Doe's anyone have pictures of the inside of the wood panel version or possibly a rev A schematic? I have two of these in for repair. The owner really liked the older wood panel version, the black tolexed one never sounded right. Supposed to make the black one sound like the wood one. Should be easy enough, but the last tech he brought them to tore the good one apart, put it back together in a strange way, then gave up before reattaching all of the wires and didn't tell the owner there were problems. He plugged it in and blew the new power tubes, and probably a few other things.
The most confusing changes are to v2. I think he thought it was a cathode follower, and I guess it may have been, but what is in there doesn't match the PCB. The black tolexed version looks the same as other pictures I have seen online, but doesn't match the schematic. No idea what would have been original.
I drew a PCB layout to try and make sense of things, think I am close but open to ideas.
Unrelated to these changes, the HT fuse on both amps is 2A, I haven't measured anything, but that seems crazy high to me. Schematic says 500mA, faceplate says 2A.
Sovtek MIG 50H versions
Moderators: pompeiisneaks, Colossal
Sovtek MIG 50H versions
You do not have the required permissions to view the files attached to this post.
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Sovtek MIG 50H versions
A 2 amp Slow blow fuse is what's typically used in on the A/C primary side a 40 to 50 watt amp with that number of tubes just like the schematic shows!
In terms of a fuse in the V+ line for the D.C. Voltage, two 6l6 outputs with about 450 volts on there plate will pull 230 ma to make about 45 to 50 watts.
If you wanted to fuse theV+ circuit then a 400 ma fuse would be what I would use!
You need to learn to look at tube specs to calculate current needs be they AC for filaments, or DC to power the circuit.
I have found that the preamp tube sockets in these amp are crap after enough play time so if you get any intermittents or crackling sounds look there first.
In terms of a fuse in the V+ line for the D.C. Voltage, two 6l6 outputs with about 450 volts on there plate will pull 230 ma to make about 45 to 50 watts.
If you wanted to fuse theV+ circuit then a 400 ma fuse would be what I would use!
You need to learn to look at tube specs to calculate current needs be they AC for filaments, or DC to power the circuit.
I have found that the preamp tube sockets in these amp are crap after enough play time so if you get any intermittents or crackling sounds look there first.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Sovtek MIG 50H versions
So, crazy high. Curious what changed between schematic and production to put a 2A in there. Maybe they ran out of 500mA fuses? To be clear, the annotated schematic is something I pulled from another forum. I believe it is accurate to a production amp, aside from v2.
Just for completeness, here's how v2 was wired when I got the thing.
You do not have the required permissions to view the files attached to this post.
Re: Sovtek MIG 50H versions
To follow up in case this is helpful to someone in the future. I determined, from pictures of parts removed by the last tech, v2 mods were done before the current owner got the amp. Instead of doing the exact same thing, I opted for Merlin's bootstrapped cathode follower circuit with an easy way to switch to the other version. The owner wanted loud and clean and this worked pretty well. Much smoother sounding than the original setup with the clean channel and high gain channel. Owner says he digs it.
Hard to say for certain what was original to either amp in some places, but here's my best guess
Wood amp: 3-4 H choke, 1.5k 5w screen resistors,1k grid stoppers, 220k grid leaks, 82k nfb, 47uf preamp filter caps, 100R humdinger
Black amp: 470R 5w resistor, two parallel 1.5k screen resistors,1.5k grid stoppers, 150k grid leaks, 47k nfb, 80 and 100uf pre filter caps, grounded filament
Fuses were replaced with 2A mains and 500mA HT I did some measuring and think 2A might be too small for someone slamming the high gain channel, but should be fine for normal use.
There was a switch sized hole next to the power tubes, so I added a nfb switch.
Hard to say for certain what was original to either amp in some places, but here's my best guess
Wood amp: 3-4 H choke, 1.5k 5w screen resistors,1k grid stoppers, 220k grid leaks, 82k nfb, 47uf preamp filter caps, 100R humdinger
Black amp: 470R 5w resistor, two parallel 1.5k screen resistors,1.5k grid stoppers, 150k grid leaks, 47k nfb, 80 and 100uf pre filter caps, grounded filament
Fuses were replaced with 2A mains and 500mA HT I did some measuring and think 2A might be too small for someone slamming the high gain channel, but should be fine for normal use.
There was a switch sized hole next to the power tubes, so I added a nfb switch.
You do not have the required permissions to view the files attached to this post.
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Sovtek MIG 50H versions
Thanks for the info!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Sovtek MIG 50H versions
Thanks, can you please make correct schematic (not layout) for wood panel version?
Re: Sovtek MIG 50H versions
The posted schematic should be fairly accurate, aside from the subtle differences in component values mentioned. Those are also just educated guesses. I never had a stock amp to work on, so no way to know what is "correct".