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I did a conversion of a Filmosound 179, this is my third foray into trying to stuff 10lbs into a 5lb bag. I honestly thing I have issues now.
This amp originally had a 6J7, 6SL7, and 6V6's plus a third 6V6 and photo tube for the sound pickup.
Three years ago, I plugged in, and it sounded horrid, filter caps were bad, very noisy, squeaky. But what did I expect from a 1947ish amp.
I gutted it and decided to build something with a 18watt feel, but a pentode as I was able to get a couple of 6SJ7, two new old stock RCA, and one used Rogers and it already had some clean 6V6s and a 6SL7.
I found a modified 18watt schematic that still used a 12AX7 in V2, and after a bunch of reading it seems a 6SL7 should work using the same values, just lower gain.
I built it up point to point with a couple of tag strips to make it as simple as possible. I then did a startup with a 100W lamp, no tubes, no shorts, checked voltages and played with some dropping resistors in the power supply and I have what I think are reasonably correct voltages based on what I saw in the schematic that supposedly worked.
I put the tubes in, again checking voltages and adjusting plate resistors, subbing a couple of voltage dividers and then plugged in.
I have sound, but it has very low output. It's bedroom volume when cranked, and has to my ears a decent amount of what I think is just pre-amp gain. It sounds like it has a master volume set to just under 1. (it has no master volume)
I've gone through it, from the input all the way to the output several times. Checked the soldering. I've metered out the transformers, checked the voltage on each winding of the power transformer, and voltages at the nodes, and tube pins and things seem right to the best of my ability to read what has been done with an EF86, what seems to be going on in a Gibson G20 for comparison.
My Node voltages are A 388 B 350, C 322, D 308.
I've attached my drawing as it sits, with voltages.
Any help pointing me where I should start, or what to look for would appreciated as to where I should start, or what could be the issue with the gain / math / voltage. As I'm subbing in old octal tubes into an amp that was designed originally for 12Ax7 in both the pre amp and phase inverter.
This amp originally had a 6J7, 6SL7, and 6V6's plus a third 6V6 and photo tube for the sound pickup.
Three years ago, I plugged in, and it sounded horrid, filter caps were bad, very noisy, squeaky. But what did I expect from a 1947ish amp.
I gutted it and decided to build something with a 18watt feel, but a pentode as I was able to get a couple of 6SJ7, two new old stock RCA, and one used Rogers and it already had some clean 6V6s and a 6SL7.
I found a modified 18watt schematic that still used a 12AX7 in V2, and after a bunch of reading it seems a 6SL7 should work using the same values, just lower gain.
I built it up point to point with a couple of tag strips to make it as simple as possible. I then did a startup with a 100W lamp, no tubes, no shorts, checked voltages and played with some dropping resistors in the power supply and I have what I think are reasonably correct voltages based on what I saw in the schematic that supposedly worked.
I put the tubes in, again checking voltages and adjusting plate resistors, subbing a couple of voltage dividers and then plugged in.
I have sound, but it has very low output. It's bedroom volume when cranked, and has to my ears a decent amount of what I think is just pre-amp gain. It sounds like it has a master volume set to just under 1. (it has no master volume)
I've gone through it, from the input all the way to the output several times. Checked the soldering. I've metered out the transformers, checked the voltage on each winding of the power transformer, and voltages at the nodes, and tube pins and things seem right to the best of my ability to read what has been done with an EF86, what seems to be going on in a Gibson G20 for comparison.
My Node voltages are A 388 B 350, C 322, D 308.
I've attached my drawing as it sits, with voltages.
Any help pointing me where I should start, or what to look for would appreciated as to where I should start, or what could be the issue with the gain / math / voltage. As I'm subbing in old octal tubes into an amp that was designed originally for 12Ax7 in both the pre amp and phase inverter.
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