Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: marczee on November 07, 2024, 11:19:55 am
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Just joined! I have a grip of old reel to reel conversions and this Magnasync Moviola 1800 tube amp that I occasionally get off the shelf to tinker with. It's a hobby I guess.. The 1800 could be considered the big brother of the URS squawk box amp. It was installed inside the green Moviola film editing machines. For this one I tried to remove all of the extra optical head / film related stuff. For audio, it's a beast. Very high gain, hissy, barely need to turn it up. I modded the input resistance to V1 to "like a Fender". I made note of the voltages after pulling out all of the film junk, those are taken with a 6.3v filament dialed in on the variac.
I would like to tame the circuit more. I lifted the V1 cathode bypass cap and it didn't change much. So just looking for some pointers here. Thanks!
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for "simple" testing;
remove C3 and C2, re-wire R10 as a volume pot
does it move you in the correct direction?
AND....
do a re-draw!! those X's n O's get me all distracted :icon_biggrin:
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Yes, draw an updated as built schematic.
It looks like you're making extra gain in the 1st 2 stages, possibly more than the power amp was designed for.
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Yeah, tons of gain without really any attenuation between stages. Aside from shooter’s good tips, if you’ve got a second 12AU7 sub that in for the 12AX7. That should take things down considerably.
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you’ve got a second 12AU7
i was trying to sneak up on that :icon_biggrin:
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you’ve got a second 12AU7
i was trying to sneak up on that :icon_biggrin:
You got caught. :laugh:
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Thanks all, I'll try Shooter's suggestions! I just remembered I have some 5751 tubes as well to try. Definitely will be re-drawing this schemo in the near future.