecting all load from the transformer and running it unloaded for an hour or so. If it gets hot with no load it might be bad. Call or email Edcor to verify 50 Hz behavior.
If all the voltages are OK and the bias is correct and stable, new tubes aren't going to help. Try to find a source to drive the amp harder to see if you can push it into clipping. My current red board amp will not clip from a CD player except for a few very loud CD's. It is a 125 WPC version though.
You can boost the gain a bit by using a 6GU5 in place of the 6CB6. It is a hexode not a pentode but it plugs in with no circuit changes and gets a bit louder.
George and Tony are correct that a transformer running on 50 Hz mains will run hotter. The Edcor XPWR139-120/240 is specified for 50/60Hz operation.
Alexontherocks comment is the first report that I've seen for an Edcor transformer operating on 50Hz mains and high temperature. I suppose others are running Edcors on 50Hz mains. Possibly others using Edcors on 50Hz mains can add their experiences about operating temperatures.
Alexontherocks description of the temperature suggests the outer surface of the transformer is in the 50 to 60 degree C range. That is probably still below the design limits of the transformer (needs to be confirmed with Edcor). However, given Alexontherocks other report of low gain and if it was my system, I would want to investigate further.
Alexontherocks :
George’s suggestion of running the transformer unloaded out of circuit is an excellent idea and will help diagnose if the transformer is at fault. His suggestion of confirming 50Hz operation with Edcor is also a good idea. And any other data that you can share such as voltage measurements and temperatures will help further the troubleshooting process.
Alexontherocks comment is the first report that I've seen for an Edcor transformer operating on 50Hz mains and high temperature. I suppose others are running Edcors on 50Hz mains. Possibly others using Edcors on 50Hz mains can add their experiences about operating temperatures.
Alexontherocks description of the temperature suggests the outer surface of the transformer is in the 50 to 60 degree C range. That is probably still below the design limits of the transformer (needs to be confirmed with Edcor). However, given Alexontherocks other report of low gain and if it was my system, I would want to investigate further.
Alexontherocks :
George’s suggestion of running the transformer unloaded out of circuit is an excellent idea and will help diagnose if the transformer is at fault. His suggestion of confirming 50Hz operation with Edcor is also a good idea. And any other data that you can share such as voltage measurements and temperatures will help further the troubleshooting process.
Last edited:
Almost certainly. Every time I saw that sort of behavior, it was an excessively gassy tube. Sometimes there's a visible bluish-purple glow, and sometimes there isn't. Bias that won't settle down is never a good thing.
If the tubes that you are using haven't been used in a long time (10+ years) it may take them a while to stabilize. Some of my tubes were set and forget but a few took a week or so to settle down. I set the bias on the low side and left the meter connected. The upward creep slowed down after a few days or so and eventually stopped. Watch carefully for the first few days.