For the longest time, I wanted to make an IT coupled amplifier. Why IT coupled? Because I haven't made one yet, and I like the simplicity.
The original goal was to use a WE404A/5847 pentode driver, IT coupled to a 300B. So, I'm hitting two birds in one stone here- the use of pentode as a driver, and IT coupling.
I haveread J.C. Morrison's article in Sound Practices 14 and I was surprised to see that I actually have a pair of Raytheon 5847. So I thought of using these tubes for the driver.
A long time ago, I had a pair of IT transformers made by my local winder. I never got to use them, and still sits here in my office. Since then, I have forgotten about IT-coupled projects.
Then for the first time, I was able to make an IT-coupled PP EL34, driven by a paralleled 6SN7. It sounded very nice, but I never got to make beyond the breadboard. The IT is a Lundahl LL1660S/10mA that my friend started distributing here in the Philippines early this year.
I asked Per Lundahl, if I can use the LL1660S in SE-SE mode instead of SE-PP. To my delight, he said yes, and I arrived at a modified ALT-T configuration.
Here's the fruit of my labor over the last 4 days...
By arnoldc
By arnoldc
At the last minute,at had a change of mind since I have NOT tested the 5847 ever, I swapped in a WE396A in parallel, instead.
The rectifier is 5AR4 and FR107 in a Graetz bridge, through CLCLC, and there's a VR150 to regulate the driver supply going to the LL1660S. The power transformer is a Lundahl L1648, and the output transformers are James JS-6113HS. I'm operating the 300B within the output transformer current limit.
Please do not ask me for the sonic virtues of the amp yet, as I haven't smoke tested it
The original goal was to use a WE404A/5847 pentode driver, IT coupled to a 300B. So, I'm hitting two birds in one stone here- the use of pentode as a driver, and IT coupling.
I haveread J.C. Morrison's article in Sound Practices 14 and I was surprised to see that I actually have a pair of Raytheon 5847. So I thought of using these tubes for the driver.
A long time ago, I had a pair of IT transformers made by my local winder. I never got to use them, and still sits here in my office. Since then, I have forgotten about IT-coupled projects.
Then for the first time, I was able to make an IT-coupled PP EL34, driven by a paralleled 6SN7. It sounded very nice, but I never got to make beyond the breadboard. The IT is a Lundahl LL1660S/10mA that my friend started distributing here in the Philippines early this year.
I asked Per Lundahl, if I can use the LL1660S in SE-SE mode instead of SE-PP. To my delight, he said yes, and I arrived at a modified ALT-T configuration.
Here's the fruit of my labor over the last 4 days...
An externally hosted image should be here but it was not working when we last tested it.
By arnoldc
An externally hosted image should be here but it was not working when we last tested it.
By arnoldc
At the last minute,at had a change of mind since I have NOT tested the 5847 ever, I swapped in a WE396A in parallel, instead.
The rectifier is 5AR4 and FR107 in a Graetz bridge, through CLCLC, and there's a VR150 to regulate the driver supply going to the LL1660S. The power transformer is a Lundahl L1648, and the output transformers are James JS-6113HS. I'm operating the 300B within the output transformer current limit.
Please do not ask me for the sonic virtues of the amp yet, as I haven't smoke tested it
Hi Ck,
I have the schematic in Visio but allow me to finalize everything, including voltage readings, to make it easier for anyboy interested.
I do have a Shih Tzu who loves to nose around I will have a cover made for the Lundahl transformers soon
Incidentally, I just realized that the two Nichicon Muse electrolytics are in the wrong direction (polarity), good thing to always make another round of review before powering up.
I have the schematic in Visio but allow me to finalize everything, including voltage readings, to make it easier for anyboy interested.
I do have a Shih Tzu who loves to nose around
I will have a cover made for the Lundahl transformers soon Incidentally, I just realized that the two Nichicon Muse electrolytics are in the wrong direction (polarity)
, good thing to always make another round of review before powering up.Finally, music!
Thanks to one of my mentor friend, who spent time with me tonight in troubleshooting the problem. We've covered all the usual suspects, checked and validated. Everything turned out right and I hav spent hours finding the problem. I was about to call it a night when I had this gutfeel to isolate a very unsuspecting component - the hum balance pot. While it gives me the proper resistance reading, it just don't work when power is applied. Geez! But that's over now.
Because it's too late, I played female vocals only - Hayley Westenra and Patricia Barber. So far, I'm impressed. The vocals are simply gorgeous, the details marvelous. The best amp I've brewed thus far, and definitely a different league compared to all my capacitor-coupled designs. I haven't played any rock or heavy metal so far, but I like it very much already.
Rock or no rock, my 300B tubes will no longer gather dust!
Thanks to one of my mentor friend, who spent time with me tonight in troubleshooting the problem. We've covered all the usual suspects, checked and validated. Everything turned out right and I hav spent hours finding the problem. I was about to call it a night when I had this gutfeel to isolate a very unsuspecting component - the hum balance pot. While it gives me the proper resistance reading, it just don't work when power is applied. Geez! But that's over now.
Because it's too late, I played female vocals only - Hayley Westenra and Patricia Barber. So far, I'm impressed. The vocals are simply gorgeous, the details marvelous. The best amp I've brewed thus far, and definitely a different league compared to all my capacitor-coupled designs. I haven't played any rock or heavy metal so far, but I like it very much already.
Rock or no rock, my 300B tubes will no longer gather dust!
Hi Shoog,
Did you mean information technology? Geez, I was part of its evolution, spent 13 years with Unix from System 6 to AT&T System V R3. But now, I do Microsoft. Built my first Altair-style Intel 8008 chip based computer when I was young.
My sonic description was based on what it is right now... Single section (should be paralleled) 396A, 150V B+ off the 0D3, LED on the cathode.
My ears are not complaining about lack of top end sparkle, but I have to see it on the scope.
There is no plan to make a PP 300B.
Sonically, this SE 300B is a league above the PP EL34 with the same LL1660S.
Cheers!
Did you mean information technology? Geez, I was part of its evolution, spent 13 years with Unix from System 6 to AT&T System V R3. But now, I do Microsoft. Built my first Altair-style Intel 8008 chip based computer when I was young.
My sonic description was based on what it is right now... Single section (should be paralleled) 396A, 150V B+ off the 0D3, LED on the cathode.
My ears are not complaining about lack of top end sparkle, but I have to see it on the scope.
There is no plan to make a PP 300B.
Sonically, this SE 300B is a league above the PP EL34 with the same LL1660S.
Cheers!
Guys, need some help here...
I was trying to measure the voltages of the amp, and I found something weird...
My current driver is a single section of WE396A, and I'm using LED on the cathode... THe voltage across the LED is 2V, which is what I expect it to be. So for both channels, I'm drawing 16mA.
I'm using a VR150 to regulate the voltage going to the driver at 150V (fed thru the LL1660S), what I was shocked to find out was that, the voltage to the anode of the VR150 is some 300V after a 15K dropping resistor. And that seems, the drivers are no drawing the 16mA they should. Just for kicks, I changed the dropping resistor to 30K, and I'm still getting close to 300V!
I went back to the loadline of the 396A and to estimate where I should be with -2V on the grid and 150V plate voltage- and it says around 8mA...
Why is it behaving like this? Is my VR tube faulty?
Your thoughts will be much appreciated..
I was trying to measure the voltages of the amp, and I found something weird...
My current driver is a single section of WE396A, and I'm using LED on the cathode... THe voltage across the LED is 2V, which is what I expect it to be. So for both channels, I'm drawing 16mA.
I'm using a VR150 to regulate the voltage going to the driver at 150V (fed thru the LL1660S), what I was shocked to find out was that, the voltage to the anode of the VR150 is some 300V after a 15K dropping resistor. And that seems, the drivers are no drawing the 16mA they should. Just for kicks, I changed the dropping resistor to 30K, and I'm still getting close to 300V!
I went back to the loadline of the 396A and to estimate where I should be with -2V on the grid and 150V plate voltage- and it says around 8mA...
Why is it behaving like this? Is my VR tube faulty?
Your thoughts will be much appreciated..
Very odd problem Arnold..
First I would check that meter, then the next question is why the VR150 is not doing its thing. There really can't be 300V across a VR150 - which seems to imply that it might be bad or miswired - some large resistance between it and ground?
Double check that you were measuring what you thought you were - I can't tell how you often I measured one thing and forgot to move the meter reference point (gnd, etc.) and then got a totally unexpected result..
I'd put everything back the way it was, get another VR150, and a different meter and recheck the result. If anything that 15K should be smaller, I calculated a total current based on the numbers you gave us above of 16.67mA through that resistor, if you want 16mA for the 396's in total you need to add a minimum of 5mA additional for just the VR150. So figure on something close to 11K being the right number. (Note that the VR tube can handle the full load current without the 396 installed so you can check that it functions properly before risking the driver tubes.)
First I would check that meter, then the next question is why the VR150 is not doing its thing. There really can't be 300V across a VR150 - which seems to imply that it might be bad or miswired - some large resistance between it and ground?
Double check that you were measuring what you thought you were - I can't tell how you often I measured one thing and forgot to move the meter reference point (gnd, etc.) and then got a totally unexpected result..
I'd put everything back the way it was, get another VR150, and a different meter and recheck the result. If anything that 15K should be smaller, I calculated a total current based on the numbers you gave us above of 16.67mA through that resistor, if you want 16mA for the 396's in total you need to add a minimum of 5mA additional for just the VR150. So figure on something close to 11K being the right number. (Note that the VR tube can handle the full load current without the 396 installed so you can check that it functions properly before risking the driver tubes.)
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