Bird,
Sorry for the late reply. I finally have my amp tested with the scope and found that it was running pretty good at anode of 5670 . With the square wave, it was all square from 20 to 45k, but it was a bit urgy at output with 8ohm loaded. Might be the result of this Hammond opt. Any ideas?
Albert
Sorry for the late reply. I finally have my amp tested with the scope and found that it was running pretty good at anode of 5670 . With the square wave, it was all square from 20 to 45k, but it was a bit urgy at output with 8ohm loaded. Might be the result of this Hammond opt. Any ideas?
Albert
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Sorry for such a delayed response myself. I have been off the grid a lot lately and do apologize, please next time send me a private message so that way there I can get an email and respond quicker. Life has been sucking extra hard for me lately so I have been not on the forum much lately.
When doing square wave testing for high frequency response you don't want to use 10kHz square wave, that would indicate you are looking for response at 100kHz which I doubt any output transformer is going to show good performance. Ideally you want to check with a 2kHz square wave. The transformer manufacturer should put the resonance well above the audible range. The ringing you are seeing is probably the resonance of the output transformer. I do still see a little bit of ringing on the 1kHz square wave so it must be the transformer. Can you put your probe on the plate of the 6HJ5?
Which Hammond OPT are you using? I haven't been impressed with their output transformers so I went with Transcendar for this build. Let me do some testing with my amp for comparison purposes, from memory I did some at 1kHz and it looked fine but that was almost 2 years ago.
When doing square wave testing for high frequency response you don't want to use 10kHz square wave, that would indicate you are looking for response at 100kHz which I doubt any output transformer is going to show good performance. Ideally you want to check with a 2kHz square wave. The transformer manufacturer should put the resonance well above the audible range. The ringing you are seeing is probably the resonance of the output transformer. I do still see a little bit of ringing on the 1kHz square wave so it must be the transformer. Can you put your probe on the plate of the 6HJ5?
Which Hammond OPT are you using? I haven't been impressed with their output transformers so I went with Transcendar for this build. Let me do some testing with my amp for comparison purposes, from memory I did some at 1kHz and it looked fine but that was almost 2 years ago.
Bird,
Wish you well.
My Hammond are 1640SE and this is the 1.25K OPT and I run them at 4ohm for my 8 ohm speakers.
I did check with the anode of the 6HJ5 and it was fine with almost the same square forms. It was good up to 25K. I thought it is the problem of the OPT and this is why I let them sit at the bench for so long without touching them.
Wish you well.
My Hammond are 1640SE and this is the 1.25K OPT and I run them at 4ohm for my 8 ohm speakers.
I did check with the anode of the 6HJ5 and it was fine with almost the same square forms. It was good up to 25K. I thought it is the problem of the OPT and this is why I let them sit at the bench for so long without touching them.
I built one of the 6HJ5 SET, but used a 6AG9 wired as a Kimmel mu stage for the driver. I used 2.5K OT instead of 3K used by OP.
I just recently changed the triode mode wiring for the 6HJ5. I connected the previously unused UL tap of the transformer to the screen through a 100V-5W zener & 100R resistor to stay below the 220V screen voltage rating. Plate voltage is 294V and screen voltage is 199V measured from the cathode at idle. Cathode voltage 43V through a 610R resistor. Screen current is about 5mA. To my ears this change seems to have tightened up the bass considerably compared to triode mode. Not sure what the long term effects of this will be for the 6HJ5 as it's only been running for a few hours now. Everything seems fine for now. Just an FYI in case someone wants to try it. I posted photos in the gallery about a month ago, I have attached them here also. Happy Holidays!
I just recently changed the triode mode wiring for the 6HJ5. I connected the previously unused UL tap of the transformer to the screen through a 100V-5W zener & 100R resistor to stay below the 220V screen voltage rating. Plate voltage is 294V and screen voltage is 199V measured from the cathode at idle. Cathode voltage 43V through a 610R resistor. Screen current is about 5mA. To my ears this change seems to have tightened up the bass considerably compared to triode mode. Not sure what the long term effects of this will be for the 6HJ5 as it's only been running for a few hours now. Everything seems fine for now. Just an FYI in case someone wants to try it. I posted photos in the gallery about a month ago, I have attached them here also. Happy Holidays!
