Here is the final schematic on the triode wired 8417 amp. As you can see I swapped the 7247 for the 12bh7, I put the feedback in and I corrected the driver tubes plate resistor cathode resistor issues by making them both 15K. Also you will see the feedback in variable. I listened to her for about an hour last night and she was definately improved. Tighter bass, cleaner sound overall with a bit more presences. Also the voltages have been added. Over the coming weekend I will add a 10 ohm 1/2 watt resistor to each 8417 to act as a fuse and I will put each 8417 on its own bias pot for tube to tube adjustment.
Thanks for everything guys.
Next I am taking a pair of McGohan M1003 8417 push pull amps and converting them to 2A3 PP amps. Thinking all transformer coupled. We'll see.
Thanks for everything guys.
Next I am taking a pair of McGohan M1003 8417 push pull amps and converting them to 2A3 PP amps. Thinking all transformer coupled. We'll see.
Just an update on this amp and a interesting point which I would love feedback on. The amps have been finished and playing on and off in my system for some time now. RCA 8417 playing fine class A triode mode 200mA per pair per amp. Sound great. These started there life as Bogen 8417 amps. Now when I renovated them I never connected the 16, 10 or 4 ohm taps. Only connected the 8 ohm tap for use. The rest also including the 70v tap and a feedback winding were all taped off. Recently I got into Quads and I picked up a pair of 57's and 63's. Reading in the forums that the 16 ohm tap my work very well for the 57's I decided to solder up the the 16 and 4 ohm taps to binding posts. I did not solder up the 10 ohm tap or the 70v tap. Nor did I do anything with the feedback winding other then leaving them as they were which is taped off.
I put things back together and the amps tone changed, they got louder (IE larger headroom). I had to readjust the feedback considerablly and they took on a slightly overall different sound and generally more pleasant.
Now I do not think I am crazy as it was not like the amps weren't being used and all of a sudden I made this change and plugged them in for the first time in weeks. I was listening to them the day before and for months before and made the change in 2 hours one evening and played then right then and there and the above happened.
Anybody have any thoughts on this?
Thanks in advance
I put things back together and the amps tone changed, they got louder (IE larger headroom). I had to readjust the feedback considerablly and they took on a slightly overall different sound and generally more pleasant.
Now I do not think I am crazy as it was not like the amps weren't being used and all of a sudden I made this change and plugged them in for the first time in weeks. I was listening to them the day before and for months before and made the change in 2 hours one evening and played then right then and there and the above happened.
Anybody have any thoughts on this?
Thanks in advance
I have some questions.
Just curious as to why you used a 6J5 instead of say a 6FQ7? Is it because you used a 6SL7 the first time around and had to stick to a octal tube now?
Why so low a B+ on the 8417? I was thinking it ran on about 450VDC in its prior life.
How is the low end on the amp? Being it was a commercial 70 volt amp I was under the assumption the bass would be rather limited under 70hz or so.
Just curious as to why you used a 6J5 instead of say a 6FQ7? Is it because you used a 6SL7 the first time around and had to stick to a octal tube now?
Why so low a B+ on the 8417? I was thinking it ran on about 450VDC in its prior life.
How is the low end on the amp? Being it was a commercial 70 volt amp I was under the assumption the bass would be rather limited under 70hz or so.
"Just curious as to why you used a 6J5 instead of say a 6FQ7? Is it because you used a 6SL7 the first time around and had to stick to a octal tube now?"
Just like it. No other real reason.
"Why so low a B+ on the 8417? I was thinking it ran on about 450VDC in its prior life."
More actually but its triode so 300 is the max due to screen issues.
"How is the low end on the amp? Being it was a commercial 70 volt amp I was under the assumption the bass would be rather limited under 70hz or so."
Bogen transformers are complete sleepers and sound very good. Bass is very extended and clean but the "clean" is a product of the design really.
Just like it. No other real reason.
"Why so low a B+ on the 8417? I was thinking it ran on about 450VDC in its prior life."
More actually but its triode so 300 is the max due to screen issues.
"How is the low end on the amp? Being it was a commercial 70 volt amp I was under the assumption the bass would be rather limited under 70hz or so."
Bogen transformers are complete sleepers and sound very good. Bass is very extended and clean but the "clean" is a product of the design really.
hey-Hey!!!,
The lower B+ offers opportunity to approach Class A...matter of fact, achieve it. The quad of 8417 can sink 400 mA at that B+, and with the stock loading in triode mode you've got Class A. Now I do have my doubts about the power TX being able to provide that much...
cheers,
Douglas
The lower B+ offers opportunity to approach Class A...matter of fact, achieve it. The quad of 8417 can sink 400 mA at that B+, and with the stock loading in triode mode you've got Class A. Now I do have my doubts about the power TX being able to provide that much...
cheers,
Douglas
Bandersnatch said:hey-Hey!!!,
The lower B+ offers opportunity to approach Class A...matter of fact, achieve it. The quad of 8417 can sink 400 mA at that B+, and with the stock loading in triode mode you've got Class A. Now I do have my doubts about the power TX being able to provide that much...
cheers,
Douglas
What I am thinking about next is to regulate the screen supply using a zener stack or VR tubes. Not sure I need to think about it a bit.
I would like to keep the screen 30v below the plate at all times and steady as that is supposed to be the key to tight sound anywhere in the range of the amp.
Any thoughts?
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