Just learned of this site... here's my current project. Another rusty old PA amp

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dorrisant
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by dorrisant »

pompeiisneaks wrote: Thu Jan 11, 2018 5:30 pm man that leslie sure is gorgeous, would love to hear some samples of it too. I had an old pedal that had a leslie simulation in it that I loved to mess with :P

~Phil
Very pretty! You'd have to mic it in stereo... Otherwise it sounds like a regular tremolo.
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va3dxv
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

pompeiisneaks wrote: Thu Jan 11, 2018 5:30 pm man that leslie sure is gorgeous, would love to hear some samples of it too. I had an old pedal that had a leslie simulation in it that I loved to mess with :P

~Phil
I'll get around to it some day. It's not really a desirable model for guitar unfortunately. This model was made specifically for Lowrie organs, not Hammond. It was also meant to be the base unit for another Leslie extension cab (the other is the 103). I guess the way it worked was when you wanted the tremolo/vibrato sound, you hit the switch and it muted the middle 6x9 up top (it has 4 + the 15", all 1968 Jensen), and turned on the rotating one on the bottom... the rotating drum also rotates a pulley that spins something in the pre-amp to add an effect to the bass speaker.

I bought it because I wanted to pull the amp and build a guitar amp out of it, and mod the cab to add some better Leslie stuff (like horns)... the problem is that unlike the rest of the junk I manage to find, it's 100% unmolested... and I'm hesitant to screw with it. The amp is 4 channels so I'd have to split my signal if I want to play through it without modding the amp. Someday soon I'll get around to just wiring up 4 of the raw speakers to another amp and see what they sound like for guitar. Probably not great but you never know.

edit: oops, I screwed up and multi-posted, sorry!
Last edited by va3dxv on Thu Jan 11, 2018 7:11 pm, edited 2 times in total.
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by pompeiisneaks »

Gotcha, nice, yeah I deleted the duplicates.

~Phil
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

Making some progress... finally had some time.

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

...and the black one cleaned up pretty damn nice too...
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by pompeiisneaks »

whoa quite an improvement!

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by modman »

Thought I'd bump this thread.... very nice stuff.
The more intelligent among us have realized by now that scoring old tube mono block is the way to go. I have a bunch of Italian Geloso PA amps that I paid <100EUR a piece... just the power transformers would cost me more when buying new ones. I think I've seen these designs before -- are they Knight/Allied Electronics?
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

modman wrote: Fri Jan 19, 2018 8:54 amI have a bunch of Italian Geloso PA amps that I paid <100EUR a piece
Yup, these are a similar thing. The tubes these came with would have cost me more to buy. The red one was $25 CAD ...the black one was $40 and came with other stuff. Out of them I got 4 good 6V6's, 6SC7's, 6SF5's, 5z3 and a few others, not to mention the iron! If you know where to look they're out there.
modman wrote: Fri Jan 19, 2018 8:54 am I think I've seen these designs before -- are they Knight/Allied Electronics?
I've been unable to identify them, and they came from different places. I assume the red one was some kind of kit. Just due to the many holes in the chassis, it looks like it could have been multi-purpose but I don't know. There are 2 small holes in the lid where it looks like a logo may have been riveted, and more on the back where it may have had a number plate... but anything identifying it is long gone.

The black one is a similar mystery, even fewer markings than the other... but it came hooked up in a turntable cabinet with a rogers majestic radio and a 10" speaker from a manufacturer I'd never heard of. The turntable motor has a black textured finish that matches the amp, so maybe they're related. I'm sure they're not original to the rogers radio though.
Last edited by va3dxv on Fri Jan 19, 2018 5:10 pm, edited 1 time in total.
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

Well it makes sound! I had three 6sc7's around here, 2 of which were good, one was bad... but I can't find the second good one. So I powered it up with the weak one and it works, just can't get much gain out of it till I find a new tube. 360v plate to cathode voltage, which is higher than I'd like, so I think I'll tweek the values of the B+ dropping resistors. Also had to put 440 ohms in the bias instead of the 250 the 5c4 calls for. This is just a video I made for a few facebook friends.

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by modman »

Great idea making the video, thanks. There is no feeling like getting sound from an old amp.
Do you use perfboard for permanent build, or just for testing?
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

It's my first ever build, I just used what I had kicking around. I was concerned about the extra capacitance the copper holes on the back would add, not to mention maybe arcing, so I scraped off the copper from a lot of them near the danger spots. I'll probably re-do it at a later date with my own board.
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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by va3dxv »

perfboard just for testing?
On the subject of the board, I scored some nice vintage bakelite sheets at another estate sale... I'm thinking of maybe drilling a couple them out for turrets to use as boards in these amps. I know this stuff is brittle though, anyone got any insight on doing that? (besides the fact it's basically poison lol). One sheet is ~4mm thick the others are ~2mm.

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by pompeiisneaks »

I don't know much about bakelite, but drilling fragile stuff works better with some backing material so it won't blow out, I learned this the hard way :D

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Re: Just learned of this site... here's my current project. Another rusty old PA amp

Post by ChopSauce »

You should avoid drilling anything without some backing material, anyway. It makes holes much nicer / easier to deburr on the exit side. I always keep scrap pieces of wood close to my drill press, therefore.

Nice boards, by the way 8)
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