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Free gear is fun gear!

posted on #1
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Joined: 22.02.21
I got this 1980 Bassman 70 for free when I bought a pair of empty 112 cabs from a local seller. He had it in pieces in his basement and was clearing out stuff in preparation for a move. Someone had messed up a switch repair in it and it wasn't working so they pulled a few tubes for use in another amp and left it a pile of parts.

[img]https://i.imgur.com/BGnVvhl.jpg[/img]

It only took about 5 minutes to get that sorted out and fixed. I put a new set of JJ 6L6GC's and a 12AT7 in it to replace the missing tubes, fired it up and it sounds great.

[img]https://i.imgur.com/ijRTRoS.jpg[/img]

Being an ultra linear amp I figured it to be clean all the way up the dial and it pretty much is the pedal platform amp I expected. A couple of days ago I hooked it up to my attenuator, cranked the normal channel's volume and the master up to 7 and hit the front end with an old Route 66 OD which is the closest thing I have to a Tube Screamer then ran the attenuator's line out into my interface so I wouldn't be shaking the walls of my house at 5 a.m. Holy smokes does this amp sing! :W
Edited by Riffraff on December 22 2021 20:24
posted on #2
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Joined: 29.04.16
Woow thats a great sound :J:W:J
music is the language all people understand so lets make music instead of war❤
posted on #3
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Joined: 22.02.21
I made a little video to celebrate my new toy and put 'loops track #232888. :D

[youtube]qSGwGCUYApk[/youtube]
Edited by Riffraff on April 26 2022 19:38
posted on #4
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There have been a few developments since I originally posted this. It seems my attenuator is not quite up to the task of handling this amp at full attenuation. The MASS100 I'm using is good for knocking a few db's off the top of a 100W tube amp but if you are using it at the full attenuation setting like I do in order to prevent blowing my poor sweet sleeping wife out of bed at 5am you need to de-rate it to 60W. Of course the "70" in Bassman 70 stands for 70 watts. I'm also boosting it with a tube screamer type overdrive which pushes the output a little higher.

I was playing one morning and noticed a burning smell. I checked the amp and that was fine then I touched the metal box of the attenuator and it was hot enough to fry eggs on. :D I opened it up to make sure I didn't melt the insulation off of any wires or toast some resistors and everything was fine. It was likely the paint under the chassis mounted resistors in the unit. So I turned the amp down, turned the OD down and with that my enthusiasm for the amp also dropped some. :@

I thought about buying another attenuator for this amp because it has a 4 ohm output and my bigger attenuator is only good for 16 ohms. I really didn't want to buy a 3rd attenuator. That's just too much stuff to have laying around and I already have a mountain of it, believe me. Then I remembered I had a pair of 5881 tubes in my tube caddy. The 6L6GC's I was running in the amp are good for 30W each. 5881's are a shorter, stockier version of the tube with an output of 23 watts each. A lot of people use them in 6L6 powered amps to get earlier tube breakup.

So now that I had an answer I just needed to modify the amp a little so I could bias it to run 5881 tubes. The Bassman 70 has 500VDC on the plates so there aren't many 5881's out there that can handle the high plate voltage but I had a pair of JAN Sylvania 6L6WGB's which are the same thing and military spec. I figure they must be able to handle the higher voltage. JJ's look like a good fit moving forward.

I'm REALLY happy to have this amp back in rotation. I made a little video of my journey through this rabbit hole, I hope you enjoy it.

[youtube]v7kw-orblAM[/youtube]
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